Auto exhaust catalyst composition having low H.sub.2 S emissions and method of making the catalyst

A catalyst suitable for use as a three-way catalyst having low H.sub.2 S emissions for emission control and with substantially no ceria present is made with a refractory oxide particle or powder support having deposited thereon about 0.5-20% by weight of a non-rate earth oxide stabilizer, at least 0.5 to about 5% by weight of an alkali metal oxide as a promoter, and a catalytically-effective amount of one or more platinum group metals. The preferred refractory oxide is alumina and the non-rare earth oxide stabilizer can be an oxide such as ZrO.sub.2, MgO, CaO, SnO, CaO, Y.sub.2 O.sub.3, TiO.sub.2, ZnO, B.sub.2 O.sub.3, P.sub.2 O.sub.5, SnO.sub.2, Bi.sub.2 O.sub.3, or SiO.sub.2 with the preferred oxide being zirconia.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a catalyst for use in auto emission control which 
has improved, lower H.sub.2 S emissions while serving as a three-way 
catalyst (TWC). 
2. Description of the Previously Published Art 
With the arrival of the new "High Tech" auto exhaust catalysts coupled with 
the new operating conditions of the current state-of-the-art engine 
air/fuel management systems, there has resulted a new emission problem. 
That problem emission is H.sub.2 S. It is responsible for the rotten egg 
odor which occurs after certain modes of operation (e.g., sudden braking 
and quick starting). Additives such as nickel have been added to 
conventional catalyst compositions which consist typically of platinum 
group metals supported on a rare earth oxide promoted alumina. Such rare 
earth oxide and Ni compositions are currently in commercial use. While 
nickel is effective in lowering H.sub.2 S emissions, it is a suspected 
human carcinogen. Thus nickel may at some time be restricted in its use 
because of the potential threat to the environment as well as to public 
health. Some West European countries have not recommended its use. My 
approach is to formulate catalysts with additives which do not pose such a 
threat to the public health and the environment. 
While rare earths and especially cerium have been used commercially in auto 
emission control catalysts for a number of years, these catalysts when 
used in conjunction with the new closed loop air/fuel management systems 
have been found to produce significant H.sub.2 S emissions. This is most 
likely a result of ceria's efficacy for storing sulfur and for generating 
hydrogen via the water gas shift reaction under fuel rich (O.sub.2 
deficient) conditions the latter having been pointed out by G. Kim in 
"Ceria Promoted Three-Way Catalysts for Auto Exhaust Emission Control", 
I&EC Product Research & Development, 1982, 21, 267. These H.sub.2 S 
emissions have reached levels that the consumers feel are objectionable. 
All of the more common rare earths (viz., La, Ce, Nd, and Pr) to varying 
degree when incorporated into auto exhaust catalysts generate undesirable 
levels of H.sub.2 S. Catalysts lacking cerium oxide as a major component 
generally do not have sufficient activity to catalytically remove carbon 
monoxide under the conditions which the current state-of-the-art engines 
operate. That is the reason that higher levels of cerium oxide and other 
rare earth oxides have been incorporated into the so-called "High Tech" 
catalysts. "High Tech" performance has led to increased incidence of 
abnormally high levels of H.sub.2 S emission. My desire has been to 
achieve satisfactory carbon monoxide removal, but without the creation of 
new pollution problems. 
3. Objects of the Invention 
It is an object of this invention to obtain a catalytic composition which 
produces low H.sub.2 S emissions and is capable of meeting the EPA 
requirements for CO, HC, and NOx emissions. 
It is further object of this invention to achieve good CO and HC 
conversions under fuel rich, oxygen deficient conditions, with minimal 
H.sub.2 S emissions. 
It is further object of this invention to obtain a catalytic composition 
which is relatively non-toxic, and which does not pose potential threats 
to public health and the environment as current nickel containing 
catalysts may do. 
It is further object of this invention to obtain a catalyst suitable for 
use as a three-way catalyst having low H.sub.2 S emissions for emission 
control which has substantially no ceria present and which has a formed 
refractory oxide particle or refractory oxide powder support which has 
deposited thereon a non-rare earth oxide stabilizer, an alkali metal oxide 
promoter, and one or more platinum group metals as the catalyst metals. 
