GB2581330A - Catalytic materials for passive soot oxidation and methods of their manufacture - Google Patents

Abstract

A catalytic material comprising ceria-metal oxide-alumina in a molar ratio of Ce:M:Al ions of from 75:25:100 to 25:75:100, wherein M represents zirconium or a zirconium at least partially substituted by a light lanthanide selected from the group consisting of lanthanum, praseodymium, neodymium and samarium. M may be neodymium and the catholic material may be heat-treated to more than 500°C and less than 1100°C. The catalytic material may be impregnated with 0.1-7.5% of copper by weight of the catalytic material. The catholic material may be a composite metal oxide having more than one phase, preferably a carbonate phase. The catalytic material may be formed into a catalytic composite and used as part of an exhaust gas treatment system for an internal combustion engine. The catalytic material may be manufactured by co-precipitation using potassium carbonate or cesium carbonate as the precipitating agent. The precipitate may be washed to remove potassium or cesium ions.

Description

CATALYTIC MATERIALS FOR PASSIVE SOOT OXIDATION AND METHODS OF THEIR MANUFACTURE

TECHNICAL FIELD

The present disclosure relates to a catalytic material, a catalytic composite for removing soot from an exhaust stream of an internal combustion engine, wherein the catalytic composite comprises such a catalytic material, an exhaust gas treatment system comprising such a catalytic composite, a vehicle comprising an internal combustion engine and such an exhaust gas treatment system, a method of removing soot from an exhaust stream of an internal combustion engine, and a method of manufacturing a catalytic material.

BACKGROUND

Soot particles form as a consequence of incomplete or partial combustion of fuel in both diesel and gasoline vehicle engines. This can occur due to high temperatures and local nonstoichiometric oxygen conditions which prevent full combustion to carbon dioxide (CO2).

This was historically an issue for diesel-engined vehicles, as their compression-ignition (CI) engines inject fuel directly into the combustion chamber, preventing sufficient air/fuel mixing at a molecular level, resulting in localised fuel-rich regions which do not undergo full combustion. More recently, increased use of more fuel-efficient gasoline direct injection (GDI) over port fuel injection (PH) engines has resulted in a similar problem emerging in gasoline-engined vehicles as well.

The most straightforward method of reducing emissions of particulate matter (PM) like soot is by using a filter to trap particulates. Due to the longstanding limitations on diesel PM emissions, there is widespread use of diesel particulate filters (DPFs) in diesel passenger vehicles. Several types of filters have been developed, including foam and flow-through filters. However the most effective and widely used are ceramic wall-flow filters, which are the only type of filter capable of complying with the most recent emissions limits on PM. These comprise a large honeycomb-structured monolith usually made from cordierite or silicon carbide (SiC).

The main drawback of particulate filters is an increase in backpressure associated with the accumulation of PM on the filter walls. Excessive backpressure leads to degradation of engine performance and, if allowed to continue to rise, can ultimately lead to engine failure. To avoid this outcome it is therefore necessary to remove PM from the filter before the backpressure reaches a predetermined limit. This can be achieved by regeneration of the filter by oxidising PM to CO2. Filter regeneration falls into two categories: "passive" and "active" regeneration. Passive regeneration occurs when the temperature of the exhaust is sufficient for the oxidation of PM to take place during normal driving, without intervention. This can be achieved in heavy-duty diesel vehicles, such as heavy goods vehicles, using the continuously regenerating trap (CRT) invented by Johnson Matthey. However, to reach the required temperature for this method to function for a DPF in a light-duty diesel vehicle, such as a diesel-engined passenger vehicle, would require driving speeds which are not achieved under urban driving conditions. Therefore, for these situations, it is currently necessary to employ an active regeneration strategy. This involves periodically injecting additional fuel into the engine with different valve timings in order to raise the exhaust gas temperature sufficiently to allow PM oxidation to take place. This may, for example, be carried out when the vehicle is cold, in which case the engine speed at idle is also raised (known as a "jacked idle"). This is controlled by a detector, which monitors the backpressure caused by the filter, and typically takes place every 400 to 2000 km. The disadvantages to this active regeneration strategy are multiple and include a decrease in fuel economy, and reduced lifespan of the filter due to the damage that can be caused if there is an uncontrolled exotherm produced by the ignition of the soot. Passive regeneration by means of decreasing the soot oxidation temperature using a catalyst would therefore be more desirable.

