U.S. patent application number 12/732819 was filed with the patent office on 2011-09-29 for zrox, ce-zrox, ce-zr-reox as host matrices for redox active cations for low temperature, hydrothermally durable and poison resistant scr catalysts.
This patent application is currently assigned to UMICORE AG & CO. KG. Invention is credited to John G. Nunan, Barry W. L. SOUTHWARD.
Application Number | 20110236282 12/732819 |
Document ID | / |
Family ID | 44544737 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110236282 |
Kind Code |
A1 |
SOUTHWARD; Barry W. L. ; et
al. |
September 29, 2011 |
ZROX, CE-ZROX, CE-ZR-REOX AS HOST MATRICES FOR REDOX ACTIVE CATIONS
FOR LOW TEMPERATURE, HYDROTHERMALLY DURABLE AND POISON RESISTANT
SCR CATALYSTS
Abstract
The present invention relates to application of catalysts for
the Selective Catalytic Reduction of oxides of Nitrogen using
N-containing reductant. The catalysts are characterised as phase
pure lattice oxide materials into which catalytically active
cations are incorporated at high levels of dispersion such that
conventional analysis reveals a highly phase pure material. The
materials are further characterised by high activity, hydrothermal
durability and poison tolerance in the intended application.
Inventors: |
SOUTHWARD; Barry W. L.;
(Frankfurt am Main, DE) ; Nunan; John G.; (Tulsa,
OK) |
Assignee: |
UMICORE AG & CO. KG
Hanau-Wolfgang
DE
|
Family ID: |
44544737 |
Appl. No.: |
12/732819 |
Filed: |
March 26, 2010 |
Current U.S.
Class: |
423/239.1 ;
502/304; 502/73 |
Current CPC
Class: |
B01J 21/066 20130101;
B01J 23/002 20130101; B01J 29/072 20130101; B01J 2523/00 20130101;
B01J 2523/00 20130101; B01J 23/10 20130101; B01J 37/0036 20130101;
B01J 35/002 20130101; B01J 2523/00 20130101; B01D 2255/504
20130101; B01J 37/03 20130101; B01J 29/46 20130101; B01J 29/7215
20130101; B01J 2523/00 20130101; B01J 29/723 20130101; B01D
2251/206 20130101; B01J 2523/00 20130101; B01J 2523/00 20130101;
B01D 53/9418 20130101; B01J 23/83 20130101; B01J 29/40 20130101;
B01J 2523/00 20130101; B01D 2255/20761 20130101; B01J 23/30
20130101; B01J 29/7007 20130101; B01J 2523/00 20130101; B01J
2523/00 20130101; B01J 2523/17 20130101; B01J 2523/3712 20130101;
B01J 2523/48 20130101; B01J 2523/56 20130101; B01J 2523/3718
20130101; B01D 2255/502 20130101; B01J 2523/48 20130101; B01J
2523/48 20130101; B01J 2523/48 20130101; B01J 2523/56 20130101;
B01J 2523/24 20130101; B01J 2523/36 20130101; B01J 2523/3718
20130101; B01J 2523/842 20130101; B01J 2523/3706 20130101; B01J
2523/3706 20130101; B01J 2523/3712 20130101; B01J 2523/48 20130101;
B01J 2523/3725 20130101; B01J 2523/842 20130101; B01J 2523/3718
20130101; B01J 2523/3718 20130101; B01J 2523/3725 20130101; B01J
2523/36 20130101; B01J 2523/36 20130101; B01J 2523/3706 20130101;
B01J 2523/3718 20130101; B01J 2523/3712 20130101; B01J 2523/48
20130101; B01J 2523/3706 20130101; B01J 2523/3712 20130101; B01J
2523/24 20130101; B01J 2523/842 20130101; B01J 2523/23 20130101;
B01J 2523/3712 20130101; B01J 2523/3712 20130101; B01J 2523/3712
20130101; B01J 2523/3712 20130101; B01J 2523/3718 20130101; B01J
2523/3718 20130101; B01J 2523/3712 20130101; B01J 2523/3706
20130101; B01J 2523/3712 20130101; B01J 2523/36 20130101; B01J
2523/48 20130101; B01J 2523/36 20130101; B01J 2523/56 20130101;
B01J 2523/36 20130101; B01J 2523/56 20130101; B01J 2523/3706
20130101; B01J 2523/48 20130101; B01J 2523/3712 20130101; B01J
2523/48 20130101; B01J 2523/48 20130101; B01J 2523/842 20130101;
B01J 2523/3712 20130101; B01J 2523/56 20130101; B01J 2523/36
20130101; B01J 2523/3706 20130101; B01J 2523/48 20130101; B01D
2251/2067 20130101; B01D 2251/2065 20130101; B01D 2255/20738
20130101; B01J 37/0246 20130101; B01J 35/023 20130101; B01J 2523/00
20130101; B01J 2523/00 20130101; B01J 29/061 20130101; B01D
2255/9205 20130101; B01D 2255/407 20130101; B01J 29/7015 20130101;
B01J 2523/3706 20130101; B01J 2523/3718 20130101; B01J 2523/48
20130101; B01J 2523/3712 20130101; B01J 2523/56 20130101; B01J
2523/48 20130101; B01J 2523/3706 20130101; B01J 2523/00 20130101;
B01J 23/20 20130101; B01J 2523/00 20130101; B01J 2523/00 20130101;
B01D 2258/012 20130101; B01D 2251/2062 20130101; B01J 29/06
20130101 |
Class at
Publication: |
423/239.1 ;
502/304; 502/73 |
International
Class: |
B01D 53/56 20060101
B01D053/56; B01J 23/10 20060101 B01J023/10; B01J 29/40 20060101
B01J029/40; B01J 29/46 20060101 B01J029/46 |
Claims
1. A method for the conversion of the oxides of nitrogen to
nitrogen by contacting said nitrogen oxides with a
nitrogen-containing reductant in the presence of a base metal oxide
catalyst comprising: (a) a phase pure crystal lattice structure,
and (b) catalytically active cations dispersed within said lattice
structure
2. A method according to claim 1, wherein the phase pure lattice
structure is derived from the oxides of zirconium.
3. A method according to claim 1, wherein the phase pure lattice
structure is derived from the oxides of cerium-zirconium solid
solution.
4. A method according to claim 1, wherein the phase pure lattice
structure is derived from the oxides of cerium-zirconium-yttrium
solid solution.
5. A method according to claim 1, wherein the phase pure lattice
structure is derived from the oxides of cerium-zirconium-rare
earth, wherein rare earth means the 30 elements composed of the
lanthanide and actinide series of the Periodic Table of
Elements.
6. A method according to claim 1, wherein the phase pure lattice
structure is derived from the oxides of
cerium-zirconium-yttrium-rare earth, wherein rare earth means the
30 elements composed of the lanthanide and actinide series of the
Periodic Table of Elements.
7. A method according to claim 1, wherein the catalyst contains
cation doped lattice structures wherein the doped lattice
structures comprise a mixture of at least 2 lattice structures
selected from the group consisting of oxides of zirconium, oxides
of cerium-zirconium solid solution, cerium-zirconium-yttrium solid
solution, oxides of cerium-zirconium-rare earth and oxides of
cerium-zirconium-yttrium-rare earth, wherein rare earth means the
30 elements composed of the lanthanide and actinide series of the
Periodic Table of Elements.
8. A method according to claim 1, wherein the active dispersed
cations are selected from 1 or more elements of the transition
metal series of the Periodic Table of Elements.
9. A method according to claim 1, wherein the active dispersed
cations are selected from 1 or more elements of the alkaline earth
metal group of the Periodic Table of Elements.
10. A method according to claim 1, wherein the active dispersed
cations are selected from 1 or more elements of the alkali metal
group of the Periodic Table of Elements.
11. A method according to claim 1, wherein the active dispersed
cations are selected from the group consisting of Cu, Fe, Nb, Ta, W
and mixtures thereof.
12. A method according to claim 1, wherein said conversion takes
place with reduction of oxides of nitrogen via reaction with a
nitrogen-containing reducing agent at a temperature of at least
100.degree. C.
13. The method according to claim 12, wherein the temperature is
from about 150.degree. C. to about 700.degree. C.
14. The method according to claim 1, wherein the conversion of
oxides of nitrogen to nitrogen is performed under conditions of an
excess of oxygen.
15. The method according to claim 1, wherein a source of
nitrogen-containing reductant is introduced to give an effective
NH.sub.3:NOx ratio (.alpha. ratio) at catalyst inlet of 0.5 to
2.
16. The method according to claim 15, wherein the NO:NO.sub.2 ratio
recorded at the inlet of the catalyst is from 1:0 to 1:3 by
volume.
17. The method according to claim 16, wherein an oxidation catalyst
is employed prior to the base metal oxide (SCR) catalyst to enable
generation of NO.sub.2-enriched exhaust gas.
18. The method according to claim 15, wherein the
nitrogen-containing reductant is an organo-nitrogen compound known
to produce NH.sub.3 under conditions of hydrolysis or
decomposition, selected from group consisting of urea
((NH.sub.2).sub.2CO), ammonium carbonate, ammonium carbamate,
ammonium hydrogen carbonate, ammonium formate and mixtures
thereof.
19. The method according to claim 1, wherein the nitrogen oxides
are in a nitrogen oxide-containing gas stream which is an effluent
stream generated from a combustion process.
20. A method according to claim 19, wherein the combustion process
comprises the combustion of fuel in an internal combustion
engine.
21. A method according to claim 19, wherein the internal combustion
engine is a vehicular internal combustion engine operating under
fuel lean/oxygen rich conditions.
22. A method for making a catalytically active cation doped lattice
as a catalyst comprising incorporating a phase pure crystal lattice
structure with catalytically active cations without the formation
of additional phases, such that phase analysis by conventional
x-ray diffraction method reveals a substantially phase pure
material (>95%), with bulk metal oxide dopant phase being
recorded at <5% and dopant metal oxide particle size, as
determined by line-broadening/Scherrer equation determination, is
about 30 .ANG. to about 100 .ANG..
23. The method according to claim 22, wherein the catalytically
active cation doped into the lattice structure is from about 0.01
wt % to 15wt %, based upon the total mass of the catalyst.
24. The method according to claim 22, wherein the catalytically
active cation doped into the lattice structure is from about 0.1 wt
% to 10 wt %, based upon the total mass of the catalyst.
25. The method according to claim 22, wherein the catalytically
active cation doped into the lattice structure is from about 1 wt %
to 7.5%, based upon the total mass of the catalyst
26. The method according to claim 22, wherein the catalytically
active cation doped lattice material is produced by a direct
synthesis via co-precipitation.
27. The method according to claim 22, wherein the catalytically
active cation doped lattice material is produced by contacting the
lattice material with a precursor solution of dissolved cations
under conditions of high pH and low hydronium ion (H.sub.3O.sup.+)
content, followed by drying and calcination to remove any solvent
and to convert the cations into highly dispersed metallic or metal
oxide ensembles or clusters.
28. The method according to claim 22, wherein the catalytically
active cation doped lattice material is produced by contacting the
lattice material with a precursor solution of dissolved cations and
an organic depositing reagent which is an aqueous soluble organic
capable of forming a hydrogen-bonded, gel-like matrix when the
water or other solvent is removed by heating; said gel-like matrix
supporting ions of precursor cations to maintain high homogeneity
and high dispersion within and on the lattice.
29. The method according to claim 22, wherein the catalytically
active cation doped lattice material is produced by contacting the
lattice material with a precursor solution of dissolved cations
under conditions of low pH and high hydronium ion (H.sub.3O.sup.+)
content, followed by drying and calcination to remove any solvent
and to convert the cations into highly dispersed metallic or metal
oxide ensembles or clusters.
30. The method according to claim 12, wherein the catalyst
additionally contains an inert oxide binder selected from the group
consisting of alumina, titania, non-zeolitic silica-alumina,
silica, zirconia, composites and mixtures thereof.
31. The method according to claim 22, wherein the catalyst
additionally contains a minor concentration co-catalyst based upon
a zeolite/zeotype or metal exchanged zeolite/zeotype.
32. The method according to claim 31, wherein the optional
zeolite/zeotype or metal exchanged zeolite/zeotype is from about 1
wt % to about 35 wt % of total catalyst mass.
33. The method according to claim 31, wherein the optional
zeolite/zeotype or metal exchanged zeolite/zeotype is selected from
the group consisting of ZSM5, zeolite .beta., chabazite, SAPO-34,
zeolites characterized by a structure containing an 8-ring pore
opening structure and mixtures thereof.
34. The method according to claim 31, wherein the metal employed in
the metal exchanged zeolite/zeotype is selected from the group
consisting of copper, iron and mixtures thereof.
35. The method according to claim 34, wherein exchanged copper and
iron or mixture thereof is present at 0.5 to about 7.5 wt % based
on the mass of zeolite/zeotype.
36. The method according to claim 22, wherein the catalyst and a
binder are coated on a flow through ceramic monolith, metal
substrate or foam.
37. The method according to claim 22, wherein the catalyst and a
binder are coated on a wall-flow ceramic filter substrate.
38. The method according to claim 22, wherein the catalyst is
extruded with appropriate binder and fibres to yield a fully formed
monolith.
39. A heterogeneous base metal catalyst, with optional low
zeolite/zeotype content with said catalyst consisting of: (a) a
phase pure crystal lattice structure, wherein the lattice structure
is selected from one or a mixture of oxides based upon zirconium,
cerium-zirconium composite, cerium-zirconium-yttrium composite,
cerium-zirconium-rare earth composite or
cerium-zirconium-yttrium-rare earth composite, and (b)
catalytically active cations dispersed with said lattice structure,
wherein the catalytically dispersed cations are selected from the
group consisting of the transition metal series, alkaline earth
metal group, alkali metal group of the Periodic Table of Elements
and mixtures thereof.
40. The catalyst according to claim 39 wherein said cations are
selected from the group consisting of Cu, Fe, Nb, Ta, W and
mixtures thereof.