It is further object of this invention to make a catalyst which is suitable 
for use as a three-way catalyst with low H.sub.2 S emissions for emission 
control by impregnating a refractory oxide support with a solution 
containing either a non-rare earth stabilizer salt or a non-rare earth 
stabilizer salt plus an alkali metal compound; heating the impregnated 
support to at least decompose the non-rare earth stabilizer salt; and 
applying one or more catalytic platinum group metals and optionally at 
least one alkali metal promoter. 
It is further object of this invention to treat exhaust gases so as to 
reduce H.sub.2 S emissions by passing the exhaust gases over a catalyst 
suitable for use as a three-way catalyst having low H.sub.2 S emissions 
for emission control which has substantially no ceria present according to 
this invention. 
These and further objects will become apparent as the description of the 
invention proceeds. 
SUMMARY OF THE INVENTION 
It has been found that greatly lowered H.sub.2 S emissions and acceptable 
catalyst performance for control of CO, HC, and NOx emissions can be 
obtained even if the rare earths and especially ceria are substantially 
eliminated from auto exhaust catalyst compositions. In place of the rare 
earths a catalyst is formed from a refractory oxide particle or refractory 
oxide powder support having deposited thereon about 0.5-20% by weight of a 
non-rare earth oxide stabilizer, at least about 0.5 to about 5% by weight 
of an alkali metal oxide as a promoter, and a catalytially-effective 
amount of one or more platinum group metals selected from the group of Pt, 
Pd, Ir, Rh, or mixtures thereof; binary mixtures of Pt-Pd, Pt-Rh, or 
Pd-Rh; and tertiary mixtures of Pt-Pd-Rh. The non-rare earth oxide 
stabilizer is preferably one or more of the oxides of ZrO.sub.2, MgO, CaO, 
SrO, BaO, Y.sub.2 O.sub.3, TiO.sub.2, ZnO, B.sub.2 O.sub.5, P.sub.2 
O.sub.5, SnO.sub.2, Bi.sub.2 O.sub.3 and SiO.sub.2 with ZrO.sub.2 being 
preferred. The refractory oxide is preferably aluminum oxide. The 
components of the catalyst can be deposited in various combinations and 
orders with the non-rare earth oxide stabilizer generally being added 
first. These catalysts can be used to treat exhaust gases so as to reduce 
H.sub.2 S emissions while still possessing good three-way catalyst 
performance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The non-rare earth oxide (preferably alumina) stabilizer, which can be used 
include one or more of the following metal oxides: zirconia (ZrO.sub.2); 
the alkaline earth oxides which are MgO, CaO, SrO, and BaO; and the 
following additional oxides SiO.sub.2, Y.sub.2 O.sub.3, TiO.sub.2, ZnO, 
B.sub.2 O.sub.5, SnO.sub.2, or Bi.sub.2 O.sub.3. This non-rare earth oxide 
stabilizer can be present in an amount of about 0.5-20% based on the 
weight of the catalyst and preferably from about 1-5%. 
The promoters used in the catalyst are one or more alkali earth oxides 
which are Li.sub.2 O, Na.sub.2, K.sub.2 O, or Cs.sub.2 O. This alkali 
metal oxide is present in an amount from about at least about 0.5% to 5% 
based on the weight of the catalyst and preferably from at least about 
0.5% to 2%. 
The noble metals include one or more of Pt, Pd, Rh, Ir, Ru or mixtures 
thereof; especially mixtures of Pt-Pd, Pt-Rh, or Pd-Rh; and tertiary 
mixtures of Pt-Pd-Rh. 
The platinum group metals can be provided in the form of water soluble 
platinum group metal compounds such as sulfito complexes of platinum group 
metals, chloroplatinic acid, potassium platinum chloride, ammonium 
platinum thiocyanate, platinum tetrammine hydroxide, platinum group metal 
chlorides, oxides, sulfides, nitrites and nitrates, platinum tetrammine 
chloride, palladium tetrammine chloride, sodium palladium chloride, 
hexammine rhodium chloride, and hexammine iridium chloride. 
The catalyst composition can be applied equally well on powdered refractory 
oxide particles such as alumina particles to make a washcoat for a 
monolithic catalyst or the refractory oxide such as alumina can be in a 
pelleted catalyst form such as spheres, beads, pellets, tablets or 
extrusions. The preferred B.E.T. surface area for the refractory oxide 
support is from 50.250 m.sup.2 /g. When forming a monolithic catalyst, the 
weight percentages for the various additives are based on the weight of 
the washcoat mixture and not upon the weight of the inert support 
monolith. For the particle form, the preferred size is to have a mesh size 
between 4-10 U.S. mesh. For the powder embodiment, the preferred powder 
size is to have an average particle size of 100 microns or less. The 
preferred B.E.T. surface area for the catalyst is from 50 to 250 m.sup.2 
/g. 
