U.S. patent application number 14/691173 was filed with the patent office on 2015-08-13 for method for thepreparation of a catalysed particulate filter and catalysed particulate filter.
This patent application is currently assigned to Haldor Topsoe A/S. The applicant listed for this patent is Haldor Topsoe A/S. Invention is credited to Keld Johansen.
Application Number | 20150224477 14/691173 |
Document ID | / |
Family ID | 44947023 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150224477 |
Kind Code |
A1 |
Johansen; Keld |
August 13, 2015 |
METHOD FOR THEPREPARATION OF A CATALYSED PARTICULATE FILTER AND
CATALYSED PARTICULATE FILTER
Abstract
A catalysed particulate filter coated with a wash coat on its
dispersion side and its permeate side and within partition walls of
the filter. The wash coat contains a first catalyst active in
burning off soot, together with a second catalyst active in a
selective catalytic reduction of nitrogen oxides.
Inventors: |
Johansen; Keld;
(Frederikssund, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Haldor Topsoe A/S |
Lyngby |
|
DK |
|
|
Assignee: |
Haldor Topsoe A/S
Lyngby
DK
|
Family ID: |
44947023 |
Appl. No.: |
14/691173 |
Filed: |
April 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13879664 |
Apr 16, 2013 |
|
|
|
PCT/EP2011/005504 |
Nov 1, 2011 |
|
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14691173 |
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Current U.S.
Class: |
502/2 |
Current CPC
Class: |
B01D 53/9463 20130101;
B01D 2255/2065 20130101; B01D 2255/904 20130101; B01D 2255/20776
20130101; B01D 2255/50 20130101; B01D 2255/65 20130101; B01D
2255/407 20130101; B01J 23/30 20130101; B01D 2255/20761 20130101;
B01D 53/944 20130101; F01N 2510/065 20130101; B01J 37/0215
20130101; B01J 37/0036 20130101; B01J 23/10 20130101; B01D
2255/9155 20130101; B01D 2255/20738 20130101; B01D 53/9418
20130101; F01N 3/023 20130101 |
International
Class: |
B01J 23/30 20060101
B01J023/30; B01D 53/94 20060101 B01D053/94 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 2010 |
DK |
PA 2010 00991 |
Claims
10. A catalysed particulate filter coated with a wash coat on its
dispersion side and its permeate side and within partition walls of
the filter, said wash coat containing a first catalyst active in
burning off of soot, together with a second catalyst active in a
selective catalytic reduction of nitrogen oxides.
11. The catalysed particulate filter of claim 10, wherein the
filter is in form of a wall flow monolith with a plurality of
longitudinally extending passages formed by longitudinally
extending walls bounding and defining flow passages, the dispersion
side of the passages have an open inlet end and a closed outlet
end, and the permeate side of the passages have a closed inlet end
and an open outlet end.
11. The catalysed particulate filter of claim 10, wherein the first
and second catalyst in the wash coat suspension have a particle
size smaller than the mean pore size of the filter walls.
12. The catalysed particulate filter of claim 10, wherein the first
or the second catalyst in the wash coat suspension has a particle
size equal to or larger than the mean pore size of the filter
walls.
Description
[0001] This is a division of application Ser. No. 13/879,664, filed
Apr. 16, 2013, which is a 371 of PCT/EP2011/005504, filed Nov. 1,
2011, which claims priority to Danish Application No. PA 2010
00991, filed Nov. 2, 2010.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention:
[0003] The present invention relates to multifunctional catalysed
diesel particulate filters. In particular, the invention relates to
a method for the preparation of catalysed diesel particulate
filters having both an activity in the removal of nitrogen oxides
by the known selective catalytic reduction (SCR) process and an
activity in the burning of soot having been captured on the
filter.
[0004] The invention provides furthermore a catalysed filter with a
catalyst being active in the SCR and a catalyst for improved
burning of soot.
[0005] 2. Description of the Related Art:
[0006] In addition to unburnt hydrocarbons, diesel exhaust
contains, nitrogen oxides (NOx) and particulate matter. In
particular NOx and particulate matter are material and chemical
compounds representing a health and environmental risk and must be
reduced or removed from the engine exhaust gas.