Description
INTRODUCTION AND BACKGROUND
[0001] Oxides of Nitrogen, specifically NO and NO.sub.2
collectively referred to as NOx, are well known and toxic
by-products of internal combustion engines e.g. motor vehicles,
fossil fuel powered electricity generation systems and industrial
processes. NOx, and more specifically NO, is formed via the
reactions of free radicals in the combustion process, as first
identified by Y. B. Zeldovich (Acta Physico-chern. USSR, 21 (1946)
577), viz:
N.sub.2+O..fwdarw.NO+N. (1)
N.+O.sub.2.fwdarw.NO+O. (2)
[0002] As indicated Nitrogen Oxides are directly toxic to living
beings (P. E. Morrow J. Toxicol Environ Health 13(2-3), (1984),
205-27), in addition NOx directly contributes to and is an indirect
factor in several sources of environmental pollution. Thus Nitrogen
oxides are directly involved in the formation of acid rain but are
also reagents in the processes for the production of photochemical
smog and ozone which have been correlated to significant adverse
impacts on human health (M. V. Twigg, Applied Catalysis B, vol. 70,
(2007), 2). Hence increasingly stringent legislative limits have
been introduced in order to regulate the emission of such compounds
from the exhausts of both gasoline and diesel internal combustion
engines e.g. Euro 5 or Euro 6 [Regulation (EC) No 715/2007 of the
European Parliament and of the Council, 20 Jun. 2007, Official
Journal of the European Union L 171/1, see also Twigg, Applied
Catalysis B, vol. 70, (2007), p 2-25 and R. M. Heck, R. J. Farrauto
Applied Catalysis A vol. 221, (2001), p 443-457 and references
therein].
[0003] The challenge for meeting the legislative NOx targets for
stoichiometric gasoline engines is readily fulfilled by the
application of the well established chemistry of the three way
catalytic converter (e.g. see SAE 2005-01-1111). However the
converse is true for NOx reduction for diesel compression ignition
engines or other fuel lean i.e. oxygen rich combustion cycles, e.g.
lean gasoline direct injection, since three-way catalytic
conversion is only effective under stoichiometric air: fuel ratios
(SAE 2005-01-1111). Thus while diesel/compression ignition engines
may offer increased durability, provide high torque at low engine
rpm, and increased fuel economy/decreased emissions their inherent
lean burn operation provides a major challenge to fulfilling
legislative NOx targets. Hence a range of exhaust after-treatment
technologies have been developed to address this requirement. These
technologies include, but are not limited to, engine control
methodologies/modification, alternate combustion cycles and the use
of after-treatment systems e.g. catalytic control devices which
eliminate exhaust pollutants by promoting chemical changes to
convert the unwanted NOx species into nitrogen. Currently
technologies for NOx control include the Diesel NOx Trap/NOx
Storage Catalyst (DNT/NSC), Urea/NH.sub.3 Selective Catalytic
Reduction catalyst (SCR) and Hydrocarbon-SCR catalyst.
[0004] The chemistry of the Urea/Ammonia SCR catalyst comprises a
complex set of decomposition (eqn 3--for Urea feed) and
reduction-oxidation reactions (eqns 4-9) with diverse surface
intermediates which form the basis for extensive academic and
practical study e.g. App Cat B 13 (1997) 1-25, App Cat B 84 (2008)
497, J. Phys. Chem. C (2009), 113, 1393, SAE 2008-01-1184, SAE
2008-01-1323 etc. These reactions are summarised in eqns 3-9.
Equations 4-6 detail the desired chemistries of the Selective
Catalytic Reduction (SCR) catalyst i.e. the interaction between an
oxidised form of Nitrogen (NO, NO.sub.2) and a reduced form of
Nitrogen (NH.sub.3) with a subsequent condensative reaction to give
N.sub.2 and H.sub.2O as principle reaction products. However in
certain instances additional and competing processes may be
initiated which can result in loss of reductant concentration i.e.
so-called parasitic oxidation (eqns 7-9) of the injected
Urea/Ammonia resulting in the formation of N.sub.2 and H.sub.2O (as
a best case scenario--eqn 7), the generation of N.sub.2O, powerful
Greenhouse gas (approximately 300 stronger than CO.sub.2 eqn 9), or
even additional NOx (eqn 8).
TABLE-US-00001 (3) (NH.sub.2)CO + 4H.sub.2O .fwdarw. 2NH.sub.3 +
6CO.sub.2 Urea hydrolysis (4) 4NO + 4NH.sub.3 + O.sub.2 .fwdarw.
4N.sub.2 + 6H.sub.2O standard/`slow` SCR (5) 3NO.sub.2 + 4NH.sub.3
.fwdarw. (7/2)N.sub.2 + 6H.sub.2O NO.sub.2 only SCR (6) NO +
NO.sub.2 + 2NH.sub.3 .fwdarw. 2N.sub.2 + 3H.sub.2O `Fast` SCR (7)
4NH.sub.3 + 3O.sub.2 .fwdarw. 2N.sub.2 + 6H.sub.2O parasitic
NH.sub.3 oxidation to N.sub.2 (8) 4NH.sub.3 + 5O.sub.2 .fwdarw. 4NO
+ 6H.sub.2O parasitic NH.sub.3 oxidation to NO (9) 2 NH.sub.3 +
2O.sub.2 .fwdarw. N.sub.2O + 3H.sub.2O parasitic NH.sub.3 oxidation
to N.sub.2O
[0005] The principal reaction mechanism is represented in equation
(3). However, under practical conditions it has been repeatedly
demonstrated that the reaction of NO/NO.sub.2 mixtures with ca. 50%
of the NOx present as NO.sub.2 results in the highest rate of NOx
conversion by NH.sub.3 (eqn 4) (E. S. J. Lox Handbook of
Heterogeneous Catalysis 2.sup.nd Edition, p 2274-2345 and
references therein). Furthermore, while the reaction between
NH.sub.3 and NO.sub.2 is known to occur (eqn 5), it is not
kinetically dominant, hence as NO.sub.2 concentration increases
above ca. 50% there is a concomitant decrease in catalyst activity
and overall rates (A. Grossale, I. Nova, E. Tronconi, D.
Chatterjee, M. Weibel, J. Catal, 256 (2008) 312-322). However, it
should always be stressed that the rates of reactions will also
vary greatly depending on the reaction temperature in this especial
instance on the sort of the catalyst used and indeed upon the
presence of reactive poisons in the gas stream and the relative
poison tolerance of the different catalyst formulations employed
therein.
[0006] NH.sub.3 SCR has been applied successfully for >20 years
for the remediation of NOx from the exhaust gases of large
industrial plants e.g. power stations. Hence there is extensive
prior art in the field. The following discussion will attempt a
brief precis of this body of work.
[0007] The first class of materials developed for the process is
based upon vanadium oxide supported on titanium oxide. This class
of catalyst may additionally be promoted by other metals such as
Tungsten (or other acidic metals to enhance NH.sub.3
activation/adsorption) or Alkali or Alkaline Earth metal (as a NOx
trap). Such technologies were initially developed for power
stations but have more recently been applied to mobile
applications. Their long commercial history, relatively low cost
and high performance in the preferred operational window of ca.
200-400.degree. C. makes this class of technology attractive for
some applications. There are however several drawbacks to such
catalysts which are especially severe for vehicular applications.
These drawbacks include limited hydrothermal durability, especially
under the rigorous conditions of DPF (diesel particulate filter)
regeneration, limited catalyst lifetime, susceptibility to
poisoning by exhaust components e.g. SOx, and poor activity at low
(<250.degree. C., NH.sub.3 activation and NO reduction is low)
and higher temperatures (>ca. 400.degree. C. parasitic oxidation
of NH.sub.3 being problematic). Exemplary references for
Vanadia-Titania SCR include U.S. Pat. No. 4,085,193, U.S. Pat. No.
4,916,107, U.S. Pat. No. 4,929,586, U.S. Pat. No. 5,827,489, U.S.
Pat. No. 6,475,944, U.S. Pat. No. 7,431,895, U.S. Pat. No.
7,498,010 and US2005/0069477 A1 amongst others.
[0008] The second class of materials for SCR catalysts is based
upon Zeolites. Zeolites are microporous crystalline aluminosilicate
materials characterised by well ordered 3-D structures with uniform
pore/channel/cage structures of 3 to 10 Angstroms (depending on
framework type) and the ability to undergo ion exchange to enable
the dispersion of catalytically active cations throughout the
structure. Zeolites, metal exchanged Zeolites and promoted versions
thereof have been studied in great detail for many years and
provide highly active low and intermediate temperature SCR
catalysts e.g. Japanese Patent 51-69476 (1976). Given the
aforementioned flexibility in structure type and modification of
Zeolites it is therefore unsurprising that an enormous body of
papers and patents have accrued in this field. For example, U.S.
Pat. No. 5,417,949 (Mobil 1995) describes a process for converting
NOx with NH.sub.3 to N.sub.2/H.sub.2O under lean conditions using a
molecular sieve having a Constraint Index of up to about 12, with
the molecular sieve selected from the group having the structure of
Zeolite Y, Zeolite L, Zeolite .beta., ZSM-4, ZSM-20, Mordenite,
VPI-5, SAPO-11, SAPO-17, SAPO-34, SAPO-37, MCM-36, and MCM-41.
Similarly there have been studies addressing the manipulation of
the Silica:Alumina characteristics of the Zeolite to enhance
activity and hydrothermal durability e.g. U.S. Pat. No. 7,118,722,
U.S. Pat. No. 7,182,927. In addition there has been a considerable
body of work examining the synthesis, characterisation and
application of proton (U.S. Pat. No. 6,569,394 and U.S. Pat. No.
5,589,147) and Copper and Iron ion-exchanged Zeolites (U.S. Pat.
No. 4,961,917, U.S. Pat. No. 6,843,971, U.S. Pat. No. 7,005,116 and
U.S. Pat. No. 7,049,261). This large body of research has confirmed
the high activity, broad temperature window and improved
hydrothermal durability and poison tolerance of Zeolite systems cf.
Vanadia-titania based SCR systems. However Zeolite SCR catalysts
are not without drawbacks. For example extended or severe
hydrothermal aging results in dealumination of the framework
structure with a resultant loss of acidity (Y. Cheng, J. Hoard, C.
Lambert, J-H. Kwakb and C. H. F. Peden, Catal Today 36 (1-2),
(2008), 34-39). Moreover, HC retention in the Zeolite structure has
been demonstrated as a limitation of conventional Zeolites due to
accumulation of carbonaceous deposits and resultant active site
blocking (Y. Huang, Y. Cheng and C. Lambert, SAE Int. J. of Fuels
& Lubricants, vol. 1 (2009), 466-470). Additionally it has been
demonstrated that combustion of retained HC, e.g. during
post-injection, in ion-exchanged Zeolites can result in
uncontrolled HC combustion and internal exotherm which steams and
extracts cations from the Zeolite (J. Girard, R. Snow, G. Cavataio
and C. Lambert, SAE 2008-01-0767).
[0009] More recently a new sub-class of Zeolite and Zeotype
(structural isotypes/isomorphs based upon for example
alumina-phosphate, silica-alumina-phosphate i.e. ALPO, SAPO)
materials for SCR have been introduced. These materials are based
upon so-called `8-ring` structures of the structure type CHA
(Chabazite) and related structure types e.g. AEI, AFT, AFX, DDR,
ERI, ITE, ITW, KFI, LEV, LTA, PAU, RHO, and UFI. These alternate
Zeolite structures show promise in addressing issues related to HC
(hydrocarbon) uptake/site blocking and also for limiting
deactivation by in-situ combustion, as the `critical-diameter` of
the Zeolites are so small that ingress of HCs into the internal
porosity of the materials is limited, e.g. for CHA the channel
diameters are 3.8*3.8 .ANG., thus only limited quantities of small
HC molecules may enter. Moreover it has been found that both
Chabazite (`pure` aluminosilicate) and SAPO-34
(silica-alumino-phosphate isomorph) display a surprisingly high
hydrothermal durability and retain good activity after hydrothermal
aging cycles as high as 900.degree. C. (WO 2008/106519 A1 and WO
2008/118434 A1 for Chabazite and SAPO34 resp.). However,
notwithstanding these significant improvements in durability and HC
poisoning tolerance it should be highlighted that the these new
Zeolites/Zeotypes still present common issues to all Zeolites in
that they are comparatively expensive, time consuming to produce,
and require specialised autoclaves operating at high pressure and
temperature and have a somewhat limited supply base to serve the
forthcoming volumes required to fulfil market requirements in the
coming years.
[0010] In order to address the cost and supply concerns for Zeolite
SCR catalysts there have been many efforts to develop simpler,
robust mixed metal oxide catalyst systems of comparable efficacy.