The catalyst can be used for stationary source emissions as well as mobile 
source emissions. 
There are at least three embodiments by which the non-rare earth 
stabilizer, the alkali metal and the catalytic noble metals can be applied 
to the alumina support. They will be referred to as Embodiments A, B, and 
C. 
Embodiment A--Stabilizer First and Alone 
The non-rare earth stabilized catalyst, which is especially suitable for 
use as a three-way catalyst for control of auto emissions, is preferably 
made by impregnating with a solution containing a non-rare earth compound, 
a refractory oxide support, preferably an alumina support, which is either 
in a powder form or as formed particulates. The aluminum oxide is in a 
transition form. The transition phases are chi, gamma, eta, delta, theta, 
iota, and kappa. The particularly preferred forms are gamma, eta, delta 
and theta. In general, the aluminum oxide will have been heated to at 
least 300.degree. C. because otherwise it will not be in the transition 
form. 
The impregnated support is optionally dried at 100.degree.-200.degree. C. 
and then is heated to at least decompose the non-rare earth compound so as 
to obtain a non-rare earth oxide impregnated support. In a preferred 
embodiment the heating is done at a temperature of from about 400.degree. 
to 1100.degree. C. to thermally stabilize the support. The temperature for 
heating will depend on the precursor used to form the transition alumina. 
For alumina made from boehmite the temperature is preferably about 
400-700.degree. C. whereas for alumina made from pseudoboehmite the 
temperature is preferably about 800-1100.degree. C. The separate drying 
step is optional because in a large plant operation as the impregnated 
support is being sent into a calciner, it will automatically be given a 
drying operation as it enters the calciner where the initial temperature 
will be lower. Next, one or more alkali metals and one or more platinum 
group metals are applied by either one of the two procedures. 
In the first procedure (Al) the non-rare earth stabilized alumina support 
is impregnated with a first noble metal plus an alkali metal compound. The 
impregnated material is then dried at ambient temperature for 0-4 hours 
and at about 100-200.degree. C. and a second noble metal solution is 
added. Again the impregnated material is dried at ambient temperature for 
0-4 hours and at about 100-200.degree. C. 
In the second embodiment (A2) a combination of two or more noble metals and 
the alkali metal compound are impregnated in a single impregnation of the 
non-rare earth oxide stabilized alumina support. The impregnated material 
is then dried at ambient temperature for 0-4 hours and at about 
100-200.degree. C. 
Embodiment B--Stabilizer and Alkali Metal Together 
In this embodiment when the non-rare earth stabilizer is applied to the 
substrate, it is also applied along with the alkali metal. Thus the 
solution of the stabilizer compound and the alkali metal compound are 
applied to the substrate and after impregnation the substrate is dried at 
100-200.degree. C. It is next activated at 400-1100.degree. C. after which 
there can be two further possible procedures to apply the noble metals. In 
one procedure (B1) the noble metal solution is applied and the impregnated 
material is then dried at 100-200.degree. C. In the other procedure (B2) 
the noble metal is applied with some additional alkali metal which can be 
either a different alkali metal or some more of the same alkali metal. 
After impregnation the material is again dried at 100-200.degree. C. 
Activation for Embodiments A and B 
Finally the impregnated catalyst made by either Embodiment A or B is 
activated at a temperature of about 300.degree.-650.degree. C. by one of 
three procedures. The first is to just heat the treated support in air 
within this temperature range. The second procedure, and the more 
preferred reductive activation, is to heat within this temperature range 
in the presence of hydrogen which is generally 3-5 vol % H.sub.2 for 
practiced commercial applications and more preferably at 
550.degree.-650.degree. C. The third procedure is to carry out the second 
hydrogen reduction procedure in the presence of 20-50 vol. % steam along 
with 3-5 vol. % hydrogen. 
Embodiment C--Alkali Metal After Noble Metals 
In this embodiment the substrate is first impregnated with the non-rare 
earth stabilizer and the material is dried at 100-200.degree. C. as in the 
first step of Embodiment A. It is then activated at a temperature of 
between 400-1100.degree. C. and it can then be further treated either one 
of two procedures. 
