U.S. patent application number 10/932611 was filed with the patent office on 2005-03-31 for low nox carbon monoxide combustion promoter.
Invention is credited to Xu, Mingting.
Application Number | 20050067322 10/932611 |
Document ID | / |
Family ID | 34381151 |
Filed Date | 2005-03-31 |
United States Patent
Application |
20050067322 |
Kind Code |
A1 |
Xu, Mingting |
March 31, 2005 |
Low NOx carbon monoxide combustion promoter
Abstract
The amount of NOx formed during regeneration of a cracking
catalyst in the presence of a metallic carbon monoxide combustion
catalyst is decreased by utilizing as the carbon monoxide
combustion catalyst rhodium and/or iridium on an oxide support such
as alumina.
Inventors: |
Xu, Mingting; (Edison,
NJ) |
Correspondence
Address: |
Gus Hampilos
Engelhard Corporation
101 Wood Ave.
PO Box 770
Iselin
NJ
08830
US
|
Family ID: |
34381151 |
Appl. No.: |
10/932611 |
Filed: |
September 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60505805 |
Sep 25, 2003 |
|
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Current U.S.
Class: |
208/113 |
Current CPC
Class: |
C10G 11/02 20130101 |
Class at
Publication: |
208/113 |
International
Class: |
C10G 011/00 |
Claims
What is claimed is:
1. A process for cracking hydrocarbons comprising: (1) cycling
particulate cracking catalyst between a cracking zone and a
catalyst regeneration zone, in a catalytic cracking system; (2)
cracking said hydrocarbons in contact with said catalyst at
cracking conditions in said cracking zone whereby coke is formed on
said catalyst; (3) burning coke off said catalyst with an
oxygen-containing gas at regeneration, and, wherein a flue gas from
said catalyst regeneration zone includes carbon monoxide (4)
combusting said carbon monoxide in said regeneration zone by
contacting said flue gas with a CO oxidation promoter consisting
essentially of rhodium and/or iridium supported on a particulate,
non-zeolitic oxide solid.
2. A process according to claim 1 wherein said CO oxidation
promoter consists essentially of rhodium.
3. A process according to claim 1 wherein said CO oxidation
promoter consists essentially of iridium.
4. A process according to claim 1 wherein said CO oxidation
promoter consists essentially of rhodium and iridium.
5. A process according to claim 1 wherein said particulate oxide
solid includes at least one of alumina and silica.
6. A process according to claim 1 wherein said particulate oxide
solid includes alumina.
7. A process according to claim 1 wherein said CO oxidation
promoter is a particulate solid separate from said particulate
cracking catalyst.
8. The process of claim 7 wherein said CO oxidation promoter
circulates between the cracking zone and regeneration zone.
9. A process according to claim 7 wherein said CO oxidation
promoter is maintained in said regeneration zone.
10. A process according to claim 8 wherein said CO oxidation
promoter is added in the fresh state to the inventory of
particulate cracking catalyst.
11. A process according to claim 9 wherein said CO oxidation
promoter is added in the fresh state to said regeneration zone.
12. A process according to claim 1 wherein the concentration of
rhodium and/or iridium on said particulate oxide solid ranges from
0.01 to 1% by weight.
13. A process according to claim 12 wherein said rhodium
and.backslash.or iridium is present on said particulate oxide solid
in amounts of 0.02 to 0.5% by weight.
14. A process according to claim 1 wherein said rhodium and/or
iridium is present in the form of free metal, or the oxides,
sulfides, or sulfates thereof.
15. A process according to claim 1 wherein said cracking is
performed in the absence of externally-supplied hydrogen.
16. A process according to claim 1 wherein said hydrocarbons
contain nitrogen-containing compounds.
17. A process according to claim 2 wherein said particulate oxide
solid is alumina.
18. A process according to claim 3 wherein said particulate oxide
solid is alumina.