For example U.S. Pat. No. 5,552,128 describes the use of acidic
solid Group IVB metal oxide modified with oxy-anion Group VIB metal
and containing at least 1 metal ex Group IB, IVA, VB, VIIB, VIII
and mixtures thereof, with Ni, Fe, Mn, Sn, Cu, Ru and mix Group IVB
is Zr and Group VIB is W being especially favoured. More recently
there have also been efforts to develop SCR catalysts based upon
Zr--Si-Oxide, Zr--Si--W-Oxide and Zr--Ti--Si--W Oxides
(WO/2008/046920, WO/2008/046921 and SAE 2007-01-0238). The use of
TiO.sub.2-containing systems is also recorded in JP 52-42464 which
cites a catalyst containing 50-97 (atomic %) titanium oxide as its
first active ingredient, 2-49 (atomic % percent) cerium oxide as
its second active ingredient, and 1-30% (atomic percent) of at
least one compound selected from molybdenum oxide, tungsten oxide,
vanadium oxide, iron oxide, and copper oxide as its third active
ingredient with illustrative examples including Ti--Ce--Cu,
Ti--Ce--Fe, Ti--Ce--W and Ti--Ce--Mo. Additionally WO/2008/150462
describes a complex multi-phase oxide catalyst system with high
activity for NH.sub.3--SCR of NOx comprising at least two
components wherein `the first component is selected from oxides of
a transition metal other than the metal contained in the second
component`, with V.sub.2O.sub.5, MoO.sub.3, WO.sub.3, and mixtures
and combinations thereof being preferred. This active phase is
present at 0.1% to 30% and is supported by a second component from
oxides of Cerium or Lanthanide or
Cerium/Lanthanide/Titanium/Zirconium or combinations and mixtures
thereof. Further examples of oxide base SCR may be found in EP
1736232 which describes a complex oxide consisting of 2 or more
oxides selected from silica, alumina, titania, zirconia, and
tungsten oxide; and a rare earth metal or a transition metal except
Cu, Co, Ni, Mn, Cr, and V. The use of Zirconium oxide support for
SCR catalysts is also recorded in N. Apostolescu et al. in Appl
Catal B: Env 62 (2006) 104-114, for a 1.4mol % Fe and 7.0 mol %
WO.sub.3 on ZrO.sub.2 catalyst. Similarly U.S. Pat. No. 5,552,128
cites Group IVB (Zr) metal oxide as a support with catalytic
modification being provided by an oxyanion of a Group VIB metal
(e.g. W) with further promotion by use of at least one metal
selected from the group consisting of Group IB, Group IVA, Group
VB, Group VIIB and Group VIII (Fe) and mixtures thereof.
Additionally sulphated Zirconia may be employed as a support for an
SCR catalyst, again in conjunction with specific transition metals
e.g. tungsten or molybdenum oxide (JP 2003-326167). More recently
US 2008/0095682 A1 proposes the use of composite oxides based upon
Cerium Zirconium with additionally containing Mo/Mn W, Nb, Ta.
Further examples may also be found in GB 1473883, WO/2008/085265
and WO 2009001131. However, in all cases the activity displayed by
such systems remain somewhat below that observed by the preferred
Zeolite systems, particularly after hydrothermal aging cycles.
[0011] Hence what is required in the art is a technology to provide
highly active and selective SCR catalysis with improved
hydrothermal durability and decreased cost. Additionally the new
technology must provide the aforementioned improvements whilst
retaining a wide operating range, tolerance to high NO.sub.2
contents and also possessing enhanced resistance to HC and SOx
poisons present in the exhaust stream to fulfil the requirements of
modern multi-brick emission control architectures.
SUMMARY OF THE INVENTION
[0012] The invention disclosed herein describes active lattice
based catalysts for the selective catalytic reduction (SCR) of
Oxides of Nitrogen (NOx) using a NH.sub.3 or an appropriate
organo-Nitrogen compound. The active lattice based catalysts herein
employ the favourable structural matrices of ZrOx, Zr--CeOx and
Zr--Ce-REOx crystal structures with their proven hydrothermal
durability. Into these durable matrices one may disperse active
cations (redox, acid or alkali/alkaline, or transition metal) with
high (atomic) dispersion both without negatively impacting redox
function but additionally incorporating a secondary catalytic site
and function. It is proposed, and will be demonstrated, that stable
and active NH.sub.3/Urea-SCR catalysts may be derived from
employing one or a combination of ZrOx, CeZrOx or CeZrREOx (RE=Y or
one or more Rare Earth metals or combinations of Y and Rare Earth
Metals) phases as a host matrix for active cations which facilitate
SCR catalysis. As used herein, the term "Rare Earth" means the 30
rare earth elements composed of the lanthanide and actinide series
of the Periodic Table of Elements.
[0013] Specifically, it is proposed that high activity is obtained
by the application of the aforementioned solid solutions that have
been promoted by the inclusion of specific di-valent (e.g. Ca, Cu,
Sr etc), tri-valent (e.g. Co, Fe, Mn etc.) and Penta-valent (e.g.
Nb, Ta) dopants at high dispersion within the oxide matrix. The
choice of base, i.e. non-Precious Group, metal or metal(s) to be
incorporated within the oxide matrix is based upon various
properties proposed to facilitate the SCR process. For example, but
without wishing to be bound by theory, the dopant may enhance redox
function and therefore enhance NH.sub.3 activation (H abstraction)
or NO activation/oxidation. Alternatively the dopant may be
selected to enhance the acidic character of the lattice structure
which in turn facilitates NH.sub.3 adsorption and activation. A
further possibility is the use of a chemically basic dopant e.g.
alkali, alkaline earth metal or transition metal which is
introduced to provide highly dispersed centres for the adsorption
of NOx to facilitate SCR. Finally the cation may posses a
combination of these characteristics e.g. redox acid, however in
all cases the choice of cation dopant will be based upon chemical
characteristics known to be beneficial for Urea/NH.sub.3 SCR. Thus
typical dopants could comprise Ca, Sr, Cu, Mn, Fe, Nb etc.
[0014] In another aspect, the invention relates to a method for
making a catalytically active cation doped lattice as a catalyst
comprising incorporating a phase pure crystal lattice structure
with catalytically active cations without the formation of
additional phases, such that phase analysis by conventional x-ray
diffraction method reveals a substantially phase pure material
(>95%), with bulk metal oxide dopant phase being recorded at
<5% and dopant metal oxide particle size, as determined by
line-broadening/Scherrer equation determination, is about 30 .ANG.
to about 100 .ANG..
[0015] The catalytically active cation can be doped into the
lattice structure from about 0.01 wt % to 15wt %, based upon the
total mass of the catalyst. Preferably the catalytically active
cation is doped into the lattice structure from about 0.1 wt % to
10 wt %, based upon the total mass of the catalyst and more
preferably from about 1 wt % to 7.5%, based upon the total mass of
the catalyst.
[0016] The catalytically active cation doped lattice material can
be produced in a number of ways such as by a direct synthesis via
co-precipitation.
[0017] In another way, the catalytically active cation doped
lattice material is produced by contacting the lattice material
with a precursor solution of dissolved cations under conditions of
high pH (pH>8) and low hydronium ion (H.sub.3O+) content,
followed by drying and calcination to remove any solvent and to
convert the cations into highly dispersed metallic or metal oxide
ensembles or clusters.
[0018] Also, the catalytically active cation doped lattice material
can be produced by contacting the lattice material with a precursor
solution of dissolved cations and an organic depositing reagent
which is an aqueous soluble organic capable of forming a
hydrogen-bonded, gel-like matrix when the water or other solvent is
removed by heating; said gel-like matrix supporting ions of
precursor cations to maintain high homogeneity and high dispersion
within and on the lattice.
[0019] Still further, the catalytically active cation doped lattice
material is produced by contacting the lattice material with a
precursor solution of dissolved cations under conditions of low pH
(pH.gtoreq.4) and high hydronium ion (H.sub.3O+) content, followed
by drying and calcination to remove any solvent and to convert the
cations into highly dispersed metallic or metal oxide ensembles or
clusters.
[0020] In another embodiment, the present invention describes a
method for removal of NOx pollutants from the exhaust stream of a
diesel/compression ignition engine. This is achieved by contacting
the NOx-containing exhaust stream with the novel catalysts
described herein in the presence of Urea, Urea-derived fraction,
NH.sub.3 or other N-based reductant, where the catalyst comprises
one or more active components derived from phase pure cation doped
crystal lattice structures wherein the crystal lattice is based
upon ZrOx, CeZrOx or CeZrREOx.
[0021] The use of ZrOx, CeZrOx or CeZrREOx in automotive emissions
control catalysis applications is itself not unprecedented. Indeed,
application of solid electrolytes with crystal lattices based on
Zirconia (ZrO.sub.2), thorium (ThO.sub.2), and ceria (CeO.sub.2)
doped with lower valent ions have been extensively studied for
emissions control, e.g. U.S. Pat. No. 6,585,944 and U.S. Pat. No.
6,387,338. This work has shown that the introduction of lower
valent ions, such as Rare Earths and Alkaline Earths (strontium
(Sr), calcium (Ca), and magnesium (Mg)), results in the formation
of oxygen vacancies in order to preserve electrical neutrality. The
presence of the oxygen vacancies in turn gives rise to oxygen ionic
conductivity (OIC) at high temperatures (>800.degree. C.).
Typical commercial or potential applications for these solid
electrolytes thus not only include three-way-conversion (TWC)
catalysts but also includes their use in solid oxide fuel cells
(SOFC) for energy conversion, oxygen storage (OS) materials in,
electrochemical oxygen sensors, oxygen ion pumps, structural
ceramics of high toughness, heating elements, electrochemical
reactors, steam electrolysis cells, electrochromic materials,
magnetohydrodynamic (MHD) generators, hydrogen sensors, catalysts
for methanol decomposition and potential hosts for immobilizing
nuclear waste.
[0022] Both CeO.sub.2 and ThO.sub.2 solid electrolytes exist in the
cubic crystal structure in both doped and undoped forms. In the
case of doped ZrO.sub.2, partially stabilized ZrO.sub.2 consists of
tetragonal and cubic phases while the fully stabilised form exists
in the cubic fluorite structure. The amount of dopant required to
fully stabilize the cubic structure for ZrO.sub.2 varies with
dopant type. For Ca it is in the range of about 12-13 mole%, for
Y.sub.2O.sub.3 and Sc.sub.2O.sub.3 it is >18 mole % of the Y or
scandium (Sc), and for other rare earths (e.g., Yb.sub.2O.sub.3,
Dy.sub.2O.sub.3, Gd.sub.2O.sub.3, Nd.sub.2O.sub.3, and
Sm.sub.2O.sub.3) it is in the range of about 16-24 mole % of
ytterbium (Yb), Dy, gadolinium (Gd), Nd, and samarium (Sm).
[0023] As indicated, solid solutions consisting of ZrO.sub.2,
CeO.sub.2 and trivalent dopants are widely used in
three-way-conversion (TWC) catalysts as oxygen storage (OS)
materials and are found to be more effective than pure CeO.sub.2
both for higher oxygen storage capacity and in having faster
response characteristics to air-to-fuel (A/F) transients. In
addition there is increasing use of comparable materials in fuel
lean emission control applications e.g. the Diesel Oxidation
Catalyst (U.S. Ser. No. 12/408,411), the Diesel Catalysed
Particulate Filter (U.S. Ser. No. 12/363,329) and the NOx
Storage/Regeneration trap (U.S. Ser. No. 12/240,170).
[0024] In this application, we expand upon some of these concepts
and take specific advantage of the favourable and durable
structural matrices of ZrOx, Zr--CeOx and Zr--Ce-REOx crystal
structures into which the active cations can be dispersed with high
dispersion both without negative impact to redox function whilst
incorporating a secondary catalytic site and function. In fact, it
has been shown the incorporation of base metal cations can result
in a dramatic and durable promotion of the normal redox
characteristics of OS materials (see for example U.S. Pat. No.
6,387,338, U.S. Pat. No. 6,585,944, U.S. Pat. No. 6,605,264 and
U.S. patent applications Ser. Nos. 12/363,310, 12/363,329,
12/408,411). An analogy to this idea is the addition of Ce.sup.4+
to the ZrO.sub.2 matrix. The role of Ce in the catalytic oxidation
of CO for example is based upon its redox activity as follows:
Ce.sup.3++O.sub.2.fwdarw.O.sub.2--+Ce.sup.4+, followed by reaction
of the O.sub.2-- anion with CO (NO) to give CO.sub.3-- (NO.sub.3)
and subsequent decomposition to CO.sub.2(NO.sub.2) and O-- and
finally regeneration of Ce.sup.3+. This reaction cycle can occur on
pure CeO.sub.2 and the nature/energy barrier of the
Ce.sup.4+.revreaction.Ce.sup.3+ redox cycle can be probed using TPR
(Temperature Programmed Reduction) with reduction peaks for surface
CeO.sub.2 at 350-600.degree. C. No bulk CeO.sub.2 is reduced at
these temperatures the crystal lattice as the CeO.sub.2 cannot
accommodate formation of the larger Ce.sup.3+ ions and hence O
mobility away from the bulk in order to preserve electrical
neutrality cannot occur. However, when Ce.sup.4+ ions are dispersed
into the ZrO.sub.2 lattice the redox activity of Ce.sup.4+ is not
negatively impacted but in fact is greatly enhanced, not primarily
through modification of the inherent chemistry/reducibility of the
Ce.sup.4+ ion itself but more by a geometric mechanism as noted
above where all the Ce.sup.4+ ions are now accessible. Further, the
presence of the ZrO.sub.2 matrix greatly stabilises the material
from surface area loss, crystallite growth and loss of porosity.
ZrO.sub.2 may also inhibit or protect Ce.sup.4+ from formation of
undesirable stable compounds with the acidic exhaust components
such as CO.sub.2 and SO.sub.2 due to the inherent acidity of
ZrO.sub.2 relative to CeO.sub.2. Thus the aim is to incorporate
additional functional cations into the crystal lattices of the
aforementioned ZrOx, CeZrOx and CeZrREOx materials to achieve
similar chemical and accessibility benefits and thus facilitate
enhanced SCR performance.
[0025] The ZrOx material of the invention is characterised as
having >75% Zr as oxide and <25% of cation dopants to provide
both functionality and ensure the material is present as an active
and single phase pure cubic component. The CeZrOx and CeZrREOx
materials of the invention are an OIC/OS material having about 0.5
to about 95 mole % zirconium, about 0.5 to about 90 mole % cerium,
and optionally about 0.1 to about 20 mole % RE, wherein RE is
selected from the group consisting of rare earth metal(s), alkaline
earth metal(s), Yttrium and combinations comprising at least one of
the foregoing, based upon 100 mole % metal component in the
material. Again the materials are further characterised by a high
phase purity, as determined by conventional powder X-Ray
Diffraction (XRD) method. The phase purity of all materials is
preferably >95% i.e. <5% of additional phases and most
preferably >99% single phase. All of the crystal materials are
further characterised by having fresh surface areas, as determined
by the standard N2 physisorption (BET) method of >25 m.sup.2/g
and more preferably >50 m.sup.2/g. The surface area is derived
from the porous nature of the materials which may comprise small
(<20 nm), or more preferably of medium pore dimension (pore
diameter 20<x>100 nm). This `mesoporosity` is a preferred
trait due to the specific enhancements afforded to the catalyst by
this textural characteristic e.g. thermal durability, enhanced mass
transfer etc.