[0007] Particulate matter consists mainly of soot and is
conventionally removed from the exhaust gas by passage through a
filter arranged in the exhaust system of the engine.
[0008] Typically these filters are honeycomb wall flow filters,
wherein the soot is captured on or in partition walls of the
honeycomb filter. By time, the build-up of captured particulate
matter on the walls increases the pressure drop over the filter and
the particulate matter must be removed, usually by way of burning
the soot. Burning off of the soot is usually accomplished passively
in the presence of a soot combustion catalyst or actively by a
periodically increase of the temperature of the exhaust gas.
[0009] Filters provided with a catalyst catalysing a burning off of
the soot are known in the art.
[0010] Beside a particulate filter, diesel exhaust gas cleaning
systems disclosed in the art comprise a catalyst unit active in the
selective reduction of NOx by reaction with ammonia.
[0011] Multifunctional diesel particulate filters coated with
catalysts catalysing different reactions are also known in the
art.
[0012] In the known multifunctional filters the different catalysts
are segmentary or zone coated in different zones of the filter.
[0013] Segmentary or zone coating of different catalysts on the
filter is, however, an expensive and difficult preparation
process.
DESCRIPTION OF THE INVENTION
[0014] The present invention suggests a comparatively easier method
for the preparation of particulate filers catalysed with different
catalysts for the burning off of soot and a selective reduction of
NOx.
[0015] Accordingly, the invention relates to a method for the
preparation of a catalysed particulate filter comprising the steps
of
[0016] a) providing a catalyst wash coat containing a first
catalyst active in burning off of soot in combination with a second
catalyst active in selective catalytic reduction of nitrogen
oxides;
[0017] b) coating a particulate filter body with the catalyst wash
coat on the dispersion side and the permeate side of the filter
body and within partition walls of the filter body; and
[0018] c) drying and heat treating the coated filter body to obtain
the catalysed particulate filter.
[0019] The terms "dispersion side" and "permeate side" as used
herein refer both to the flow passages of the filter facing the
soot containing exhaust gas and to the flow passages facing the
filtrated exhaust gas, respectively.
[0020] The main advantage of the method according to the invention
is that the filter can be coated with a single wash coat containing
two types of catalyst catalysing different reactions. Thereby the
preparation of a multifunctional catalysed filter is much improved
in terms of a facilitated and cost-saving production setup.
Additionally, the intimate mixture of the first and the second
catalyst provides process advantages when the first catalyst
presents some activity for the second reaction and the second
catalyst presents some activity for the first reaction. This
synergy increases the soot combustion activity and SCR activity
compared to a solution with only one of the catalysts. An example
of this process advantage is demonstrated when the filter has a low
soot loading because then the SCR NOx removal of the optimised SCR
catalyst is supplemented by the SCR activity of the soot combustion
catalyst. Thus the appropriate catalyst is available in the filter
where the reaction is needed, which is an improvement compared to a
segmentary wash coated filters.
[0021] A further advantage of coating a filter with different types
of catalysts as a mixture of catalyst particles is found in an
improved heat transfer and a warm-up during a cold start due to a
low thermal mass of the combined filter catalyst brick and thus
makes it possible to start injection of a reductant and the SCR
reaction earlier than hitherto known.
[0022] In one embodiment of the invention, the first catalyst
particles active in combustion of soot with oxygen or nitrogen
dioxide may comprise catalysts or catalyst precursors of one or
more rare earth metal oxides. In addition to rare earth oxides, the
first catalyst may further comprise zirconia, alumina, titania,
silica, zeolite or combinations thereof.
[0023] The first catalyst comprises preferably cerium oxide and
zirconium oxide.
[0024] In yet another embodiment of the invention, the second
catalyst particles in the wash coat being active in the selective
catalytic reduction of NOx may comprise at least one of a zeolite,
a silica aluminum phosphate, an ion exchanged zeolite, a silica
aluminum phosphate optionally promoted with iron and/or copper, one
or more base metal oxides and a catalyst support of at least one of
cerium tungsten oxide on a titanium oxide support, an alumina
support, a zirconium oxide support or a silica support.
