Claims:1. A catalyst composition comprising at least two layers of wash coat compositions wherein the
wash coat composite comprises 20 – 37% ceria; 30 – 46% zirconia; 3 – 34% alumina; 0 – 10%
zeolites, 1 – 5% lanthana; 0 – 3% neodymia; 0 – 5% yttria; 0 – 3.6% barium oxide; 0.1 – 2%
nickel.
2. The catalyst composition as claimed in claim 1 wherein the first layer of wash coat composition
comprises; 22 – 28% ceria; 25 – 35% zirconia; 20 – 40% alumina; 0 – 10% zeolites, 0 – 3.6%
barium oxide; 0.5 – 3.2% lanthana; 2.5 – 2.8% neodymia; 0 – 2.5% yttria; 0.1 – 2% nickel,
thermal stabilizers such as magnesium oxide, strontium oxide, calcium oxide, cobalt,
praseodymia, ruthenium and manganese, and precious metals such as palladium, rhodium and
platinum;
3. The catalyst composition as claimed in claim 1 wherein the second layer of the wash coat
composition comprises 16-17% ceria; 45-47% zirconia; 29-34% alumina; 0 – 2% nickel; 0.9 –
3% lanthana; 0 – 2.3% neodymia; 0 – 3% yttria, thermal stabilizers such as magnesium oxide,
strontium oxide, calcium oxide, cobalt, praseodymia, ruthenium and manganese, and precious
metals such as palladium, rhodium and platinum;
4. A catalyst composition as claimed in claim 1 wherein the thermal stabilizers are added in each
layer of the wash coat composition such that the ratio of the thermal stabilizer compounds to
the overall composition is 0 - 3% magnesium oxide, 0 – 1% strontium oxide, 0 - 4% calcium
oxide, 0 – 1% cobalt, 0 – 3% praseodymia, 0 – 0.3% ruthenium and 0 – 1% manganese are
added in each layer of the wash coat composition
3. A catalyst composition as claimed in claim 1 wherein precious metals are added in the wash
coat composition such that the ratio of the precious metals to the overall composition is 0.01-
4.3%, palladium; 0.002-1.6% rhodium; 0.06-0.24% platinum
4. The catalyst composition as claimed in claim 1 wherein the ceria and zirconia is a
nanocomposite ceria stabilized zirconia which comprises about 24 - 45% by weight of ceria, 0
– 5.5% by weight of neodymia, 0 – 5% by weight of lanthana, 0 – 5% by weight of yttria, 45 -
76% by weight of zirconia
5. The catalyst composition as claimed in claim 1 wherein the alumina is lanthana modified
alumina, comprises 2.5 – 5% lanthana
6. The catalyst composition as claimed in claim 1 wherein the zeolite used is NaZSM-5, KLzeolite,
Fe-beta zeolite or NaL-zeolite or mixtures thereof
7. A catalyst composition prepared by a single layer wash coat composition wherein the wash
coat composition comprises 20 - 37% ceria; 0 – 3% neodymia; 1 – 5% lanthana; 0 – 5% yttria;
0 – 3.6% barium oxide; 0.1 – 2% nickel; 0 – 0.3% ruthenium; 30 - 46% zirconia; 3 – 34%
alumina; 0 – 10% zeolite; 0 - 3% magnesium oxide, 0 – 1% strontium oxide; 0 – 4% calcium
oxide, 0 – 3% praseodymia, 0 – 1% cobalt; 0 – 1% manganese; 0.01 –4.3% palladium; 0.002
– 1.6% rhodium; 0.06 – 0.24% platinum. , Description:Field of invention
The present invention relates to the preparation of a catalyst composition comprising a three-way
catalyst used for the effective removal of carbon monoxide, hydrocarbons and nitrogen oxide gases
emitted by internal combustion engines operating using gasoline and natural gas in stoichiometry
or fuel rich conditions. Three-way catalysts are those catalysts which simultaneously effect the
conversion of three gases, which in the case of the subject invention are carbon monoxide,
hydrocarbons and nitrogen oxide gases. The catalyst composition is prepared by single or multiple
layers of a wash coat composition using promoter compounds and precious metals which are in
turn coated onto a honeycomb substrate. The advantage of using multi-layered wash coat
compositions over a single layered wash coat composition is that it substantially increases the
catalytic activity of the catalyst composition.
The wash coat composition broadly comprises the following:
Active Materials:
a) 20 – 37% ceria;
b) 30 – 46% zirconia;
c) 3 – 34% alumina;
d) 0 – 10% zeolites,
e) 1 – 5% lanthana;
f) 0 – 3% neodymia;
g) 0 – 5% yttria;
h) 0 – 0.3% ruthenium;
Each layer of the wash coat composition is also incorporated with the following materials which
enhance the thermal stability of the catalyst composition:
Thermal Stabilisers:
a) 0 – 3.6 % barium oxide,
b) 0.1 – 2% nickel;
c) 0 – 3% magnesium oxide,
d) 0 – 1% strontium oxide,
e) 0 – 4% calcium oxide,
f) 0 – 3% neodymia
g) 0 – 3% praseodymia
h) 0 – 1% cobalt
i) 0 – 1% manganese
Precious Metals:
Additionally, each layer of the wash coat composition is also incorporated with precious metals
such as:
a) 0.01 –4.3% palladium;
b) 0.002 – 1.6% rhodium;
c) 0.06 – 0.24% platinum
Catalyst compositions prepared using multi-layered wash coat compositions found to exhibit
higher conversion of pollutants and greater oxygen storage capacity after hydrothermal aging.