[0026] The use of the ZrOx/CeZrOx/CeZrREOx crystal lattice as a
framework for effective dispersion of dopant cations also provides
effective tools for control of the fundamental chemical of the
subsequent powder. For example, one option for this class of
compounds is the control of overall acidity of the support by
inclusion of appropriate alkaline or acidic cations as outlined
above. Similarly it is possible to control and modify the ionic
conductivity characteristics via manipulation of the vacancy
density. The vacancy density can be controlled by adding the five
valent Nb to the nominally 4-valent/3-valent Zr/RE.sup.3+ matrix
with necessary inclusion of oxygen for electrical neutrality. These
type compositions are already covered in U.S. Pat. Nos. 6,585,944
and 6,468,941 and more recently similar compositions have been
claimed in WO 2003 082740 and WO 2003 082741 respectively although
these patents do not refer specifically to SCR applications or to
utilising the crystal lattice system as a generic host matrix for
other catalytically active ions. In summary the above represent
specific examples of the generic flexibility afforded by this new
class of materials and represent a powerful means of addressing a
specific catalytic challenge.
[0027] Benefits and features include: [0028] a) The ability to
introduce cations, catalytically active for the SCR process, at
high dispersion within the lattice of the solid solution with
minimal disruption of either the redox activity or catalytic
function for SCR for ions such as: Ag, Co, Cu, Fe, Mn, Nb etc. In
fact incorporation of such ions has been shown to enhance redox
activity (U.S. Pat. No. 6,387,338, U.S. Pat. No. 6,585,944, U.S.
Pat. No. 6,605,264, U.S. patent applications Ser. Nos. 12/240,170
and 12/363,310). The choice of the cations is highly flexible and
may include species to promote redox, enhance acidity or basicity
or indeed a combination e.g. redox acid. [0029] b) The ability to
introduce specific catalytic functions or synergies, for example
the combination of a cubic lattice material into which Alkali
metal, Alkaline Earth metal or Transition metal is introduced at
near atomic dispersion with aforementioned dopant metal chosen so
as to provide a means of storing high concentrations of NOx on its
surface and retaining such species until their subsequent SCR to
N.sub.2 may be facilitated. [0030] c) Improved performance and
durability of performance due to the inherent stability of the
crystal lattice employed as a framework for dispersion of
aforementioned cations. The stability of the system and absence of
steam leaching effects, as seen for cation-exchanged/impregnated
Zeolite systems, provides for this enhanced stability. [0031] d)
The ability to engineer specific single phase and phase pure cation
doped systems by appropriate selection of co-dopants (Y, La, Gd and
other Rare Earths as shown in U.S. Pat. No. 6,387,338, U.S. Pat.
No. 6,585,944 and U.S. Pat. No. 6,605,264). The generation of phase
pure systems is known, and will be further demonstrated, to provide
optimal performance for SCR and other processes. This is in
contrast to US 2008/0095682 A1 wherein complex multi-oxide and
multi-phase systems dubbed
Ce.sub.a--Zr.sub.b--R.sub.c-A.sub.d-M.sub.e-O.sub.x are claimed as
active SCR catalysts. [0032] e) The provision of great flexibility
in structural/chemical modification to optimise performance: this
can include the use of a wide variety of di- and tri- and
penta-valent cations for control of the crystal lattice parameter,
maximise phase purity, defect density within the lattice or modify
surface acidity/basicity etc. [0033] f) The ability to manipulate
and tailor the textural characteristics of the doped lattice system
to generate meso-porous systems of high and durable pore volume and
surface area. This stable surface area, derived from the large pore
system when combined with the high, possibly mono-atomic dispersion
of the cations in the lattice, results in high accessibility of the
gaseous reactants to the redox active/acidic/basic cations, thereby
limiting mass transfer effects and providing associated enhanced
performance [0034] g) Provision of a lower cost, non
Zeolite/Zeotype SCR catalyst with competitive low temperature
reactivity, excellent hydrothermal durability and tolerance to
general exhaust gas poisons e.g. CO, SOx and especially
hydrocarbons. The latter is a known poison of SCR activity due to
accumulation of carbonaceous deposits (Y. Huang, Y. Cheng and C.
Lambert, SAE Int. J. of Fuels & Lubricants vol. 1 (2009),
466-470). Additionally it has been shown that the rapid combustion
of HC retained in ion-exchanged ZSM5 and Zeolite .beta. systems can
also result in a catastrophic deactivation due to uncontrolled HC
combustion and exotherm which both steams and extracts cations from
the Zeolite matrix (J. Girard, R. Snow, G. Cavataio and C. Lambert,
SAE 2008-01-0767). These effects are not seen for the new class of
lattice dispersed cation catalysts. [0035] h) The synthesis of
cation doped lattice or cubic lattice cation doped materials is
also simpler, quicker and requires no subsequent post-synthesis
processing as is the case for metal exchanged/doped Zeolites. The
dispersion of the cations and the framework are also more
hydrothermally durable than conventional Zeolite systems.
[0036] This strategy contrasts to that of conventional SCR NOx
control catalysts in which there are no formal attempts to generate
synergy between redox and other desired chemical functions of SCR
by the use of a well defined highly durable and poison resistant
host matrix. For example while US 2008/0095682 A1 employs Cubic
Fluorite phases as a catalytic component, it further discloses the
presence of additional phases e.g. MnWO.sub.4, thereby conceding
the multi-phasic nature of the materials exploited therein.
[0037] The above-described and other features will be appreciated
and understood by those skilled in the art from the following
detailed description, drawings, and appended claims
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 shows the Engine Dynamometer Performance of OS1, OS2
and OS3 vs commercial SCR reference after 50 h dyno aging at
660.degree. C. Performance is with pre DOC.
[0039] FIG. 2 depicts the Engine Dyno Performance of OS4, OS5 and
OS6 versus commercial SCR reference after 50 h dyno aging at
660.degree. C. Performance is with pre DOC.
[0040] FIG. 3 illustrates the Engine Dyno Performance of OS4 after
20 h dyno aging at 830.degree. C. Performance is with and without
pre DOC.
[0041] FIG. 4 is the Engine Dyno Performance of OS7 with and
without 3% Fe-ZSM5 vs commercial SCR reference after 50 h dyno
aging at 660.degree. C. Performance is with pre DOC.
[0042] FIG. 5 illustrates the impact of a Pre-DOC on the Engine
Dyno Performance of OS8, OS9 and OS10 vs commercial SCR reference
after 50 h dyno aging at 660.degree. C.
[0043] FIG. 6 shows the Engine Dyno Performance of OS11 variants
and OS12 versus commercial SCR reference after 50 h dyno aging at
660.degree. C. Performance is with pre DOC.
[0044] FIG. 7 depicts the Engine Dyno Performance of OS12 variants
vs commercial SCR reference after 50 h dyno aging at 660.degree. C.
Performance is with pre DOC.
[0045] FIG. 8 highlights the Engine Dyno Performance of OS13, OS14
and OS15 versus commercial SCR reference after 50 h dyno aging at
660.degree. C. Performance is with pre DOC
[0046] FIGS. 9a and 9b show the transient SCR response of the
Cu-ZSM5 reference versus OS8-Cu-ZSM5. The test examined meshed
powders on the Synthetic Gas Bench (SGB) after 24 h, 10% steam air
oven aging at 700.degree. C. Performance is without DOC.
[0047] FIGS. 10a and 10b compare the NH3 desorption/`plume`
responses of the Cu-ZSM5 reference versus OS8-Cu-ZSM5. The test
examined meshed powders on the Synthetic Gas Bench (SGB) after 24
h, 10% steam air oven aging at 650.degree. C.
DETAILED DESCRIPTION OF THE INVENTION
[0048] The present invention relates to the development and use of
phase pure lattice oxide materials based upon ZrOx, CeZrOx,
CeZrYOx, CeZrREOx (where RE=Rare Earth Metal) or CeZrYREOx or
mixtures thereof as active catalysts for the SCR of NOx using
N-bearing reductant. These lattice materials are further
characterised by the presence of catalytically active cations
dispersed within the lattice structure such that conventional XRD
analysis reveals a highly phase pure material. The cations
themselves derive their catalytic efficacy by their intrinsic
reactivity which include the characteristics of redox activity,
acidic or basic nature or a combination thereof. Thus a redox
active cation dopant may increase the rate of NH.sub.3 activation
(H abstraction) or promote the dopant would likely increase the
bonding strength and quantity of NH.sub.3 adsorption and hence
facilitate its activation whilst the use of a chemically basic
dopant would provide highly dispersed centres for the adsorption of
NOx to again facilitate SCR. In a further example the cation may
exhibit multiple functions e.g. be a redox acid, thereby
facilitating activated adsorption of NH.sub.3. It must be stressed
that such conjuncture notwithstanding the choice of cation or
cations doped into the lattice structure(s) are all characterised
by their ability to enhance activity for the Urea/NH.sub.3 SCR
process.
[0049] Table 1 summarises the effect of MHSV and DOC on engine dyno
performance of the OS-based technologies ex FIG. 9 vs SCR reference
after 50 h dyno aging at 660.degree. C.
TABLE-US-00002 TABLE 1 Engine Dyno Test Details Parameter Setting
Engine setpoint 2400 rpm Test Temperatures 400, 350, 300, 250, 200,
175.degree. C. Exhaust Flow 27 .+-. 1 g/s Engine backpressure 11
.+-. 1 kPa NOx concentration 320 .+-. 20 ppm NH.sub.3 injection 320
.+-. 20 ppm Sampling 2 Hz for 300 s at each setpoint
[0050] The following set of data include a diverse range of
compositions which are listed at the end of the specification as
illustrative examples of the flexibility of the Cubic, and more
specifically Cubic Fluorite structure as a framework for the stable
dispersion of redox and catalytically active cations for SCR
catalysis. The data was generated using coated monoliths (typically
4.66 inch round by 6 inch long, 400 cells per square inch) tested
and aged in parallel on an engine dynamometer (hereafter dyno) in
flowing engine exhaust. During aging flow balancing through all
four legs of the exhaust spider was employed to ensure equivalent
aging of the monoliths. Typical aging cycles were performed in
flowing exhaust at an inlet temperature of 660.degree. C. for 50
hours. Subsequent testing was also performed on the dyno using a
Fiat 1.9 L engine and the conditions listed in Table 1. During
testing inlet temperature was controlled by means of a heat
exchanger assembly and a Diesel Oxidation Catalyst was optionally
placed in the exhaust spider, prior to the NH.sub.3 injection
point, to enable examination of the impact of NO.sub.2 generation
on the activity of the catalysts.
[0051] FIG. 1 contrasts the performance of three OS based SCR
catalysts, OS1, OS2 and OS3, with a conventional Cu-exchanged ZSM5
(MFI with SAR of 40) based technology. Testing was performed with a
pre-DOC (70 gcf Pt-only, aged 50 hours at 660.degree. C.). Herein
while there is a benefit for the commercial reference the three OS
technologies, all coated at only 2 g/in.sup.3 total washcoat load
and only 1.5 g/in.sup.3 of active OS, still display good activity
with peak NOx conversions of >80% at 300.degree. C. Thus it is
apparent that dispersion of Fe, Nb or a combination of the two
cations with a CeZrREOx lattice provides for effective NOx
reduction chemistry. It should be stressed that in the absence of
these cations activity for the CeZrREOx is neglible. However, given
the very similar performance characteristics of the three samples
it is not possible to differentiate activity based upon any
specific structure-function relationship other than that activity
is correlated to cationic dispersion in lattice. The compositions
for OS1, OS2, OS3 and others, are set forth in a list at the end of
the specification.
[0052] The activity of cation-doped CeZrREOx is further illustrated
in FIG. 2. Again the aged performance with pre-DOC is compared. In
this instance however there are clear differences between the
activities of the OS materials. Thus OS4 is seen to significantly
higher activity than OS5 and OS6. Indeed, the performance of this
material is very similar to that of the commercial reference over
the majority of the temperature range examined. Thus at 300 and
350.degree. C. a peak NOx conversion of ca. 87% is seen. This is in
contrast to OS5 and OS6 which exhibit peak NOx conversions of ca.
53% and 63% respectively. This marked difference in activity is
attributed the structural characteristics of the materials, as
determined by conventional X-Ray Diffraction (XRD) analysis and
summarised in Table 2. Hence for OS4 the material is a single,
phase pure Cubic Fluorite structure i.e. there has been successful
incorporation of the Nb cation in the lattice. This is in contrast
to OS5 and OS6. Both of these materials exhibit multiple Cubic
phases and in the case of OS6 the presence of a bulk phase due to
Nb.sub.2O.sub.5, thereby confirming that the cation has not been
fully incorporated into a cubic lattice. Given the otherwise
comparable textural and chemical properties of the three samples we
hereby attribute the high activity of OS4 to its phase pure
characteristic and the redox and dispersion benefits related
thereto.
[0053] Table 2 summarises the XRD phase analysis of OS4, OS5 and
OS6 powders.