An object of the present invention has therefore been to provide catalytic materials for the clean combustion of trapped soot particulate, without the need for the addition of heat or reactants to an exhaust stream from an internal combustion engine, with the aim of achieving the continuous regeneration of particulate filters for two exhaust stream aftertreatment processes: diesel compression-ignition, and gasoline direct-injection spark-ignition. It is therefore desirable that the catalytic materials should be suitable for application as a washcoat to a substrate for both diesel and gasoline particulate filters (DPF and GPF).

The present invention has been conceived against this background.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a catalytic material, a catalytic composite for removing soot from an exhaust stream of an internal combustion engine, wherein the catalytic composite comprises such a catalytic material, an exhaust gas treatment system comprising such a catalytic composite, a vehicle comprising an internal combustion engine and such an exhaust gas treatment system, a method of removing soot from an exhaust stream of an internal combustion engine, and a method of manufacturing a catalytic material.

According to an aspect of the invention, there is provided a catalytic material comprising ceria-metal oxide-alumina in a molar ratio of Ce:M:Al ions of from 75:25:100 to 25:75:100 inclusive, wherein M represents one of zirconium and zirconium at least partially substituted by a light lanthanide selected from the group consisting of lanthanum, praseodymium, neodymium and samarium.

These catalytic materials have the advantage that they can catalyse the oxidation of soot in an exhaust stream from an internal combustion engine at temperatures which are low enough not to require the exhaust stream to be actively heated to allow soot oxidation to take place. In other words, such materials can be used for passive soot oxidation in filters in a wider range of vehicles than catalytic materials of the prior art allow, thereby reducing the fuel consumption of such vehicles having an exhaust gas treatment system comprising such a catalytic material.

In some embodiments, M may represent neodymium and the catalytic material may have been heat treated at more than 500 degrees Celsius and less than 1100 degrees Celsius.

In such cases, the catalytic material may have been heat treated in a flowing atmosphere at more than 700 degrees Celsius and less than 1100 degrees Celsius.

The flowing atmosphere may be an oxidative atmosphere. The oxidative atmosphere may be dry air.

In such embodiments, the catalytic material may be impregnated with from 0.1 to 7.5 % inclusive of copper by weight of the catalytic material.

In other embodiments, M may represent lanthanum and the molar ratio of Ce:La ions may be from 55:45 to 1:3 inclusive. Preferably, the molar ratio of Ce:La ions is from 1:2 to 1:3 inclusive.

In further embodiments, M may represent both zirconium and lanthanum and the molar ratio of Zr:La ions may be from 45:55 to 55:45 inclusive.

In any of the above various different embodiments, the catalytic material may be a 5 composite metal oxide having more than one phase. The two or more phases may comprise a carbonate phase.

In still other embodiments, M may represent one or more of praseodymium and samarium. If M represents praseodymium, the catalytic material may be a composite metal oxide having 10 more than one phase. The two or more phases may comprise a phase of Pr6011.

In any of the above various different embodiments, other than where the catalytic material is already impregnated with copper, the catalytic material may be impregnated with from 0.1 to 5 % inclusive of silver by weight and from 2 to 15 % inclusive of potassium by weight of the catalytic material.

In yet further embodiments, M may represent zirconium and the molar ratio of Ce:Zr ions may be from 45:55 to 55:45 inclusive.

If so, the catalytic material may be a mixed metal oxide of Ce and Zr ions in solid solution.

The catalytic material may be impregnated with from 0.1 to 7.5 % inclusive of copper by weight of the catalytic material.

In another aspect, the invention also provides a catalytic composite for removing soot from an exhaust stream of an internal combustion engine, wherein the catalytic composite comprises a catalytic material as described herein, coated onto a substrate.

