Note: Descriptions are shown in the official language in which they were submitted.
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Exhaust gas catalyst
The present invention relates to an internal combustion
engine exhaust gas catalyst which has a single-layered,
catalytically active coating of high surface area support
oxides on an inert support structure, wherein the coating
contains palladium as the only catalytically active noble
metal.
Internal combustion engines emit carbon monoxide (CO),
unburnt hydrocarbons (HC) and nitrogen oxides (NOX) as the main
pollutants in the exhaust gas, a high percentage of these
being converted into the harmless components water, carbon
dioxide and'nitrogen by modern exhaust gas treatment
catalysts. Conversion takes place under substantially
stoichiometric conditions, that is the oxygen in the
exhaust gas is controlled using a so-called. lambda sensor
in such=a way that the oxidation of carbon monoxide and
hydrocarbons and the reduction of nitrogen oxides to
nitrogen can take place almost quantitatively. The
catalysts developed for this purpose are called three-way
catalytic converters.
Stoichiometric conditions prevail when the normalised
air/fuel-ratio k is 1. The normalised air/fuel-ratio k is
the air/fuel ratio standardised to stoichiometric
conditions. The air/fuel ratio states how many kilograms of
air are required for complete combustion of one kilogram of
fuel. In the case of conventional petrol engine fuels, the
stoichiometric air/fuel ratio has a value of 14.6. The
engine exhaust gas has more or less large, periodic
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variations in normalised air/fuel-ratio depending on the
load and the engine speed. To produce better conversion of
oxidizable hazardous components under these conditions,
oxygen-storing components such as, for example, cerium
oxide are used which bind oxygen when it is present in
excess and release it again for oxidative conversion when
there is a deficiency of oxygen in the exhaust gas.
Future exhaust gas limits for internal combustion engines
require an increasingly stringent reduction in the
emissions of hazardous substances in standardised driving
cycles. Given the current status of exhaust gas treatment,
the hazardous substance emissions which still remain are
produced during the cold-start phase. A substantially
improved hazardous substance.conversion over an entire
driving cycle is therefore only possible by reducing cold-
start emissions. This can be achieved, for example, by a
catalyst with the lowest possible light-off temperature for
hazardous substance conversions and/or by locating the
catalyst only just downstream of the exhaust gas outlet
from the engine in order to reduce the heating-up time
required to reach the operating temperature of the
catalyst.
If the catalyst is installed near to the engine, it is
subjected to exhaust gas temperatures of up to 1100 C
during continuous operation of the engine, and at full
speed. Thus catalysts which are temperature-resistant and
have long-term stability are required for this type of use.
The present invention deals with catalyst coatings on
inert, monolithic support structures, normally honeycomb
structures with parallel flow channels for the exhaust gas.
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The number of flow channels per cross-sectional area is
called the cell density. Inert supports with cell densities
between 10 and 250 cm2 are used, depending on the
requirements of the application. These may be extruded,
ceramic supports made from cordierite, mullite or similar,
temperature resistant materials. Alternatively, honeycomb
structures made from steel sheeting may be used.
The catalytic coating generally contains several noble
metals from the platinum group of the Periodic System of
elements as catalytically active components, these being
deposited in highly dispersed form on the specific surface
area of high surface area support materials. The coating
also contains further components such as oxygen-storing
materials, promoters and stabilisers. The coating is
applied to the internal walls of the flow channels by known
coating processes, using an aqueous coating dispersion
which contains the various components of the catalyst.
The inert monolithic supports are also called support
structures in the context of this invention in order to be
able to differentiate them more easily from the high
surface area support materials for the catalytically active
components. High surface area materials are those materials
whose specific surface area, or BET surface area (measured
in accordance with DIN 66132), is at least 10 m2/g. So-
called active aluminium oxides satisfy this condition.
These are finely divided aluminium oxides which have the
crystal structures of the so-called transition phases of
aluminium oxide. These include chi, delta, gamma, kappa,
theta and eta-aluminium oxide.
