Doubly promoted catalyst with high geometric surface area

An extrudate catalyst suitable for auto emission control is made from a solid, transitional aluminia with a partially hollow interior. Deposited on the extrudate are two promoters, ceria and an alkali metal, and one or more platinum group metals. The preferred alkali metal is in the oxide form as lithia. The cylindrical extrudate has internal reinforcing vanes or ribs extending from the inner wall to the center of the extrudate particle. This configuration permits the catalyst to have the large geometric surface area per reactor volume yet, because of the openings inside the extrudate, the catalyst particles do not exhibit a large pressure drop when packed in a deep bed. These catalysts provide greater hydrocarbon and carbon monoxide conversions than do similar size spherical particles and they have improved light-off characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS 
U.S. Ser. No. 542,363, filed Oct. 17, 1983, discloses and claims the 
internally vaned extrudates employed as catalyst supports in this 
invention. 
U.S. Ser. No. 542,346 filed Oct. 17, 1983, discloses and claims the 
embodiment where the catalyst is used for auto emission control. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an improved catalyst which is suitable for use as 
a catalyst for auto emission control, especially as a three-way catalyst. 
2. Description of the Previously Published Art 
Auto emission catalysts have been made from two types of supports. One is a 
large monolith solid structure which has many channels through it per 
square inch of cross section. These monoliths are traditionally wash 
coated with a slip material to provide porosity to increase the surface 
area. A problem with the monoliths is that they are difficult to replace 
in a catalytic converter. Furthermore, they are limited in their 
performance by laminar-flow transport properties. 
The other type of support is a particulate material such as a bead or an 
extrudate. An example of a bead is disclosed in Sanchez U.S. Pat. No. 
4,390,456. These beads have been very satisfactory for automobile use. 
Because of their solid nature and close packing, however, they can present 
a design problem when making a deep packed catalyst bed. Such a deep bed 
will exhibit a large pressure drop. 
Hollow ceramic pellets for an auto exhaust catalyst support have been 
suggested by C. B. Lundsager in U.S. Pat. No. 3,907,710. However, the 
support in the examples was made from cordierite which has a low BET 
nitrogen surface area. It was thus necessary to coat the cordierite 
support with an alumina slip which contained a ceria promoter and the 
catalytic metals such as platinum or palladium. These coated pellets were 
large with a diameter of 0.25 in. (6.35 mm). 
3. Objects of the Invention 
It is an object of this invention to provide a doubly promoted catalyst 
suitable for use as an oxidizing, reducing or three-way catalyst for 
emission control and especially automotive emission control having good 
conversion efficiency after a sufficiently long period of aging. 
It is a further object of this invention to produce a catalyst suitable for 
use as an auto emission catalyst where they can be packed in a bed without 
a large pressure drop across the bed. 
It is a further object of this invention to produce a catalyst suitable for 
use as an auto emission catalyst in the form of a hollow cylindrical 
extrudate which is internally vaned and where it is not necessary to 
provide a slip coating on the extruded support. 
It is a further object of this invention to produce a catalyst suitable for 
use as an auto emission catalyst which is made of a transitional alumina 
extrudate to provide a large internal or BET nitrogen surface area. 
It is a further object of this invention to produce a catalyst which is 
doubly promoted with ceria and an alkali metal to provide good conversion 
efficiency when used for auto emission control. 
It is a further object of this invention to produce a catalyst suitable for 
use as an auto emission catalyst which has a large geometric surface area 
per reactor volume. 
It is a further object of this invention to convert noxious components of 
exhaust gas to innocuous entities using the catalyst of this invention. 
These and further objects will become apparent as the description of the 
invention proceeds. 
SUMMARY OF THE INVENTION 
As disclosed and claimed in U.S. Ser. No. 542,346 filed Oct. 17, 1983, a 
catalyst which is suitable for auto emission control is made from a solid, 
transitional alumina extrudate having a partially hollow interior and a 
catalytically-effective amount of one or more platinum group metals 
deposited on the extrudate. The extrudate is cylindrical with an annular 
configuration having internal reinforcing vanes or ribs extending from the 
inner wall to the center of the extrudate particle. The transitional 
alumina provides the catalyst with a large BET nitrogen surface area of at 
least 50 m.sup.2 /g with even more preferable value of at least 100 
m.sup.2 /g. The outside diameter can be up to about 6.5 mm for optimum 
results which is slightly larger than 1/4 inch and the aspect ratio, which 
is the ratio of the length to the diameter, can vary from about 1 to 5 
with especially preferred values of 1 to 2. The vanes or ribs inside the 
cylindrical portion of the extrudate provide at least 25% additional 
geometric surface area over what would be just the surface area of a 
hollow tube having the same inside and outside diameter. The pore volume 
of the catalyst is at least 0.3 cm.sup.3 /g with a preferred embodiment 
having at least 0.5 cm.sup.3 /g. When the catalyst particles are packed 
into a reactor the geometric surface area of the catalyst obtained per 
reactor volume is at least 5 cm.sup.2 /cm.sup.3 with a more preferred 
value being at least 20 cm.sup.2 /cm.sup.3. This extrudate configuration 
permits the catalyst to have the large geometric surface area per reactor 
volume yet, because of the openings inside the extrudate, the catalyst 
particles do not exhibit a large pressure drop when packed in a deep bed. 
According to the present invention, the extrudate is doubly promoted with 
ceria and an alkali metal which in a more preferred embodiment is lithia. 
