Platinum gold catalyst for removing NO.sub.x and NH.sub.3 from gas streams

Selective reduction of NO.sub.x with NH.sub.3 as well as decomposition of excess NH.sub.3 is provided over a wide temperature range by a platinum-gold catalyst.

Acid rain damages crops, forests and wildlife often many miles from the 
original source of pollution. Accumulating in lakes and rivers, it kills 
fish and aquatic plants, while interfering with the reproduction of 
survivors. Nitric and sulfuric acids in rain water slowly dissolve marble 
and granite of statutes and buildings, including such treasures as the 
Parthenon, which has been slowly crumbling, largely from the effects of 
automotive and industrial pollution in Athens. Since it is thought that 
one of the major corrosive components of acid rain is formed when NO.sub.2 
combines with water droplets in rain clouds to form nitric acid, to 
forestall these losses governments have enacted regulations limiting the 
amount of nitrous oxides (either NO or NO.sub.2, usually NO.sub.x for 
short), which may be discharged into the atmosphere by automobiles and 
industrial facilities. Usually, no distinction is made between NO.sub.2 
and NO in a discharge, since NO reacts with atmospheric oxygen to form 
NO.sub.2. 
Oxides of nitrogen are often removed from oxygen containing gas streams by 
adding ammonia (and oxygen, if necessary) to the stream, then passing that 
stream at elevated temperatures over a vanadium pentoxide catalyst to form 
nitrogen and water. While this method is quite effective in removing 
NO.sub.x, it has relatively severe limitations. The most troublesome of 
these is that about 0.8 to 0.9 mole of ammonia should be introduced to the 
stream for each mole of NO.sub.x to be reduced. If there is too little 
ammonia, NO.sub.x passess through unreacted. If there is too much, ammonia 
in the effluent may itself be a significant pollutant or may react with 
oxygen to form NO.sub.x. Thus, the ammonia level must be carefully matched 
to the NO.sub.x level in the stream. Typically, this would require costly 
and potentially troublesome measuring and control equipment. Further, 
vanadium pentoxide provides ideal catalytic action only between about 
300.degree. and 550.degree. C. At lower temperatures, NH.sub.3 and 
NO.sub.x may pass through unreacted, potentially yielding explosive 
ammonium nitrate. At higher temperatures, ammonia may be oxidized, forming 
NO.sub.x. The object of this invention is to provide catalysts and 
catalyst systems which are useful in alleviating the problems encountered 
in reducing NO.sub.x using vanadium pentoxide catalyst. It has been 
discovered that platinum gold catalysts are useful in reducing NO.sub.x 
with ammonia and oxygen over the range of from about 225.degree. to 
400.degree. C. Thus, this catalyst may either be used to reduce NO.sub.x 
in streams within that temperature range, or if the gold platinum catalyst 
is used following the previously known vanadium pentoxide catalysts, then 
effective reduction of NO.sub.x may be carried out by the system over the 
range of about 225.degree. to 550.degree. C. However, an even more 
important advantage of using platinum gold catalysts is that, in contrast 
to vanadia, platinum gold also preferentially catalyzes the decomposition 
of ammonia into hydrogen and nitrogen. Thus, the problem of matching the 
ammonia level to the NO.sub.x level of the stream is obviated if platinum 
gold is used either following or instead of the vanadium pentoxide 
catalyst. In the preferred embodiment of the present invention, effective 
reduction of NO.sub.x over a wide temperature range is provided by 
platinum gold catalyst placed downstream of a vanadium pentoxide catalyst. 
Thus, normally the vanadium pentoxide reduces much of the NO.sub.x, while 
the platinum gold decomposes the unreacted ammonia. If, for some reason, 
the temperature of the stream decreases, then the platinum gold catalyst 
will serve to both reduce NO.sub.x and decompose ammonia. Thus, this 
arrangement provides extremely desirable results: the effective 
temperature range is increased, the problem of exactly matching the 
ammonia concentration to the NO.sub.x concentration is obviated, and the 
danger of producing ammonium nitrate is reduced. 
PLATINUM GOLD CATALYST 
The platinum gold catalysts used in this invention can be prepared by 
distributing platinum and gold on a carrier, then fixing the platinum and 
gold to the carrier. The platinum and gold may be distributed either as 
elements or as precursor compounds. The platinum in the platinum-gold 
catalyst composition may be present in elemental or combined forms, such 
as platinum or platinum oxide. One can utilize the method described in 
U.S. Pat. No. 4,021,374, wherein the carrier is contacted with a solution 
containing at least one soluble salt of platinum and at least one soluble 
salt of gold (such as, e.g., the ions, complexes or hydroxides of platinum 
and/or gold), and the impregnated support is reduced with hydrogen at a 
temperature of 0.degree.-100.degree. C. and a pressure of 1 to 10 
atmospheres. If the principal use of the catalyst is to be decomposition 
of ammonia, palladium and platinum-palladium admixtures can be substituted 
for platinum in like amounts. 
Another effective method of distributing and fixing the catalytic metals on 
the carrier is disclosed in U.S. Pat. No. 3,565,830. In the preferred 
methods, the carrier is immersed into a solution containing a 
water-soluble salt of platinum and a water-soluble salt of gold, which is 
agitated to insure uniform distribution of the metal. Thereafter, in order 
to fix the catalyst onto the support, the catalyst can be calcined within 
the range of from about 150.degree. C. to 700.degree. C. The calcination 
can be conducted in air such as, e.g., flowing dried air, or it may be 
carried out in contact with other gases such as, e.g., oxygen, nitrogen, 
hydrogen, flue gas, or under vacuum conditions. 