The catalytic composite may comprise at least one additional component selected from the group consisting of platinum group metals, transition metals, refractory metal oxide supports, promoters, binders and stabilizers, coated onto the substrate in the same layer as or in a different layer from the catalytic material.

In a further aspect, the invention also provides an exhaust gas treatment system for treating an exhaust stream of an internal combustion engine, wherein the system comprises an exhaust conduit in fluid communication with the internal combustion engine via an exhaust manifold, and a particulate filter comprising a catalytic composite as described herein.

According to yet another aspect of the invention, there is provided a method of removing soot from an exhaust stream of an internal combustion engine, the method comprising flowing the exhaust stream across a catalytic material as described herein or across a catalytic composite as described herein.

In a still further aspect, the present invention provides a method of manufacturing a catalytic material, wherein the method comprises co-precipitating a ceria-zirconia-alumina catalytic material using potassium carbonate (K2CO3) or caesium carbonate (Cs2CO3) as a precipitating agent.

The method may comprise washing the precipitate to remove potassium or caesium ions.

If so, the method may comprise washing the precipitate with at least one of deionised water and acetone.

The method may comprise heating the precipitate at more than 500 degrees Celsius and less than 1100 degrees Celsius. Preferably, the method comprises heating the precipitate at more than 700 degrees Celsius and less than 1100 degrees Celsius.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic cross-sectional view of an embodiment of a catalytic composite; Fig. 2 is a schematic block diagram of an embodiment of an exhaust gas treatment system for treating an exhaust stream of an internal combustion engine, wherein the exhaust gas treatment system comprises a catalytic composite such as that shown in Fig. 1; Fig. 3 is a schematic perspective view of an embodiment of a vehicle comprising an internal combustion engine and an exhaust gas treatment system such as that shown in Fig. 2; Fig. 4 is a schematic flow diagram of an embodiment of a method of manufacturing a catalytic material; Figs. 5A to 5C are graphs obtained by thermogravimetric analysis of examples of cerianeodymium oxide-alumina catalytic materials according to the invention in different molar ratios; Figs. 6A to 6C are graphs obtained by thermogravimetric analysis of examples of ceria-neodymium oxide-alumina catalytic materials according to the invention subjected during their manufacture to different heat treatment conditions; Figs. 7A to 7E are graphs obtained by thermogravimetric analysis of examples of different catalytic materials according to the invention, each impregnated with 5 % of copper by weight of the catalytic material acting as a support for the copper; Figs. 8A to 8C are graphs obtained by thermogravimetric analysis of examples of ceria-lanthana-alumina catalytic materials according to the invention in different molar ratios; Figs. 9A to 9C are graphs obtained by thermogravimetric analysis of examples of cerialanthana-zirconia-alumina catalytic materials according to the invention in different molar ratios; Figs. 10A to 10C are graphs obtained by thermogravimetric analysis of examples of ceria-zirconia -alumina catalytic materials according to the invention in different molar ratios; and Figs. 11A to 11E are graphs obtained by thermogravimetric analysis of examples of different catalytic materials according to the invention, each impregnated with 2 % of silver and 10 % of potassium by weight of the catalytic material acting as a support for the silver and potassium.

DETAILED DESCRIPTION

Fig. 1 schematically shows an embodiment of a catalytic composite 10. The catalytic composite 10 comprises a catalytic material 12 as described herein, coated onto a substrate 14 as a washcoat using one of several different techniques which are known to a person of ordinary skill in the art. The substrate 14 may, for example, comprise a ceramic such as cordierite or silicon carbide (SiC) and/or a metal alloy, such as stainless steel. The substrate 14 can have a variety of different forms which are also known to a person of ordinary skill in the art, such as a honeycomb structure having a cylindrical shape, wherein through-holes or cells are provided as exhaust gas passages in an axial direction of the cylinder, whereby an exhaust gas can come into contact with dividing walls or ribs which separate the cells from each other. Alternatively or additionally, the form of the substrate can be foam-like, and the external shape of the substrate as a whole can be an elliptic cylinder or a polygonal cylinder, for example, instead of a circular cylinder. The catalytic composite 10 may also comprises various other additional components, such as one or more platinum group metals, one or more transition metals, one or more refractory metal oxide supports, and/or one or more promoters, binders and/or stabilizers. Some of these additional components may be coated onto the substrate 14 in the same layer as the catalytic material 12, whereas other of these additional components may be coated onto the substrate 14 in a different layer from the catalytic material 12.