Background of the invention
The use of oxides of cerium, zirconium, aluminum, silicon, zeolites, rare earth metals, alkaline
earth metals, transition metals and precious metals in the treatment of automotive exhaust gases is
known to exhibit satisfactory performance for the effective conversion of carbon monoxide,
hydrocarbons and nitrogen oxide gases when the internal combustion engine is operating in
stoichiometry or fuel rich conditions.
However, conventional catalysts do not exhibit satisfactory performance in converting carbon
monoxide, hydrocarbons and nitrogen oxide gases after running for long periods. Such
conventional catalysts also do not exhibit satisfactory performance when exposed to high
temperature conditions. This can be observed when the temperature of the exhaust gas sometimes
reaches as high as about 1000 degree Celsius during the operation because of the changes in the
engine load. Additionally, conversion of nitrogen oxides using a conventional catalyst at a wider
temperature range with small quantity of precious metal also difficult to achieve. The subject
invention aims at overcoming these short comings of conventional catalysts.
The subject invention is well developed with conversion capabilities of >99% for carbon
monoxide, hydrocarbons and nitrogen oxide gases.
A common exhaust catalyst design for passenger cars is to have one honeycomb substrate /
monolith in a close coupled (CC) position with the second honeycomb substrate / monolith in the
underbody (UB) location. The CC catalyst is often designed to favor rapid heat up, small size
substrates, high cell density and high loading of precious group metals (platinum, palladium,
rhenium, rhodium, ruthenium, osmium and iridium) to have faster light-off. Alternatively, the UB
catalyst can be designed with larger volume, lower cell density and lower loading of precious
group metals.
Conventional three-way catalysts use rare-earth stabilized alumina and oxygen storage materials
for enhancing the hydrothermal stability and sustained performance over a period. Additionally,
in conventional three-way catalysts, the precious group metals and promoter metals are
incorporated in a lone support and uniformly dispersed throughout the monolith. However, such
conventional three-way catalysts were not found to effectively perform the conflicting
requirements of oxidation of carbon monoxide and hydrocarbons and reduction of nitrogen oxide
gases.
The subject invention mainly aims at overcoming the aforementioned short comings of
conventional catalysts by effectively converting carbon monoxide, hydrocarbons and nitrogen
oxide gases when the internal combustion engine is operating in stoichiometry or fuel rich
conditions. The subject invention has conversion capabilities of greater than 99% for carbon
monoxide, hydrocarbons and nitrogen oxide gases, wherein the precious metals and the thermal
stabilizers are loaded onto more than one active material support, thereby providing greater
efficiency in removing exhaust gases when compared to conventional catalysts.
The wash coat composition which constitutes the subject invention is then applied to a honey comb
substrate to produce a catalyst sample which is then introduced into a vehicle for the purposes of
removing exhaust gases. The catalyst sample is then placed in a close-coupled position in a
passenger car to improve the removal of exhaust gases. The term “close-coupled position”
indicates that the catalyst sample is placed in close proximity to the engine of the passenger car.
The catalyst sample is placed in a close-coupled position as it works more effectively when the
temperature of the engine increases. Another advantage of introducing the sample through the
close coupled position is that a honey comb substrate of higher cell density and smaller substrate
size can be employed thereby providing for removal of a larger quantity of exhaust gases.
Additionally, a catalyst sample can also be placed in the underbody of a passenger car. The catalyst
sample when introduced into the underbody of a passenger car can be designed in such a manner
that a larger volume of the catalyst sample at low PGM density can be used at a time. Such an
alternative would require only a minimum amount of precious metals in addition to the active
materials and the thermal stabilizers within the wash coat composition to effectively remove the
exhaust gases.
Moreover, it is understood that catalytic activity is a function of several factors including the
following:
(i) Rate of diffusion of the gases from exhaust
(ii) Mass transfer limitations
(iii) Heat resistance of the catalyst
If there is a fluctuation in any of the aforementioned factors, it can lead to an inactivation of the
catalyst performance during over-heating or ageing of the engine.
The subject invention aims at resolving these limitations and comprises multiple layers of a wash
coat composition with unequal distribution of precious metals, thermal stabilizers and active
materials to improve the emission performance of pollutants emitted from internal combustion
engines with lower precious metal inventory.