In one of the preferred embodiments, the platinum and gold are 
coimpregnated onto the carrier. A platinum-gold bearing solution comprised 
of one or more water-soluble platinum salts and one or more water soluble 
gold salts is prepared, applied to the carrier, and the support dried to 
reduce its moisture content and decompose the platinum and gold salts to 
the active species, usually metallic gold and platinum or gold and 
platinum oxide. 
Any of the water-soluble platinum salts known to those skilled in the art, 
which decompose upon heating to either platinum or an active platinum 
species, can be used to prepare the solution comprised of the platinum 
salt(s) and the gold salt(s). Thus, by way of illustration, one can use 
chloroplatinic acid, potassium platinum chloride, ammonium platinum 
thiocyanate, platinum tetramine hydroxide, platinum chloride, platinum 
tetramine chloride, tetraminoplatinum, tetrachlorodiamine platinum, 
platinum bromide, platinum fluoride and amine solutions of H.sub.2 
Pt(OH).sub.6, ammonium platinum sulfite, and the like. Similarly, one may 
use water-soluble gold salts, which decompose upon heating to either gold 
or an active gold species such as, for example, gold bromide, gold 
chloride, cyanoauric acid, nitratoauric acid, and the like. If desired, 
solvents other than water may be used, provided that the precious metal 
compounds may be dissolved or suspended and the solvent removed without 
excessive difficulty. 
Sufficient amounts of platinum and gold salts are used in the impregnating 
solution, so that the final catalyst composition contains from about 5 to 
about 95 weight percent of platinum (by weight of platinum and gold) and 
from about 5 to about 95 weight percent (by weight of platinum and gold) 
of gold. Thus, the ratio of platinum to gold can vary from about 1:20 to 
about 20:1, while maintaining the ability to catalyze ammonia 
decomposition. It is preferred that the catalyst composition contain from 
about 20 to about 90 weight percent of platinum and from about 80 to about 
10 weight percent of gold. It is more preferred that the catalyst 
composition contain from about 40 to about 80 weight percent of platinum 
and from about 60 to about 20 weight percent of gold. It is most preferred 
that the composition contain from about 60 to about 80 weight percent of 
platinum, by weight of platinum and gold, and from about 40 to about 20 
weight percent of gold. As used in this specification, the terms 
"platinum" and "gold" include both the elemental and active combined 
forms of platinum and gold but, in combined forms, all weight ratios are 
based upon the weight of an equivalent number of moles of metal. 
The platinum-gold bearing solution can be applied to the carrier by any of 
the means known to those skilled in the art. Thus, for example, the 
carrier can be immersed in the solution, the solution can be sprayed onto 
the carrier, or the platinum or gold can be deposited individually in a 
sequential process. The carrier can be immersed in platinum, gold or a 
combination platinum-gold bearing solution, such that the carrier is 
surrounded by large excess of solution or it may be impregnated such that 
the total volume of the impregnation solution represents some fraction of 
the pore volume of the support being impregnated. 
It is preferred that the carrier be coimpregnated with a single 
platinum-gold solution. However, the carrier may be impregnated with 
separate platinum and gold solutions. The coimpregnation technique is 
preferred, for it ensures that the platinum and gold active species are 
thoroughly intermingled. 
After the carrier is impregnated with the platinum and gold, it may be 
dried at a temperature of from about 80.degree. C. to about 130.degree. C. 
(preferably 110.degree. C.), until it contains less than about 5 
(preferably 1.5) weight percent (by weight of impregnated carrier) of 
moisture. After drying, the soluble salts may be decomposed by heating the 
dry impregnated carrier to a temperature of from about 200.degree. C. to 
about 600.degree. C. (preferably 400.degree. C. to 500.degree. C.) in 
either a reducing or oxidizing atmosphere for 0.5 to 2 hours. During the 
second heating, the water-soluble platinum and gold salts decompose to 
either platinum, an active platinum species, gold, or an active gold 
species. Thus, for example, when chloroplatinic acid is used as the 
water-soluble salt, subsequent heating of the impregnated carrier drives 
off hydrogen chloride to produce elemental platinum. It is the intent of 
this invention that the platinum and gold be in close proximity to each 
other. The techniques for depositing each soluble metal salt of either 
gold or platinum alone or together or non-soluble entities of platinum or 
gold must be such that when on the support they can interact to provide 
selectivity both for selective reduction of NO.sub.x and for decomposition 
of ammonia over a wide temperature range. 
THE VANADIUM OXIDE CATALYST 
Vanadium oxide catalyst compositions used in this invention can be prepared 
by means well known to those skilled in the art. Thus, the catalyst can be 
applied to the alumina carrier by the well-known immersion method; any 
suitable vanadium oxide, such as VO.sub.2, V.sub.2 O.sub.3 and V.sub.2 
O.sub.5 can be used in this method. Where vanadium trioxide is used, one 
can heat ammonium metavanadate supported on a carrier in a stream of 
hydrogen at a temperature of from 250.degree. C. to 650.degree. C. to 
produce the desired vanadium trioxide. As disclosed in U.S. Pat. No. 
4,003,854, the disclosure of which is hereby incorporated into this 
specification by reference, ammonium metavanadate or vanadium pentoxide 
can be dissolved in an aqueous solution of oxalic acid having a 
concentration of 10-360 grams/liter, the solution can be used to 
impregnate the alumina carrier, the carrier can then be dried at 
110.degree.-220.degree. C., and the dried carrier can be calcined at a 
temperature of 400.degree.-600.degree. C. Thus, as is disclosed in U.S. 