In the first procedure (C1) one or more noble metals are added to the 
stabilized material and the material is dried at 100-200.degree. C. Then 
the material is given an activation treatment by one the three activation 
procedures described above. After activation, an additional impregnation 
is conducted with an alkali metal and the material is again ambient 
temperature for 0-4 hours and at about 100-200.degree. C. At this point 
the material is ready for use. However, there can be an additional 
optional activation which would be done in air and at 300-650.degree. C. 
In the other procedure (C2), one or more noble metals are applied to the 
non-rare earth oxide stabilized alumina by impregnation and the material 
is ambient temperature for 0-4 hours and at about 100-200.degree. C. Then 
a further alkali metal impregnation is conducted and again the impregnated 
product is dried at 100-200.degree. C. Finally, activation occurs by one 
of the three techniques discussed above to obtain the final product. 
In those catalysts which are made with Na, K, or Cs, the preferred method 
is add the alkali metal along with or after the noble metals are applied, 
although one can incorporate them with the ZrO.sub.2 or in a sequential 
application. 
It is prefered for lithia to be added with the zirconia, but it can be 
added at a later step. 
Having described the basic aspects of my invention, the following examples 
are given to illustrate specific embodiments thereof. 
EXAMPLE 1 
This example describes the preparation of a catalyst of this invention 
having low H.sub.2 S emissions and good catalyst performance when compared 
to a commercially available catalyst having the same noble metals, and 
loading and which is heavily loaded with cerium oxide. 
9,265 grams of -5+8 U.S. mesh alumina beads supplied by Rhone Poulenc as 
SCM-99XT having a compacted bulk density of 0.56 grams/cc, a water pore 
volume of 0.73 cc/gram and a total volatile content of 2.61% were 
impregnated with a zirconyl nitrate solution. The zirconyl nitrate 
solution was prepared by diluting 923.77 grams of a commercially available 
zirconyl nitrate solution which has the equivalent of 20.034 grams of 
zirconium oxide per 100 grams of said solution to a total volume of 6,425 
milliliters. This impregnating solution had a pH of 1.05. It was applied 
by spraying through atomizing nozzles. The impregnated beads were then 
allowed to stand one hour in the wet state, followed by drying at 
135.degree. C. for 16 hours. The support was further heated at 704.degree. 
C. for one hour. This represents the incorporation of 2% zirconium oxide 
by weight. At this point the support has a compacted bulk density of 0.57 
grams/cc, a water pore volume of 0.73 cc/gram, and a total volatile 
content of 0.57%. 
The above zirconia containing substrate (9,261 grams) was impregnated with 
a sulfited palladium nitrate solution prepared by diluting 67.92 grams of 
ammonium bisulfite (48% weight concentration) to 5 liters with deionized 
water. 83.1286 grams of palladium nitrate (8.9129% palladium 
concentration) was added, followed by 200.48 grams of potassium nitrate 
(99.8% assay). The solution was further diluted to 6423 milliliters. The 
solution which had a pH of 1.55 was impregnated onto the beads in a 
rotating vessel via atomizing spray. The wet beads were allowed to stand 
in the wet state for two hours. Following the wet hold the beads were 
dried in a mechanical convection oven at 135.degree. C. for 16 hours. The 
beads were then reimpregnated with a mixed platinum and rhodium sulfite 
solution. The rhodium sulfite solution was prepared by reacting 11.224 
grams of rhodium chloride solution (5.501% rhodium concentration) with 
16.00 grams of sulfurous acid (7.57% SO.sub.2 weight concentration) at a 
rhodium titer of 2 grams per liter at 60.degree. C. for two hours. The 
cooled rhodium solution was then combined with 25.9524 grams of 
(NH.sub.4).sub.6 Pt(SO.sub.3).sub.4 solution (9.51636% platinum 
concentration) and then further diluted to 6,085 milliliters with 
deionized water. The pH was 2.70. This solution was likewise applied by 
atomizing spray followed by a two hour wet hold and then drying at 
135.degree. C. for 16 hours. 
This catalyst was then reduced at 649.degree. C. for one hour in a flow of 
40.2% steam with the balance being a mixture of 5% hydrogen and 95% 
nitrogen. The level of potassia corresponds to 1% by weight of the overall 
catalyst composition. This sample will be identified as Catalyst 1. 