These doubly promoted catalysts provide greater hydrocarbon and carbon 
monoxide conversions than do similar size spherical particles and they 
have improved light-off characteristics.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The doubly promoted extrudate according to the present invention is 
fabricated in the form of a small tubular extruded member having a series 
of vanes which extend through the center of the axis of rotation of the 
tubular member. Viewed from the center, they appear as a series of ribs 
which extend out to the outer tubular element. In the embodiment shown in 
FIG. 1, there are 4 vanes or ribs and in the embodiment illustrated in 
FIG. 2 there are 6 vanes or ribs. 
This unique geometry produces a structure having a large geometric surface 
area and a large void fraction. Because the support is made of a 
transitional alumina it is very porous. The effective surface area is 
vastly increased over what would be measured from the geometry alone. 
Moreover, it is also possible to directly impregnate the extrudate with 
catalytic metals which will adhere directly to the porous surface of the 
transitional alumina without the need for any washcoat. 
The ribbed extrudates with the hollow interior can be fabricated in various 
configurations. In FIG. 1 there are 4 internal reinforcing vanes or ribs. 
The overall diameter, b, can range in size up to about 1/4 inch (6.35 mm) 
which can be rounded up in metric to about 6.5 mm. Smaller sizes can be 
used with a smaller size of about 1/16 inch (1.59 mm) being near the lower 
practical limit because it becomes difficult to fabricate hollow 
extrudates which are significantly smaller in size. An optimum size 
extrudate with four vanes is the 1/10 inch (2.54 mm) size. The thickness 
of the vanes can also be varied. Generally, they are from about 0.10 to 
0.30 of the diameter with especially preferred values being of from about 
0.15 to 0.20 of the diameter. 
In another embodiment in FIG. 2, a 6-vaned extrudate is formed. Again, the 
overall diameter, d, can range in size up to about 1/4 inch (6.35 mm) 
which can be rounded up in metric to about 6.5 mm. Smaller sizes can be 
used with a smaller size of about 1/10 inch (2.54 mm) being near the lower 
practical limit because it becomes difficult to fabricate hollow 
extrudates which are significantly smaller in size. An optimum size 
extrudate with six vanes is the 1/8 inch (3.18 mm) size. Again, the 
thickness of the vanes can also be varied. Generally, they are from about 
0.10 to 0.30 of the diameter with especially preferred values of from 
about 0.07 to 0.15 of the diameter. In the embodiment illustrated in FIG. 
2, the die has been configured so that where the vanes come together they 
form a circular hub which has a diameter, c, which can be adjusted in 
size. The hub is an optional structural feature to provide additional 
crush strength for the extrudate. It can be used with either the 4 or the 
6-vaned embodiments. 
The thickness of the wall of the extrudate, shown as e in FIG. 2, can also 
be varied. The thicker the wall, the stronger will be the extrudate in 
terms of crush strength. Generally, it is preferred to have a wall 
thickness which is about 0.10 to about 0.30 of the diameter of the 
extrudate based on calculations to be made infra for the optimum design of 
the extrudate when subjected to parallel reactions which are controlled by 
external mass transfer and by kinetics. It is our experience that an even 
more preferred ratio is from about 0.15 to about 0.20. 
The aspect ratio is the ratio of the length of the particle to its 
diameter. Aspect ratios can vary from 1 to 5 with generally preferred 
aspect ratios of 1 to 2. 
The optimum design of the extrudate according to the present invention in 
terms of the ratio of the cylindrical wall thickness to the extrudate 
diameter where the wall and the vane have the same thickness can be made 
for reacting systems containing independent parallel reactions that are 
controlled by external mass transfer or by reaction kinetics. 
For extrusions whose external dimensions are given by a diameter, d, and 
length, L, and a fixed density, the reactant concentration, c, for an 
isothermal first-order reaction in a plug-flow tubular reactor is given by 
EQU dc/dx=-kc/SV (1) 
where 
k is the rate constant, 1/sec 
SV is the space velocity, cm.sup.3 /cm.sup.3 -sec 
x is the fractional position in the bed 
In the case of an impregnated 4-ribbed extrudate under reaction control, 
the effectiveness factor defined as the ratio of the actual reaction rate 
to the rate in the absence of diffusional resistances is unity and 
EQU k=k.sub.r (1-.epsilon..sub.int) (1-.epsilon..sub.o) (2) 
where, 
.epsilon..sub.o is the void fraction in between extrudates 
k.sub.r is the rate constant defined on a catalyst volume basis and is 
constant when the cm.sup.2 of metals per volume of catalyst is invariant. 
.epsilon..sub.int is the void fraction within the extrusion and is 
approximated using geometric considerations by 
##EQU1## 
where, x=t/d 
t=thickness of the vane 
As given in equations (1)-(3), for kinetically controlled reactions 
increasing internal voidage reduces the volume of catalyst in the reactor 
and decreases reactant conversion given by 
##EQU2## 
This situation is depicted schematically in FIG. 3, curve (a). 