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The catalyst components may be added to the coating
dispersion in a variety of forms:
a) as "finely divided solids"
This is understood to mean powdered materials with particle
sizes between 1 and about 50 pm. In the English language
literature, the expressions "bulk material" or "particulate
material" are used for these.
b) as "colloidal solids"
These have particle sizes of less than 1 pm. The
particulate structure of finely divided and colloidal
solids is retained even in the final catalyst coating.
c) in the form of soluble "precursor compounds"
Precursor compounds are converted into actual catalyst
components only by subsequent calcination and optionally
reduction and are then present in a highly dispersed form.
The catalytically active metals from the platinum group or
stabilisers such as lanthanum oxide.and barium oxide are
preferably incorporated into the coating as soluble
precursor compounds in the coating dispersion or introduced
only later by impregnating the coating. After a subsequent
calcination procedure, these materials are present in a
highly dispersed form (crystallite sizes in general of less
than 5-10 nm) on the specific surface areas of the high
surface area, finely divided components of the catalyst.
They are also called "highly dispersed materials" in the
context of this invention.
An aim of the present invention is to develop a catalyst
suitable for use in the area mentioned above which operates
exclusively with palladium as the catalytically active
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noble metal.. Palladium is characterised, as compared with
platinum, by a lower price, which is important with regard
to the economic viability of the catalyst. In addition, it
is known that palladium is a very effective catalyst for
5 the oxidation of unburnt hydrocarbons, in particular
paraffins and aromatic compounds. It has a superior effect,
with reference to the same mass, to that of platinum.
US 4,624,940 describes a three-way catalytic converter in
the form of a coating on a monolithic support structure
which contains only palladium as a catalytically active
component and which retains its catalytic activity even
after ageing at temperatures higher than 1000 C. The
coating contains at least three different finely divided
materials: thermally stable aluminium oxide as support
material for a metal from the platinum group, further metal
oxides as promoters which do not contain metals from the
platinum group and inert, thermally stable fillers. The
support material is stabilised with lanthanum, barium and
silicon. The lanthanum oxide used for stabilising purposes
may contain up to 1.0 wt.% of praseodymium oxide. Cerium
oxide, zirconium oxide or mixtures thereof are used as
promoters. Finely divided cordierite, mullite,
magnesium/aluminium titanate and mixtures thereof are used
as fillers. Palladium is preferably used as a metal from
the platinum group. According to US 4,624,940, care has to
be taken to ensure that palladium is not deposited on the
cerium oxide-containing promoters because this would impair
the effectiveness of both the palladium and the promoter.
US 5,057,483 describes a catalyst composition which
consists of two discrete layers on a monolithic support
structure. The first layer contains a stabilised aluminium
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oxide as support material for platinum and finely divided
cerium oxide. The first layer may also contain finely
divided iron oxide and nickel oxide to suppress hydrogen
sulphide emissions and also highly dispersed barium oxide
and zirconium oxide as thermal stabilisers, these being
distributed throughout the entire layer. The second layer
contains a coprecipitated cerium/zirconium mixed oxide,
onto which rhodium is deposited, and an activated aluminium
oxide as support material for platinum. The coprecipitated
cerium/zirconium mixed oxide preferably contains 2 to
30 wt.% of cerium oxide.
US 4,294,726 describes a single-layered catalyst
composition on an inert support structure which has
platinum, rhodium and base metals as catalytically active
components, these being deposited on an active aluminium
oxide. The active aluminium oxide contains cerium oxide,
zirconium oxide and iron oxide. The catalyst is obtained by
impregnating active aluminium oxide with an aqueous
solution of cerium, zirconium and iron salts. After
calcining the aluminium oxide treated in this way, it is
then impregnated again with an aqueous solution of platinum
and rhodium salts.
US 4,965,243 also describes a single-layered, thermally
stable, three-way catalytic converter on a monolithic
support structure which is obtained by coating the support
structure with a coating dispersion which contains a metal
from the platinum group, active aluminium oxide, cerium
oxide, a barium compound and a zirconium compound.