Catalyst 1 has a B.E.T. surface area of 112 m.sup.2 /g. 
EXAMPLE 2 
A catalyst of commerce which was manufactured by another catalyst supplier 
was obtained and used as the reference catalyst. This represents the "High 
Tech" high H.sub.2 S emission catalyst which we want to replace with a low 
H.sub.2 S emitting version. 
This catalyst has the same noble metals loading (volume basis) as the 
catalyst described in Example 1. Furthermore, it is supported on the same 
alumina beads from same manufacturer as used in Example 1. This catalyst 
serves as commercial reference and is identified as Catalyst 2. Chemical 
analysis via ICP (Inductively Coupled Plasma) of this catalyst reveals 
that it contains 7.3% cerium oxide and 2.0% lanthanum oxide as the primary 
active base metals components. 
EXAMPLE 3 
This example describes the preparation of a catalyst of this invention 
having low H.sub.2 S emissions and good catalyst performance for CO as 
compared to a commercially available catalyst having the same noble metal 
loading, but which is heavily loaded with cerium oxide. 
9,259 grams of -5+8 U.S. mesh alumina beads supplied by Rhone Poulenc as 
SCM-99XT having a compacted bulk density of 0.56 grams/cc, a water pore 
volume of 0.73 cc/gram and a total volatile content of 2.62% were 
impregnated with a zirconium ammonium carbonate solution. The zirconium 
solution was prepared by diluting 921.56 grams of a commercially available 
zirconium ammonium carbonate solution which had the equivalent of 20.067 
grams of zirconium oxide per 100 grams of said solution to a total volume 
of 6,083 milliliters. This impregnating solution had a pH of 9.04. It was 
applied by spraying through atomizing nozzles. The impregnated beads were 
then allowed to stand one hour in the wet state, followed by drying at 
135.degree. C. for 16 hours. The support was further heated at 704.degree. 
C. for one hour. This represents the incorporation of 2% zirconium oxide 
by weight. At this point the support has a compacted bulk density of 0.57 
grams/cc, a water pore volume of 0.75 cc/gram, and a total volatile 
content of 0.225%. 
The above zirconia containing substrate (9,196 grams) was impregnated with 
a sulfited palladium nitrate solution prepared by diluting 34.84 grams of 
ammonium bisulfite (48% weight concentration) to 5 liters with deionized 
water, followed by 83.1286 grams of palladium nitrate (8.9129% palladium 
concentration) and then 411.62 grams of potassium nitrate (99.8% assay). 
The solution was further diluted to 6552 milliliters. The solution which 
had a pH of 1.78 was impregnated onto the beads in a rotating vessel via 
atomizing spray. The wet beads were allowed to stand in the wet state for 
two hours. Following the wet hold the beads were dried in a mechanical 
convention oven at 135.degree. C. for 16 hours. The beads were then 
reimpregnated with a mixed platinum and rhodium sulfite solution. The 
rhodium sulfite solution was prepared by reacting 21.817 grams of rhodium 
chloride solution (5.501% rhodium concentration) with 31.1 grams of 
sulfurous acid (7.57% SO.sub.2 weight concentration) at a rhodium titer of 
2 grams per liter of 60.degree. C. for two hours. The cooled rhodium 
solution was then combined with 100.894 grams of (NH.sub.4).sub.6 
Pt(SO.sub.3).sub.4 solution (9.51636% platinum concentration) and then 
further diluted to 6,207 milliliters with deionized water. The pH was 
2.81. This solution was likewise applied by atomizing spray followed by a 
two hour wet hold and then drying at 135.degree. C. for 16 hours. 
This catalyst was then reduced at 649.degree. C. for one hour in a flow of 
40.6% steam with the balance being a mixture of 5% hydrogen and 95% 
nitrogen. The level of potassia corresponds to 2% by weight of the overall 
catalyst composition. This sample will be identified as Catalyst 3. 
Catalyst 3 has a B.E.T. surface area of 108 m.sup.2 /g. 
EXAMPLE 4 
This is an example of a platinum rich noble metals formulation currently 
used in the automotive industry for exhaust emissions control. 
A catalyst of commerce which was manufactured by another catalyst supplier 
was obtained and used as the reference catalyst which represents the "High 
Tech" high H.sub.2 S emission catalyst which we want to replace with a low 
H.sub.2 S emitting version. This catalyst has the same noble metals 
loading (volume basis) as the catalyst described in Example 3. 