Fig. 2 schematically shows an embodiment of an exhaust gas treatment system 1 for treating an exhaust stream of an internal combustion engine 20. The exhaust gas treatment system 1 comprises a catalytic converter 40 and an exhaust conduit 30, which is in fluid communication with the internal combustion engine 20 via an exhaust manifold. Without limitation, the catalytic converter 40 may be any one of a diesel particulate filter (DPF), a selective catalytic reduction filter combined with a soot filter (SCRF) or a gasoline particulate filter (GPF). The catalytic converter 40 contains a catalytic composite, such as the catalytic composite 10 described above in relation to Fig. 1. The exhaust stream of the internal combustion engine 20 flows in the direction indicated by the arrows in Fig. 2 from the internal combustion engine 20 through the exhaust conduit 30 to the catalytic converter 40, where the exhaust stream flows across the catalytic composite contained therein, before venting to atmosphere.

Fig. 3 shows an embodiment of a vehicle 2 comprising an internal combustion engine and an exhaust gas treatment system, such as the exhaust gas treatment system 1 shown in Fig. 2.

Fig. 4 schematically shows an embodiment of a method 100 of manufacturing a catalytic material as described herein. The method 100 comprises co-precipitating 101 a ceriazirconia-alumina catalytic material using potassium carbonate (K2CO3) or caesium carbonate (Cs2CO3) as a precipitating agent, washing 102 the precipitate with deionised water and/or acetone to remove potassium or caesium ions, and heat treating 103 the precipitate at more than 500 degrees Celsius and less than 1100 degrees Celsius in a manner which will be described in greater detail below by way of several examples. Whereas one possible embodiment of a method of manufacturing a catalytic material is represented in Fig. 4, it is possible for some steps of the illustrated method to be omitted. For example, it may be desired to retain potassium or caesium ions on the precipitate by omitting washing 102 the precipitate and/or to omit heat treating 103 the precipitate at more than 500 degrees Celsius and less than 1100 degrees Celsius, according to requirements.

Definitions The term "cede" as used herein refers to one or more oxides of cerium in any oxidation state.

The term "zirconia" as used herein refers to one or more oxides of zirconium in any oxidation state.

The term "alumina" as used herein refers to one or more oxides of aluminium in any oxidation state.

The term "light lanthanide" as used herein refers to one or more elements with atomic number from 57 to 62 inclusive, that is to say, lanthanum, cerium, praseodymium, neodymium, promethium and samarium. The light lanthanide may be present in any oxidation state, that is to say, with valence zero or as an ion.

The term "composite metal oxide" as used herein refers to a material comprising oxides of any oxidation state of two or more metals present in more than one phase.

The term "mixed metal oxide" as used herein refers to a material comprising oxides of any oxidation state of two or more metals present in a single phase.

The term "platinum group metal" as used herein refers to one or more elements having an atomic number from 44 to 46 inclusive or from 76 to 78 inclusive, that is to say, one or more metal selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium and platinum. The platinum group metal may be present in any oxidation state, that is to say, with valence zero or as an ion. Preferably, the platinum group metal is one or more metal selected from the group consisting of rhodium, palladium and platinum.

The term "transition metal" as used herein refers to one or more elements in groups 3 to 12 inclusive and in periods 4 to 6 inclusive of the periodic table, but excluding lanthanum. The transition metal may be present in any oxidation state, that is to say, with valence zero or as an ion. Preferably, the transition metal is one or more metal having an atomic number from 26 to 29 inclusive, 47 or 79, that is to say, one or more metal selected from the group consisting of iron, cobalt, nickel, copper, silver and gold. More preferably, the transition metal is one or more metal selected from the group consisting of copper, silver and gold.