The following are inventions which can constitute as prior art to the subject invention. The
advantages of the subject invention in comparison to each prior art has been described in
brief:
IN20100526P2 by BASF claims a layered catalyst composite with three layers. The first layer
comprising a platinum component on a support, the second layer comprising a rhodium component
on a support and third layer comprising a palladium on a third support
IN200901577P4 teaches a layered catalyst composite useful for treating exhaust gas support e.g.
nitrogen oxides comprise first layer of palladium deposited on a carrier, second layer of rhodium
deposited on first layer and third layer of palladium deposited on second layer
IN239069B teaches a catalyst support powder comprising ceria and zirconia and platinum
supported thereon
IN201000850P4 claims a catalyst for treating gas containing hydrocarbons, CO and NOx. The
ceria-zirconia composite comprises ceria (5 wt%) and lanthana (1-10 wt%). The ceria-zirconia
composite further comprises lanthana, neodymia, praseodymia, samarium and / or yttria. The
palladium component (0.1% wt%) is associated onto the ceria-zirconia composite
IN20070065511 claims an improved process for the preparation of noble metal, three-way autoexhaust
catalyst having a high activity and a longer life for loading on a commercially available
ceramic honeycomb monolith. Two promoters, lanthanum and cerium are used with noble metals
(combination of platinum and rhodium).
IN20090192713 claims a method for producing an exhaust gas purifying catalyst wherein rhodium
and at least one of platinum and palladium are employed as noble metal catalyst components.
IN201001859P2 claims a catalyst wash coat comprising precious metals selected from the group
consisting of platinum, palladium, ruthenium, iridium, rhodium and combinations thereof
IN201005857P4 claims a catalyst for treating an exhaust gas from an internal combustion engine,
which comprises a catalyst active component comprising at least both palladium and magnesium
US Patent 5593647 describes a catalytic converter which includes a substrate having a tri-metal
catalyst system thereon. The tri-metal catalyst system includes a double coat system in which
platinum and rhodium are together on one layer and palladium is separate on a second layer. The
first layer consists essentially of palladium and the second layer consists of platinum and rhodium.
This invention however predominantly uses precious metals in their wash-coat composition to
produce the catalyst sample, whereas the subject invention employs precious metals in addition to
active materials and thermal stabilizers to constitute the wash coat composition, thereby deeming
the composition of both these inventions sufficiently different.
US Patent 5672557 describes a palladium three-way catalyst supported on a unique ceria-lanthanaalumina
support wherein the alumina content is lower than previously believed necessary to
maintain catalyst activity. Preferably the ceria and lanthana constitute the major proportion of the
support. The advantage of the subject invention is that the wash coat composition comprises a
unique combination of active materials, precious metals and thermal stabilizers unequally
distributed over two layers to produce higher catalytic activity in comparison to the prior art. The
use of active materials is not limited to merely ceria and lanthana and a major part of the wash coat
is a combination of various active materials in varying proportions.
US Patent 5981427 describes a catalyst composition comprising at least one first support, at least
one first precious metal component, at least one second support, and at least one second precious
metal component. The total amount of the first precious metal component comprises from 1 to 99
weight% based on the total of the first and second precious metal components. The average particle
size of the second support is greater than the average particle size of the first support. The
disadvantage of this prior art in comparison to the subject invention is that the prior art only
comprises of precious metals which are highly expensive to procure. The subject invention,
although comprising precious metals, pre-dominantly uses active materials and thermal stabilizers
to improve the catalytic activity. Since the amount of precious metals used in the wash coat is
significantly lesser in comparison to the prior art, the cost to produce the subject invention is
significantly lower in comparison to the prior art.
US Patent 6087298 describes an exhaust gas treatment catalytic article having an upstream
catalytic zone and at least one downstream catalytic zone. The upstream catalytic zone has an
upstream composition which has a first upstream support, and at least one first upstream palladium
component. The upstream zone can have one or more layers. The prior art pre-dominantly uses
precious metals in order to produce catalytic activity in comparison to the subject invention which
uses active materials, precious metals and thermal stabilizers to produce improved catalytic
activity.
Summary of the invention
This invention relates to a catalytic composition comprising a three-way catalyst for removing
carbon monoxide, hydrocarbons and nitrogen oxide gases from the exhaust gas emitted from
vehicles fueled with gasoline, ethanol blended gasoline, liquefied petroleum gas or natural gas
operating in stoichiometry or rich conditions.
The catalyst composition is prepared by multiple layers of a wash coat composition
The catalysts are prepared with different amount of precious and base metals incorporated in a
mixture containing high surface area ceria-zirconia hydroxide, alumina, zeolites or ceria-zirconiaalumina
composite oxide and wash coated onto the honeycomb substrate with single or multiple
layers with an objective to enhance the conversion of HC particularly in the temperature range of
200 – 600 deg C without compromising the removal of CO and NOx generated by the internal
combustion engines operated with gasoline, liquefied petroleum gas and natural gas. In addition,
the single or multi-layered catalysts of this invention sustain their catalytic activity after aging at
>1000 deg C. The multi-layered three-way catalyst was fitted in a close-couple position is found
to enhance the activity not exhibited by catalysts prepared by single layer.