Furthermore, it is supported on the same alumina beads as used in Example 
2. This catalyst serves as a commercial reference and is identified as 
Catalyst 4. Chemical analysis via ICP (Inductively Coupled Plasma) of this 
catalyst reveals that it contains 6.7% cerium oxide as the primary active 
component. 
EXAMPLE 5 
H.sub.2 S testing is carried out on the samples described in Examples 1-4 
in laboratory bench scale equipment according to the following protocol. 
An 8.5 cc sample in a tubular quartz reactor with 2.5 cm I.D. is heated to 
550.degree. C. with only nitrogen gas flowing. Once 550.degree. C. is 
reached the stoichiometric exhaust as described below in Table I was 
introduced and maintained for 15 minutes. At the end of the 15 minute 
stoichiometric treatment, by means of a solenoid valving system the 
exhaust gas feed is instantaneously changed to the strongly reducing 
condition described also in Table I. 
TABLE I 
______________________________________ 
Laboratory H.sub.2 S Test Conditions 
______________________________________ 
Catalyst Charge Volume, cm.sup.3 
8.5 
Total Gas Flow Rate, 1(NTP)/min 
2.83 
GHSV, hr.sup.-1 20,000 
______________________________________ 
Stoichiometric Rich 
Condition Condition 
Component 
(R = 0.99) (R = 0.025) 
______________________________________ 
CO 0.375 5.00 
H.sub.2 
0.125 1.67 
HC(C.sub.3 H.sub.6 /C.sub.3 H.sub.8 = 3) 
0.0400 0.0382 
O.sub.2 
0.34 0.0 
CO.sub.2 
14.5 13.9 
H.sub.2 O 
13.0 12.4 
SO.sub.2 
0.0035 0.0033 
NO 0.185 0.177 
N.sub.2 
Balance Balance 
Bed Temperature, .degree.C. 
550 550 
Delta P, inches H.sub.2 O 
15 15 
Exposure time, minutes 
15 10 
______________________________________ 
The exhaust gas is analyzed for H.sub.2 S emissions by passing the entire 
exhaust into a heated (100.degree. C.) two stage dilution system capable 
of reducing the H.sub.2 S concentration by as much as 400 fold. The usual 
dilution ratio is 200 times. The hot diluted gas stream is continuously 
sampled during the 10 minute reducing cycle via a Tracor-Atlas model 825RD 
H.sub.2 S analyzer. The output from the analyzer is recorded. At least 
three such lean-reducing cycles are carried out on each catalyst. The more 
meaningful assessment of H.sub.2 S emissions behavior is carried out after 
the catalyst has been exposed to a typical exhaust gas composition for 
some period of time. 
This conditioning treatment essentially brings all the catalysts to an 
equal footing as far as thermal history is concerned and additionally 
introduces and stores sulfur as what might occur, for example, during a 
high speed cruise. The conditioning treatment is carried out in a 
simulated auto exhaust stream. The auto exhaust stream is simulated in a 
pulse flame combustion apparatus (a typical description of which has been 
presented by K. Otto, etal. APCA Journal, volume 24, No. 6., June 1974) 
which burns isooctane fuel which has been doped with typical exhaust 
contaminants such as lead, zinc, phosphorus, and sulfur. The combustion is 
carried out a stoichiometric air/fuel ratio. 18 cc of catalyst is treated 
for three hours at 700.degree. C. at a gas hourly space velocity of 16,000 
hr.sup.-1. 
At the end of the conditioning treatment, the catalyst is removed and a 
portion analyzed in a LECO Model SC132 sulfur analyzer to determine the 
sulfur content. Another portion is used to characterize the H.sub.2 S 
emissions. The H.sub.2 S emissions characteristics of catalysts (1) and 
(2) are compared graphically in FIG. 1. The H.sub.2 S emissions 
characteristics of catalyst (3) and (4) are compared graphically in FIG. 
2. These data show the effectiveness of the catalysts of this invention 
for minimizing H.sub.2 S emissions despite the comparable levels of sulfur 
stored on the catalyst. Below in Table II is a tabulation of the sulfur 
levels prior to H.sub.2 S emissions testing, and what is defined as the 
peak H.sub.2 S release for the initial emissions test (pass 1) of catalyst 
Examples 1 -4. 