The term "support" as used herein refers to one or more materials which receive one or more catalytic materials, promoters, binders and/or stabilizers through a process such as precipitation, association, dispersion, or impregnation. Examples of supports include, but are not limited to, refractory metal oxides.

The term "refractory metal oxide" as used herein refers to one or more materials, such as oxides of one metal (for example, ceria, zirconia, alumina, Mania, silica, magnesia and neodymia), oxides of more than one metal (for example, magnesium aluminate (MgA1204), barium aluminate (BaA112O19) and lanthanum aluminate (LaAIO3)), doped oxides of one metal (for example, Ba-doped alumina, Ce-doped alumina and La-doped alumina), doped oxides of more than one metal (for example, Y-, La-, Pr-and Nd-doped ceria-zirconia), and other materials known for use as supports.

The term "washcoat" as used herein refers to a thin, adhering coating of a catalytic or other material applied to a substrate, such as to a honeycomb flow-through monolith substrate or to a filter substrate, which is sufficiently porous to permit the passage therethrough of an exhaust gas stream.

The term "binder" as used herein refers to one or more materials for binding one or more catalytic materials to a support, as are known for such use.

The term "promoter" as used herein refers to one or more materials which are not in themselves catalytic materials, but which when mixed with a catalytic material, increases the efficiency of operation of the catalytic material, as are known for such use.

The term "stabilizer" as used herein refers to one or more materials designed to prevent degradation of a catalytic material over time, as are known for such use.

EXAMPLES

Example 1

Several catalytic materials were prepared by a co-precipitation method using a MetrohmT" 902 TitrandoTM system for the addition of a nitrate precursor solution and carbonate precipitating agent. 0.25M solutions of ammonium cerium nitrate, zirconyl oxynitrate hydrate, lanthanum nitrate hexahydrate, praseodymium nitrate hexahydrate, neodymium nitrate hexahydrate and aluminium nitrate nonahydrate were used as the nitrate precursor solutions. For each catalyst preparation, these solutions were mixed into a single 200m1 solution, according to the desired composition of metal oxides and their molar ratios, e.g. a catalytic material consisting of Ce:Zr:Al in a molar ratio of 7:3:10 would require a precursor solution containing 70m1, 30m1 and 100m1 of 0.25M solutions of ammonium cerium nitrate, zirconyl oxynitrate hydrate and aluminium nitrate nonahydrate, respectively. 1M solutions of sodium/potassium/caesium carbonate were used as the precipitating agents.

20m1 of the nitrate solution was added to a precipitation vessel and heated to 80°C under constant mechanical stirring. The precipitating agent was then added until pH 9 was reached. The nitrate solution was then added at a rate of 3 ml min-1 for 50 minutes, while the precipitating agent was added at an appropriate rate to maintain a pH of 9. Once the addition of the nitrate solution was completed, the suspension was allowed to age at 80°C for 1 hour. The resulting precipitate was filtered and washed with various volumes of warm deionised water, as specified below. This precipitate was then dried at 110°C for 16 hours. Finally, the dried solid was heat treated under various conditions described in further detail below.

Example la: Preparation of Ce-Zr-Al-Ox catalytic materials, varying precipitating agent and washing conditions Ceria-zirconia-alumina catalytic materials were prepared in a Ce:Zr:Al molar ratio of 7:3:10 by the method described above. Each catalyst was heat treated under static air at 500°C at a heating rate of 10°C min-', dwelling at the final temperature for 5 hours. Table 1A below summarises the catalytic materials prepared and indicates which conditions were altered between each preparation.