Brief description of the drawings
The present disclosure can be better understood by referring to the following figures.
Fig. 1 is a graph of oxygen storage capacity for fresh and aged three-way catalyst samples obtained
by plotting the values obtained in micromoles of oxygen per gram of catalyst in vertical axis and
working embodiment examples 1 – 6 in the horizontal axis
Fig. 2 is a graph of BET-surface area for fresh and aged three-way catalyst samples obtained by
plotting BET-surface area values obtained in square meter per gram of catalyst in vertical axis and
working embodiment examples 1 – 6 in the horizontal axis
Fig. 3 is a graph of light-off temperature values for fresh three-way catalysts obtained by plotting
light-off temperatures values measured in deg C in vertical axis and working embodiment
examples 1 – 6 in the horizontal axis
Fig. 4 is a graph of conversion of CO, HC and NOx measured at 450 deg C for fresh catalysts
obtained by plotting conversion values measured in volume% in vertical axis and working
embodiment examples 1 – 6 in the horizontal axis
Detailed description of the invention:
The catalyst is intended for use especially for the purification of the exhaust gases such as carbon
monoxide, hydrocarbons and nitrogen oxide gases of internal combustion engines which are fueled
using gasoline and natural gas.
The subject invention is prepared by single or multiple layers of wash coat compositions which
are in turn coated onto a honeycomb substrate to produce a catalyst sample. The wash coat
composition in the first layer of multi-layered wash coat composition comprises the following
active materials:
a) 22 – 28% ceria;
b) 25 – 35% zirconia;
c) 20 – 40% alumina;
d) 0 – 10% zeolites,
e) 0.5 – 3.2% lanthana;
f) 2.5 – 2.8% neodymia;
g) 0 – 2.5% yttria;
h) 0 – 0.3% ruthenium;
Each layer of the wash coat composition is also incorporated with the following thermal stabilizers
which enhance the thermal stability of the catalyst composition such as:
j) 0 – 3.6 % barium oxide,
k) 0.1 – 2% nickel;
l) 0 – 3% magnesium oxide,
m) 0 – 1% strontium oxide,
n) 0 – 4% calcium oxide,
o) 0 – 3% praseodymia
p) 0 – 1% cobalt
q) 0 – 1% manganese
Additionally, each layer of the wash coat composition is also incorporated with precious metals
such as:
d) 0.01 –4.3% palladium;
e) 0.002 – 1.6% rhodium;
f) 0.06 – 0.24% platinum
The wash coat composition in the second layer of the multi-layered wash coat comprises the
following active materials:
a) 16-17% ceria;
b) 45-47% zirconia;
c) 29-34% alumina;
d) 0.9 – 3% lanthana;
e) 0 – 2.3% neodymia;
f) 0 – 3% yttria;
The second layer of the wash coat composition also comprises following thermal stabilizers which
enhance the thermal stability of the catalyst composition such as:
a) 0 - 2% nickel
b) 0 – 1% cobalt
c) 0 – 1% manganese
Additionally, the second layer of the wash coat composition is also incorporated with precious
metals such as:
a) 0.01 – 4.3% palladium;
b) 0.002 – 1.6% rhodium;
c) 0.06 – 0.24% platinum
The honeycomb substrate of the present invention may be a ceramic or a metallic substrate with a
honeycomb structure, wherein the substrate has a plurality of channels and the required porosity.
Porosity is substrate dependent as is known in the art. In addition, the number of channels present
per square inch (100 to about 1200) of each honeycomb substrate plays a role in improving the
mass transfer of the exhaust gases.
The ceramic honeycomb substrate may be formed from cordierite, silicon carbide, aluminum
nitride, mullite, spodumene or combinations thereof. Other ceramic substrates would be apparent
to one skilled in the art. If the substrate is metallic honeycomb substrate, the metal may be a heatresistant
base metal alloy in which iron is a major component. The surface of the metallic
honeycomb substrate may be oxidized at above 1000 degree Celsius to improve the corrosion
resistance of the metallic honeycomb substrate by forming an oxide layer on the surface of the
metallic honeycomb substrate. This oxide layer on the surface of the metallic honeycomb substrate
may also enhance the adherence of a wash coat to the surface of the monolith substrate. Preferably,
all of the substrates, either metallic or ceramic, offer a three-dimensional support structure.
The substrate can also be any suitable filter for particulates. Some suitable forms of filter substrates
may include, without limitation, wall flow filters, woven ceramic filters, wire meshes, wall flow
filters, metallic foams and other suitable filters. Wall flow filters are similar to honeycomb
substrates but may differ from the honeycomb substrate that may be used to manufacture normal
exhaust catalyst samples in that the channels of the wall flow filter may be alternately plugged at
an inlet and an outlet so that the exhaust gas is forced to flow through the porous walls of the wall
flow filter while passing from the inlet to outlet of the wall flow filter.