TABLE-US-00003 TABLE 2 XRD Phase Analysis of OS4, OS5 and OS6
Lattice Size of CeZrO Constant of cubic phase (.ANG.) Phase
Identification cubic phase(.ANG.) CS R(%) OS4 Cubic phase 5.210(1)
91(2) 6.56 OS5 One major cubic 5.275(1) 75(2) 10.03 One trace cubic
5.4395 too weak to calculate OS6 Two segregated cubic 5.273(1)
83(2) 9.57 phases 5.4218 too weak to calculate Nb.sub.2O.sub.5:
Orthorhombic 6.167 .times. 3.648 .times. 3.917
[0054] The performance of OS4 was further examined after severe
aging. In the severe aging protocol hydrocarbon was permitted to
`slip` into the SCR catalyst, again at an inlet temperature of
660.degree. C. and subsequently combust over the SCR brick, thereby
resulting in an in bed temperature of 830.degree. C. i.e. an
internal exotherm of 170.degree. C. was generated in the catalyst,
in order to provide a `worst-case scenario` mode of aging. The
catalyst was then re-tested, both with and without pre-DOC giving
the results depicted in FIG. 3. These data both indicate almost no
loss in performance (cf. with DOC data in FIG. 2) after the severe
aging but also show enhanced activity of the formulation in the
absence of DOC at lower temperatures, in contrast to general
findings which show higher NO.sub.2 i.e. with pre-DOC favours low
temperature performance. This good activity in the absence of the
DOC is exemplary of the high poison tolerance of this approach,
with the significant levels of CO, HC, SOx and other species having
no impact on activity, especially in the low temperature region
where one would normally catalyst poisoning/site blocking phenomena
to be most clearly evident. Moreover analysis of the NH.sub.3
conversion data reveals another significant difference between the
behaviour of the OS4 and a conventional Zeolite SCR technology. For
conventional catalysts the performance is limited by selectivity
rather than activity i.e. NH.sub.3 conversion is also high, but a
significant proportion of the activity responsible for the high
conversion is derived from parasitic oxidation of NH.sub.3 to
N.sub.2 or more deleteriously to N.sub.2O or NOx i.e. contributing
to pollutant generation. In the case of OS4, the selectivity is not
limiting with 95-99% (with DOC) and 98-99.8% (without DOC), i.e.
N.sub.2O formation or parasitic oxidation of NH.sub.3 to NOx is
practically zero. Thus it may be seen that providing successful
incorporation of the cation into the lattice is achieved, that the
result material displays extremely high hydrothermal durability, in
excess of that seen for conventional Zeolite-based SCR
technologies.
[0055] The ability of OS-based catalysts to be combined with
conventional Zeolite SCR materials is examined in FIG. 4. Herein
the aged activity of Cu-modified OS plus 0, 0.5 and 1 g/in.sup.3 is
contrasted favourably with the Cu-ZSM5 reference. Indeed, the
samples containing Fe-ZSM5 show near identical performance to the
reference, even at lower temperatures wherein Fe-Zeolite SCR
technology is known to exhibit lower activity. Moreover at higher
temperatures these samples offer superior performance to the
reference, this is ascribed to the lower rate of parasitic
oxidation of NH.sub.3 cf. the reference. It should also be noted
that there is no appreciable difference in performance between the
0.5 and 1 g/in.sup.3 loadings suggesting an effective synergy
between the OS and Zeolite even at very low loadings of Zeolite. In
contrast the OS7 only sample does exhibit some weakness,
principally for temperatures <250.degree. C. At higher
temperatures however the activity approaches that of the
Zeolite-containing monoliths giving a peak NOx conversion of 79% at
350.degree. C. Thus these data further confirm the effectiveness of
cationic species dispersed in a lattice and also their ability to
combined with conventional Zeolite technology and provide
competitive performance at significantly decreased
Zeolite/decreased cost versus a commercial reference.
[0056] The activity of several more variants of cubic lattice
dispersed Nb.sub.2O.sub.5 were then examined, yielding the
performance data of FIG. 5. Herein aged data (50 hours at
660.degree. C. on the dyno) with and without pre-DOC are recorded.
The low temperature performances of the OS-containing monoliths for
NOx conversion while using the pre-DOC are generally equal to the
Cu-ZSM5 reference, with a possible benefit seen for OS8. In
contrast at .gtoreq.350.degree. C. all the OS-only technologies
offer increasingly large benefits vs the reference, this benefit is
again ascribed to lower rates of parasitic ammonia oxidation. In
comparison the DOC-free activity is quite low for temperatures
<250.degree. C. and indeed it is less than seen for the extreme
aged sample of FIG. 3, suggesting aggressive aging may actually
enhance DOC-free activity for these systems. However in comparison
with the conventional SCR technology there are still obvious
benefits for the OS-based parts which becomes large with increasing
temperature. Thus once again OS8 offers the highest activity with
NOx conversions as high 79% recorded at 400.degree. C., which is
equal to that seen for the case with the pre-DOC, and about double
to that seen for the Cu-ZSM5-based reference. OS9 and OS10 also
exhibit good performance with peak N.sub.2 yields in excess of 70%
observed. Thus there appears to be an especial benefit for
Nb.sub.2O.sub.5 disposed and dispersed within the cubic structure
of the CrZrREOx matrix, a benefit that is not fully realised when
the Nb.sub.2O.sub.5 is present as `extra-framework` to lattice as
seen in FIG. 2.
[0057] Based upon the successful application of redox, acidic and
redox acidic cation dopants into the cubic lattice an examination
of the use of basic dopants dispersed in the lattice was undertaken
(FIG. 6). In this instance the objective was to employ Alkaline
earth doped OS systems as a means of trapping NOx upon the surface
of the catalyst to thereby facilitate the SCR process. This aim was
achieved as all samples demonstrated appreciable activity, in
excess to that seen for un-doped CeZrOx. However the activity of
this class of OS samples was only moderate low temperature activity
cf. commercial reference, with OS12 being the best performer. This
is ascribed to the lower ability of these systems to activate
NH.sub.3 cf. the acidic doped OS systems e.g. OS4, OS8, OS9 and
OS10. At higher temperatures, wherein NH.sub.3 activation is more
facile, this barrier is overcome and the OS12 offers now equivalent
and indeed superior performance to the reference and provides a
peak NOx conversion of 87%. XRD analysis was again performed with
OS12 exhibiting a phase pure character, but OS11 was found to be
bi-phasic. This is consistent with previous observations (FIG. 2,
Table 2) and re-confirms the correlation of superior activity of
phase pure materials i.e. thereby correlating the effective
dispersion of the dopant cation into the cubic lattice with high
activity.
[0058] Table 3 summarizes the XRD phase analysis of OS11 and OS12
powders.
TABLE-US-00004 TABLE 3 XRD Phase Analysis of OS11 and OS12 Lattice
Size of CeZrO Constant of cubic phase (.ANG.) Phase Identification
cubic phase(.ANG.) CS R(%) OS11 Two segregated cubic 5.300 58(7)
6.47 phases 5.430 too weak to calculate OS12 Cubic phase 5.222
65(2) 6.9
[0059] In order to enhance the activities of the basic doped OS
systems three approaches were adopted. The first approach was the
addition of a proton Zeolite (H-ZSM5 with a SAR of 40) to boost
acidity, the second a further promotion of the combined OS-Zeolite
system by the addition of Copper to enhance the redox function, and
the third a promotion of the OS only with Copper. In the cases of
Copper addition this was achieved via the post-impregnation of
Cu(NH.sub.3OH).sub.4--following the method of OS promotion as
described in U.S. applications Ser. Nos. 12/363,310, 12/363,329 and
12/408,411 which are relied on and incorporated herein by
reference. In all cases the various promoters are added due to
their ability to increase NH.sub.3 adsorption and activation/redox
function at lower temperatures, which appears to be a limiting
factor based upon the data of FIG. 6. The results of these
approaches are summarised in FIG. 7. The data show two of the three
approaches provide significant promotion of the OS12 material. Thus
the addition of H-ZM5 was found not only to not promote low
temperature activity, it actually resulted in a decrease in SCR
activity in the intermediate temperature region (250-300.degree.
C.). In contrast both samples to which Copper was added showed
improved low and intermediate temperature activity. Indeed in the
case of the Copper+ZSM5+OS12, the activity is now competitive with
the commercial reference sample but at significantly lower Zeolite
load/cost. Hence it becomes apparent that the lattice maybe used to
effectively disperse combination of cations, introduced during
synthesis or by specific post-modification, with each cation
imbuing the CeZrREOx with specific functionalities which may
operate in a synergistic manner to yield optimal performance and
durability in the desired application.
[0060] FIG. 8 illustrates the impact of Rare Earth doping, in this
instance the specific doping of the lattice with Pr.sub.6O.sub.11,
on the performance of aged Nb-containing OS materials OS13, OS14
and OS15. It should be stressed that for all three OS materials
care was taken to balance Y and Nb concentrations in order to
facilitate effective Nb incorporation, following the teachings of
U.S. Pat. No. 6,605,264. This approach appears effective with all
samples displaying comparable performance to the commercial
reference thereby confirming the flexibility of the lattice
composition. Of the three test parts ranking follows
OS15>OS13>OS14, although the differences are small but still
may indicate that there are no apparent benefits from Nb
contents>10% by mass.
[0061] In order to further examine the performance characteristics
of OS-based SCR technologies a series of Synthetic Gas Bench (SGB)
were performed. In the first of these tests the dynamic SCR
characteristics of OS8-CuZSM5 was compared to the commercial
reference. The test was performed on meshed powders derived from
the washcoat slurries used in coating of the full size parts for
consistency. The powders were aged in a static oven (24 h, 10%
steam/air at 700.degree. C.) prior to testing. The test protocol is
as described in Table 4, i.e. first the catalyst is stabilised at
temperature in the full reactive gas, with the exception of
NH.sub.3, at a specific time NH.sub.3 is then introduced, at an
.alpha.=1 (ratio of NH.sub.3:NO), and the time response for the
catalyst to achieve peak conversion is determined. Once stable SCR
activity is realised the NH.sub.3 is then removed and the time
taken for activity to decay to zero NOx conversion is again
monitored. The purpose of the test to compare how well the
OS-technologies respond to the dynamic NOx concentration, and hence
required NH.sub.3, changes that exist under `real` application
conditions.
[0062] Table 4 lists the conditions employed in the SGB Transient
SCR Activity test.
TABLE-US-00005 TABLE 4 SGB transient SCR activity conditions
(30,000 h.sup.-1, balance N.sub.2) T/.degree. C. % NO % NH.sub.3 %
CO % O.sub.2 % H.sub.2O Time/min 300 0.03 0 0.01 9.95 10 15 300
0.03 0.03 0.01 9.95 10 10 300 0.03 0 0.01 9.95 10 30 ramp 0.03 0
0.01 9.95 10 n/a 400 0.03 0 0.01 9.95 10 15 400 0.03 0.03 0.01 9.95
10 10 400 0.03 0 0.01 9.95 10 30
[0063] The results of this study are summarised in FIGS. 9a
(300.degree. C. test) and 9b (400.degree. C. test). With respect to
response upon NH.sub.3 introduction the OS8-CuZSM5 offers a small
benefit in response at the higher temperature whilst at 300.degree.
C. the response is identical. However upon removal of the NH.sub.3
the responses of the two technologies are quite different. In both
cases the 058-CuZSM5 exhibits a significantly faster response to
NH.sub.3 removal. Thus at 300.degree. C., effective NOx conversion
drops form 60% at peak to <5% in about 10 minutes. In contrast
the commercial sample requires about 20 minutes for NOx conversion
to decrease to <5%. The responses at 400.degree. C. while
quicker follow the same trend. Hence the OS8-CuZSM5 sample requires
about 6 minutes to go from peak conversion to <5% while the
commercial Zeolite technology needs about 14 minutes. These data
are telling and suggest that a further benefit may be realised from
an OS rich, or OS only, technology in that such technologies are
better suited to the dynamic responses required in the vehicular
application. This benefit is ascribed to the lower NH.sub.3 uptake
of these materials and also consistent with the higher
selectivity/lower NH.sub.3 parasitic oxidation of such materials.
Hence unlike a Zeolite or Zeotype material the OS technologies do
not introduce a large NH.sub.3 adsorption which in turn enables a
better calibration of the required NH.sub.3 injection concentration
to achieve the desired a ratio to obtain peak performance without
wasting reductant by over-dosing or contributing to NOx formation
by rapid oxidation of `excess` NH.sub.3 chemisorbed within the
Zeolite.
[0064] The second performance characteristic of OS-based SCR
examined on the SGB was the NH.sub.3 desorption properties under
temperature excursions, again in an attempt to examine the impact
of the dynamic operating conditions of the vehicle. The tests were
performed using 0.03% NO, 0.03% NH.sub.3, 9.95% O.sub.2, 0.01% CO,
5% CO.sub.2, 10% H.sub.2O balance N.sub.2 at 30,00 h.sup.-1. In the
tests the sample was stabilized/soaked at each temperature and the
performance determined prior to increasing the temperature, in full
reactive gas mix. During the temperature step the activity and any
desorption of NH.sub.3 monitored. The sample was then stabilized at
the next temperature, with the time taken for stability also
recorded. The temperature steps and `soak` times employed were as
follows: 150/45 min, 200/45 min, 250/45min, 300/30 min, 350/min,
400/30 min, 450/30 min, 500/30 min. FIGS. 10a (NH.sub.3
conversion/desorption) and 10b (NOx ppm outlet) illustrate the
response of OS8-CuZSM5 versus Cu-ZSM5 (tested as oven aged
powders--28 hours 650.degree. C. 10% steam air). Both technologies
achieve stabilisation of NOx conversion within the first few
minutes of each soak step with the exception of the lowest
temperatures of (especially) 150 and 200.degree. C., in agreement
with FIG. 9, wherein an induction period is observed. In contrast
NH.sub.3 conversion and desorption responses shows marked
differences between the technologies. In both cases initial
NH.sub.3 conversion at 150.degree. C. is very high with 0 ppm
observed. This is ascribed to a combination of NH.sub.3 adsorption
and conversion. However, over the next ca. 15 minutes conversion is
seen to decrease and stabilise with average ppm NH.sub.3 out of 265
and 245 ppm for the reference and OS8-CuZSM5 respectively. Then as
the temperature is ramped to 200.degree. C., and indeed for each
subsequent temperature ramp to 350.degree. C., there is a large
desorption of NH.sub.3. This `plume` of NH.sub.3 is seen for both
catalysts, with the extent of plume being directly related to
catalyst composition. Thus the OS8-CuZSM5 has a peak NH.sub.3
desorption of only about 30-40 ppm higher than the steady state
conversion seen immediately prior to the onset of the ramp. In
contrast the commercial Cu-ZSM5 exhibits much larger plumes which
vary with temperature step as 120, 240, 85 and 85 ppm peak above
previous steady state conversion. These data highlight a
fundamental weakness of this class of technology since such large
emissions are not permissible in a vehicular application. Thus a
further benefit of the OS-containing washcoat is the ability to
provide competitive NOx conversion over the entire temperature
region, each after aging, but with enhanced transient SCR function
and low NH.sub.3 slip during temperature transients.