For external transport limited reactions, or when the dominant resistance 
is interparticle mass transfer limited, the reactor concentration profile 
is given by equation (1) with 
EQU k=k.sub.m a.sub.r (5) 
where, 
k.sub.m =mass transfer coefficient, cm/sec 
a.sub.r =geometric surface area per reactor volume, cm.sup.2 /cm.sup.3 
and 
##EQU3## 
S.sub.x /V.sub.a =geometric surface area per volume of alumina a.sub.r can 
be approximated using geometric considerations as, 
##EQU4## 
From equations (1), (3), (4)-(7), for external transport limited reactions, 
in extrudates of the same external geometry, increasing internal extrudate 
voidage (by decreasing wall thickness) results in an increase in external 
surface area per reactor volume, a.sub.r, and conversion increases. This 
is shown as curve (b) in FIG. 3. 
Thus optimal extrudate shape and wall thickness can be prescribed depending 
on whether the primary reaction is kinetically on interphase diffusion 
controlled. In automobile exhaust, under lean conditions the conversion of 
CO and hydrocarbons (HC) are external, mass transfer controlled. Under 
rich conditions, they are reaction controlled, especially CO and NO. Thus, 
for reactors with both types of reactions occurring, an optimal extrudate 
wall thickness can be chosen such that conversion of both types of 
reactions is maximized. Optimal t/d ratios of from 0.10 to 0.30 are 
advantageous with especially preferred values of 0.15 to 0.20 as shown in 
FIG. 3. 
The extrudate support can be characterized in terms of pore structure, pore 
radius and pore volume by the mercury penetration technique using 
pressures up to and over 60,000 psig which is well known in the art as 
mercury porosimetry. A Micromeritics Auto-Pore 9200 porosimeter is used 
with the results plotted to show the cumulative volume of mercury 
penetration per gram of sample on the vertical axis and the porosimeter 
pressure on the horizontal axis on a logarithmic scale. The present 
extrudate support is bimodal with two types of pores which are the 
micropores and the macropores. The porosimeter curve for the bimodal 
support shows two steps. The inflection point between the ends of the 
first step starting from the origin of the curve represents the breakpoint 
between the macropores and the micropores in the support, the portion of 
the curve to the left of the inflection point representing the macropore 
structure and that to the right representing the micropore structure. The 
pore radius for the two types of pores can be directly calculated from the 
pressure applied in the test for any given pressure. The cumulative macro 
and micropore volumes in cc/g. may be read directly from the curve. The 
pore radius and volume information is then used to calculate the integral 
average values for the pore radii. The integral averaging for the 
macropores proceeds from 0 to the macropore volume as discussed above 
while that for the micropores proceeds from the macropore volume to the 
total volume. The details of the test and of curve analysis and 
calculations are fully set forth in, among others, "Chemical Engineering 
Kinetics" by J. M. Smith, McGraw-Hill Publishing Company, New York, Second 
Edition, 1970. 
A significant advantage of these ribbed extrudates over conventional 
spheres is their ability to both provide a large geometric surface area 
per packed volume of reactor and to provide a lower pressure drop across 
the bed than is obtained by spheres having a comparable geometric surface 
area per packed volume. To determine pressure drops 50 cm.sup.3 samples of 
the 4-vaned extrudate according to the present invention and three 
different sizes of spheres were each placed in a glass tube (ID=2.16 cm) 
having a glass frit at the bottom. The tube diameter was over 7 times the 
diameter of the largest particle tested, thus minimizing wall effects. 
Catalyst pellets were screened to remove fines. The support was 
periodically unloaded and the empty tube pressure-drop measured to ensure 
that there was no frit plugging. Bed pressure drops were measured using a 
U-tube manometer. From the calibration curves for the empty tube and the 
pressure drop in a tube packed with catalyst, the pressure drop across the 
support alone was obtained by difference. 
The variation of bed-pressure drop (in cm of H.sub.2 O/ cm bed) is shown as 
a function of the superficial velocity of air at 25.degree. C. and 1 atm 
in Table 1. 
TABLE 1 
______________________________________ 
Catalyst Bed Pressure Drop 
Superficial 
3/32 inch 
velocity, 4-vaned 1/10 inch 1/16 inch 
1/32 inch 
(cm/sec) extrudate 
spheres spheres 
spheres 
______________________________________ 
5.1 .02 .04 .12 .18 
13.4 .06 .08 .21 .51 
21.9 .10 .16 .34 .83 
29.3 .15 .24 .45 1.17 
37.5 .18 .31 .61 1.58 
45.2 .25 .40 .80 2.03 
53.2 .32 .51 1.00 2.51 
60.7 .40 .61 1.19 3.07 
133.0 .94 1.58 4.06 9.11 
______________________________________ 
The data in Table 1 clearly show that for each superficial velocity there 
is a lower pressure drop for the extrudate than for any of the spheres of 
the same nominal size or smaller. 
The optimal pressure drop comparison should be made for a sphere having the 
same geometric surface area per packed volume. To determine the diameter 
of such a sphere the surface area per reactor volume of the extrudate is 
first calculated as follows. For L=0.3424 cm and d=0.2680 cm the volume of 
the cylinder extrusion is given by 
##EQU5## 
The number of 4-vaned extrudates per cm.sup.3 of packed volume is measured 
as 39.1. From this .epsilon..sub.o, the void fraction between extrudates, 
is calculated to be 0.245. For the 4-vaned extrusion, x=t/d=0.151 and 
a.sub.r is calculated using equation (7) to be 28.13 cm.sup.-1. In the 
calculation of equivalent sphere size we use 
##EQU6## 
Since packed beds containing spheres have .epsilon..sub.o =0.38, the 
equivalent sphere diameter is calculated as 1/20 (1.32 mm). 