In the subject invention, we have observed that loading of various amounts of precious metals and
thermal stabilizers onto the wash coat composition is found to improve the purification of carbon
monoxide, hydrocarbons and nitrogen oxide gases according to this invention, one layer of the
multi-layered three-way catalyst composition comprising:
a) 16-17% ceria;
b) 45-47% zirconia;
c) 29-34% alumina;
d) 0.9 – 3% lanthana;
e) 0 – 2.3% neodymia;
f) 0 – 3% yttria;
and another layer of the three-way catalyst composition comprising:
g) 22 – 28% ceria;
h) 25 – 35% zirconia;
i) 20 – 40% alumina;
j) 0 – 10% zeolites,
k) 0.5 – 3.2% lanthana;
l) 2.5 – 2.8% neodymia;
m) 0 – 2.5% yttria;
n) 0 – 0.3% ruthenium;
To this invention, the weight ratio of ceria-zirconia to refractory oxide is 50 – 70%: 30 – 50%.
This also include promoters and thermal stabilzers such as BaO, SrO, La2O3, Pr2O3, Y2O3,
Nd2O3, Fe, Ni, Mn, Cu, Co, Sn, Na2O, K2O, CaO and MgO. The refractory oxide is preferably
lanthanum oxide modified alumina. The above composition excludes the precious metal content
of the catalyst. The use of precious metal is in the density range of 0.5 – 110 g/cft which provides
for the intended performance of the three-way catalyst composition fitted in the vehicles fueled
gasoline and natural gas. Catalysts of the subject invention exhibits improved catalytic activity at
a temperature greater than 1000 degree Celsius. The improved hydrothermal stability of the
catalyst could be attributed to the addition of thermal stabilizers already mentioned.
Alumina is the most commonly used wash coat support for exhaust gas purification application.
While gamma alumina is the preferred support, other forms of alumina such as delta, eta and theta
alumina may also be used. The alumina used in this invention is preferably barium or strontium
doped alumina or lanthana doped alumina. The barium or strontium doped alumina comprises
about 5 - 10 wt% of barium or strontium and the lanthana doped alumina comprises 2.5 – 5 wt%
of lanthana. Specifically, stabilizing agents are known for stabilizing the specific surfaces of the
alumina and inhibit the phase transformation of alumina at high temperatures and thereby
increasing the high temperature stability of the alumina. The precious metals are incorporated in
alumina or ceria-zirconia or partially on both the supports. The precious metals incorporated in
alumina are dispersed throughout the porous alumina and consequently generate high metal
surface area and thereby the entire precious metal atom is available to the reactants.
Furthermore, zeolites also constitute a part of the wash coat composition. Zeolites exhibit a
combination of micropores and high surface area and are found to be useful as a carrier in exhaust
catalyst. Suitable zeolites include any aluminosilicates having silica to alumina ratio of less than
10. Zeolites for this invention selected from: USY, ZSM-5, beta-zeolites, faujasite, X zeolite, type
Y zeolite and ferrierite. Zeolites such as KL and NaL zeolite or Na-ZSM-5 is used in the subject
invention as it desirably exhibits a silica to alumina ratio of 4 - 6, more preferably 5 and having
incorporated therein about 19% of potassium or sodium by weight. The zeolite is capable of
adsorbing NOx and HC from exhaust gas. The wash coat characteristically contains at least about
5 wt% not exceeding a maximum of 0-10 wt% of zeolites combined with metal oxides. Examples
of such metal oxides which can combine with zeolites are sodium oxide, potassium oxide,
strontium oxide, barium oxide, lanthanum oxide, magnesium oxide, samarium oxide, tin oxide,
ruthenium oxide, manganese oxide and cobalt oxide.
Ceria-zirconia is another well-known component used in exhaust catalysts. It is often referred to
as an oxygen storage component because it is considered to have the capability to release oxygen
when the catalyst is exposed to reducing conditions and store oxygen when exposed to oxidizing
conditions. A single-phase nanocomposite ceria-zirconia hydroxide or oxide incorporated with
dopants is stable even when exposed to high temperatures and is also known to stabilize and
promote the activity of precious metals. The dopants include lanthanum, yttrium, neodymium,
samarium, praseodymium, barium, strontium, sodium, potassium, bismuth, iron, nickel,
molybdenum, cobalt, manganese, strontium, ruthenium, tellurium and iridium. Ceria stabilized
zirconia used in this invention preferably comprises 24-45% ceria, 0.5-5% neodymia, 0-5%
lanthana, 0-5% yttria and 45-76% zirconia. The doped ceria-zirconia materials are known to
promote water gas shift (CO + H2O ? CO2 + H2) and steam reforming (CH4 + H2O ? CO +
3H2) reaction. The significance of these dopants is that it improves stabilization of the supports
to inhibit crystal structure changes and lowering of surface area.