WO 95/00235 describes a two-layered catalyst on an inert
support structure which contains only palladium as a
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catalytically active component. The first layer contains a
first support material and at least one first palladium
component and a first oxygen-storing component which is in
intimate contact with the palladium component. The second
layer contains a second support material and at least one
second palladium component. y-aluminium oxide is used as a
first support material and palladium is deposited on this
by impregnating with an aqueous palladium nitrate solution.
The aluminium oxide obtained in this way is processed with
a colloidal dispersion of cerium oxide (particle size about
10 nm), cerium nitrate crystals, lanthanum nitrate
crystals, barium acetate crystals, a zirconium acetate
solution, a cerium/zirconium mixed oxide powder and a
nickel oxide powder to give a coating dispersion for the
first layer. For the second layer, a coating dispersion is
made up which contains aluminium oxide coated with
palladium in the same way as for the first layer as well as
lanthanum nitrate crystals, neodymium nitrate crystals,
zirconium nitrate crystals and strontium nitrate crystals.
After each coating procedure, the support structure is
calcined at 450 C in order to convert the precursor
compounds of the various coating components into the
corresponding oxides.
An object of the present invention is a catalyst which
contains only palladium, which can be prepared very cost-
effectively and which has, in addition to good degrees of
conversion for hydrocarbons, carbon monoxide and nitrogen
oxides{, exceptional heat and ageing resistance.
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This object is achieved by an internal combustion engine
exhaust gas catalyst which contains, on a support
structure, a single-layered, catalytic coating containing
the following components:
a) finely divided, stabilised, active aluminium oxide,
b) at least one finely divided oxygen-storing component,
c) optionally, finely divided nickel oxide,
d) additional highly dispersed cerium oxide,
zirconium oxide and barium oxide and
e) as the only catalytically active noble metal,
palladium which is in close contact with all the
components in the coating.
y-aluminium oxide with a specific surface area of more than
100 m2/g and stabilised with lanthanum is preferably used
for the catalyst. 2 to 4 wt.% of lanthanum oxide, which may
for example be incorporated in the aluminium oxide in a
known manner by impregnation, is sufficient for stabilising
purposes.
A cerium/zirconium mixed oxide which can be obtained, for
example, by coprecipitation in the way described in E.P.O.
605,274 is preferably used as an oxygen-storing
component. The material preferably contains 15 to 35 wt.%
of zirconium oxide, with reference to its total weight. If
the amount of zirconium oxide is less than 15 wt.%, the
ageing resistance of the material is no longer sufficient.
Due to its high cerium oxide content, this material has an
outstanding oxygen-storage Gapacity.
If very high temperatures of up to 1100 C are expected
during use of the catalyst, it is recommended that the
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mixed oxide mentioned above be replaced, entirely or
partly, by a zirconium-rich cerium/zirconium mixed oxide
containing 70 to 90 wt.% of zirconium oxide. Due to its
high zirconium oxide content, this material is particularly
heat resistant, but it has a lower oxygen-storage capacity
in the freshly-prepared state.
As an alternative to this, a material may also be used
which comprises cerium oxide in highly dispersed form on
finely divided zirconium oxide. The highly dispersed cerium
oxide may be fixed on the zirconium oxide by impregnation
followed by calcination. This material has sufficient
oxygen-storage capacity even with a cerium oxide
concentration of only 10 to 30 wt.g. Highly dispersed
mixtures of cerium oxide and praseodymium oxide on
zirconium oxide are also particularly advantageous, wherein
1 to 20 wt.% of praseodymium oxide is present, with
reference to cerium oxide.
Another finely divided oxygen-storage component, which is
characterised by particularly good ageing stability, is
obtained by impregnating the cerium-rich cerium/zirconium
mixed oxide mentioned above with 1 to 10 wt.%, with
reference to the total weight of the final component, of
praseodymium oxide.