Thus the sphere to be compared to the extrudate is one having a diameter of 
1/20 inch (1.32 mm). Although there is not one of this size in Table 1, 
the pressure drop value for such a sphere would be between the values of 
the 1/16 inch and the 1/32 inch sphere. Just comparing the extrudate with 
the 1/16 inch spheres shows a factor of 3-7 times less pressure drop for 
the extrudates according to the present invention. In Table 2 below, the 
pressure drop values for 1/20 inch spheres have been obtained from Table 1 
data by interpolation between 1/16 inch and 1/32 inch spheres. 
TABLE 2 
______________________________________ 
Catalyst Bed Pressure Drop 
Superficial 3/32 inch 
velocity, 4-vaned 1/20 inch 
(cm/sec) extrudate 
spheres 
______________________________________ 
5.1 .02 .14 
13.4 .06 .32 
21.9 .10 .49 
29.3 .15 .68 
37.5 .18 .90 
45.2 .25 1.2 
53.2 .32 1.5 
60.7 .40 1.70 
133.0 .94 5.8 
______________________________________ 
The pressure drop for the extrudate according to the present invention is 
4-7 times less than the corresponding extrapolated pressure drops for 
sphere with 1/20 inch diameter. 
When making catalysts according to the present invention the amount of 
CeO.sub.2 promoter applied is preferably between 1 to 10 wt. % and more 
preferably between 2-6 wt. %. The amount of the alkali metal promoter 
applied, expressed as the weight percent of the oxide M.sub.2 O, is any 
effective amount up to about 5 wt. % and more preferably from about 0.5 to 
3 wt. %. The preferred alkali metal is lithium which in the oxide form is 
lithia. 
The platinum group metal component may be platinum, palladium, rhodium, 
ruthenium, iridium, osmium, and mixtures thereof, with the preferred 
metals being Pt, Pd, Rh either alone or in any combination. When the 
platinum group metal contains more than one of such components, the 
component may be composed of a major amount of platinum or palladium and a 
minor amount of one or more of the other platinum group metals such as 
rhodium. The catalytic metals mixture may comprise from about 1 to about 
15 wt. % rhodium and from about 85 to about 99 wt. % platinum, palladium, 
or mixtures thereof and preferably from about 5 to 10 wt. % rhodium and 
about 90 to 95 wt. % platinum, palladium, or mixtures thereof. 
Various compounds, complexes, or fine metal dispersions of any of the 
platinum group metals in aqueous or organic medium may be used to achieve 
deposition of the platinum group metal component on the composite. A 
suitable liquid medium will not react with the platinum group metal 
component and is removable on drying which can be accomplished as part of 
the preparation or in use of the catalyst. Water soluble platinum group 
metal compounds or complexes may conveniently be used. Suitable platinum 
group metal compounds include 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. 
In a preferred embodiment of this invention, the impregnation solution 
contains an ammonium sulfito complex of platinum group metal prepared 
according to the methods described in U.S. Pat. No. 3,932,309 to Graham et 
al. The use of these complexes provides excellent dispersion and control 
of penetration depth of the platinum group metal. Preferably, rhodium is 
incorporated in the catalyst by impregnation with an acid rhodium sulfito 
complex prepared by reacting rhodium trichloride or rhodium hydrous oxide 
with sulfurous acid. 
After the impregnations are completed, the composition may be dried, for 
example, at a temperature of from about 100.degree. C. to about 
150.degree. C. for about 2 to about 20 hours. The salt composition may be 
decomposed and the catalyst activated under conditions which provide a 
composition having characteristics that enhance the desired reaction. The 
temperature of this activation is low enough to permit neither noble metal 
sintering nor sintering of the support. It is preferably done in a 
reducing atmosphere, e.g., by about a 1 hour reduction in flowing nitrogen 
containing 5 volume percent hydrogen at about 250.degree.-550.degree. C. 
and more preferably at about 400.degree. C. 
In the catalyst of this invention, the platinum group metals provide 
catalytic sites for oxidation, reduction and decomposition reactions and 
are present in amounts sufficient to maintain long term activity for 
catalyzing these reactions. Generally, the amount of platinum group metal 
used is a minor portion of the catalyst composite and typically does not 
exceed about 10 weight percent of the calcined composite. The amount may 
be about 0.05 to 10 percent and is preferably about 0.1 to 6 percent based 
on the weight of the calcined composite to maintain good activity with 
prolonged use. 
In order to demonstrate the superiority of the auto exhaust catalyst 
according to the present invention, a series of tests have been performed. 
The complete details of the procedures are set forth in a later section 
entitled Test Procedures. 
To measure the long term performance of the catalyst, pulsator aging tests 
have been employed which simulate engine conditions. The test subjects the 
catalyst to alternating oxidizing and reducing conditions over a period of 
time with a fuel feed which contains an increased level of poisons, such 
as Pb, P and S. 
After the catalysts have been aged, various evaluation tests are employed. 
In one test, the HC, CO and NO.sub.x conversions are measured at the 
stoichiometric point as well as under lean and rich conditions to 
determine the three-way performance of the catalyst. The results are shown 
in Table 5 and again, the catalyst according to the present invention had 
better conversions than conventional beads. 
Another test performed on the pulsator aged catalyst is an oxidizing 
warm-up test. This test measures the light-off properties to determine the 
extent of permanent deactivation. The test is done under oxidizing 
conditions and the time for 50% conversion of CO and HC is measured as 
well as the HC and CO conversion efficiencies and the time required to 
attain from 10% to 90% CO conversion. The results presented in Table 6 
also show superior performance for the present catalyst. 