Pat. No. 4,048,112, the disclosure of which is hereby incorporated herein 
by reference, one can use a vanadium salt, such as vanadyl sulfate or 
vanadyl chloride, dissolved in oxalic acid to prepare the impregnating 
solution. 
The preferred vanadium oxide is vanadium pentoxide. The vanadium 
oxide/carrier composition can contain from about 0.5 to about 20 weight 
percent (by weight of vanadium oxide and carrier) of vanadium oxide. It is 
preferred that the vanadium oxide/carrier composition contain from about 2 
to about 10 weight percent of vanadium oxide, based on the weight of the 
carrier, and it is most preferred that the composition contain from about 
3 to about 8 weight percent of vanadium oxide. 
In one preferred embodiment, the vanadium oxide/carrier composition 
consists essentially of vanadium oxide and carrier. 
THE CATALYST CARRIER 
Any of the carriers known to those skilled in the art for supporting one or 
more catalysts can be used in the catalyst compositions used in the 
process of this invention. 
In one embodiment, the carrier used in the catalyst composition used in 
this invention is a solid unitary or monolithic skeletal body, having a 
plurality of unobstructed openings or channels therethrough in a direction 
of desired fluid flow. Advantageously, the unitary body is shaped to fit 
the reaction zone into which it is to be disposed. In one of the preferred 
aspects of this embodiment, the carrier is constructed of a substantially 
chemically inert, substantially catalytically-inactive, rigid, solid 
material capable of maintaining its shape and strength at high 
temperatures, for instance, up to 1100.degree. C. or more. Advantageously, 
the carrier may be either a refractory oxide or a metal. The preferred 
refractory oxides have a bulk density of about 0.45 to 1.05 grams per 
cubic centimeter, preferably about 0.5 to 0.9 grams per cubic centimeter, 
are unglazed, and can contain a major proportion of crystalline material. 
Preferably, it is essentially crystalline in form and advantageously 
contains at least about 90% crystalline material, and is marked by the 
absence of any significant amount of glassy or amorphous matrices of the 
type found in porcelain materials. Further, the carrier should have 
considerable accessible porosity as distinguished from the substantially 
non-porous porcelain utilized for electrical appliances, for instance, 
spark plug manufacture, which have relatively little accessible porosity, 
typically about 0.011 cc./gram. The accessible pore volume of the support 
of this invention, not including the volume of the fluid flow channel, 
preferably is at least 0.03 cubic centimeters per gram of support, 
preferably in the range of from 0.1 to 0.3 cc./g. 
When the carrier is a unitary skeletal support, it can contain macropores 
in communication with the channels to provide increased accessible 
catalyst surface and, preferably, an absence of small pores for high 
temperature stability and strength. While the superficial surface area of 
such structures may be on the order of 0.001 to 0.01 m..sup.2 /g. 
including the channels, the total surface area is typically many times 
greater, so that much of the catalytic reaction will take place in the 
large pores. The skeletal structure can have a macropore distribution such 
that at least 95% of the pore volume is in pores of a size, i.e., (a 
diameter) of over 2,000 A. and at least 5% of the pore volume is in pores 
having a size of over 20,000 A. Generally, the total surface area (that 
is, including the pores of the support or carrier of the present invention 
as distinguished from the apparent or superficial surface area), is at 
least about 0.08 square meter per gram, preferably about 0.2 to 2 square 
meters per gram. The geometric superficial or apparent surface area of the 
carrier, including the walls of the openings, should be as large as is 
consistent with an acceptable back pressure in the fluid flow system. 
When the carrier is a unitary skeletal support, the openings through the 
body can be of any shape and size consistent with the desired superficial 
surface and should be large enough to permit free passage of the fluids to 
be reacted and to prevent plugging by any particulate matter that may be 
present in the fluids. In one embodiment, the channels or openings are 
generally parallel and extend through the support from one to an opposite 
side, such openings being usually separated from one another by preferably 
thin walls defining the openings. In another embodiment, a network of 
channels permeates the body. The channels are unobstructed or 
substantially unobstructed to fluid flow. For most efficient operation, 
the openings are distributed across essentially the entire face or 
cross-section of the support. 
It is preferred that the carrier used in the catalyst composition of this 
invention comprise a refractory inorganic oxide. Refractory inorganic 
oxides possess particular physical characteristics which permit adaption 
to the rather unique environment encountered in the operation of a motor 
vehicle, as well as other commercial applications. One desirable physical 
characteristic, for example, is that extremely high temperatures 
apparently do not affect the capability of the material to function as 
desired. Some of the preferred refractory inorganic oxides which can be 
used in the catalyst composition of this invention include, for example, 
alumina, sillimanite, magnesium silicates, zircon, petalite, spodumene, 
cordierite, aluminosilicates, mullite, silica, magnesium aluminum 
titanate, and the like. 
Alumina and titania are more preferred refractory metal oxides for the 
carrier, although silica and zirconia can also be used advantageously. In 
one preferred embodiment, the carrier contains from about 50 to about 100 
weight percent of alumina. Suitable forms of alumina include the chi, 
kappa, gamma, delta, eta and theta forms, the so-called gamma form being 
most preferred. Titania may be used in either the anatase or rutile form, 
although anatase is preferred. Since vanadia is known to promote sintering 
of alumina, known stabilizers may be used to counteract this tendency if 
alumina is to be used as the carrier for the vanadia catalyst. Stabilized 
aluminas which are resistant to high temperatures are disclosed in U.S. 