19. A process according to claim 18 wherein said CO oxidation
promoter further includes an alkaline earth oxide.
20. A process according to claim 19 wherein said alkaline earth
oxide is BaO.
21. A process according to claim 6 wherein the said support is
substantially .alpha.-alumina.
Description
RELATED APPLICATIONS
[0001] This application is based on U.S. Provisional Application
Ser. No. 60/505,805, filed Sep. 25, 2003.
FIELD OF THE INVENTION
[0002] This invention relates to regeneration of spent catalyst in
a fluid catalytic cracking (FCC) process and the reduction of NOx
formed during regeneration of the cracking catalyst in the presence
of a carbon monoxide combustion promoter.
BACKGROUND OF THE INVENTION
[0003] Catalytic cracking of heavy petroleum fractions is one of
the major refining operations employed in the conversion of crude
petroleum oils to useful products such as the fuels utilized by
internal combustion engines. In fluidized catalytic cracking
processes, high molecular weight hydrocarbon liquids and vapors are
contacted with hot, finely-divided, solid catalyst particles,
either in a fluidized bed reactor or in an elongated transfer line
reactor, and maintained at an elevated temperature in a fluidized
or dispersed state for a period of time sufficient to effect the
desired degree of cracking to lower molecular weight hydrocarbons
of the kind typically present in motor gasoline and distillate
fuels.
[0004] In the catalytic cracking of hydrocarbons, some non-volatile
carbonaceous material or coke is deposited on the catalyst
particles. Coke comprises highly condensed aromatic hydrocarbons
and generally contains from about 4 to about 10 weight percent
hydrogen. When the hydrocarbon feedstock contains organic sulfur
and nitrogen compounds, the coke also contains sulfur and nitrogen
species. As coke accumulates on the cracking catalyst, the activity
of the catalyst for cracking and the selectivity of the catalyst
for producing gasoline-blending stocks diminishes.
[0005] Catalyst which has become substantially deactivated through
the deposit of coke is continuously withdrawn from the reaction
zone. This deactivated catalyst is conveyed to a stripping zone
where volatile deposits are removed with an inert gas at elevated
temperatures. The catalyst particles are then reactivated to
essentially their original capabilities by substantial removal of
the coke deposits in a suitable regeneration process. Regenerated
catalyst is then continuously returned to the reaction zone to
repeat the cycle.
[0006] Catalyst regeneration is accomplished by burning the coke
deposits from the catalyst surfaces with an oxygen containing gas
such as air in a regenerator separate from the fluidized reactor
used in catalytic cracking. In the catalyst regenerator, the coke
burns off, restoring catalyst activity and heating the catalyst to,
e.g., 500-900.degree. C., usually 600-750.degree. C. Flue gas
formed by burning coke in the regenerator may be treated to remove
particulates and convert carbon monoxide, after which the flue gas
is normally discharged into the atmosphere.
[0007] The removal of carbon monoxide from the waste gas produced
during the regeneration of deactivated cracking catalyst can be
accomplished by conversion of the carbon monoxide to carbon dioxide
in the regenerator or carbon monoxide boiler after separation of
the regeneration zone effluent gas from the catalyst. When sulfur
and nitrogen containing feedstocks are utilized in catalytic
cracking process, the coke deposited on the catalyst contains
sulfur and nitrogen. During regeneration of coked deactivated
catalyst, the coke is burned from the catalyst surface that then
results in the conversion of sulfur to sulfur oxides and nitrogen
to nitrogen oxides (NOx).
[0008] Initially, there was little incentive to attempt to remove
substantially all coke carbon from the catalyst, since even a
fairly high carbon content had little adverse effect on the
activity and selectivity of amorphous silica-alumina catalysts.
Most of the FCC cracking catalysts now used, however, contain
zeolites, or molecular sieves. Zeolite-containing catalysts have
usually been found to have relatively higher activity and
selectivity when their coke carbon content after regeneration is
relatively low. An incentive arose for attempting to reduce the
coke content of regenerated FCC catalyst to a very low level.