Having described the basic aspects of the invention, the following examples 
are given to illustrate specific embodiments thereof. 
EXAMPLE 1 
The extrudate support was made as follows. Into a bench mix muller was 
added 490 g of pseudo boehmite made according to the procedure in the M. 
G. Sanchez and N. R. Laine U.S. Pat. No. 4,154,812 which was dried at 
about 135.degree. C. to a TV of 29.23%, 10 g of Methocel (made by Dow 
Chemical Co.), and about 200 ml of deionized water. The mixture was mulled 
for 10 minutes, followed by the addition of another 200 ml of water and 
further mulling for a total of 45 minutes. The mixture was extruded 
through a 1/8 inch inside diameter die with four inserts at a pressure of 
about 2500-3000 psi. The extrudates having the cross section shown in FIG. 
1 were oven dried at 116.degree. C. overnight. These dried extrudates were 
used to make catalysts in the following examples. 
To further characterize the extrudates, a portion was calcined at 
538.degree. C. for 3 hours. The average diameter was 0.1105 inch (2.81 mm) 
and the average length was 0.1386 inch (3.52 mm), giving an aspect ratio 
of 1.25. The density was 0.442 g/cc. 
EXAMPLE 2 
This example prepares extrudate catalysts for comparison which are only 
promoted with ceria. 
The extrudates from Example 1 were activated at 538.degree. C. for 3 hours. 
A batch of these activated extrudates was then air calcined for 2 hours at 
982.degree. C. A 20.10 g portion of this material was contacted with 30.0 
cc of cerous nitrate solution containing 0.622 g of CeO.sub.2 as follows. 
The extrudates were allowed to soak for 15 min. at room temperature after 
dropping into the solution, followed by thorough mixing under the overwet 
condition. It was first slowly dried at 70.degree. C. for 1 hour, with 
gentle mixing once every 10 min. so that most of the excess solution, 
amounting to about 120% of incipient wetness, could be picked up by the 
extrudates. It was then dried overnight at 135.degree. C. before air 
calcination at 732.degree. C. for 1 hour. 
The rhodium stock solution, which as an acid in-situ sufito complex 
solution containing 2 g of Rh per Kg of solution, was prepared as follows. 
11.06 g of sulfurous acid containing 3.38% SO.sub.2 was added to 60.00 g 
of deionized water in a polyethylene bottle. To this was added 1.0404 g of 
RhCl.sub.3 solution bearing a total of 200 mg Rh, and the solution was 
diluted to exactly 100.00 g. The solution was sealed in the bottle, and 
then soaked in 60.degree. C. water for 2 hours, with occasional agitation. 
The solution was cooled to room temperature before use. 
The above resulting extrudates promoted with 3 wt. % CeO.sub.2 were loaded 
with Pt and Rh as follows. Exactly 20.01 g (40.2 cc) of the ceria-promoted 
extrudates were contacted by soaking with 25.0 cc of solution containing 
9.27 mg of Pt in the form of (NH.sub.4).sub.6 Pt(SO.sub.3).sub.4. See the 
Graham et al U.S. Pat No. 3,932,309 which shows how to prepare this 
solution. It was dried in the same manner as in the ceria incorporation 
step, i.e., two-step drying at 70.degree. and 135.degree. C. The 
extrudates were resoaked in 22 cc of solution bearing 23.82 mg of Pt in 
the form of (NH.sub.4).sub.6 Pt(SO.sub.3).sub.4 and 1.99 mg of Rh in the 
form of acid in-situ sulfito complex solution of Rh obtained by diluting 
the stock solution. Finally the catalyst was activated by 1-hour reduction 
at 400.degree. C. in flowing N.sub.2 containing 5 vol. % H.sub.2. The 
resulting catalyst had physical properties as set forth in Table 3 infra. 
The metals loading of this catalyst in terms of g of each metal per liter 
of packed volume is 0.791 Pt and 0.0475 Rh excluding the 4% excess allowed 
to compensate for the possible metal losses. 
EXAMPLE 3 
This example prepares spherical catalysts for comparison which are only 
promoted with ceria. 
Grace alumina beads made according to the procedure in M. G. Sanchez and N. 
R. Laine U.S. Pat. No. 4,179,408 were dried at 135.degree. C. for at least 
3 hours and were air calcined at 1038.degree. C. for one hour. A large 
batch of these calcined beads were impregnated to incipient wetness with a 
cerous nitrate solution, dried at 135.degree. C. for at least 3 hours, and 
then air calcined at 732.degree. C. for one hour to obtain alumina beads 
promoted with 3 wt. % CeO.sub.2. A portion of the resulting beads in the 
size range between 5 and 10 meshes having 3.0 mm major and 2.6 mm minor 
axes, were converted to a Pt-Rh catalyst loaded with 0.791 g Pt and 0.0475 
g Rh per liter of catalyst as follows, allowing 4% excess metals in order 
to compensate for the possible metals loss. 7,942 g of ceria-promoted 
beads were sprayed in a rotary mixer with fine mist of 6,800 cc of 
(NH.sub.4).sub.6 Pt(SO.sub.3).sub.4 solution bearing 3.786 g of Pt. See 
the Graham et al U.S. Patent No. 3,932,309 which shows how to prepare this 
solution. The beads were then dried overnight at 135 .degree.. 