Characteristics of the subject invention
Oxygen Storage capacity:
Oxygen storage capacity is a significantly important property for a three-way catalyst in achieving
the conversion of carbon monoxide, hydrocarbons and nitrogen oxide gases during the rich and
lean fluctuation of an engine. The increasing quantity of ceria content in the ceria-zirconia
hydroxide is found to improve the oxygen storage capacity when the catalyst ages at high
temperature. To improve the oxygen storage capacity, ceria-zirconia employed in this invention
has small particles having a relatively high surface area. The nanocomposite ceria-zirconia
hydroxide employed in this invention possesses a pure monophasic cubic or tetragonal crystal
structure. In order to meet future emission standards, it is necessary that catalysts exhibit high
oxygen storage capacity after exposure to greater than 1000 degree Celsius. In this invention, the
various ceria-zirconia samples with different ceria content and dopants were examined for their
oxygen storage capacity and mass emission performance.
To examine the catalyst samples prepared with different ceria-zirconia and alumina materials
(comprising few or several of the materials which includes Ce, Zr, Al, Si, Ni, Mn, Fe, Cu, Sn, Ag,
Gd, Nd, Pr, La, Ba, Ca, Mg, Pt, Pd, Rh) of the present invention for OSC, BET-SA. About <0.3%
platinum, <5% of palladium and <2% rhodium is incorporated in the catalytically active porous
materials by pore volume impregnation method and by filling 95% of the pores with precious metal
solution. The OSC and mass emission performance of the catalyst found to depend on SMSI
(strong metal support interaction) of the precious metal and the porous support. The SMSI is
affected by the temperature of treatment of the catalyst samples. In this invention the fresh samples
are calcined at <600 deg C and aged samples are treated at >900 deg C. The wash coat is designed
to have nearly same OSC in the temperature range of 200 – 800 deg C to have same conversion
performance of the catalyst under different driving conditions. The rare-earth dopants like Nd, Y,
Pr and La found to show higher thermal stability than the material prepared without dopants.
Among Nd, Y, Pr and La, the support modified with only Nd or mixture of Nd, Y and La or mixture
of Pr and La showed to improve the OSC and thermal stability of the catalyst. Typically, OSC is
reported in micromoles O2 / gram of catalyst.
The wash coated catalytic converters have been tested for their ability to store and release oxygen
according to a test method developed in-house. The fresh samples are calcined at 550oC and aged
catalysts are prepared by hydrothermally treating at 1000oC for 4 h in air followed by cooling
under the flow of nitrogen. 0.2 g of calcined or aged sample is charged into a Quantachrome /
Micromeritics micro-reactor and thereafter reduced by passing H2/N2 and consequently oxidized
by pulsing O2/He over the samples at a specific temperature. Then the oxygen flow is terminated
and then CO/He is injected on the sample by pulsing method. The time required to detect CO
breakthrough is measured and is used to give a reproducible assessment of OSC. OSC is generally
reported in units of micromole of oxygen per gram of sample. OSC of the materials were measured
on Quantachrome ChemBET Pulsar. Total OSC, which represents the overall amount of
transferable oxygen at a fixed temperature, is generally measured by total consumption of
hydrogen or oxygen. Under real exhaust conditions, the A/F ratio oscillates with a frequency of
about 1 Hz around stoichiometry which in principle makes measurement of redox behavior under
dynamic conditions. Dynamic OSC measurement involves alternately pulsing the reducing agent
(CO or H2) and O2 over the material. The OSC values measured for the used or fresh catalyst
explain whether the catalyst is performing as specified and required or there observed any
significant losses in catalyst activity. OSC is also used as a signature to monitor the efficiency of
the catalytic converter.
About 0.15 g of catalyst is taken in quartz reactor tube and it is mounted in the sample holder. The
sample is purged with He with a flow rate of 125 ml/min then the gas flow is switched to 10%H2/N2
with the flow rate of 125 ml/min and the temperature is increased at 10 deg C / min up to 800 deg
C. The temperature of the sample is brought down to 400 deg C by flowing He and then oxygen
pulse titration is conducted with the loop volume of 232 µl. At the same temperature CO pulse
titration is carried out using the loop volume of 1000 µl using ascarite as the CO2 trap. The
dynamic OSC (DOSC) measured for the fresh and aged samples (Ex-1 to Ex-6). The DOSC values
for the fresh and aged catalyst samples are about 150 micromoles O2 / gram. This shows that the
examples of this invention can perform nearly equivalent as fresh catalysts after aging.
BET-Surface Area
About 0.1 g of catalyst sample is taken in quartz reactor tube and degassed at 300 deg C under
vacuum or with nitrogen flow for 3 h. Thereafter it is mounted in the sample holder by flowing
nitrogen through the sample. A cold trap of -196 deg C is used. BET-SA was measured on
micromeritics Tristar II 3020 by N2-physisorption. The BET-surface area for the samples is
ranging between 90 and 110 m2/g for the fresh samples while after aging at 1000 deg C, it ranges
between 39 and 58 m2/g.