Table 1A: Catalytic materials prepared by automated co-precipitation method Catalytic material Precipitating Washing (vol/litres) Short name agent Cep 35Z1.015A10 501 75 Na2CO3 (1 M) 0.5 Na-CZA0.5L Ce0.35Zr0.15A10.501.75 Na2CO3 (1M) 1.0 Na-CZA1.0L Ce0.35Zr0.15A10.501.75 Na2CO3 (1 M) 1.5 Na-CZA1.5L Ce0.35Zr0.15A10.501.75 Na2CO3 (1 M) 2.0 Na-CZA2.0L Ce0 35Zr0.15A10.501.75 K2CO3 (1 M) 0.5 K-CZA0.5L Ce0.35Zr0.15A10.501.75 K2CO3 (1 M) 2.0 K-CZA2.0L Ce Zr Al 0 Cs2CO3 (1M) 0.5 Cs-CZA0.5L _o.so 0,15--0.5 -1/5 Example 1 b: Preparation of Ce-M-Al-0, catalytic materials Ceria-zirconia-alumina, ceria-lanthana-zirconia-alumina, ceria-lanthana-alumina, ceriapraseodymium oxide-alumina and ceria-neodymium oxide-alumina catalytic materials were prepared by the method described above. The precipitating agent used in each case was 1M sodium carbonate, and washing also remained constant at 2.0L warm deionised water during filtration. Table 1B summarises the catalytic materials prepared by the above method, and indicates which conditions were altered between each preparation.

Table 1 B: Ce-M-Al-0, catalytic materials prepared by automated co-precipitation method Molar ratio Heat treatment Catalytic material Ce:M:Al conditions Short name Cea35Zr0.15A110.501.75 Zr 7:3:10 500°C, Static air CZA 7:3:10 Ce0.25Zr0.25A10.50135 Zr 5:5:10 500°C, Static air CZA 5:5:10 Geo.) ar0.35Alo.501.75 Zr 3:7:10 5000C Static air CZA 3:7:10 Ceo.35Lao.o75Zro.075A10.501.71 La,Zr 7:1.5:1.5:10 500°C, Static air CLZA 7:3:10 Ce0 25Lao losZro 125A10 501 69 La,Zr 5:2.5:2.5:10 4 500°C, Static air CLZA 5:5:10 Ce0.15La0.175Zr0.175A10.501.66 La,Zr 3:3.5:3.5:10 500°C, Static air CLZA 3:7:10 CA La AI 0 -035-0 15-.0.5 1,68 Ce0.251-a025A10.501.63 Ce0151-a035A10.501.58 La 7:3:10 5000C, Static air CLA 7:3:10 La 5:5:10 500°C, Static air CLA 5:5:10 La 3:7:10 500°CI Static air CLA 3:7:10 ceos5Pro.15A10.501.72 Ce0 25Pr0.25A10.501 1 ceo15Pro.35m0.501.69 Pr 7:3:10 500°C, Static air CPA 7:3:10 Pr 5:5:10 500°C, Static air CPA 5:5:10 Pr 3:7:10 5000C, Static air CPA 3:7:10 7:3:10 500°C, Static air CNA 7:3:10 5:5:10 500°C, Static air CNA 5:5:10 3:7:10 500°C, Static air CNA 3:7:10 Ce035NC10,15A10,501 68 Nd Ce0.25Ndo.25A10501 63 Nd Ce0.15Nd0.35A10.501.58 Nd CNA 750°C Static Ce035Nd0.15A10 501 68 Ce0.35Nd0.15A1o.50168 Ce0.35NcloAsAlo sal 68 Nd 7:3:10 7500C, Static air air CNA 7500C Flowing air CNA 750°C H2/Ar 750°C Flowing air 750°C, Flowing H2 Nd 7:3:10

Example 2

The three CNA catalysts prepared according to Example 1 above with the short names given in Table 1B above as CNA 7:3:10, CNA 5:5:10 and CNA 3:7:10 were each analysed by x-ray diffraction. Whereas the x-ray diffractograms of the CNA 7:3:10 catalyst contained only the cubic fluorite reflections of ceria, indicating that a mixed metal oxide of Ce and Nd in solid solution had been formed, the x-ray diffractograms of the CNA 5:5:10 and CNA 3:7:10 catalytic materials were found to contain peaks attributable to the presence of neodymium dioxycarbonate, Nd2O2CO3, as well. This demonstrated that in these latter cases, a composite metal oxide having more than one phase and comprising a carbonate phase had been formed instead. The presence of this extra phase suggested that the heat treatment conditions were not sufficient to fully decompose neodymium carbonate, Nd2(CO3)3, formed during the co-precipitation to neodymium oxide, Nd202.