In the meantime, a batch of acid in-situ sulfito complex solution of Rh was 
readied as follows. To 300 cc of 60.degree. C. water in bottle was added 
23.47 g of sulfurous acid containing 6.78 wt. % SO.sub.2. To this was then 
added 17.350 g of RhCl.sub.3 solution containing 4.676 wt. % Rh. After 
diluting with water to 405 cc, the bottle was sealed and placed in a 
60.degree. C. water bath for a 1 hour soak. It was then cooled to room 
temperature before use. 
The above-dried beads were resprayed in the same manner with 6,400 cc of 
solution bearing 9.375 g of Pt and 0.811 g of Rh. The impregnating 
solution was prepared as follows: 105.601 g of (NH.sub.4).sub.6 
Pt(SO.sub.3).sub.4 solution containing 9.219 wt. % Pt was diluted with 
water along with the entire batch of the above-prepared acid in-situ 
solution of Rh to 6,400 cc the resulting solution had a pH of 2.46. 
After drying once again at 135.degree. C., the beads were reduced in 
flowing N.sub.2 containing 5 vol. % H.sub.2 for 1 hour at 400.degree. C. 
The physical properties for the beads are given in Table 3. 
A comparison of the impregnated extrudate of Example 2 with the similarly 
impregnated sphere of Example 3 is given in Table 3. 
TABLE 3 
______________________________________ 
Comparison of 4-Ribbed Extrudate and Sphere Catalysts 
4-Vaned 
Sphere Extrudate 
______________________________________ 
Pore volume, cm.sup.3 /g 
0.994 0.606 
Macropore volume, cm.sup.3 /g 
0.380 0.041 
Micropore volume, cm.sup.3 /g 
0.614 0.565 
Macropore radius, microns 
0.420 34.0 
Micropore radius, AU 65.2 58.0 
Pellet density, g/cm.sup.3 
0.766 1.089 
BET (N.sub.2) Surface area, m.sup.2 /g 
114 162 
Bulk density, g/cm.sup.3 
0.475 0.498 
Average length, mm.sup.(1) 
3.02 3.42 
Average diameter, mm.sup.(2) 
2.62 2.68 
Geometric surface area per pellet, cm.sup.2 
0.31 0.71 
Number of pellets per cm.sup.3 of 
49.5 39.1 
packed reactor volume 
Geometric surface area per packed 
15 28 
reactor volume, cm.sup.-1 
______________________________________ 
where AU = Angstrom units 
.sup.(1) Major axis diameter 
.sup.(2) Minor axis diameter 
The micropore region is: 
0-200 AU for extrudate 
0-600 AU for sphere 
Although the spheres and extrudates have comparable diameters and lengths, 
because of the hollow nature of the extrudates, there is a significantly 
larger geometric surface area per packed volume for the extrudate which is 
almost double the value for the sphere. 
EXAMPLE 4 
In this example, ceria-lithia promoted extrudate catalysts are made 
according to the present invention. Another batch of Pt-Rh catalyst 
supported on the extrudates of Example 1 was prepared essentially in the 
same manner as in Example 2 using the soaking procedure as follows. A 
batch of 454.degree. C. activated extrudates with 20.08 g dry weight was 
contacted with 25 cc of solution containing 0.634 g of CeO.sub.2 and 0.423 
g of Li.sub.2 O in the form of cerous nitrate and lithium nitrate. As in 
Example 2, the extrudates were well mixed immediately after contacting. 
They were then treated in exactly the same manner as in the ceria 
incorporation step as in Example 2, i.e. room temperature soak, 70.degree. 
and 135.degree. C. drying, and then air calcination at 982.degree. C. for 
2 hours. The additive loadings in the resulting material are 3 wt. % 
CeO.sub.2 and 2 wt. % Li.sub.2 O. 
The above ceria-lithia-promoted extrudates were loaded with Pt and Rh using 
the soaking procedure in a manner slightly different from the procedure 
described in Example 2. A 20.08 g (40.2 cc) batch of this doubly promoted 
extrudates were contacted first with 20 cc of solution containing 1.99 mg 
of Rh in the form of acid in-situ sulfito complex solution and 0.14 
millimole of dibasic ammonium citrate solution. After 15 min. soak at room 
temperature and the two-step drying at 70.degree. and 135.degree. C., the 
extrudates were resoaked in 19 cc solution bearing 33.09 mg Pt in the form 
of (NH.sub.4).sub.6 Pt(SO.sub.3).sub.4. It was soaked at room temperature 
and dried in the same fashion before finally activating by 1 hour 
reduction in flowing H.sub.2 (5 vol. %)/N.sub.2 (95 vol. %) at 400.degree. 
C. The resulting catalyst had a bulk density of 0.480 g/cc and a BET 
(N.sub.2) surface area of 129 m.sup.2 /g. The metals loading of this 
catalyst, g of metals per unit volume is identical to that of the catalyst 
in Example 2. 
EXAMPLE 5 
This example prepares spherical catalysts for comparison which are doubly 
promoted with ceria and lithia. 