Pat. Nos. 3,945,946, 3,956,188 and 3,966,311. 
In preferred embodiments, the catalyst compositions used in this invention 
include a catalytically-active calcined composite having a surface area of 
at least 20 square meters per gram (m.sup.2 /g) after calcination. 
The calcined composite may be formed to any desired shape such as a powder, 
beads, spheres, extrudates, saddles, pellets. This shaping or fabricating 
is accomplished before calcination to promote particle adhesion. After 
calcination, at least one catalyst metal is added to the composite. 
Additionally, the composite can be applied or deposited on a relatively 
inert support or substrate and the catalyst metal then added, or the 
catalyst composition can be applied or deposited onto the inert support. 
PROCESS CONDITIONS 
In the process of this invention, a waste gas is contacted with at least 
one catalyst composition to reduce the amount of nitrogen oxides 
(NO.sub.x) therein. 
The waste gas treated in the process of this invention may be effluent from 
various nitration processes, an internal combustion gas or diesel engine, 
and the like. In general, the waste gas contains, by volume, 10 ppm or 
more of nitrogen oxide, 0 to 15 percent water vapor, the balance being 
oxygen, inert gases such as carbon dioxide, nitrogen, argon, helium, 
pollutants which do not poison the catalyst and the like. Preferably, the 
gas contains from about 2 to about 22% oxygen. In one embodiment, the 
waste gas is the effluent from a nitric acid process and contains, on a 
dry basis, from about 0.1 to about 0.5 percent by volume of mixed nitric 
oxide and nitrogen dioxide, about 3-4 percent by volume of oxygen, and 
nitrogen. In another embodiment, the waste gas contains, by volume, from 
about 0 to about 2000 ppm of NO, from about 0 to about 2.0 ppm of 
NO.sub.2, (the amount of NO and NO.sub.2 being present exceeding 10 ppm) 
from about 0 to about 10 percent of H.sub.2 O, from about 1 to about 22 
percent of oxygen, with the remainder of the gas consisting essentially of 
one or more inert constituents, such as nitrogen and/or argon; the waste 
gas may also contain water is amounts up to about 15 percent by volume, 
without any detrimental effect. 
To reduce the NO.sub.2, from about 0.8 to about 1.4 moles of ammonia are 
added to the waste gas for each mole of either nitrogen oxide. It is 
preferred to use from about 0.9 to about 1.3 moles of ammonia per mole of 
nitrogen oxide. In a more preferred embodiment, from about 0.9 to about 
1.2 moles of ammonia are used for each mole of nitrogen oxide in the waste 
gas. In still more preferred embodiments, about 0.9 to about 1.1 moles of 
ammonia are used for each mole of the waste gas. Of course, in the most 
preferred embodiment, just slightly over 1.0 mole of ammonia is used for 
each mole of nitrogen oxide in the waste gas, if the NO.sub.x 
concentration remains constant enough to permit such fine tuning. 
After ammonia addition, the waste gas is contacted with a supported 
vanadium oxide catalyst, and then the effluent from the first reaction 
stage is passed over the platinum-gold catalyst composition in a second 
reaction stage. The reaction sequence is critical, and if the sequence is 
reversed (with platinum-gold in the first stage and the vanadium oxide in 
the second stage), at temperatures above 225.degree. C., the platinum gold 
catalyst will decompose the ammonia before it can reduce the NO.sub.x. 
The ammonia-waste gas mixture may be passed or fed over and into contact 
with the supported platinum-gold catalyst at a space velocity of from 
about 3,000 to about 200,000 standard volumes of gas per volume of 
catalyst per hour. It is preferred to use a space velocity of from about 
5,000 to about 40,000 standard volumes of gas per volume of catalyst per 
hour. 
The ammonia-water gas mixture may be maintained at any convenient pressure 
while it is in contact with the platinum-gold catalyst composition. It is 
preferred to maintain the reaction temperature of this mixture at from 
about 250 to about 550 degrees centigrade, while it is being passed over 
the platinum-gold catalyst. 
When a vanadium oxide catalyst is used by itself to treat waste gas, the 
effluent often contains ammonia. However, in the two stage process of this 
invention, the waste gas is first passed through a vanadium oxide catalyst 
and then through a platinum-gold catalyst, an extremely important 
unexpected benefit is obtained, as the effluent contains greatly reduced 
amounts of ammonia, as the excess is preferentially decomposed by the 
platinum-gold catalyst. 
The two stages of this process of this invention can be physically arranged 
in any of the manners known to those skilled in the art. Thus, one can 
utilize two catalysts on two different supports in different portions of 
the same reactor; for example, the first portion of the catalyst bed of a 
reactor can contain the vanadium oxide catalyst and the second portion can 
contain the platinum-gold catalyst. Alternatively, one can utilize the 
vanadium oxide catalyst in one reactor and then feed the effluent from the 
first reactor to a second reactor, where it is contacted with the Pt/Au 
catalyst. Also, one end of a single support may be coated with vanadium 
pentoxide while the other end may be coated with the platinum gold 
catalyst.

The following examples are presented to illustrate the invention which is 
limited only by the claims. Unless otherwise specified, all parts are by 
weight and all temperatures are in degrees centigrade. 