[0009] When the regenerators operate in a complete CO combustion
mode, the mole ratio of CO.sub.2/CO is at least 10 in the
regenerator flue gas. During regeneration operated at complete
combustion mode, several methods have been suggested for burning
substantially all carbon monoxide to carbon dioxide to avoid air
pollution, recover heat, and prevent afterburning. Among the
procedures suggested for use in obtaining complete carbon monoxide
combustion in an FCC regeneration have been: (1) increasing the
amount of oxygen introduced into the regenerator relative to
standard regeneration; and either (2) increasing the average
operating temperature in the regenerator or (3) including various
carbon monoxide oxidation promoters in the cracking catalyst to
promote carbon monoxide burning. Various solutions have also been
suggested for the problem of afterburning of carbon monoxide, such
as addition of extraneous combustibles or use of water or
heat-accepting solids to absorb the heat of combustion of carbon
monoxide.
[0010] Specific examples of treatments applied to regeneration
operated in the complete combustion mode include the addition of a
CO combustion promoter metal to the catalyst or to the regenerator.
For example, U.S. Pat. No. 2,647,860 proposed adding 0.1 to 1
weight percent chromic oxide to a cracking catalyst to promote
combustion of CO. U.S. Pat. No. 3,808,121 taught using relatively
large-sized particles containing CO combustion-promoting metal into
a regenerator. The small-sized catalyst is cycled between the
cracking reactor and the catalyst regenerator while the
combustion-promoting particles remain in the regenerator. Also,
U.S. Pat. Nos. 4,072,600 and 4,093,535 teach the use of Pt, Pd, Ir,
Rh, Os, Ru, and Re in cracking catalysts in concentrations of 0.01
to 50 ppm, based on total catalyst inventory to promote CO
combustion in a complete burn unit. Most FCC units now use a
platinum-containing CO combustion promoter.
[0011] When using carbon monoxide combustion-promoting metals, such
as platinum, associated with a small fraction of the total
particulate solids inventory, essentially complete carbon monoxide
combustion has been obtained commercially. Low levels of coke on
regenerated catalyst, another desirable result, have also been
obtained. On the other hand, the amount of undesirable nitrogen
oxides formed in the regenerator flue gas has substantially
increased in catalyst regenerators using combustion-promoting
promoting metals contained on a small fraction of the circulating
particulate solids. This has created an air pollution problem in
disposing of the regenerator flue gas. Use of combustion promoters
comprising only a small fraction of the total solids inventory in a
cracking system is nevertheless often preferable to use of a small
amount of promoting metal on a large fraction of the catalyst
solids. This is because of the operating flexibility obtainable
when using a small amount of combustion-promoting additive
particles. For example, use of the additive can be discontinued
rapidly without removing a large portion of the catalyst inventory
from circulation in a unit.
[0012] Accordingly, it is difficult in a catalyst regenerator to
completely burn coke and CO without increasing the NOx content of
the regenerator flue gas. Many jurisdictions restrict the amount of
NOx that can be in a flue gas stream discharged to the atmosphere.
In response to environmental concerns, much effort has been spent
on finding ways to reduce NOx emissions.
[0013] For example, NOx is controlled in the presence of a
platinum-promoted complete combustion regenerator in U.S. Pat. No.
4,290,878, issued to Blanton. Recognition is made of the fact that
the CO promoters result in a flue gas having an increased content
of nitrogen oxides. The excessive amounts of undesirable NOx was
suppressed by using in addition to Pt, a small amount of Rh or Ir
on the same additive particle.
[0014] U.S. Pat. No. 4,300,997 to Meguerian et. al discloses the
use of a promoter comprising palladium and ruthenium to promote the
combustion of CO in a complete CO combustion regenerator without
simultaneously causing the formation of excess amounts of NOx. The
ratio of palladium to ruthenium is from 0.1 to about 10.