A large batch of activated Grace alumina beads obtained by 135.degree. C. 
drying overnight and 454.degree. C. air calcination was promoted with 3 
wt. % CeO.sub.2 and 2 wt. % Li.sub.2 O by incipient wetness impregnation 
with a mixed solution containing both cerous and lithium nitrates, 
followed by 135.degree. C. drying overnight and 1 hour air calcination at 
1038.degree. C. 7,782 g of the resulting beads in the size range between 5 
and 10 meshes, having 3.1 mm major and 2.6 mm minor axes, were sprayed 
with 6,800 cc of solution containing Pt in the same manner as described in 
Example 3. The impregnating solution was prepared as follows. To 3,000 cc 
of water was added 53.06 g of ammonium bisulfite solution containing 
47.49% NH.sub.4 HSO.sub.3. The resulting solution was raised to a pH of 
8.30 from 5.84 using an NH.sub.4 OH solution. To this was then added 
45.959 g of chloroplatinic acid solution containing 20.593 wt. % Pt. The 
solution had a pH of 2.32. The solution was allowed to stand at room 
temperature for 2 hours, resulting in colorless solution. Finally, the 
solution was diluted with water to 6,800 cc. 
After 135.degree. C. air drying overnight, the beads were resprayed with 
6,400 cc of solution bearing 4.056 g of Pt and 0.811 g of Rh. This 
impregnating solution was prepared as follows. To 1,200 cc of water was 
added 22.78 g of ammonium bisulfite solution containing 47.49 wt. % 
NH.sub.4 HSO.sub.3. After raising the pH of this solution to 8.30 from 
5.81 using an NH.sub.4 OH solution, 19.693 g of chloroplatinic acid 
solution containing 20.593 wt. % Pt was added and mixed. The resulting 
solution had a pH of 2.29. Two hours later this solution was mixed with 
405 cc of acid in-situ sulfito complex solution of Rh which was prepared 
in exactly the same manner as in Example 2. The mixed solution was then 
diluted to 6,400 cc, adjusting pH to 2.20 from 2.00 with NH.sub.4 OH. 
Finally, the beads were dried overnight at 135.degree. C., and then 
activated by 1 hour reduction in flowing N.sub.2 containing 5 vol. % 
H.sub.2 at 400.degree. C. The metals loading, g of metals per liter of 
catalyst, for this batch is identical to that of catalyst in Example 2. 
EXAMPLE 6 
An 8.5 cc sample each of the catalysts made in Examples 2-5 was subjected 
to accelerated aging on a pair of pulse flame combustors or "pulsators" 
for periods of 45 and 90 hours, at approximately 60 pulses/minute using 
n-hexane containing 0.132 g/liter Pb, 0.05 g/liter P, and 0.08 wt. % S. 
The apparatus for this procedure is described by M. V. Ernest and G. Kim 
in Soc. Automot. Eng. Paper No. 800083. During the period of aging the 
catalyst samples were allowed to experience cycling temperatures. The 
cycle consisted of a lower temperature of 566.degree. C. which was 
maintained for 75 minutes and then a higher temperature of 732.degree. C. 
which was maintained for 15 minutes. 
Each catalyst sample was then evaluated by the "Perturbed Sweep Test" 
procedure described in Ind. Eng. Chem. Prod. Res. Dev., 21, 267 (1982), 
using the simulated exhaust gas feed shown in Table 4. 
TABLE 4 
______________________________________ 
Simulated Auto Exhaust Gas Mixture 
for the "Perturbed Sweep Test" 
Gas Vol. % 
______________________________________ 
HC.sup.a 0.0400 
CO 0.295-0.80 
H.sub.2 0.098-0.267 
NO 0.185 
SO.sub.2 0.0020 
O.sub.2 0.245-0.725 
CO.sub.2 14.5 
H.sub.2 O 10.0 
N.sub.2 balance 
______________________________________ 
.sup.a A mixture of C.sub.3 H.sub.6 and C.sub.3 H.sub.8 at a molar ratio 
of C.sub.3 H.sub.6 /C.sub.3 H.sub.8 = 4/1. 
The average reducing or oxidizing condition of the feed mixture is 
represented by the ratio R given below: 
##EQU7## 
where [O.sub.2 ], [NO], [CO], [C.sub.3 H.sub.8 ] and [C.sub.3 H.sub.6 ] 
are the molar concentrations in the feed gas. The conversions of HC, CO 
and NO are determined as a function of the ratio R. A constant inlet 
temperature of 482.degree. C. is maintained throughout the test with a 
GHSV of approximately 60,000 and a superficial linear velocity of about 49 
cm/sec in the reactor. 
The results presented in Table 5 represent TWC performance under a lean 
(R=1.5), stoichiometric (R=1.0), and a rich (R=0.7) conditions. 
TABLE 5 
__________________________________________________________________________ 
Performance of Pulsator-Aged Catalysts 
in TWC Tests.sup.a at Approximately 60,000 GHSV 
Support 
In Promoters 
Aged 
Rich (R = 0.7) 
Stoichiometric (R = 1.0) 
Lean (R = 1.5) 
Example 
Shape (Wt. %) 
(Hrs.) 
HC CO NO HC CO NO HC CO NO 
__________________________________________________________________________ 
2 Extrudate 
3% CeO.sub.2 
0 94 74 85 96 85 73 98 92 51 
45 89 48 74 90 59 62 90 72 43 
90 78 34 62 82 42 54 83 54 33 
3 Bead 3% CeO.sub.2 
0 93 69 82 96 81 68 96 89 50 
45 78 44 70 81 53 57 82 66 38 
90 66 34 52 70 42 44 71 54 28 
4 Extrudate 
3% CeO.sub.2 
0 94 70 83 96 81 73 96 90 47 
2% LiO.sub.2 
45 86 60 77 86 72 62 85 79 41 
90 77 50 70 81 61 60 82 72 43 
5 Bead 3% CeO.sub.2 
0 91 56 87 94 73 78 95 84 50 
2% LiO.sub.2 
45 79 40 71 83 50 61 83 66 42 
90 73 40 63 77 49 51 79 63 32 
__________________________________________________________________________ 
.sup.a The values for HC, CO and NO are the percent conversion of these 
three components. The higher the value the better. 