EXAMPLE 1 
Preparation of 0.3% Reference Platinum Catalyst (11087-25-A) 
202.0 grams of 5-8 mesh, gamma alumina spheres having a BET surface area of 
100.+-.20 m.sup.2 /g, crush strength of 18.+-.4 lbs, a bulk density of 
approximately 43 lbs/ft.sup.3, and a water uptake of 0.64 cc/g were placed 
into a pyrex dish having a diameter of 170 mm by a depth of 90 mm, and 
rotated at 35 RPM at a 45 degree angle on a device designed for that 
purpose. An aqueous solution of 3.02 grams of chloroplatinic acid (H.sub.2 
PtCl.sub.6) (0.60 g Pt) in 125 milliliters of deionized water was 
prepared; the pH of this solution was 1.95. The solution was added by 
pouring the solution rapidly on the beads, then mixed with the beads for 
five mintues, while continuously being rotated in the dish at 35 RPM. 
Thereafter, the impregnated beads were dried by a hot air stream at a 
temperature of 110.degree. C. for about 40 minutes; the dried beads 
contained about 3% weight percent of the moisture. The dried beads were 
placed in a pyrex tube in an electrically-heated two zone furnace and 
reduced with a 7% H.sub.2 /93% N.sub.2 gas mixture at 430.degree. C. for 
two hours. The beads were then cooled to room temperature in nitrogen. 
EXAMPLE 2 
Preparation of 0.4% Reference Gold Catalyst (11154-2C) 
Gold catalyst was prepared as in Example I, except that the gamma alumina 
spheres were impregnated with an aqueous solution containing 1.6018 g of 
gold chloride in 125 milliliters of deionized water at a pH of 1.5. 
EXAMPLE 3 
Preparation of 0.3% Pt/0.4% Au Catalyst (11087-25-B) 
The procedure of Example 1 was substantially followed, with the exception 
that the impregnating solution containing 3.02 grams of chloroplatinic 
acid (0.6 g Pt) and 1.6 grams of gold chloride (0.8 g Au) in 125 
milliliters of deionized water, and the pH of the impregnating solution 
was 1.95. 
EXAMPLE 4 
Preparation of 0.05% Pt/0.4% Au Catalyst (11154-2-B) 
The procedure of Example 2 was substantially followed, with the exception 
that the impregnating solution contained 0.5035 grams of chloroplatinic 
acid (0.1 g Pt) and 1.6075 grams of gold chloride (0.9 g Au). 
EXAMPLE 5 
Preparation of 0.61% Pt/0.15% Au Catalyst (1154-12) 
404 grams of alumina (preferably gamma alumina), which has a BET surface 
area of 180 m.sup.2 /g, and having a water uptake of approximately 0.94 
cc/g, were charged into a dough mixer. 34.512 grams of gold chloride were 
dissolved in 200 milliliters of deionized water, and 21.7 grams of 
chloroplatinic acid was added to this solution; deionized water was then 
added to bring the total volume of 320 milliliters. The impregnating 
mixture was added to the gamma alumina by rapidly pouring the solution on 
the powder as it is being mixed, then the gamma alumina and the 
impregnating solution were mixed for 10 minutes. 28 grams of glacial 
acetic acid were added to the reaction mixture and mixed for 10 minutes. 
Thereafter, 30 milliliters of hydrogen peroxide were added to the reaction 
mixture and mixed for 10 minutes. The reaction mixture was then placed in 
a 1/2-gallon porcelain mill jar with 4 lbs. of grinding media. The 
composition was milled for 17 hours on a ball mill rack at about 110 RPM. 
The resulting slurry having a solids content of 45% was used to coat two 
11/2" diameter by 3" long Corning 300 cells/in.sup.2 cordierite monoliths. 
The coating was applied by dipping the monoliths in the slurry for two 
minutes, removing, draining, then blowing off excess slurry with a 
hand-held air gun. The resulting units were dried four hours at 
110.degree. C. in a forced air oven and calcined in air for two hours at 
425.degree. C. The washcoat loading was 1.74 g/in.sup.3 for both units. 
EXAMPLE 6 
Preparation of a 0.23% Pt/0.06% Au Catalyst (11154-21) 
404 grams of gamma alumina were charged into the mixer used in Example 5. 
6.17 g of platinum as H.sub.2 Pt(OH).sub.6 solubilized in monoethanolamine 
were diluted with a sufficient amount of deionized water to form a 280 
milliliter solution. This platinum impregnating mixture was added to the 
gamma alumina powder by rapidly pouring the solution on the powder as it 
is being mixed, with continuous mixing for 15 minutes. 3.0894 grams of 
gold chloride were dissolved in 80 milliliters of deionized water and the 
gold impregnating solution was added to the impregnated gamma alumina 
powder in the same manner. 28 milliliters of acetic acid were added to the 
reaction mixture, which was mixed for 15 additional minutes, then placed 
in the 1/2-gallon mill jar used in Example 5 and was milled for 17 hours 
at about 110 RPM. The resulting slurry having a solids content of 42% was 
used to coat two Corning 300 cell/in.sup.2 cordierite monoliths, which 
were 11/2" in diameter by 3" long. The units were dipped in slurry for two 
minutes, removed, excess slurry drained, and remaining slurry was removed 
with a hand-held air gun. Both units were dried in the oven and furnace 
described in Example 5 for 16 hours at 110.degree. C., followed by 1 hour 
at 425.degree. C. The resulting washcoat was determined to be 1.48 
g/in.sup.3 average for both units. 