SUMMARY OF THE INVENTION
[0015] In the present invention, a method is provided for
restricting the formation of nitrogen oxides formed in a
hydrocarbon cracking catalyst regeneration zone wherein carbon
monoxide is combusted with a molecular oxygen-containing gas in
contact with a carbon monoxide combustion promoter including a
combustion-promoting metal or compound of a metal selected from
rhodium, iridium, or mixtures thereof associated with at least one
particulate porous inorganic solid.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention is used in connection with a fluid
catalyst cracking process for cracking hydrocarbon feeds. The same
hydrocarbon feeds normally processed in commercial FCC systems may
be processed in a cracking system employing the present invention.
Suitable feedstocks include, for example, petroleum distillates or
residuals, either virgin or partially refined. So-called synthetic
feeds such as coal oils, bitumen and shale oils are also suitable.
Suitable feedstocks normally boil in the range from about
200.degree.-600.degree. C. or higher. A suitable feed may include
recycled hydrocarbons which have already been subjected to
cracking.
[0017] The cracking catalyst employed may be a conventional
particulate acidic racking catalyst, such as silica-alumina. The
catalyst may, for example, be a conventional non-zeolitic cracking
catalyst containing at least one porous inorganic oxide, such as
silica, alumina, magnesia, zirconia, titania, etc., or a mixture of
silica and alumina or silica and magnesia, etc, or a clay or
acid-treated clay or the like. The catalyst may also be a
conventional zeolite-containing cracking catalyst including a
zeolitic crystalline aluminosilicate associated with a porous
refractory matrix which may be, for example, silica-alumina. The
matrix generally constitutes 70-95 weight % of the cracking
catalyst, with the remaining 5-30 weight % being a zeolite
component dispersed on or embedded in the matrix. The zeolite may
be rare earth-exchanged or hydrogen-exchanged. Conventional
zeolite-containing cracking catalysts often include an X-type
zeolite or a Y-type zeolite. Low (less than 1%) sodium content
Y-type zeolites are particularly good. As will be apparent to those
skilled in the art, the composition of the acidic cracking
component in the catalyst particles employed in the system is not a
critical feature of the present method. Thus, the catalyst
particles may be either completely amorphous or partly amorphous
and partly crystalline.
[0018] Cracking conditions employed in the cracking or conversion
step in an FCC system are frequently provided in part by
pre-heating or heat-exchanging hydrocarbon feeds to bring them to a
temperature of about 315.degree.-400.degree. C. before introducing
them into the cracking zone; however, pre-heating of the feed is
not essential. Cracking conditions normally include a
catalyst/hydrocarbon weight ratio of about 3-10. A hydrocarbon
weight space velocity in the cracking zone of about 5-50 per hour
is preferably used. The average amount of coke contained in the
catalyst after contact with the hydrocarbons in the cracking zone,
when the catalyst is passed to the regenerator, is preferably
between about 0.5 weight % and about 2.5 weight %, depending in
part on the carbon content of regenerated catalyst in the
particular system, as well as the heat balance of the particular
system.
[0019] The catalyst regeneration zone used in an FCC system
employing an embodiment of the present invention may be of
conventional design. The gaseous atmosphere within the regeneration
zone normally includes a mixture of gases in concentrations which
vary according to the locus within the regenerator. The
concentrations of gases also vary according to the coke
concentration on catalyst particles entering the regenerator and
according to the amount of molecular oxygen and steam passed into
the regenerator. Generally, the gaseous atmosphere in a regenerator
contains 5-25% steam, varying amounts of oxygen, carbon monoxide,
and carbon dioxide. Nitrogen and nitrogen oxides are also present
such as from the use of air as the coke combustion source and/or
from the combustion of nitrogen-containing coke. The present
invention is applicable in cases in which oxygen (O.sub.2) or air
is employed for combustion of coke in the catalyst regenerator. As
will be appreciated by those skilled in the art, air is almost
invariably employed to provide some or all of the oxygen needed for
combustion in FCC regenerators.