It is apparent from these data that the internally vaned extrudate catalyst 
according to the present invention is superior to the bead catalysts 
currently available. The extrudate catalyst doubly promoted with Li.sub.2 
O-CeO.sub.2 far exceeds the aging performance of both Li.sub.2 O-CeO.sub.2 
promoted beads or the Ce-promoted beads. For example, under the 
stoichiometric condition (R=1.0) the Li.sub.2 O-CeO.sub.2 -promoted 
extrudate catalyst of Example 4 exhibits HC, CO and NO conversion 
efficiencies of 81%, 61%, and 60%, respectively, after aging for 90 hours. 
The CeO.sub.2 -promoted bead of Example 3 had much lower conversion 
efficiencies of 70%, 42% and 44%. Even the Li.sub.2 O-CeO.sub.2 -promoted 
beads of Example 5, had lower performance of only 77%, 49%, 51%, 
respectively, for the three pollutants. 
The superiority of the Li.sub.2 O-CeO.sub.2 -promoted extrudate catalyst of 
the present invention in Example 4 over the CeO.sub.2 -promoted extrusion 
catalyst in Example 2 is especially seen in CO performance. After 90 hours 
of aging, the CO conversions for R=0.7, 1.0 and 1.5 are 34%, 42% and 54% 
for the ceria promoted extrudate of Example 2, whereas much higher values 
of 50%, 61% and 72% are achieved, respectively, for the LiO.sub.2 
-CeO.sub.2 promoted extrudates of Example 4. 
EXAMPLE 7 
The fresh catalysts from Examples 2-5 and these same catalysts which had 
been pulsator aged by the procedure of Example 6 were subjected to the 
oxidizing warm-up test. This test is used to determine the extent of 
permanent deactivation. It basically utilizes the test described by M. V. 
Ernest and G. Kim in Soc. Automot. Eng. Paper No. 800083. The test 
involves a scaled-down version of a full size converter test which is 
designed to measure both the lightoff characteristics of a catalyst as 
well as steady-state CO and HC conversion efficiencies. In the procedure 
the catalyst, initially at ambient temperature, is contacted with a 
preheated gas mixture consisting of 3 vol.% CO, 4.5% O.sub.2, 10% H.sub.2 
O, 433 ppm C.sub.3 H.sub.8 and the balance N.sub.2. Because of the high 
level of oxidizable species present in the feed, the temperature of the 
catalyst bed rises depending upon the activity of the catalyst. These 
catalysts were tested at a GHSV of 59,000 and a superficial linear 
velocity of 40 cm/sec. The results are set forth in Table 6. 
TABLE 6 
__________________________________________________________________________ 
(Source: Table II July 8 Report) 
Performance.sup.a of Fresh and Aged Catalysts 
in Oxidizing Warm-up Tests at Approximately 38,500 GHSV 
Support 
in Promoters 
Aged 
.DELTA.t 
t.sub.50 CO 
t.sub.50 C.sub.3 H.sub.8 
Eff. C.sub.3 H.sub.8 
Eff. CO 
Example 
Form.sup.c 
(Wt. %) 
(Hrs.) 
(sec) 
(sec) 
(sec) 
% (%) 
__________________________________________________________________________ 
2 E 3% CeO.sub.2 
0 19 56 71 86 99+ 
90 25 90 .sup.b 
49 98 
3 B 3% CeO.sub.2 
0 18 46 62 84 99+ 
90 104 
98 .sup.b 
36 92 
4 E 3% CeO.sub.2 
0 20 56 89 79 99+ 
2% LiO.sub.2 
90 30 95 .sup.b 
48 96.4 
5 B 3% CeO.sub.2 
0 18 55 65 87 99+ 
2% LiO.sub.2 
90 19 102 .sup.b 
36 95 
__________________________________________________________________________ 
.sup.a .DELTA.t = Time required to attain 90% conversion from 10% 
conversion of CO. 
t.sub.50 = Time required to attain 50% 
Eff. = % conversion attained under a steadystate 
.sup.b Unavailable because the % conversion required was not 
.sup.c E = extrudate 
B = bead 
The oxidizing warm-up test data for the aged catalysts in Table 6 also show 
the better performance of the ceria-lithia promoted extrudates over the 
beads. The t.sub.50 CO is lower for the 90 hour aged extrudate of Example 
4 with 95 sec. compared to the 102 sec. for the bead of Example 5. The HC 
conversion for the extrudate of Example 4 is 48% compared to 36% for the 
bead and the CO conversion was 96.4% compared to 95% for the bead. 
Focusing on the increase in CO conversion, for the doubly promoted 
ceria-lithia system, the beads in Example 5 had a conversion of 95% which 
means that 5% of the CO was not converted. By using the extrudate the CO 
conversion was 96.4% which means that only 3.6% of the CO was not 
converted. To be able to reduce the amount of unwanted unconverted CO from 
5% to 3.6% represents a 28% reduction in CO emission which is a 
significant improvement in exhaust quality. 
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.