EXAMPLE 7 
Preparation of 0.039% Pt 0.014% Au Catalyst (11154-30) 
In substantial accordance with the procedure of Example 5, 404.0 grams of 
gamma alumina were charged into the mixer. 0.777 grams of gold chloride 
were dissolved in 100 milliliters of deionized water, and to this solution 
was added a solution of 2.6167 grams of chloroplatinic acid in 60 
milliliters of deionized water. Additional deionized water was added to 
bring the total volume of the impregnating solution up to 350 milliliters, 
and the impregnating solution was added to the gamma alumina powder and 
mixed for 15 minutes, by rapidly pouring the solution on the powder as it 
is being mixed. 28 milliliters of acetic acid were added to the 
impregnated gamma alumina, and the composition was mixed for 15 minutes, 
by rapidly pouring the solution on the powder as it is being mixed with a 
paddle mixer at about 120 RPM. The reaction mixture was placed into the 
1/2-gallon ball mill used in Example 5, and milled for 17 hours at about 
110 RPM. 
The resulting slurry having a solids content of 43.5% was used to coat two 
Corning 300 cells/in.sup.2 cordierite monoliths, which were 11/2" in 
diameter by 3" long. Units were dipped in slurry for 2 minutes, removed, 
excess slurry drained, then the remaining slurry was removed with a 
hand-held air gun. Both units were dried in oven and furnace described in 
Example 5 for 16 hours at 110.degree. C. and 1 hour at 500.degree. C. in 
air. The resulting washcoat was determined to be 1.72 g/in.sup.3 average 
for both units. 
EXAMPLE 8 
Preparation of 0.005% Pt 0.0019% Au Catalyst (11154-36) 
303 grams of gamma alumina were charged into the mixer used in Example 5. 
0.2617 grams of chloroplatinic acid were dissolved in 50 milliliters of 
deionized water, and 0.0803 grams of gold chloride were dissolved in 50 
milliliters of deionized water; the two solutions were combined, and a 
sufficient amount of deionized water was added to the solution to bring 
its volume up to 265 milliliters. The platinum-gold impregnating solution 
was added to the gamma alumina powder and mixed for 15 minutes, by rapidly 
pouring the solution on the powder being mixed. 21 milliliters of acetic 
acid were added to the impregnated carrier and mixed with it for 15 
minutes by rapidly pouring the solution on the powder as it was being 
mixed. The composition was placed in the 1/2-gallon ball mill used in 
Example 5 and milled for 16 hours at about 110 RPM. 
The resulting slurry having a solids content of 44.0% was used to coat two 
units of Corning 300 cells/in.sup.2 cordierite monoliths, which were 11/2" 
in diameter by 3" long. The units were dipped in slip for 2 minutes, 
removed, drained, then excess slurry was removed, drained, then excess 
slurry was removed with air from a hand-held gun. Both units were dried 
and calcined in the equipment described in Example 5 for 4 hours at 
110.degree. C. and 1 hour at 500.degree. C. The resulting washcoat was 
determined to be 1.30 g/in.sup.3 average for both units. 
EXAMPLES 9-12 
In these examples, the ammonia-waste gas mixture contained 200 parts per 
million of NO and 5 volume % O.sub.2, the NH.sub.3 /No.sub.x mole ratio in 
the waste gas being 1.0. A stainless steel tubular metal reactor 9.0" long 
with an internal diameter of about 1.5" was filled with 1/2" diameter 
catalyst pellets, having the indicated compositions of Examples 1-4, set 
forth in Table I, and the waste gas was passed through the packed tubular 
metal reactor at a space velocity of 10,000 standard volumes of gas per 
volume of catalyst per hour, while the catalyst was maintained at the 
temperature indicated in Table I by a stream of hot gases from an 
externally-heated preheater. The effluent from the reactor was analyzed 
for its NO and NO.sub.2 content by chemiluminescent analysis. Nitrogen 
oxide conversions at various reaction temperatures were determined, and 
the results are presented in Table I. 
The combination of 0.3% platinum and 0.4% gold unexpectedly yielded 
nitrogen oxide conversions which were unexpectedly higher at 297.degree. 
C. than those obtained with either platinum or gold. Thus, it can be seen 
that the platinum gold catalyst is effective over a much broader 
temperature range than the platinum catalyst, while the gold had 
essentially no catalytic activity. 
EXAMPLES 13-16 
In these examples, the procedure of Examples 9-12 was repeated, except that 
the catalyst compositions from examples 5-8 were tested in the form of 
thin washcoats on the walls of extruded cylindrical Corning cordierite 
monoliths, 11/2" diameter by 3" long, having 300 square cells per square 
inch. The space velocity used was 10,000 standard volumes of gas per 
volume of catalyst per hour. The results of these experiments are 
presented in Table I. 
These results illustrate the effect of varying the ratio of platinum to 
gold and demonstrate that effective reduction of NO.sub.x can be obtained 
over a wide range of temperatures using this platinum-gold catalyst. 
EXAMPLE 17 
Preparation of 6.1% Vanadium Pentoxide on Gamma Alumina (11154-23) 
303 grams of gamma alumina were charged into the Blakeslee mixer used in 
Example 5. 53.77 grams of vanadyl sulfate (VOSO.sub.4.n H.sub.2 O) were 
dissolved in 240 milliliters of deionized water. The vanadyl sulfate 
impregnating solution was rapidly added to the gamma alumina powder and 
mixed for 30 minutes in a bowl-type mixer. The impregnated carrier was 
dried for about 17 hours at 110.degree. C. in a forced air oven on a pyrex 
tray. The dried composition was calcined in air by heating in a muffle 
furnace to 400.degree. C. and holding for 1 hour, and increasing the 
temperature to 500.degree. C. for 2 additional hours. 200 grams of the 
calcined composition were placed into the 1/2-gallon mill used in Example 
5 with 300 ml of deionized water and 27 ml of glacial acetic acid and 
milled for 17 hours. The resulting slurry was adjusted with deionized 
H.sub.2 O so as to give a slip having a solids content of 36.2%, which 
was used to coat 11/2" diameter by 3" long cylindrical samples of Corning 
300 cells/in.sup.2 cordierite monoliths. The samples were dipped in slurry 
for 1-2 minutes, drained and the excess slurry blown from the channels 
with high pressure air. After impregnation, the test samples were dried 
for 16 hours in a forced air oven at 110.degree. C., then calcined in air 
at 425.degree. C. for 1 hour. The average washcoat loading on the samples 
was 1.66 g/in.sup.3 or about 175 g of V.sub.2 O.sub.5 /ft.sup.3. 