The light-off characteristics and conversion efficiency of the catalytic converter was measured on
a modal gas tester using ceramic substrate 20*30L, mm; 400 cpsi. The simulated gas composition
used for the measurement is: CO=0.9%; HC=0.089%; CO2=14%; O2=1.08%; H2O=10%;
H2=0.3%; NO=0.05%; balance N2. The air to fuel ratio (A/F) is maintained at 1.004 lambda. The
simulated gas mixture passed through the Quartz reactor fitted with catalyst at a space velocity of
100K h-1. The temperature of inlet of the catalyst was increased from 100 to 450 deg C with a rate
of 10 deg C/min in order to determine the light-off temperature for CO, HC and NOx. The
conversion of reactants (CO, HC, NOx) was measured at 450 deg C using Horiba Mexa-584L
portable gas analyzer and / or FT-IR. The CO, HC and NOx light-off temperature for all examples
of this invention is in the range of 147 – 228 deg C. The conversion of CO, HC and NOx measured
at 450 deg C is > 97%.
Examples:
Example 1:
Palladium nitrate, rhodium nitrate, nickel nitrate, neodymium nitrate, praseodymium nitrate,
lanthanum nitrate, yttrium nitrate and barium acetate were dissolved in water to make a solution
for pore volume impregnation of ceria-zirconia hydroxide. The metal loadings of the impregnated
catalyst are 0.13% platinum, 1.1% palladium, 0.1% rhodium, 0.5% nickel, 2% neodymia, 0.2%
praseodymia, 4% lanthana, 0.05% yttria; 2.5% barium oxide on ceria-zirconia. The impregnated
sample was then dried at 100 deg C for 1 hour and then calcined at 500 deg C for 3 h. The calcined
sample was then mixed with water, ammonium hydroxide, alumina, zeolites, alkyl ammonium
hydroxide, acetic acid and then milled to 50% of particles having a particle size of less than 5
microns. A ceramic honeycomb of 97*80L, mm; 400 cpsi was then coated with the wash coat by
dipping and air-knifing method. The wash coated monolith was then dried at 100 deg C for 2 h
and then calcined at 500 deg C for 3 h. The mass emission performance of the catalyst was tested
on a passenger car at a close-couple position in accordance with Modified Indian Driving Cycle
(MIDC) showed CO, HC and NOx conversion of 90%, 91% and 95% respectively.
Example 2:
Ceramic honeycomb catalyst described in this example was prepared by following the same
procedure described in example 1 except that the metal loading of the first wash coat is 0.01%
platinum, 1.7% palladium, 0.59% rhodium, 1% nickel, 2.5% neodymia, 3% barium oxide on ceriazirconia.
The wash coated honeycomb is over coated with second wash coat having a composition
of 0.24% platinum, 4.3% palladium, 1.6% rhodium, 0.5% nickel, 2.2% neodymia, 16% ceria, 47%
zirconia, 34% alumina, 2% KL-zeolite, 0.9% lanthana for protecting the first layer from
inactivation and improving NOx conversion. The mass emission performance of the catalyst was
tested on a passenger car at a close-couple position in accordance with Modified Indian Driving
Cycle (MIDC) showed CO, HC and NOx conversion of 89%, 93% and 98% respectively.
Example 3:
Palladium nitrate, rhodium nitrate, nickel nitrate, neodymium nitrate, praseodymium nitrate,
lanthanum nitrate, yttrium nitrate, ruthenium chloride and barium acetate were dissolved in water
to make a solution for pore volume impregnation of ceria-zirconia hydroxide. The metal loadings
of the impregnated catalyst are 0.015% platinum, 0.6% palladium, 0.22% rhodium, 0.12%
ruthenium, 1% nickel, 2.5% neodymia, 0.15% praseodymia, 3% lanthana; 1.4% yttria; 2% barium
acetate on ceria-zirconia. The impregnated sample was then dried at 100 deg C for 1 hour and
then calcined at 500 deg C for 3 h. The calcined sample was then mixed with water,
triethylammonium hydroxide, alumina, ammonium hydroxide, zeolites, acetic acid and then milled
to 50% of particles having a particle size less than 7 microns. A ceramic honeycomb of 97*80L,
mm; 400 cpsi was then coated with the wash coat by dipping method. The wash coated monolith
was then dried at 100 deg C and then calcined at 600 deg C. The wash coated honeycomb is over
coated with second wash coat having a composition of 0.08% palladium, 0.32% rhodium, 0.3%
nickel, 1% neodymia, 16% ceria, 47% zirconia, 34% alumina, 1% KL-zeolite, 2% lanthana for
protecting the first layer from inactivation. The mass emission performance of the catalyst was
tested on a passenger car at a close-couple position in accordance with Modified Indian Driving
Cycle (MIDC) showed CO, HC and NOx conversion of 88%, 91% and 97% respectively.