The ratio by weight in the catalyst between active
aluminium oxide, the oxygen-storing component and
additional highly dispersed cerium oxide, zirconium oxide,
barium oxide and finely divided nickel oxide is preferably
adjusted to:
100 : 20-100 : 15-40 : 20-40 : 10-30 : 0-10.
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Optimum light-off temperatures and activities for the
catalyst are produced when the amount of catalyst coating
on the support structure is between 50 and 600 g/l of
support structure volume and the palladium concentration is
5 between 1 and 15, preferably 2 to 5 g/l of support
structure volume.
The actual amount of coating used on the support structure
depends on the specifications for hazardous substance
10 conversion and long-term stability as well as on the cell
density of the honeycomb structure. Average layer
thicknesses of about 30 to 50 m are preferably produced on
the channel walls. The amount of coating required for this
is 50 to 600 g/l of support structure volume, depending on
the cell density, wherein. the upper value is used for
support structures with cell densities of 250 cm Z. The
larger the amount of coating on a given support structure,
the greater is the risk that the exhaust gas oressure will
rise to an excessive extent due to narrowing of the flow
channels, thus reducing the power of the engine. This
effect restricts the amount of coating which can
realistically be applied to a maximum value.
To prepare the catalyst, an aqueous coating dispersion is
made up by dispersing the active aluminium oxide, the
oxygen-storing component and optionally nickei oxide in
powdered form in water, with the addition of soluble cerium
oxide, zirconium oxide and barium oxide precursors. The
inner walls of the flow channels in a honeycc-ib support
structure made of ceramic or metal is coated -.rith this
coating dispersion by, for example, immersion. In the case
of support structures made from strips of metal sheeting,
the films may also be applied to the strips b?fore shaping
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into the support structure. After drying and calcining the
coating, palladium is deposited on all the components in
the coating in highly dispersed form by immersing the
support structure in an aqueous impregnating solution of
soluble precursors of palladium.
As an alternative to this procedure, there is also the
possibility of first making up a coating powder which
contains all the components for the catalyst. Here, an
aqueous dispersion of powdered aluminium oxide, the oxygen-
storing component and optionally nickel oxide as well as
soluble cerium oxide, zirconium oxide and barium oxide
precursors is made up. The dispersion is dewatered, dried
and calcined. The coating powder obtained in this way is
then redispersed, a palladium precursor is added and it is
then applied to the inner walls of the support structure
using known methods. The coating obtained in this way is
then dried and calcined. Calcination may optionally be
performed in a hydrogen-containing stream of gas (for
example, forming gas consisting of 5 vol-% hydrogen, the
remainder being nitrogen) to reduce the palladium.
Both alternative methods of preparation for the catalyst
ensure the close contact between palladium and all the
other components in the catalyst which is required by the
manner in which the palladium is applied.
Suitable soluble precursors of cerium oxide, zirconium
oxide and barium oxide are nitrates, ammonium nitrates,
chlorides, oxalates, acetates, citrates, formates,
propionates, thiocyanates and oxychlorides of cerium,
zirconium and barium. Nitrates and acetates are preferably
used. A variety of palladium salts are suitable as
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precursors of palladium. Palladium nitrate is preferably
also used here.
The drying stages used during preparation of the catalyst
are not critical. They may be performed in air in the
temperature range between. 100 and 180 C for a period of
0.25 to 2 hours. Calcination is preferably performed at
temperatures between 300 and 800 C for a period of 0.5 to 3
hours.
To homogenise the coating dispersion, this is usually
milled in a ball mill until an average particle size d50 of
1 to 5, preferably 3 to 5 pm is reached for the finely
divided material to be used (d50 is understood to represent
the particle diameter which is greater than or equal to the
diameter of 50 wt.% of the material). To improve turbulence
of the exhaust gas in the flow channels, a coarse-grained
but high surface area material may be added to the coating
dispersion, as described in US 5,496,788. This roughens the
surface of the final coating and causes turbulence in the
exhaust gas and thus an improvement in material exchange
between the exhaust gas and the catalyst coating.