EXAMPLE 18 
Preparation of Pt/Au/Al.sub.2 O.sub.3 Composition (11154-36) 
303 grams of gamma-alumina were placed into the Blakeslee mixer used in 
Example 5. 0.2617 grams of chloroplatinic acid were dissolved in 50 
milliliters of deionized water; 0.0833 grams of gold chloride were 
dissolved in 50 milliliters of deionized water, the gold and platinum 
solutions were combined, and sufficient deionized water was added to the 
combined solution to bring its volume up to 265 milliliters. The 
impregnating solution was rapidly added to the gamma-alumina powder and 
mixed for 15 minutes in a dough mixer. Thereafter, 21 milliliters of 
acetic acid were added to the reaction mixture and mixing continued for 15 
minutes. The mixed composition was placed in a 1 gallon ball mill jar with 
an additional 50 ml of deionized water. The composition was milled for 16 
hours. The resulting slurry was diluted with deionized H.sub.2 O to give a 
slip with a solids content of 44%. It was used to coat Corning 300 
cells/in.sup.2 monolithic samples having a diameter of 11/2" and a length 
of 3". The samples were dipped, drained and excess slurry blown free of 
the cells by high pressure air. The resulting samples were dried for 4 
hours at 110.degree. C. in a forced air oven and calcined in air for 1 
hour at 500.degree. C. The average washcoat loading was 1.56 g/in.sup.3 
containing a loading of about 1.30 g precious metal/ft.sup.3 at 2.66 
Pt/1Au. 
EXAMPLES 19 AND 20 
In these Examples, an ammonia-waste gas mixture comprised of 2000 parts per 
million of nitrogen oxide, 5 Volume % O.sub.2 and having a NH.sub.3 
/NO.sub.x mole ratio of 1.0 was prepared. A stainless steel, tubular metal 
reactor which was 9.0" long and has an internal diameter of about 1.5" was 
packed with one of the catalyst compositions by taking one of the 11/2" 
diameter by 3" long test samples and wrapping it with a high temperature 
fibrous "wool" so that, when inserted into the reactor, the "wool" serves 
to eliminate bypass of the gases between the reactor wall and the sample. 
A second test core is wrapped and inserted into the reactor so as to give 
a catalyst bed length of 6". The distance between the first and second 
test core is approximately 1/4". In these examples, the catalyst 
compositions of Examples 17 and 18 were used as indicated in the Table. 
The waste gas mixture was passed through the tubular metal reactor at a 
space velocity of 10,000 standard volumes of gas per volume of catalyst 
per hour, while the catalyst was being maintained at a specified 
temperature in the reactor by a stream of hot gases from a preheater which 
is heated by external electric furnace. 
The effluent from the reactor was analyzed for its NO and NO.sub.2 content 
by chemiluminescent analyzer by Beckman Industries. Nitrogen oxide 
conversions at various reaction temperatures were determined, and the 
results are presented in Table 1. 
These examples demonstrate that under these conditions neither vanadium 
pentoxide nor platinum-gold catalysts are fully effective for reducing 
NO.sub.x when the mole ratio of NH.sub.3 to NO.sub.x is 1 to 1. 
EXAMPLE 21 
(From Example 1 of CR-80-67) 
In substantial accordance with the procedure of Example 17, a V.sub.2 
O.sub.5 /Al.sub.2 O.sub.3 catalyst composition was prepared by placing 353 
g of gamma alumina powder in a mixer. 94. g of vanadyl sulfate were 
dissolved in 280 ml of deionized water and rapidly added to the powder, 
which was thereafter mixed for 15 minutes. The resulting semi-wet powder 
was dried for 16 hours in air at 110.degree. C., then calcined for 1 hour 
at 400.degree. C., followed by calcining at 500.degree. C. for 1 hour. The 
calcined composite placed in a gallon ball mill with 52 ml of glacial 
acetic acid, 850 ml of deionized water and an appropriate grinding medium. 
The ball mill was run at 72 RPM for 17 hours so as to give a slurry 
suitable for coating Corning 300 cells/in.sup.2 cordierite monolith with a 
washcoat vanadia loading of 1.7 g/in.sup.3. 
In substantial accordance with the procedure of Example 9, a mixture of 
ammonia and waste gas comprised of 10% H.sub.2 O, 2000 ppm NO and 5 Volume 
% O.sub.2 was prepared; the NH.sub.3 /NO.sub.x mole ratio in the waste 
gas-ammonia mixture being 1.0. A stainless steel, tubular metal reactor 
which was 9.0" long with an internal diameter of about 1.5" was packed as 
described in Examples 9-12. The gas was passed through the reactor at a 
pressure of 7 p.s.ig. and a space velocity of 20,000 standard volumes of 
gas per volume of catalyst per hour while the catalyst was maintained at 
the specified temperature by a stream of hot gases from an 
externally-heated preheater. The effluent from the reactor was analyzed 
for its nitrogen oxide and ammonia content. The nitrogen oxide conversions 
are presented in Table 1. 