[0065] Table 5 shows the Effect of MHSV and DOC on Engine Dyno
Performance of OS only and OS+Zeolite based technologies after 50 h
dyno aging at 660.degree. C.
TABLE-US-00006 TABLE 5 Effect of MHSV and DOC (w) on Dyno
Performance of OS materials vs Zeolite SCR ex 50 h dyno aging at
660.degree. C. OS9 CuZSM II with OS8CuZSM CuZSM with DOC DOC with
DOC II 0S9 0S8CuZSM 22 g/s flow 175 44.4 35.5 42.3 33.3 26.7 22.3
200 51.3 41.4 44.4 41.4 31.9 34.4 250 88.4 85.6 82.6 54.5 49.5 43.5
300 97.3 95.5 93.1 65.3 68.5 54.5 350 97.5 99.5 99.5 78.7 83.6 69.4
400 96.4 99.2 94 90.1 94.2 83.6 33 g/s flow 300 94.3 98.4 98.7 56.4
54.5 44.2 350 98.5 99.5 99 68.2 71.3 56.9 400 92.1 94.6 88.3 79.4
85.6 71.2 450 88 89.7 87.8 88.3 87.8 79.3 44 g/s flow 300 83.2 84.6
81.9 44.4 48.5 37.8 350 93.1 96.4 88.6 52.5 60.4 49.3 400 88.3 89.3
85.2 64.3 73.7 63.8 450 86.8 87.5 80.4 75.4 79.6 74.7 500 85.4 84.1
79.5 80.8 81.5 79.1
[0066] Table 5 summarises a further dyno study; herein the aim was
to examine the impact on flow rate (Mass Hourly Space
Velocity--MHSV) and pre-DOC on performance. The aged catalysts
tested were selected from those described in FIG. 5. The catalysts
were tested on a second dyno using a larger Duramax 6.6 litre
diesel engine, which enabled higher range of flows (22+/-2 g/s,
33+/-2 g/s and 44+/-2 g/s) and temperatures (175-520.degree. C.) to
be realised during testing. NOx and NH3 concentrations were
300+/-20 ppm and 300+/-30 ppm, respectively; in all other aspects
the exhaust spider and heat exchanger configuration were as
previously stated. The data obtained shows several key
features:
[0067] i) The OS containing technologies provide effective NOx
conversion over a wide range of temperatures and flow rates both
with and without the requirement of a pre-DOC.
[0068] ii) The DOC promotes NOx conversions: This effect is
especially pronounced at lower temperatures and higher flow rates
when comparing with and without DOC results.
[0069] iii) There is a complex interaction between flow rate and
temperature with the pre DOC. Hence use of higher flow rates at
400.degree. C. shows a negative correlation with NOx conversion for
all technologies. However at 300 and 350.degree. C., the
conversions at 22 and 33 g/s are similar but in these instances
conversion is seen to decrease significantly at 44 g/s.
[0070] iv) In the absence of the DOC there is a direct negative
correlation between increasing flow rate and conversion at 300, 350
and 400.degree. C. (R2 calculations>0.95 in all cases). However
there is insufficient data to unambiguously rank the robustness of
the technologies versus flow rate but it should be stressed that in
this temperature region the OS9 technology offers the highest NOx
conversion, at all flow rates.
[0071] Table 6 illustrates the Effect of MHSV and DOC on Engine
Dyno Performance of W-promoted OS materials after 50 h dyno aging
at 660.degree. C.
TABLE-US-00007 TABLE 6 Effect of MHSV and DOC on Dyno Performance
of W-promoted OS materials ex 50 h dyno aging at 660.degree. C.
10W-OS17 10W-OS8 10W-OS18 10W-OS19 22 g/s with DOC 175 14 20.9 16.8
11.3 200 31.3 43 23.6 21.8 250 79 88.6 61.6 59.7 300 92.3 95.4 92.6
98 350 96.4 95.9 92.3 93.6 400 93.2 90.9 82.7 82.6 22 g/s no DOC
175 24.2 20.4 22 20.3 200 26.7 26.1 24.9 22.6 250 36.2 40.3 32.5
31.2 300 54.9 64 54.2 48.9 350 74.2 77.4 72.6 71.7 400 85.6 82.3 85
84 44 g/s with DOC 300 70.6 60.1 46.3 47.9 350 87.1 85.6 76.4 76.2
400 76.5 76.4 68.6 69.2 450 70.3 73.5 66.9 67 500 69.7 72.3 70.2
71.4 44 g/s no DOC 300 33.7 37.5 26.5 29.7 350 47 49.1 39.6 42.8
400 59.7 60.7 52.9 56.4 450 68.3 67.8 61.3 67.1 500 73.8 71.8 67.8
69.6
[0072] Table 6 summarises the impact of MHSV and DOC for OS based
technologies, further promoted by the post-impregnation of
Tungsten. Herein 10% W-OS8 is included as reference. This enables
comparison of redox-acid OS versus Alkaline Earth doped OS. The
performance of the aged technologies is good and follows
10W-OS8.gtoreq.10W-OS17.gtoreq.10W-OS18=10W-OS19. Clearly an
additional benefit may be realised by the addition of Tungsten to
the lattice-doped cubic OS. Further analysis reflects the trends
observed in Table 5 i.e. positive impact of DOC and negative impact
of high flow rates. Moreover the data indicate that in this
instance the activity of the catalyst may be influenced by
manipulation of the type and concentration of Rare Earth dopants in
the cubic lattice, with the combination of
Y.sub.2O.sub.3+La.sub.2O.sub.3+Pr.sub.6O.sub.11 providing the
overall best performance for the SrO-doped OS samples. Again
however none of the technologies exhibit catastrophic loss in
performance under a wide range of conditions, in the presence of
various poisons such as CO, HC, SOx and the like, in the exhaust
stream (especially in DOC free tests) confirming the technologies
to be competitive and appropriate for vehicular applications.
TABLE-US-00008 TABLE 7 Effect of Tungsten promotion, MHSV and DOC
on Dyno Performance of W-promoted, dual OS materials ex 50 h dyno
aging at 660.degree. C. 10W-OS8 10W-OS8-OS16 10W-OS16-OS8 OS8 22
g/s with DOC 175 16.5 26.3 18.4 8.5 200 35.7 36.3 26.8 25.8 250
81.3 76.6 63.9 61.9 300 89.1 83.1 87.5 95.7 350 95.3 95.5 91.4 95.8
400 91.2 91.2 87.5 94.9 22 g/s no DOC 175 21.2 24.5 20.1 14.4 200
24.6 27.8 22.4 18.9 250 36.9 38.5 32.5 25.9 300 55.5 57.2 53.5 43.0
350 75.1 76.3 74.2 76.7 400 85.9 88.5 84.9 93.5 44 g/s with DOC 300
61.6 73.3 45.6 48.2 350 79.1 90.5 73 74.9 400 74.7 80.2 69.2 77.7
450 72.3 72.9 68.7 82.9 500 74.1 72.1 71.3 87.4 44 g/s no DOC 300
36.2 37.3 36.9 26.5 350 51.5 49.8 47.1 42.7 400 63.1 63.2 60.6 64.4
450 68.1 69.0 68.7 78.0 500 71.2 72.9 70.9 86.8
[0073] Table 7 is a further summary of W-promoted OS technologies
but herein the effect of combining a lattice doped OS with
`conventional` OS materials is examined. The aim was to increase
the redox character of the washcoat by utilising a standard OS from
a three way catalyst (U.S. Pat. No. 6,387,338) known for its facile
O ion conducting characteristic and high hydrothermal durability.
The data show high performance for all technologies, again under a
diverse range of conditions. It is also apparent that while the
Tungsten promotion provides improved low temperature performance
the un-promoted OS8 material offers superior high temperature
activity. Both of these features are attributed to the ability of
the catalyst to activate NH.sub.3, at lower temperatures this is
beneficial as the activation of NH.sub.3 may play a role in the
rate determining step of the process, but at high temperatures a
high ability to activate NH.sub.3 results in increased rates of
parasitic NH.sub.3 oxidation. With respect to the concentration of
dual OS present in the washcoat the data suggest high levels of
cation-doped OS are preferred with higher loadings of non-cation
doped OS resulting in decreased performance. Again the data show
the positive role of the DOC, notwithstanding the fact that the OS
materials still retain fair NOx conversion even in the absence of
the OS--particularly for T.gtoreq.400.degree. C. where activities
are nearly identical. Similarly high flow rates are again
correlated with decreased activity, although again at higher
temperatures the differences become increasingly small, especially
for the OS8 technology.
[0074] It should be further noted that the terms "first", "second"
and the like herein do not denote any order of importance, but
rather are used to distinguish one element from another, and the
terms "a" and "an" herein do not denote a limitation of quantity,
but rather denote the presence of at least one of the referenced
items. Furthermore, all ranges disclosed herein are inclusive and
combinable (e.g., ranges of "up to about 25 weight percent (wt. %),
with about 5 wt. % to about 20 wt. % desired, and about 10 wt. % to
about 15 wt. % more desired" is inclusive of the endpoints and all
intermediate values of the ranges, e.g. "about 5 wt. % to about 25
wt. %, about 5 wt. % to about 15 wt. %" etc.
[0075] In one embodiment, a catalytic device can comprise a housing
disposed around a substrate with an SCR catalyst disposed at the
substrate. Also, the method for treating the off-gas of a gasoline
lean burn or compression ignition exhaust or lean fossil fuel
combustion exhaust stream can comprise: introducing the said
exhaust stream to an SCR catalyst; and reducing to N.sub.2 the NOx
component of said exhaust stream.
[0076] The catalyst materials are included in the formulation by
combining alumina, or other appropriate support, with other
catalyst materials to form a mixture, drying (actively or
passively), and optionally calcining. More specifically, a slurry
can be formed by combining alumina and water, and optionally pH
control agents (such as inorganic or organic acids and bases)
and/or other components. The catalytic OS materials can then be
added. This slurry can then be washcoated onto a suitable
substrate. The washcoated product can be dried and heat treated to
fix the washcoat onto the substrate.
[0077] This slurry can be dried and heat treated, e.g., at
temperatures of about 500.degree. C. to about 1,000.degree. C., or
more specifically about 500.degree. C. to about 700.degree. C., to
form the finished catalyst formulation. Alternatively, or in
addition, the slurry can be washcoated onto the substrate and then
heat treated as described above, to adjust the surface area and
crystalline nature of the support. Once the support has been heat
treated, catalyst metals may optionally be disposed on the support.
The catalyst metals, therefore, can be added after the washcoat is
fixed onto the substrate by additional washcoat steps and/or by
exposing the washcoated substrate to a liquid containing the
catalytic metal.
[0078] The catalyst comprises a phase pure lattice oxide material
based upon ZrOx, CeZrOx, CeZrYOx, CeZrREOx (where RE=Rare Earth
Metal) or CeZrYREOx or mixtures thereof as active catalysts for the
SCR of NOx using a N-bearing reductant. The lattice oxide
material(s) is/are further characterised by the presence of
catalytically active cations dispersed within the lattice structure
such that conventional XRD analysis reveals a phase pure material.
The catalyst may additionally comprise an inert refractory binder
selected from the group consisting of alumina, titania,
non-Zeolitic silica-alumina, silica, zirconia, composites thereof
or mixtures comprising at least 2 thereof. Finally the catalyst may
additionally contain (35.ltoreq. wt %) Zeolite/Zeotype or metal
exchanged Zeolite/Zeotype material selected from one or a mixture
of more than one selected from the group ZSM5, Zeolite .beta.,
Chabazite, SAPO-34 or other Zeolite characterised by a structure
containing an 8-ring pore opening structure. The metal employed in
the metal exchanged Zeolite/Zeotype is selected from one or a
mixture of Copper and Iron.
[0079] The supported catalyst can be disposed on a substrate. The
substrate can comprise any material designed for use in the desired
environment, e.g., a compression ignition/diesel engine
environment. Possible materials include cordierite, silicon
carbide, metal, metal oxides (e.g., alumina, and the like),
glasses, and the like, and mixtures comprising at least one of the
foregoing materials. These materials can be in the form of packing
material, extrudates, foils, perform, mat, fibrous material,
monoliths (e.g., a honeycomb structure, and the like), wall-flow
monoliths (with capability for diesel particulate filtration),
other porous structures (e.g., porous glasses, sponges), foams,
molecular sieves, and the like (depending upon the particular
device), and combinations comprising at least one of the foregoing
materials and forms, e.g., metallic foils, open pore alumina
sponges, and porous ultra-low expansion glasses. Furthermore, these
substrates can be coated with oxides and/or hexaaluminates, such as
stainless steel foil coated with a hexaaluminate scale.
Alternatively the cation-doped lattice material may be extruded,
with appropriate binders and fibres, into a monolith or wall-flow
monolithic structure.
[0080] Although the substrate can have any size or geometry, the
size and geometry are preferably chosen to optimise geometric area
in the given exhaust emission control device design parameters.
Typically, the substrate has a honeycomb geometry, with the combs
through-channel having any multi-sided or rounded shape, with
substantially square, triangular, pentagonal, hexagonal,
heptagonal, or octagonal or similar geometries preferred due to
ease of manufacturing and increased surface area.
[0081] Once the supported catalytic material is on the substrate,
the substrate can be disposed in a housing to form the converter.
The housing can have any design and comprise any material suitable
for application. Suitable materials can comprise metals, alloys,
and the like, such as ferritic stainless steels (including
stainless steels e.g. 400-Series such as SS-409, SS-439, and
SS-441), and other alloys (e.g. those containing nickel, chromium,
aluminium, yttrium and the like, to permit increased stability
and/or corrosion resistance at operating temperatures or under
oxidising or reducing atmospheres).