[0020] A combustion-promoting metal is employed in carrying out the
method of the present invention. The combustion-promoting metals
which are suitable for use include one or more of the metals
rhodium or iridium, or compounds thereof, such as the oxides,
sulfides, sulfates, etc. At least one of these metals or metal
compounds is used, and mixtures of two of the metals are also
suitable.
[0021] The promoting metal or metal compound is associated with a
particulate solid inorganic oxide which may be a particulate solid
other than the catalyst, e.g., a finely divided, porous inorganic
oxide, such as alumina, silica, etc., sized suitably for
circulation in an FCC system, or a particulate solid which remains
in the catalyst regenerator rather than circulating through the
cracking system with the particulate solids inventory.
[0022] The total concentration of the combustion-promoting metal,
or metals, or compounds thereof used in the cracking system, with
respect to the circulating catalyst inventory, is sufficient to
promote the desired amount of combustion of coke on the catalyst
and to promote the desired amount of combustion of carbon
monoxide.
[0023] The promoting metal, metals, or compound thereof, are
preferably employed in an FCC system in association with discrete,
promoted particulate solids, which are physically admixed with, and
circulated in the particulate solids inventory in an FCC system
with unpromoted catalyst particles. The promoted particulate solids
may be formed from any material which is suitable for circulation
in an FCC system in admixture with the catalyst. Particularly
suitable materials are the porous inorganic oxides, such as
alumina, silica, zirconia, etc., or mixtures of two or more
inorganic oxides, which may be amorphous, crystalline, or both,
such as silica-alumina, natural and synthetic clays and the like.
Crystalline aluminosilicate zeolites are not used as the supports
for the CO combustion promoters of this invention. Gamma-alumina is
particularly useful. The combustion-promoting metal or metal
compound can be added to a particulate solid to form a promoted
particulate solid in any suitable manner, as by impregnation or ion
exchange, or can be added to a precursor of a particulate solid,
as, for example, by co-precipitation from an aqueous solution with
an inorganic oxide precursor sol. The promoted particulate solids
can then be formed into particles of a size suitable for use in an
FCC system by conventional means, such as spray-drying, crushing of
larger particles to the desired size, etc.
[0024] Rhodium and/or iridium are the metals for use in the present
method. When the metal is used in association with circulating
particulate solids, the total amount of rhodium and/or iridium used
in an FCC system with respect to the circulating particulate solids
inventory is between about 0.05 to 200 parts per million, by
weight, with an amount between about 0.2 and 100 parts per million
being particularly preferred. It will be apparent that the
concentration of rhodium and/or iridium in promoted particles will
be relatively greater when a relatively small proportion of
promoted particles is used. The concentration of rhodium and/or
iridium in discrete promoted particles used in carrying out the
invention is usually within the range from 0.01 weight percent to 1
weight percent. Preferably, the concentration of rhodium and/or
iridium in promoted particles is between 0.2 and 0.5 weight
percent.
[0025] Sintering of iridium is well known under oxygen atmospheres
at elevated temperatures. McVicker et. al taught an approach for
preventing sintering and maintaining high metal dispersion of
Ir/Al.sub.2O.sub.3 catalysts. (G. B. McVicker, R. L. Garten, and R.
T. K. Baker, J. Catal., (1978), 54, 129). Group IIA-oxides of Ca,
Sr, and Ba have been reported to stabilize the Ir surface area of
Ir/Al.sub.2O.sub.3 in the presence of oxygen at elevated
temperatures. Oxidative stabilization is believed to result from
the formation of an immobile surface iridate via the reaction of a
mobile, molecular iridium oxide species with a well-dispersed Group
IIA-oxide. While the stabilization of supported iridium as
described above is known for automotive catalysis to remove
hydrocarbon and NOx pollutants, such stabilization is not believed
to have been used in FCC regenerators. Accordingly, alumina,
silica, silica-alumina, and other oxidic supports containing
TiO.sub.2, ZrO.sub.2, alkaline earth metal oxides or lanthanide
oxides can effectively be used to support, in particular, the Ir
metal for regenerator NOx removal.