The effluent was analyzed to determine whether it contained ammonia. A 
significant amount of ammonia was found in the effluents. In the 
experiment conducted at 300.degree. C., the effluent contained 0.47 moles 
of ammonia for each mole of ammonia in the feed. In the experiments 
conducted at 350.degree., 400.degree. and 450.degree. C., the effluents 
respectively contained 0.32, 0.18 and 0.04 moles of ammonia for each mole 
of ammonia in the feed. 
This example demonstrates that when a vanadium pentoxide catalyst is used, 
it is possible to obtain high conversions of NO.sub.x, but significant 
amounts of ammonia will be present in the effluent. 
EXAMPLE 22 
(From Example 2 of CR-80-67) 
A Pt/Au catalyst composition was prepared as previously described in 
Example 6. 
In substantial accordance with the procedure of Example 6, a mixture of 
ammonia and waste gas was prepared which was the same as that in Example 6 
except that the NH.sub.3 /NO.sub.x mole ratio in the waste gas-ammonia 
mixture was 1.2. A stainless steel, tubular metal reactor which was 9.0" 
long and had an internal diameter of about 1.5" was loaded as previously 
described. The gas was passed through the reactor at space velocities of 
10,000 20,000, 30,000 and 40,000 standard volumes of gas per volume of 
catalyst per hour while the catalyst was maintained at the specified 
temperature. The effluent from the reactor was collected and analyzed for 
nitrogen oxide and ammonia content. The nitrogen oxide conversions and 
ammonia at various reaction temperatures are presented in Table 1. 
For reach reaction temperature, the NO.sub.x Conversion was within .+-.5% 
of the value indicated in the Table which is an average of the four 
measured values. The amount of ammonia found in the effluent samples over 
the range of 225.degree. to 450.degree. C. was comparable to that obtained 
with vanadia catalyst at 450 C. and significantly less than that obtained 
with vanadia at lower temperatures. 
This example illustrates that when the platinum gold catalyst is used the 
problem of ammonia breakthrough into the effluent is minimized if not 
entirely eliminated, and good conversions of NO.sub.x can be obtained in 
the lower temperature range. 
EXAMPLE 23 
(From Example 3 of CR-80-67) 
A two-stage catalyst system having a first stage comprised of V.sub.2 
O.sub.5 /Al.sub.2 O.sub.3 and a second stage comprised of Pt/Au/Al.sub.2 
O.sub.3 was prepared by combining a 3" length of the Pt/Au catalyst of 
Example 22. 
In substantial accordance with the procedure of Example 9, a mixture of 
ammonia and waste gas was prepared except that the NO.sub.x /NH.sub.3 mole 
ratio in the waste gas-ammonia mixture was about 1.0:1.2. A stainless 
steel, tubular metal reactor which was 9.0" long with an internal diameter 
of about 1.5" was packed as described in Example 19. The gas was passed 
through the V.sub.2 O.sub.5 and Pt/Au catalysts at space velocities of 
20,000 and 80,000 standard volumes of gas per volume of catalyst per hour, 
respectively. The reaction pressure was 7 p.s.i.g. The effluent from the 
reactor was collected and analyzed for its nitrogen oxide and ammonia 
content. The nitrogen oxide conversions at various reaction temperatures 
are presented in Table 1. No more than 0.04 moles of ammonia were found in 
the effluent for each mole of ammonia in the feed. This example 
illustrates that when the gold-platinum catalyst is used after a vanadium 
pentoxide catalyst, effective reduction of NO.sub.x can be achieved over a 
wide range of temperatures and that excess ammonia can be safely used to 
achieve high NO.sub.x conversions without danger of ammonia breakthrough. 
TABLE I 
__________________________________________________________________________ 
% Conversion of NOx 
Temp. .degree.C. 
236 
250 
267 
297 
327 
350 
388 
400 
450 
Catalyst 
Example 
Catalyst 
Type (%) 0 Comments 
__________________________________________________________________________ 
9* 1 .3Pt 90 67 NH.sub.3 /NO = 1:1 
10* 2 .4Au 0 0 NH.sub.3 /NO = 1:1 
11 3 .3Pt-.4Au 95 87 NH.sub.3 NO = 1:1 
12 4 .05Pt-.4Au 
34 7 NH.sub.3 /NO = 1:1 
13 5 .61Pt-.15Au 
98 89 79 64 NH.sub.3 NO = 1:1 
14 6 .23Pt-.06Au 
98 95 90 81 NH.sub.3 /NO = 1:1; VHSV = 
10,000 
15 7 .039Pt-.014Au 98 92 96 86 75 NH.sub.3 /NO = 1:1 
16 8 .005Pt-.0019Au 57 86 65 NH.sub.3 /NO = 1:1 
19* 17 V.sub.2 O.sub.5 
2 8 48 NH.sub.3 /NO = 1:1 
20 18 .0047Pt-.0021Au 
57 77 65 NH.sub.3 /NO = 1:1 
21* 17 V.sub.2 O.sub.5 
68 98 89 Excess NH.sub.3 in exhaust 
22 6 .23Pt.-06Au 98 82 62 30 NH.sub.3 in effluent 
.about. O; Average 
of four VHSH's 
23 19 & 6 
Two Stage V.sub.2 O.sub.5 / 
95 95 95 96 96 NH.sub.3 in effluent 
.about. O 
.23Pt-.06Au 
__________________________________________________________________________ 
*Comparative Example, Prior Art Catalyst.