[0082] Also similar materials as the housing, end cone(s), end
plate(s), exhaust manifold cover(s), and the like, can be
concentrically fitted about the one or both ends and secured to the
housing to provide a gas tight seal. These components can be formed
separately (e.g., moulded or the like), or can be formed integrally
with the housing using methods such as, e.g., a spin forming, or
the like.
[0083] Disposed between the housing and the substrate can be a
retention material. The retention material, which may be in the
form of a mat, particulates, or the like, may be an intumescent
material e.g., a material that comprises vermiculite component,
i.e., a component that expands upon the application of heat, a
non-intumescent material, or a combination thereof. These materials
may comprise ceramic materials e.g., ceramic fibres and other
materials such as organic and inorganic binders and the like, or
combinations comprising at least one of the foregoing
materials.
[0084] Thus, the coated monolith with OS-containing catalyst is
incorporated into the exhaust flow of the fuel lean engine. This
provides a means for treating said exhaust stream to reduce the
concentrations of NOx by passing said diesel exhaust stream over
the aforementioned SCR catalyst under net oxidising conditions
(oxygen rich), in the presence of in-exhaust injected Urea or
Ammonia, or HC to facilitate catalytic conversion into
environmentally benign Nitrogen gas.
[0085] The above-described catalyst and process and other features
will be appreciated and understood by those skilled in the art from
the following detailed description, drawings, and appended
claims.
EXAMPLES
[0086] The synthesis method of the OS4 material followed the method
of Bortun and Nunan (U.S. Pat. No. 6,605,264) relied on and
incorporated herein by reference. Herein, the required
concentrations of Zr (ZrO(NO.sub.3).sub.2 solution), Ce (ex
Ce(NO.sub.3).sub.3.6H.sub.2O) and Y (Y(NO.sub.3).sub.3.6H.sub.2O)
are dissolved in deionised (D.I.) water with constant stirring to
form a homogeneous solution. Next a mixture of Nb (ex NbCl.sub.5)
in aqueous HCl, to which small quantities of H.sub.2O.sub.2 are
added (to maintain Nb.sup.5+ in solution) was prepared. This
mixture was then added slowly, and with vigorous mixing, to the
other aqueous precursors. The final mixture was then added to 3M
NH.sub.4OH, again with vigorous mixing, to form a precipitated
suspension. The suspension was mixed for 3 hours and then filtered
and repeatedly washed to remove any residual NH.sub.4Cl and
NH.sub.4NO.sub.3, prior to drying at 120.degree. C. for 24 h and
calcination at 700.degree. C. for 2 hours.
[0087] The synthesis of OS7 followed U.S. application Ser. No.
12/363,310 which is relied on and incorporated herein by reference.
Herein the required mass of copper (II) nitrate trihydrate is
dissolved in minimal D.I. water. To this solution 30 wt %
NH.sub.4OH was added until a blue-black copper tetra-ammoniacal
solution was obtained. The copper tetramine was then added to OS2
(dry basis), with mixing until a homogeneous powder was obtained.
The powder was dried and calcined at 540.degree. C. for 4
hours.
[0088] The procedure for making Parts OS1, OS2 and OS3, is as
follows: Slowly add Alumina to deionised (D.I.) water, containing
any required slurry viscosity/rheology modifiers, with milling over
ca. 15 minutes. Mill the slurry to a d.sub.50 (diameter of 50% of
the particles) of 5-7 microns, confirm d.sub.90. Next slowly add
appropriate OS powder, correct for loss on ignition (LOI), to
minimal additional D.I. water to produce a slurry of appropriate
viscosity and rheology for coating. Confirm D.sub.50 and D.sub.90
of OS slurry. Add OS slurry to Alumina slurry and mix for a minimum
of 30 minutes. Lightly mill combined slurry to homogenise and check
particle size of components. Target d.sub.50 of 3-6 microns for
combined slurry, and re-confirm d.sub.90. Check specific gravity
and pH and adjust to facilitate coating in one pass. Then coat
monolith in 1 pass and calcine at temperatures .gtoreq.540.degree.
C. for .gtoreq.1 hour.
[0089] The procedure for making Parts OS4, OS5 and OS6, is as
follows: Slowly add the Alumina to a 0.5% HNO.sub.3/D.I. water
solution, add any other required slurry viscosity/rheology
modifiers. Target a slurry of 50% solids with a final pH of 3.5-4,
adjust pH if necessary. Next mill the slurry to a d.sub.50 of 4-5
microns, and d.sub.90 of 14-16 microns. After milling the pH should
be 4-4.5, adjust if required. Next slowly add appropriate OS
powder, correct for LOI, and additional D.I. water (at 50% mass of
OS) to the alumina slurry. Then mill in a vibratory mill to a
d.sub.50 of 3-4 microns. In any case milling must not exceed 10
minutes. Check specific gravity and pH of slurry and adjust to
facilitate coating in one pass. Then coat monolith in 1 pass and
calcine at temperatures .gtoreq.540.degree. C. for .gtoreq.1
hour.
[0090] The procedure for making Part OS7-FeZEO 1: Slowly add
Alumina to D.I. water, containing any required slurry modifiers,
with milling over ca. 15 minutes. Mill the slurry to a d.sub.50 of
7-10 microns, confirm d.sub.90. Next slowly add 3% Fe-MFI27 powder,
correct for LOI, with additional D.I. water (1:1 by mass to
Zeolite) to produce a slurry of appropriate viscosity and rheology
for coating. Mill slurry to a d.sub.50 of 5-8 microns. Next slowly
add OS7 powder, correct for LOI, to minimal D.I. water to produce a
slurry of appropriate viscosity and rheology for coating. Mill to a
d.sub.50 of 4-6 microns, confirm D.sub.90. Add OS slurry to
Alumina-Zeolite slurry and mix for a minimum of 30 minutes. Lightly
mill combined slurry to homogenise particle size. Target d.sub.50
of 3-6 microns, and re-confirm d.sub.90. Check specific gravity and
pH of slurry and adjust to facilitate coating in one pass. Then
coat monolith in 1 pass and calcine at temperatures
.gtoreq.540.degree. C. for .gtoreq.1 hour.
[0091] The procedure for making Part OS7-FeZEO 2 is as follows:
Slowly add Alumina to D.I. water, containing any required slurry
modifiers, with milling over ca. 15 minutes. Mill the slurry to a
d50 of 7-10 microns, confirm d90. Adjust pH to facilitate 1 pass
coating, coat monolith and calcine at >540.degree. C. for >1
hour. Next add 3% Fe-MFI27 powder, correct for LOI, to D.I. water
(target 1:1 by mass to Zeolite) to produce a slurry of appropriate
viscosity and rheology for coating. Mill resultant slurry to a d50
of 5-8 microns. Next slowly add OS7 powder, correct for LOI, to
minimal D.I. water to produce a slurry of appropriate viscosity and
rheology. Mill to a d50 of 4-6 microns, confirm D90. Add OS slurry
to Zeolite slurry and mix for 30 minutes. Lightly mill combined
slurry to homogenise particle size of components. Target d50 of 3-6
microns for combined slurry, and re-confirm d90. Check specific
gravity and pH of slurry and adjust to facilitate coating in one
pass. Then coat monolith in 1 pass and calcine at >540.degree.
C. for >1 hour.
[0092] The procedure for making Part OS7: Slowly add Alumina to
D.I. water, containing any required slurry viscosity modifiers,
with milling over ca. 15 minutes. Mill the slurry to a d50 of 7-10
microns, confirm d90. Adjust pH to facilitate 1 pass coating, coat
monolith and calcine at >540.degree. C. for >1 hour. Next
slowly add OS7 powder, correct for LOI, to minimal D.I. water to
produce a slurry of appropriate viscosity and rheology. Mill to a
d50 of 4-6 microns, confirm D90. Add OS slurry to Zeolite slurry
and mix for at least 30 minutes. Lightly mill combined slurry to
homogenise particle size of components. Target d50 of 3-6 microns,
and re-confirm d90. Check specific gravity and pH and adjust to
facilitate coating in one pass. Coat monolith in 1 pass and calcine
at >540.degree. C. for >1 hour.
[0093] The procedure for making Parts OS8, OS9 and OS10 is as
follows: Slowly add Alumina to D.I. water, containing any required
slurry viscosity/rheology modifiers, with milling over ca. 15
minutes. Mill the slurry to a d50 of 7-10 microns, confirm d90.
Adjust pH to facilitate 1 pass coating, coat monolith and calcine
at >540.degree. C. for >1 hour. Next slowly add appropriate
OS powder, correct for LOI, to minimal D.I. water with any required
modifiers to produce a slurry of appropriate viscosity and
rheology. Mill in a vibratory mill to a d50 of 4-6 microns, confirm
D90. Target d50 of 3-6 microns for combined slurry, and confirm
d90. Check specific gravity and pH of slurry and adjust to
facilitate coating in one pass. Coat monolith in 1 pass and calcine
at >540.degree. C. for >1 hour.
[0094] The procedure for making Parts OS11a, OS11b and OS12 is as
follows: Slowly add Lanthanum-stabilised Alumina to D.I. water,
containing any required slurry viscosity/rheology modifiers, with
mixing over ca. 15 minutes. Mill to a d50 of 5-6 microns, confirm
d90, taking care to ensure slurry does not exceed 25.degree. C.
Adjust pH to facilitate 1 pass coating, coat monolith and calcine
at >540.degree. C. for >1 hour. Next slowly add appropriate
OS powder, correct for LOI, to minimal D.I. water and any required
modifiers to produce a slurry of appropriate viscosity and
rheology. Mill to a d50 of 4-6 microns, confirm D90. Check specific
gravity and pH of slurry and adjust to facilitate coating in one
pass. Then coat monolith in 1 pass and calcine at >540.degree.
C. for >1 hour.
[0095] The procedure for making Part OS12+ZSM5 is as follows:
Slowly add Lanthanum-stabilised Alumina to D.I. water, containing
any required slurry viscosity/rheology modifiers, with mixing over
ca. 15 minutes. Mill the slurry to a d50 of 5-6 microns, confirm
d90. Take care to ensure slurry does not exceed 25.degree. C.
Confirm specific gravity and pH and adjust to facilitate 1 pass
coating, coat monolith and calcine at >540.degree. C. for >1
hour. Next slowly add OS12 powder and then MFI40 powder, both
correct for LOI, to minimal D.I. water with any required modifiers
to produce a slurry of appropriate viscosity and rheology. Mill to
a d50 of 4-6 microns, confirm D90. Check specific gravity and pH of
slurry and adjust to facilitate coating in one pass. Then coat
monolith in 1 pass and calcine at >540.degree. C. for >1
hour.
[0096] The procedure for making Part OS12+ZSM5+Cu is as follows:
Slowly add Lanthanum-stabilised Alumina to D.I. water, containing
any required slurry viscosity/rheology modifiers, with mixing over
ca. 15 minutes. Mill the slurry to a d50 of 5-6 microns, confirm
d90. Take care to ensure slurry does not exceed 25.degree. C.
Confirm specific gravity and pH and adjust to facilitate 1 pass
coating, coat monolith and calcine at >540.degree. C. for >1
hour. Next slowly add OS12 powder and then MFI40 powder, both
correct for LOI, to minimal D.I. water with any required modifiers
to produce a slurry of appropriate viscosity and rheology for
coating. Mill to a d50 of 4-6 microns, confirm D90. Check specific
gravity and pH of slurry and adjust to facilitate coating in one
pass. Coat monolith in 1 pass and calcine at >540.degree. C. for
>1 hour. Next determine moisture uptake of dried part. Using
this value prepare an aqueous solution of Cu(NH.sub.3OH).sub.4, pH
should be 9-10, and post-impregnate part, dry and calcine at
>540.degree. C. for >1 hour.
[0097] The procedure for making Part OS12+Cu: Slowly add
Lanthanum-stabilised Alumina to D.I. water containing any required
slurry viscosity modifiers, with mixing over ca. 15 minutes. Mill
the slurry to a d50 of 5-6 microns, confirm d90. Take care to
ensure slurry does not exceed 25.degree. C. Confirm specific
gravity and pH and adjust to facilitate 1 pass coating, coat
monolith and calcine at >540.degree. C. for >1 hour. Next
slowly add OS12 powder, correct for LOI, to minimal D.I. water with
any required modifiers to produce a slurry of appropriate viscosity
and rheology for coating. Mill to a d50 of 4-6 microns, confirm
D90. Check specific gravity and pH and adjust to facilitate coating
in one pass. Coat monolith in 1 pass and calcine at >540.degree.
C. for >1 hour. Next determine moisture uptake or dried part.
Using this value prepare an aqueous solution of
Cu(NH.sub.3OH).sub.4, pH should be 9-10, and post-impregnate part,
dry and calcine at >540.degree. C. for >1 hour.
[0098] The procedure for making Part OS8+Cu-ZSM5 is as follows:
Slowly add the Alumina to a 0.5% HNO.sub.3/D.I. water solution, add
any other required slurry viscosity/rheology modifiers. Target a
slurry of 50% solids with a final pH of 3.5-4, adjust final pH if
necessary. Next mill the slurry to a d50 of 4-5 microns, and d90 of
<9 microns. Allow slurry to age for 24 hours to stabilise. Next
slowly add OS8 and 5% Cu-ZSM5 powders, both correct for LOI, to
minimal D.I. water with any required modifiers to produce a slurry
of appropriate viscosity and rheology. Mill to a d50 of 4-6
microns, confirm D90. During milling maintain close to pH 6 and
adjust with judicious use of organic base if pH goes below 3.5. Add
OS8-CuZSM5 slurry to alumina slurry and mix for a minimum of 30
minutes. Check specific gravity and pH of slurry and adjust to
facilitate coating in one pass. Then coat monolith in 1 pass and
calcine at >540.degree. C. for >1 hour.