Depending on the consistency of the coating dispersion, the
required amount of coating may be extracted onto the
support structure by immersing the support structure, for
example, once or several times. The solids content and
viscosity of the coating dispersion are preferably adjusted
in such a way that the amount of coating requilred can be
applied in a single coating procedure. This is the case,
for example, when the solids content of the coating
dispersion is 30 to 70 wt.% and the density is 1.4 to
3
1.8 kg/dm.
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Raw materials with the following properties were used to
make up the catalysts in the following examples and
comparison examples to explain the invention in more
detail:
La/A1203: y-aluminium oxide, stabilised with 2 to
4 wt.% of lanthanum, calculated as lanthanum
oxide;
BET surface area: 140 m2/g;
initial particle size: d50 %z- 15 pm;
Y-A-1203: pure gamma--aluminium oxide;
BET surface area: 140 m2/g
initial particle size: d50 ;z~ 15 pm;
Ce02/Zr02 (70/30) :
coprecipitated cerium/zirconium mixed oxide;
concentration of zirconium oxide: 30 wt.%;
BET surface area: 60 m2/g;
initial particle size: d50 P:~ 30 pm;
Ce02/ZrO2 (20/80) :
coprecipitated cerium/zirconium mixed oxide;
concentration of zirconium oxide: 80 wt.%;
BET surface area: 80 m2/g;
initial particle size: d50 & 2 pm;
CeO2/ZrO2/Pr6011:
highly dispersed Pr6011 on cerium/zirconium
mixed oxide with 67 wt.% of cerium oxide, 28
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wt.% of zirconium oxide and 5 wt.% of
praseodymium oxide;
BET surface area: 60 m2/g;
initial particle size: d50 %::' 17 pm;
Ce (C2H3O2) 3: cerium acetate;
ZrO (C2H302) 2 : zirconyl acetate;
Ba (C:2H302) 2: barium acetate;
NiO: nickel oxide;
BET surface: area: 20 m2/g;
initial particle size: d50 %::~ 14 pm;
support structure: honeycomb structure made from cordierite
with 62 channels per square centimetre of
cross-sectional area;
dimensions: 3.8 cm diameter; 15.2 cm length
Esample 1
A coating dispersion was made up to coat the support
structure, containing 300 g of cerium/zirconium mixed
oxide, 300 g of cerium oxide as cerium acetate, 300 g of
zirconium oxide as zirconium acetate, 200 g of barium oxide
as lbarium acetate and 43 g of nickel oxide per 1000 g of
stabilised aluminium oxide. The final coating dispersion
had a solids content of 34 wt.%.
The support structure was coated by immersing once in this
coating dispersion, dried in air at 120 C for 0.5 h and
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calcined in air for a period of 4 h at 500 C. Then the
coating was impregnated by immersing the support structure
in an aqueous solution of palladium nitrate and then dried
and calcined again. After drying and calcining, the support
5 structure had a coating concentration of about 218 g/l,
which was made up as follows:
Substance Concentration
(g/l1
La/A1203 100
CeO2/ZrO2 70/30 30
CeO2 ex acetate 30
Zr02 ex acetate 30
BaO ex acetate 20
NiO 4.3
Pd ex nitrate 3.9
Total 218.2
Comparison example 1
A comparison catalyst was made up with the same chemical
composition as that in example 1. Differently from example
1, however, the palladium was prefixed onto the aluminium
oxide before making up the coating dispersion. Here, 1000 g
of aluminium oxide were treated with an aqueous solution of
pal:ladium nitrate which contained 39 g of palladium, using
the pore volume impregnation method. In this case, the
total amount of palladium was fixed on the aluminium oxide.
ComiDarison example 2
Another comparison catalyst was made up with the same
cheinical composition as the one in example 1. Differently
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frora example 1 and comparison example 1, half of the
pal:Ladium was prefixed on the cerium/zirconium mixed oxide
and half on the aluminium oxide.