[0025] The second catalyst comprises preferably tungsten oxide and
cerium oxide supported on alumina.
[0026] In order to form the wash coat for use in the invention, the
first and the second catalyst usually in particle form are milled
to the required particle size and suspended in water or organic
solvents, optionally with addition of binders, viscosity improvers,
foaming agents or other processing aids.
[0027] The wash coat may be prepared by suspending the first and
second catalyst particles in form of a single suspension or by
preparing two different suspensions with the first and the second
catalyst, respectively, followed by mixing the two suspensions in a
volume ratio to prepare the wash coat with the required amount of
the first and the second catalyst particles.
[0028] Further binders, viscosity improvers, foaming agents may be
added after mixing.
[0029] The filter is then wash coated according to common
practice.
[0030] In a preferred embodiment of the invention, the filter body
is shaped in form of a wall flow monolith with a plurality of
longitudinally expending passages formed by longitudinally
extending walls bounding and defining flow passages, where the
dispersion side of the passages have an open inlet end and an
outlet end being plugged with plugs, and where the permeate side of
the passages have an inlet end being plugged with plugs and an open
outlet end.
[0031] In yet another preferred embodiment, the filter body of the
above wall flow monolith is wash coated before the outlet end of
the dispersion side and the inlet end of the permeation side are
plugged.
[0032] The invention provides furthermore a catalysed particulate
filter coated with a wash coat on its dispersion side and its
permeate side and within partition walls of the filter body, said
wash coat containing a first catalyst being active in burning off
of soot together with a second catalyst active in a selective
catalytic reduction of nitrogen oxides.
[0033] A preferred filter body for use in the invention comprises a
wall flow monolith with a plurality of longitudinally extending
passages formed by longitudinally extending walls bounding and
defining flow passages. The inlet portion of the passages has an
open inlet end and a closed outlet end, and the outlet passages
have a closed inlet end and an open outlet end.
[0034] Examples of suitable filter materials for use in the
invention are silicon carbide, aluminium titanate, cordierite,
alumina, mullite or combinations thereof.
[0035] The amount of first catalyst on the filter is typically 10
to 100 g/l and the amount of second catalyst on the filter is
typically 20 to 180 g/l. The total catalyst loading on the filter
is typically in the range 40 to 200 g/l.
[0036] The particle sizes of both catalysts in the wash coating
suspension are smaller than the mean pore size of the filter wall.
But a further option is the particle size of one of the catalysts
in the wash coating suspension being equal to or larger than the
mean pore size of the filter wall.
EXAMPLE
[0037] A suspension of the first catalyst is in a first step
prepared from a mixture of cerium nitrate and zirconium nitrate
followed by a heat treatment to convert the nitrate mixture into
the oxides of cerium and zirconium with a molar ratio of Ce/Zr 3:1.
In a second step, a suspension of the first catalysts is prepared
by mixing 40 g of the cerium oxide zirconium oxide mixture in 80 ml
demineralised water. A dispersing agent Zephrym PD-7000 and an
antifoam agent are added. The suspension is milled in a bead mill.
The particle sizes must be lower than the mean pore diameter of the
pores in the wall of the wall flow filter.
[0038] A suspension of the second catalyst is prepared by mixing
cerium nitrate and ammonium meta tungstate solutions followed by
impregnating the mixed solution on aluminium oxide particles and
heat treating the particles at 550.degree. C. for 4 hours in air.
Thereby alumina particles with 10% Cerium oxide and 10% tungsten
oxide are obtained. 100 g of this tungsten oxide plus cerium oxide
on aluminium oxide is dispersed in 200 ml demineralised water. A
dispersing agent Zephrym PD-7000 and an antifoam agent is added.
The suspension is milled in a bead mill. The particle sizes must be
lower than the mean pore diameter of the pores in the wall of the
wall flow filter.
[0039] A suspension of the first catalyst is then mixed into the
suspension of the second catalyst.
[0040] A high porosity (approximately 60%) unplugged SiC wall flow
filter is then wash coated with the mixture of the first and the
second catalyst and dried.
[0041] After coating, the end channels are plugged with a
commercially available cement and the plugged filter is
subsequently heat treated at 730.degree. C.
* * * * *