TABLE II 
______________________________________ 
H.sub.2 S Emissions Test Data 
% Sulfur Peak 
as H.sub.2 S 
Example Sulfate (a) 
Release (b) 
______________________________________ 
1 0.41 151 
2 0.38 526* 
3 0.53 122 
4 0.34 524 
______________________________________ 
*Peak emission exceeded instrument scale limit. 
(a) Determined by LECO Model SC132. 
(b) Peak H.sub.2 S emission (pass 1) in ppm per initial % sulfate content 
 
EXAMPLE 6 
In addition to being characterized by low H.sub.2 S emissions, the catalyst 
must have acceptable TWC performance. TWC performance is assessed using 
the test procedure described in Society of Automotive Engineers paper 
800083 entitled Development of More Active and Durable Automotive 
Catalysts, by M. V. Ernest and G. Kim, 1980. The fresh TWC activities of 
the catalysts of this invention along with the activities of the catalysts 
of commerce having the same noble metals and loading are summarized in 
Table III. 
TABLE III 
__________________________________________________________________________ 
Fresh TWC Activities 
Catalyst Components 
1 2 3 
2% ZrO.sub.2 
7.3% CeO.sub.2 
2% ZrO.sub.2 
4 
Conversion at 
1% K.sub.2 O 
2.0% LaO.sub.2 
2% K.sub.2 O 
6.7% CeO.sub.2 
R Value* 
HC CO NO HC CO NO HC CO NO HC CO NO 
__________________________________________________________________________ 
0.85 96 87 100 
84 88 98 96 87 100 
84 88 98 
1.00 98 92 100 
92 94 98 98 92 100 
92 94 98 
1.15 98 98 99 
96 99 93 98 98 99 
96 99 93 
__________________________________________________________________________ 
*R Value is a measure of air/fuel ratio defined as follow: 
##STR1## 
- where the concentration of each gaseous component is in vol.% or mole % 
R&lt;1, R=1, and R&gt;1 thus represent net reducing, stoichiometric, and net 
oxidizing conditions respectively. 
Of course, fresh activities must be at an acceptable level, but more 
importantly the TWC activity must be sustained after longer term exposure 
to the high temperatures, fuel and lubricant contaminants, and variations 
in air/fuel ratio which are typical of actual use. This is simulated in 
the laboratory by employing a modification of the pulse flame testing 
described previously. This modification involves exposing the catalyst to 
800.degree. C. in the simulated exhaust. Every minute out of two the 
air/fuel ratio is stoichiometric. The other minute involves the injection 
of additional CO (3%) and O.sub.2 (3%) to create elevated surface 
temperatures which should sinter the active components and render the 
catalyst less active. This simulated aging treatment is continued for at 
least 45 hours prior to testing for TWC activity. 
A comparison of activities after pulse flame aging of Catalysts 1 and 3 of 
this invention compared with those products of commerce Catalysts 2 and 4 
which are utilized as reference catalysts are shown in Table IV below. 
TABLE IV 
__________________________________________________________________________ 
TWC Activities After 45 Hours Pulse Flame Aging 
Catalyst Components 
1 2 3 
2% ZrO.sub.2 
7.3% CeO.sub.2 
2% ZrO.sub.2 
4 
Conversion at 
1% K.sub.2 O 
2.0% LaO.sub.2 
2% K.sub.2 O 
6.7% CeO.sub.2 
R Value* 
HC CO NO HC CO NO HC CO NO HC CO NO 
__________________________________________________________________________ 
0.85 58 59 71 62 52 66 60 73 84 62 70 88 
1.00 77 80 89 74 68 73 76 88 94 77 84 93 
1.15 83 96 84 82 88 71 81 97 82 91 95 95 
__________________________________________________________________________ 
*R Value is a measure of air/fuel ratio defined as follow: 
##STR2## 
- where the concentration of each gaseous component is in vol.% or mole % 
R&lt;1, R=1, and R&gt;1 thus represent net reducing, stoichiometric, and net 
oxidizing conditions respectively. 
The data show both of the experimental catalysts are characterized by very 
low H.sub.2 S emissions. CO conversions are equal to or better than the 
commercial catalyst despite the absence of rare earth oxides most notably 
that of cerium oxide. 
It is understood that the foregoing detailed description is given merely by 
way of illustration and that many variations may be made therein without 
departing from the spirit of this invention.