App]Lication example 1
The conversion rates of the catalysts according to example
1, comparison example 1 and comparison example 2 for the
hazardous substances CO, HC and NOx were tested after
age:Lng using a 1.8 1 petrol engine. Ageing was performed at
a bed temperature (temperature of the catalyst) of 1000 C
for a period of 40 hours. The conversion rates were
measured on an engine test-stand at a bed temperature of
400' C and with different normalised air/fuel-ratios X. To
simulate real conditions, the normalised air/fuel-ratio was
modulated with a frequency of 1 Hz and amplitudes of 0.5
A/F (air/fuel ratio) and 1.0 A/F. The space velocity
during these measurements was approximately 50000 h-1.
The results of the measurements are given in Tables 1 and
2. The experimental values recorded in the Tables are
ave:rages of at least two measurements.
Table 1: Engine test of catalysts from example 1(E1), comparison example 1
(CE1) and comparison
example 2 (CE2) after engine ageing at 1000 C for a period of 40 hours;
Exhaust gas temperature 400 C; exhaust gas modulation: 1.0 Hz 0.5 A/F
(air/fuel ratio)
Ex. 7l a 0.993 7l - 0.996 7l - 0.999 X - 1.002 X - 1.006
CO % HC % NO. % CO % HC % NO. % CO % HC % NO. % CO % HC % NO. % CO % HC % NO,
%
El 58.8 89.6 72.9 62.5 90.2 66.6 63.4 90.5 63.2 65.4 90.6 57.7 67.9 90.5 55.9
CE1 44.7 87.9 62.4 47.7 88.5 57.6 50.2 88.4 56.4 51.8 88.8 53.8 54.0 88.7 52.3
CE2 27.5 77.9 1 44.9 29.8 78.8 41.7 31.5 78.6 41.4 32.2 79.8 39.9 32.8 80.3
39.7
r ~~
Table 2: Engine test of catalysts from example 1(E1), comparison example 1
(CE1) and comparison
example 2 (CE2) after engine ageing at 1000 C for a period of 40 hours;
Exhaust gas temperature 400 C; exhaust gas modulation: 1.0 Hz 1.0 A/F
(air/fuel ratio)
Ex. X = 0.993 X - 0.996 7l = 0.999 7l = 1.002 X - 1.006
CO % HC % NO. % CO % HC % NO. % CO % HC % NO. % CO % HC % NO. % CO $ HC % NO.
%
El 63.1 88.4 77.3 68.4 88.5 77.3 85.3 91.3 73.9 91.7 91.4 62.8 93.7 91.4 57.7
CE1 61.9 88.5 74.5 67.0 88.6 71.7 75.7 89.6 67.0 81.6 89.7 60.0 86.3 90.1 55.4
CE2 36.7 66.3 34.8 36.2 67.1 36.1 52.3 81.8 46.1 57.7 83.7 44.9 63.9 85.7 43.4
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Exwaple 2
Another catalyst was prepared in accordance with the
invention. Differently from example 1, however, the
pal.ladium was not introduced into the coating by
impregnation but palladiuin nitrate was added to the coating
dis;persion. The chemical composition of the catalyst was
identical to that in example 1.
Comparison example 3
A support structure was coated with a two-layered catalyst
in accordance with example 1 in WO 95/00235. The coating
dispersions were made up exactly in accordance with the
data in the WO document. The individual preparation steps
can therefore be obtained from that document. The final
coating had the following composition:
lst layer 2nd layer
Substance [g/1] Substance [g/1]
Y-A1.203 + 43 7-A1Z03 + 43
Pd 1.94 Pd 1.94
CeO;, colloidal 18.4 Zr02 ex nitrate 6.1
CeO;, ex nitrate 30.7 La203 ex nitrate 6.1
CeO.t/Zr02 20/80 30.7 Nd203 ex nitrate 6.1
Zr0=z ex acetate 8.6 SrO ex nitrate 6.1
LaZ()3 ex nitrate 6.1
BaO ex acetate 3.7
Ni0 4.3
Total 147.44 Total 69.34
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ApE)lication example 2
The conversion rates of catalysts according to example 2
and comparison example 3 were measured after ageing as
described in application example 1. Differently from
application example 1, the measurements were performed with
an exhaust gas temperature of 450 C. The experimental
results are given in Tables 3 and 4. They show that, with
the catalyst according to the invention, the object of the
invention, a single-layered catalyst with a simple layer
str.ucture, which provides the same or better performance
dat:a than conventional catalysts, is achieved in full.