[0026] A fresh promoted particulate solid which contains at least
one metal or metal compound of the type specified above can, for
example, be physically admixed with unpromoted FCC catalyst and the
mixture can then be charged to an FCC system. The fresh promoted
particulate solids can optionally be added separately in the
desired amount to an FCC unit already containing a substantial
inventory of unpromoted or promoted FCC catalyst.
[0027] Substantially complete combustion or carbon monoxide and
coke is preferably carried out in the cracking catalyst
regenerator. Sufficient coke is preferably burned off the catalyst
during regeneration to provide an average level of coke on
regenerated catalyst of less than 0.2 weight %, and preferably less
than 0.1 weight %. The carbon monoxide produced in the catalyst
regenerator is preferably substantially all burned to carbon
dioxide. The flue gas removed from the regenerator preferably has
not more than 1000 parts per million, by volume, of CO therein,
particularly preferably not more than 500 parts per million, by
volume.
[0028] The amount of oxygen must be sufficient to burn the desired
amount of coke and carbon monoxide, but must not substantially
exceed that required to carry out the combustion step in the
regenerator. Thus, sufficient oxygen must be introduced into the
regeneration zone so that flue gas removed from the regeneration
zone contains at least 1 volume % molecular oxygen. This oxygen in
the flue gas is termed "excess" oxygen. At least 1 volume % excess
oxygen is required in order to provide the high degree of coke and
carbon monoxide burning required in the process.
[0029] Preferably, the catalyst regeneration zone includes at least
one dense-phase bed of fluidized particulate solids (density
greater than 10 pounds per cubic foot). Two or more dense beds may
be employed if a plurality of regeneration chambers is used, as in
staged regeneration. Preferably, substantially all the carbon
monoxide generated in a dense-phase catalyst bed is burned to
carbon dioxide in the dense-phase bed. It is also preferred to
control the average temperature of dense-phase beds of solids in a
regeneration zone so that the average temperature does not exceed
675.degree. C. Dense-phase burning of the carbon monoxide generated
in an FCC catalyst regenerator is indicated when the average
temperature in a dilute phase above a dense-phase catalyst bed is
only slightly different, or lower than, the average temperature in
the dense phase.
EXAMPLE 1
[0030] Rhodium is impregnated onto alumina support particles to a
level of 500 ppm from an aqueous solution of rhodium nitrate. The
dried material is calcined at 500.degree. C. for 2 h.
EXAMPLE 2
[0031] Iridium is impregnated onto alumina support particles to a
level of 500 ppm from an aqueous solution of iridium chloride. The
dried material is calcined at 500.degree. C. for 2 h.
EXAMPLE 3
[0032] Alumina support particles are impregnated with an aqueous
solution of barium acetate, dried, and calcined at 650.degree. C.
for 2 h. The product contains 10% BaO by weight.
EXAMPLE 4
[0033] Iridium is impregnated onto the product made in Example 3 to
a level of 500 ppm from an aqueous solution of iridium chloride.
The dried material is calcined at 500.degree. C. for 2 h.
EXAMPLE 5
[0034] Rhodium is impregnated onto alumina support particles to a
level of 250 ppm from an aqueous solution of rhodium nitrate. The
dried material is calcined at 500.degree. C. for 2 h. The material
is then impregnated with iridium to a level of 250 ppm from an
aqueous solution of iridium chloride. The dried material is
recalcined at 500.degree. C. for 2 h.