Comparative example:
The procedure employed in Example 3 was repeated for preparing comparative sample, except
that ruthenium, nickel, praseodymia, lanthana, yttria and KL-zeolite were not used. The mass
emission performance of the comparative sample was tested on a passenger car at a close-couple
position in accordance with Modified Indian Driving Cycle (MIDC) showed CO, HC and NOx
conversion of 82%, 86% and 92% respectively.
Example 4:
Palladium nitrate, rhodium nitrate, platinum sulfite, nickel nitrate, neodymium nitrate, lanthanum
nitrate, yttrium nitrate and barium acetate were dissolved in water to make a solution for pore
volume impregnation of ceria-zirconia hydroxide. The metal loadings of the impregnated sample
are 0.05% platinum, 1.28% palladium, 0.13% rhodium, 1.6% nickel, 2.8% neodymia, 0.5%
lanthana; 1% yttria; 3.5% barium acetate on ceria-zirconia. The impregnated sample was then
dried at 100 deg C for 1 hour and then calcined at 500 deg C for 3 h. The calcined sample was
then mixed with water, alumina, zeolites, acetic acid, ammonium hydroxide and then milled to
50% of particles having a particle size less than 5 microns. A metallic honeycomb of 40*40L, mm;
100 cpsi was then coated with the wash coat by dipping and air-knifing method. The wash coated
monolith was then dried at 100 deg C for 2 h and then calcined at 500 deg C for 3 h. The wash
coated honeycomb is over coated with second wash coat having a composition of 0.37%
palladium, 3.69% rhodium, 0.5% nickel, 2.2% neodymia, 16% ceria, 47% zirconia, 34% alumina,
1% lanthana for improving NOx conversion. The mass emission performance of the catalyst was
tested on a motorcycle having closed-loop EFI system in accordance with Worldwide Harmonized
Motorcycle Emission Test Cycle (WMTC) showed CO, HC and NOx conversion of 90%, 91%
and 99% respectively.
Example 5:
Palladium nitrate, rhodium nitrate, nickel nitrate, neodymium nitrate, lanthanum nitrate, yttrium
nitrate, ruthenium chloride and barium acetate were dissolved in water to make a solution for pore
volume impregnation of ceria-zirconia. The metal loadings of the impregnated catalyst are 0.73%
palladium, 0.76% rhodium, 0.3% ruthenium, 0.6% nickel, 2.7% neodymia, 1.2% lanthana; 0.5%
yttria; 3.5% barium oxide on ceria-zirconia. The impregnated sample was then dried at 100 deg
C for 1 hour and then calcined at 500 deg C for 3 h. The calcined sample was then mixed with
water, tetrapropylammonium hydroxide, alumina, zeolites, alumina binder, acetic acid and then
milled to 50% of particles having a particle size less than 4 microns. A ceramic honeycomb of
97*80L, mm; 400 cpsi was then coated with the wash coat by dipping and air-knifing method. The
wash coated monolith was then dried at 100 deg C for 2 h and then calcined at 500 deg C for 3 h.
The wash coated honeycomb is over coated with second wash coat having a composition of 0.06%
palladium, 0.62% rhodium, 0.03% nickel, 2.3% neodymia, 16% ceria, 47% zirconia, 34% alumina,
0.1% zeolite, 0.9% lanthana for protecting the first layer from inactivation and improving NOx
conversion. The mass emission performance of the catalyst was tested on a passenger car at a
close-couple position in accordance with Modified Indian Driving Cycle (MIDC) showed CO, HC
and NOx conversion of 91%, 92% and 97% respectively.
Example 6:
Palladium nitrate, rhodium nitrate, nickel nitrate, neodymium nitrate, lanthanum nitrate, yttrium
nitrate, ruthenium chloride and barium acetate were dissolved in water to make a solution for pore
volume impregnation of ceria-zirconia. The metal loadings of the impregnated catalyst are 0.97%
palladium, 0.04% rhodium, 1% nickel, 2.6% neodymia, 3.2% lanthana; 2.5% yttria; 3% barium
oxide on ceria-zirconia. The impregnated sample was then dried at 100 deg C for 1 hour and then
calcined at 500 deg C for 3 h. The calcined sample was then mixed with water, ammonium
hydroxide, alumina binder, alumina, zeolites, acetic acid and then milled to 50% of particles
having a particle size less than 5 microns. A ceramic honeycomb of 97*80L, mm; 400 cpsi was
then coated with the wash coat by dipping and air-knifing method. The wash coated monolith was
then dried at 100 deg C for 2 h and then calcined at 500 deg C for 3 h. The wash coated honeycomb
is over coated with second wash coat having a composition of 0.2% palladium, 0.81% rhodium,
0.16% nickel, 1.5% neodymia, 16% ceria, 47% zirconia, 34% alumina, 9% NaL-zeolite, 3%
lanthana for improving NOx conversion. The mass emission performance of the catalyst was tested
on a passenger car at a close-couple position in accordance with Modified Indian Driving Cycle
(MIDC) showed CO, HC and NOx conversion of 88%, 90% and 97% respectively.