Table 3: Engine test of catalysts from example 2 (E2) and comparison example 3
(CE3) after engine
ageing at 1000 C for a period of 40 hours;
Exhaust gas temperature 450 C; exhaust gas modulation: 1.0 Hz 0.5 A/F
(air/fuel ratio)
Ex. k = 0.993 X - 0.996 k - 0.999 X - 1.002 X - 1.006
CO % HC % NO, % CO % HC % NOx 8 CO % HC % NOx $ CO $ HC % NOx $ CO $ HC % NOx
$
E2 52.2 90.4 78.3 69.6 92.4 82.6 87.1 94.3 86.2 97.6 94.7 76.2 98.7 93.9 59.3
CE3 55.9 90.5 80.8 66.5 L91.3 79.5 78.1 91.7 76.8 29.8 92.4 69.9 95.6 92.1
57.5 O
Table 4: Engine test of catalysts from example 2 (E2) and comparison example 3
(CE3) after engine ~
ageing at 1000 C for a period of 40 hours;
Exhaust gas temperature 450 C; exhaust gas modulation: 1.0 Hz 1.0 A/F
(air/fuel ratio)
Ex. X = 0.993 X - 0.996 X - 0.999 7l = 1.002 Jl = 1.006
CO % HC % NOx % CO % HC % NOx % CO % HC % NO. % CO % HC % NO. % CO % HC % NO.
%
E2 72.9 94.5 94.4 73.6 94.1 81.6 77.0 94.2 74.7 80.5 94.2 69.9 83.0 94.08 66.0
CE3 52.1 90.1 66.2 54.0 90.2 62.0 56.1 90.7 60.8 60.2 90.9 58.6 63.6 90.9 57.4
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Ex=ple 3
Preparation of the catalyst in example 2 was repeated.
Example 4
Another catalyst according to the invention was prepared
with a slightly modified ratio of components in the coating
dispersion with respect to each other in the same way as in
example 2. Instead of the cerium/zirconium mixed oxide, the
cerium/zirconium modified. by impregnating with praseodymium
oxide was used. The composition of the final coating is
given below:
Substance Concentration
[9/1]
La/A1203 100
Ce02 / Zr02/ Pr6C-11 45
67/28/5
CeO2 ex acetate 20
Zr02 ex acetate 25
BaO ex acetate 20
NiO 4.3
Pd ex nitrate 3.9
Total 218.2
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Application example 3
The same tests were performed with the two catalysts in
exaimples 3 and 4 as with the other catalysts. The
experimental results are given in Tables 5 and 6.
Differently from the preceding examples, the catalysts were
subjected to a more intense ageing procedure in order to
demonstrate the positive effect on ageing stability of
cerium/zirconium mixed oxide modified with praseodymium
oxide. The more intense ageing procedure was performed
using a 2.0 1 petrol engine at an exhaust gas temperature
of :1050 C for a period of 40 hours. The space velocity
during measurement of the rates of conversion was again
50, 000 h-1.
Table 5: Engine test of catalysts from example 3(E3) and example 4(E4) after
intensified engine
ageing at 1050 C for a period of 40 hours;
Exhaust gas temperature 450 C; exhaust gas modulation: 1.0 Hz 0.5 A/F
(air/fuel ratio)
Ex. X = 0.993 7l - 0.996 7~ - 0.999 k - 1.002 1.006
CO % HC % NOx % CO $ HC % NO. % CO % HC % NO. $ CO $ HC % NO. $ CO % HC % NOx
%
E3 59.8 89.4 70.6 77.3 91.3 75.4 91.2 92.1 62.5 95.0 91.7 51.1 95.8 92.0 45.9
E4 64.2 90.6 78.5 83.8 93.6 80.9 97.7 94.2 63.2 98.1 93.2 55.1 98.3 93.3 48.2
A
W '..'