EXAMPLE 6
[0035] Alumina support particles are calcined to 1200.degree. C.
for 2 h to convert the transitional alumina substantially to
.alpha.-alumina. Rhodium is impregnated onto this alumina support
to a level of 500 ppm. The dried material is calcined at
500.degree. C. for 2 h.
COMPARATIVE EXAMPLE A
[0036] Platinum is impregnated onto alumina support particles to a
level of 500 ppm from an aqueous solution of a monoethanol amine
complex. The dried material is calcined at 500.degree. C. for 2
h.
EXAMPLE 7
[0037] CO oxidation testing - Experiments were carried out in a
fluid bed reactor. 6 g of fresh steamed FCC catalyst was blended
with 0.05 to 1.0 wt. % of the low NOx CO promoters prepared in the
previous examples. CO combustion was tested using the following
molar gas composition: 5% CO, 3% O2, 5% CO2, balance nitrogen. The
flow rate of gas over the catalyst and co promoter solids was 400
cc/min. The reactor temperature was 593.degree. C. The relative CO
promotion rate constant was determined by measuring the slope of
the activity (defined as -In(1 -CO conversion)) vs. space time.
These slopes are shown in Table 1.
1 TABLE 1 Comparative Example A Example 1 Example 2 Fresh Promoter
788 720 434 Steamed 196 132 154 Promoter
[0038] It was found that Pt based promoter was more active for CO
oxidation than either Rh or Ir based promoters as has been shown in
prior art.
EXAMPLE 8
[0039] Ammonia Decomposition Testing--Experiments were carried out
with a fixed bed reactor using the following gas composition: 450
ppm NH.sub.3, 15% steam, 2%-6% CO, and Ar as balance. A total gas
flow rate of 260 cc/min (STP), GHSV (39,000 h-1) was used which
would be similar to that experienced by the additive in a
commercial FCC regenerator. A 0.4 g precious metal on alumina
sample was used as the NH.sub.3 reducing additive along with 1.6 g
of a kaolin microsphere as an inert diluent. Activity data for
NH.sub.3 decomposition at different CO concentrations using 500 ppm
alumina-supported precious metals are shown in Table 2 below. It
was found that the supported Rh and Ir promoters were very active
for NH.sub.3 decomposition; whereas Pt had no activity at
700.degree. C. in the presence of 15% steam and 2-6% CO.
2TABLE 2 % Conversion of NH.sub.3 CO Concentration Sample 2% 4% 6%
Comparative A 0.sup. / / Example 1 100% 90% 75% Example 2 32% --
--
EXAMPLE 9
[0040] HCN Removal Testing Similar experiments to NH.sub.3
decomposition were carried out with the replacement of NH.sub.3 by
450 ppm HCN. Interestingly, HCN behaved similarly to NH.sub.3 over
the precious metal catalysts. As shown in Table 3, Pt had no
activity for HCN removal. Once again, Rh had significantly more
activity than Pt for HCN decomposition.
3TABLE 3 % Conversion of HCN CO Concentration Sample 2% 4% 6%
Comparative A 0.sup. 0.sup. / Example 1 100% 87% 70%
EXAMPLE 10
[0041] Ammonia and CO oxidation testing--Simultaneous ammonia and
carbon monoxide testing was carried out in a fixed bed reactor
using the following gas composition: 2% CO, 2% O2, 8% CO2, 500 ppm
NH3, 15% H2O and balance Ar at flow and temperature conditions
similar to those described in Examples 8 and 9. Results are shown
in Table 4.
4 TABLE 4 Comparative Example A Example 1 CO conversion (%) 100%
100% NH3 conversion (%) 96.sup. 96.sup. Selectivity to N2 2.sup.
43.sup. Selectivity to NOx 98.sup. 57.sup.
[0042] Under these conditions of testing although both Pt and Rh
based materials show identical conversions for CO and NH3, the
selectivity's are very different. Pt based materials almost
quantitatively convert NH3 to NOx whereas Rh based materials will
convert significant quantities of NH3 to nitrogen.
* * * * *