[0099] The procedure for making Parts OS13, OS14 and OS15 is as
follows: Slowly add Alumina to D.I. water, containing any required
slurry viscosity/rheology modifiers, with milling over ca. 15
minutes. Mill the slurry to a d50 of 7-10 microns, confirm d90.
Adjust pH to facilitate 1 pass coating, coat monolith and calcine
at >540.degree. C. for >1 hour. Next slowly add appropriate
OS powder, correct for LOI, to minimal D.I. water to produce a
slurry of appropriate viscosity and rheology for coating. Mill to a
d50 of 4-6 microns, confirm D90. Check specific gravity and pH of
slurry and adjust to facilitate coating in one pass. Then coat
monolith in 1 pass and calcine at >540.degree. C. for >1
hour.
[0100] The procedure for making Part 10W-OS8 is as follows: Slowly
add the Alumina to a 0.4% HNO.sub.3/D.I. water solution, add any
other required slurry viscosity/rheology modifiers. Target a slurry
of 50% solids with a final pH of 3.5-4, adjust final pH if
necessary. Next mill the slurry to a d50 of 4-5 microns, and d90 of
<9 microns. Allow slurry to age for 24 hours to stabilise. Next
slowly add OS8 powder, correct for LOI, to minimal D.I. water and
any required modifiers to produce a slurry of appropriate viscosity
and rheology for coating. Mill to a d50 of 4-6 microns, confirm
D90. Dissolve ammonium metatungstate
[(NH.sub.4).sub.6H.sub.2W.sub.12O.sub.40.xH.sub.2O] salt in minimal
D.I. water with constant stirring to provide appropriate loading of
Tungsten, mix for at least 15 minutes. Add Tungsten solution to OS8
slurry and mix for a minimum of 60 minutes to allow full
chemisorption of Tungsten. Add alumina slurry to OS8-W slurry and
mix for 30 minutes. Check specific gravity and pH of slurry and
adjust to facilitate coating in one pass. Then coat monolith in 1
pass and calcine at >540.degree. C. for >1 hour.
[0101] The procedure for making Parts 10W-OS8-OS16 and 10W-OS16-OS8
is as follows: Slowly add Alumina to a 0.4% HNO.sub.3/D.I. water
solution, add any other required slurry viscosity/rheology
modifiers. Target a slurry of 50% solids with a final pH of 3.5-4,
adjust final pH if necessary. Mill the slurry to a d50 of 4-5
microns, and d90 of <9 microns. Allow slurry to age for 24 hours
to stabilise. Next slowly add required OS8 and OS16 powders,
correct for LOI, to minimal D.I. water and any required modifiers
to produce a slurry of appropriate viscosity and rheology for
coating. Mill to a d50 of 4-6 microns, confirm D90. Dissolve
ammonium metatungstate
[(NH.sub.4).sub.6H.sub.2W.sub.12O.sub.40.xH.sub.2O] salt in minimal
D.I. water with constant stirring to provide appropriate loading of
Tungsten, mix for at least 15 minutes. Add Tungsten solution to OS8
slurry and mix for a minimum of 60 minutes to allow full
chemisorption of Tungsten. Add alumina slurry to OS8-W slurry and
mix for 30 minutes. Check specific gravity and pH of slurry and
adjust to facilitate coating in one pass. Then coat monolith in 1
pass and calcine at >540.degree. C. for >1 hour.
[0102] The procedure for making Parts 10W-OS17, 10W-OS18 and
10W-OS19 is as follows: Slowly add the Alumina to a 0.4%
HNO.sub.3/D.I. water solution, add any other required slurry
viscosity/rheology modifiers. Target a slurry of 50% solids with a
final pH of 3.5-4, adjust final pH if necessary. Next mill the
slurry to a d50 of 4-5 microns, and d90 of <9 microns. Allow
slurry to age for 24 hours to stabilise. Next slowly add
appropriate OS powder, correct for LOI, to minimal D.I. water and
any required modifiers to produce a slurry of appropriate viscosity
and rheology for coating. Mill to a d50 of 4-6 microns, confirm
D90. Dissolve ammonium metatungstate salt in minimal D.I. water
with constant stirring to provide appropriate loading of Tungsten,
mix for at least 15 minutes. Add Tungsten solution to OS8 slurry
and mix for a minimum of 60 minutes to allow full chemisorption of
Tungsten. Add alumina slurry to OS8-W slurry and mix for 30
minutes. Check specific gravity and pH of slurry and adjust to
facilitate coating in one pass. Then coat monolith in 1 pass and
calcine at >540.degree. C. for >1 hour.
[0103] List of OS Compositions Employed: [0104] OS1 CeO.sub.2 31.99
ZrO.sub.2 50.9 La.sub.2O.sub.3 4.9 Y.sub.2O.sub.3 4.88
Fe.sub.2O.sub.3 7.33 [0105] OS2 CeO.sub.2 44.75 ZrO.sub.2 36.28
Nd.sub.2O.sub.3 9.87 Pr.sub.6O.sub.11 4.48 Nb.sub.2O.sub.5 4.62
[0106] OS3 CeO.sub.2 44.72 ZrO.sub.2 35.33 Nd.sub.2O.sub.3 9.68
Pr.sub.6O.sub.11 4.59 Nb.sub.2O.sub.5 4.72 Fe.sub.2O.sub.3 0.96
[0107] OS4 CeO.sub.2 31.76 ZrO.sub.2 54.79 Y.sub.2O.sub.3 6.44
Nb.sub.2O.sub.5 7.01 [0108] OS5 CeO.sub.2 44.33 ZrO.sub.2 38.06
La.sub.2O.sub.3 9.77 Pr.sub.6O.sub.11 4.66 Fe.sub.2O.sub.3 3.18
[0109] OS6 CeO.sub.2 44.4 ZrO.sub.2 35.36 La.sub.2O.sub.3 9.77
Pr.sub.6O.sub.11 4.74 Nb.sub.2O.sub.5 4.58 Fe.sub.2O.sub.3 1.15
[0110] OS7 CeO.sub.2 38.75 ZrO.sub.2 47.7 La.sub.2O.sub.3 4.82
Pr.sub.6O.sub.11 4.72 CuO 4 [0111] OS8 CeO.sub.2 32.07 ZrO.sub.2
54.1 Y.sub.2O.sub.3 6.39 Nb.sub.2O.sub.5 7.44 [0112] OS9 CeO.sub.2
36.07 ZrO.sub.2 54.19 Y.sub.2O.sub.3 4.87 Nb.sub.2O.sub.5 4.87
[0113] OS10 CeO.sub.2 32.26 ZrO.sub.2 51.95 La.sub.2O.sub.3 2.05
Y.sub.2O.sub.3 6.29 Nb.sub.2O.sub.5 7.45 [0114] OS11 CeO.sub.2 44
ZrO.sub.2 39.5 La.sub.2O.sub.3 9.5 Pr.sub.6O.sub.11 4.5 CaO 2.5
[0115] OS12 CeO.sub.2 31.5 ZrO.sub.2 52.3 La.sub.2O.sub.3 5
Y.sub.2O.sub.3 5 SrO 5 [0116] OS13 CeO.sub.2 30.22 ZrO.sub.2 52.16
Y.sub.2O.sub.3 7.84 Pr.sub.6O.sub.11 2.05 Nb.sub.2O.sub.5 7.73
[0117] OS14 CeO.sub.2 30 ZrO.sub.2 48.4 Y.sub.2O.sub.3 9.85
Pr.sub.6O.sub.11 2.02 Nb.sub.2O.sub.5 9.73 [0118] OS15 CeO.sub.2
30.14 ZrO.sub.2 54.16 Y.sub.2O.sub.3 7.85 Nb.sub.2O.sub.5 7.85
[0119] OS16 CeO.sub.2 31.5 ZrO.sub.2 58.6 La.sub.2O.sub.3 4.9
Y.sub.2O.sub.3 5 [0120] OS17 CeO.sub.2 31 ZrO.sub.2 57
Y.sub.2O.sub.3 5 La.sub.2O.sub.3 3 Pr.sub.6O.sub.11 3 SrO 1 [0121]
OS18 CeO.sub.2 31 ZrO.sub.2 58 Y.sub.2O.sub.3 5 La.sub.2O.sub.3 5
SrO 1 [0122] OS19 CeO.sub.2 31 ZrO.sub.2 58 Y.sub.2O.sub.3 5
Pr.sub.6O.sub.11 5 SrO 1
[0123] Washcoat definitions in g/in.sup.3, the commercial reference
catalysts used in these studies are all based upon 5% Cu-MFI40.
[0124] FIG. 1: [0125] 0.5 Al.sub.2O.sub.3 1.5 OS1 [0126] 0.5
Al.sub.2O.sub.3 1.5 OS2 [0127] 0.5 Al.sub.2O.sub.3 1.5 OS3 [0128]
FIG. 2: [0129] 1.3 Al.sub.2O.sub.3 2.7 OS4 [0130] 1.3
Al.sub.2O.sub.3 2.7 OS5 [0131] 1.3 Al.sub.2O.sub.3 2.7 OS6 [0132]
FIG. 3: [0133] 1.3 Al.sub.2O.sub.3 2.7 OS4 [0134] FIG. 4: [0135]
0.5 Al.sub.2O.sub.3 1 3% Fe-MFI(27) 2 OS7 [0136] 1.1
Al.sub.2O.sub.3 0.5 3% Fe-MFI(27) 2 OS7 [0137] 1.1 Al.sub.2O.sub.3
2.5 OS7 [0138] FIG. 5: [0139] 1.1 Al.sub.2O.sub.3 pass 1|2.5 OS8
pass 2 [0140] 1.1 Al.sub.2O.sub.3 pass 1|2.5 OS9 pass 2 [0141] 1.1
Al.sub.2O.sub.3 pass 1|2.5 OS10 pass 2 [0142] FIG. 6: [0143] 1.1 4%
La.sub.2O.sub.3--Al.sub.2O.sub.3 pass 1|2.5 OS11 pass 2 [0144] 1.5
4% La.sub.2O.sub.3--Al.sub.2O.sub.3 pass 1|2.5 OS11 pass 2 [0145]
1.5 4% La.sub.2O.sub.3--Al.sub.2O.sub.3 pass 1|2.5 OS12 pass 2
[0146] FIG. 7: [0147] 1.5 4% La.sub.2O.sub.3--Al.sub.2O.sub.3 pass
1|0.5 MFI(40) 2 OS12 pass 2 [0148] 1.5 4%
La.sub.2O.sub.3--Al.sub.2O.sub.3 pass 1|0.5 MFI(40) 2 OS12 pass
2|0.225 Cu(NH.sub.3OH).sub.4 [0149] 1.5 4%
La.sub.2O.sub.3--Al.sub.2O.sub.3 pass 1|2.5 OS12 pass 2|0.225
Cu(NH.sub.3OH).sub.4 [0150] FIG. 8: [0151] 1.1 Al.sub.2O.sub.3 pass
1|2.5 OS14 pass 2 [0152] 1.1 Al.sub.2O.sub.3 pass 1|2.5 OS13 pass 2
[0153] 1.1 Al.sub.2O.sub.3 pass 1|2.5 OS15 pass 2 [0154] FIG. 9:
SGB Analysis of Transient SCR Response at a) 300.degree. C. and b)
400.degree. C. 0.5 Al.sub.2O.sub.3 1.5 5% CuMFI(40) 1.5 OS8 [0155]
FIG. 10: SGB Analysis of NH.sub.3 `Plume` Formation during
Temperature ramp. 0.5 Al.sub.2O.sub.3 1.5 5% CuMFI(40) 1.5 OS8
[0156] Table 1: Engine Dyno Test Details [0157] Table 2: XRD Phase
Analysis of OS4, OS5 and OS6 [0158] Table 3: XRD Phase Analysis of
OS11 and OS12 [0159] Table 4: SGB Analysis [0160] 1.1
Al.sub.2O.sub.3 pass 1|2.5 OS9 pass 2 [0161] 0.5 Al.sub.2O.sub.3
1.5 5% CuMFI(40) 1.5 OS8 [0162] Table 5: Effect of MHSV and
presence of DOC (w) on Engine Dyno Performance of OS materials vs
commercial SCR reference after 50 h dyno aging at 660.degree. C.
[0163] 1.1 Al.sub.2O.sub.3 pass 1|2.5 OS9 pass 2 [0164] 0.5
Al.sub.2O.sub.3 1.5 5% CuMFI(40) 1.5 OS8 [0165] Table 6: Effect of
MHSV and presence of DOC on Engine Dyno Performance of W-promoted
OS materials after 50 h dyno aging at 660.degree. C. [0166] 0.35
Al.sub.2O.sub.3 0.2889W 2.6OS8 [0167] 0.35 Al.sub.2O.sub.3 0.2889W
1.7334OS8 0.8666OS16 [0168] 0.35 Al.sub.2O.sub.3 0.2889W 1.7334OS16
0.8666OS8 [0169] 1.1 Al.sub.2O.sub.3 pass 1|2.5 OS8 pass 2 [0170]
Table 7: Effect of Tungsten promotion, MHSV and presence of DOC on
Engine Dyno Performance of W-promoted, dual OS materials after 50 h
dyno aging at 660.degree. C. [0171] 0.35 Al.sub.2O.sub.3 0.2889W
2.6OS17 [0172] 0.35 Al.sub.2O.sub.3 0.2889W 2.6OS8 [0173] 0.35
Al.sub.2O.sub.3 0.2889W 2.6OS18 [0174] 0.35 Al.sub.2O.sub.3 0.2889W
2.6OS19
[0175] While the invention has been described above with reference
to exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
and the general principle of the invention. In addition, many
modifications may be made to adapt a particular situation or
material to the teachings of the invention without departing from
the essential scope thereof. Therefore, it is intended that the
invention not be limited to the particular embodiment disclosed as
the best mode contemplated for carrying out this invention, but
that the invention will include all embodiments falling within the
scope of the appended claims.
* * * * *