Table 6: Engine test of catalysts from example 3(E3) and example 4 (E4) after
intensified engine
ageing at 1050 C for a period of 40 hours;
Exhaust gas temperature 450 C; exhaust gas modulation: 1.0 Hz 1.0 A/F
(air/fuel ratio)
Ex. k = 0.993 X - 0.996 1l - 0.999 7l = 1.002 J~ = 1.006
CO % HC % NO. % CO % HC % NO. $ CO % HC % NO. % CO % HC % NO. % CO % HC % NO.
$
E3 53.7 90.6 56.4 55.5 90.7 54.6 57.0 90.6 53.1 63.5 90.9 49.1 66.8 91.3 46.5
E4 71.5 93.7 73.1 76.9 94.0 70.2 79.2 93.9 67.9 82.8 93.9 63.2 85.5 94.1 57.2
CA 02234355 1998-04-08
24
Example 5
Ariother catalyst was prepared in the same way as described
iri example 4. However, 20 g of the Ce02/Zr02/Pr6011 were
replaced by 70 g of the z:irconium-rich cerium/zirconium
mixed oxide with a concer-tration of zirconium of 80 wt.%.
This meant that the concentration of CeO2 in the catalyst
was approximately the same as in example 4. The source of
ttie CeO2 was now distributed between Ce02/Zr02/Pr6011,
CE:0Z/ZrO2 (20/80) and highly dispersed cerium oxide. The
composition of the final coating is given below.
Substance Concentration
Ig/l1
La/A1203 100
Ce02/Zr02/Pr6011 25
67/28/5
Ce02/Zr02 20/80 70
CeOz ex acetate 20
Zr02 ex acetate 25
BaO ex acetate 20
NiO 4.3
Pd ex nitrate 3.9
Total 268.2
Apsnlication example 4
One catalyst from each of examples 4 and example 5 were
subjected to an intensified ageing procedure at 1050 C for
a, period of 40 hours, as described in application example
3. Measuring the rates of conversion for the catalysts was
performed at double the space velocity, i.e. at 100000 h-'.
The results of the measurements are given in Tables 7 and
B.
Table 7: Engine test of catalysts from example 4 (E4) and example 5 (E5) after
intensified engine
ageing at 1050 C for a period of 40 hours;
Exhaust gas temperature 450 C; exhaust gas modulation: 1.0 Hz 0.5 A/F
(air/fuel ratio)
Ex. X = 0.993 X - 0.996 Jl = 0.999 1 - 1.002 - 1.006
CO % HC % NO. $ CO % HC % NO, $ CO % HC % NO, $ CO $ HC % NO, % Co % HC $ NO.
%
E4 59.9 81.4 55.4 66.7 81.4 52.3 69.7 81.9 49.4 74.5 81.7 46.6 80.3 81.6 42.9
E5 71.0 86.6 69.8 80.9 87.1 66.2 86.0 87.5 60.0 88.9 86.9 52.7 93.2 86.7 43.6
N vWi
Ln
Table 8: Engine test of catalysts from example 4 (E4) and example 5 (E5) after
intensified engine
ageing at 1050 C for a period of 40 hours;
Exhaust gas temperature 450 C; exhaust gas modulation: 1.0 Hz 1.0 A/F
(air/fuel ratio)
Ex. X = 0.993 k - 0.996 k - 0.999 1 = 1.002 1.006
CO % HC % NO. % CO % HC % NO, % CO % HC % NO. % CO $ HC $ NO. % CO % HC % NO.
%
E4 40.1 77.0 43.4 42.2 77.2 41.0 44.4 77.4 40.5 45.2 76.6 38.0 45.6 77.3 37.9
E5 57.2 84.9 55.0 62.2 85.0 51.2 64.4 84.8 47.8 64.8 84.4 45.4 65.2 84.5 44.8