The same three CNA catalysts were each tested for soot oxidation by thermogravimetric analysis (hereinafter referred to as TGA) on a SetaramTM LabsysTm TG-DTA/DSC instrument. A catalyst:soot ratio of 10:3 by mass was used in each case. 20mg of catalyst and 6mg of soot were mixed and placed in a crucible. In order to test the thermal stability of the catalytic materials, the catalysts were retrieved and mixed with fresh soot and the test repeated. In this case, the mass of soot used was dependent on the mass of catalyst that could be retrieved, abiding by the 10:3 ratio. Samples were heated from 30°C to 900 °C at 5°C min-1, under an atmosphere of flowing air. Major loss of mass in the sample during a test was attributed to oxidation of soot. SetsoftTM software was used to collect TGA data.

The derivative of the TGA plot (hereinafter referred to as dTG) was used to determine the onset temperature (To), extrapolated onset temperature (Teo), peak temperature (Tp) and final temperature (Tr) of soot oxidation for each test.

Each of the samples of the catalytic materials was re-tested in order to determine their thermal stability. It was observed that each of these CNA catalysts was significantly more active on its second test run than it had been on its first. This can be seen from the dTG plots which are reproduced in Figs. 5A, 5B and 5C and which respectively show the derivative of the TGA plot for CNA 7:3:10, CNA 5:5:10 and CNA 3:7:10. In each of Figs. 5A, 5B and 5C, the solid line indicates the first test run, the dashed line indicates the second test run, and the dotted line indicates the third test run, with each of the graphs offset by 1%min-1 for ease of comparison. The soot oxidation data extracted from these dTG plots is reproduced in Table 2 below.

Table 2: Soot oxidation temperatures of soot mixed with CNA catalysts on their first, second and third use Catalyst 1st To (2C) 2nd 3rd run 1 st Tea (2C) 2nd 3rd 1st Tp (2C) 2nd 3rd pi T, (2C) 2nd 3rd run run run run run run run run run run run Soot (no catalyst) 7:3:10 5:5:10 3:7:10 411 465 398 464 535 441 547 622 528 617 651 579 419 383 356 475 451 434 550 525 515 633 581 590 418 389 383 467 439 4451 551 514 515 6101 575 562 383 444 519 567 Table 2 shows that the soot oxidation temperature decreased at every temperature marker for each of the catalysts between the first and second test runs. Remarkably, the peak soot oxidation temperature decreased by over 20°C, 35°C and 30°C for CNA 7:3:10, CNA 5:5:10 and CNA 3:7:10, respectively.

The catalysts were subjected to a third round of testing in order to determine whether their improved activity could be sustained, the results of which are also provided in Figs. 5A, 5B and 5C and in Table 2 above. The third test runs confirm the thermal stability of the improved CNA catalysts, with the peak soot oxidation temperatures remaining at the lower temperatures observed on the second test runs. The results suggest a significant structural change has taken place to the catalysts after subjection to high temperatures, resulting in a considerable improvement in catalytic activity, which is sustained upon repeated use. The structural change in question may be the decomposition of the Nd2O2CO3 phase detected in the x-ray diffraction analysis.

Example 3

The three CNA catalysts prepared according to Example 1 above with the short names given in Table 1B above as CNA 750°C Static air, CNA 750°C Flowing air and CNA 750°C H2/Ar were heat treated under three different atmospheres. Since the three CNA catalysts of Example 2 above had all been heat treated under static air, this atmosphere was chosen in order to establish whether the higher temperature alone was sufficient to improve the catalyst. Flowing air was the atmosphere used under the soot oxidation tests of the TGA, therefore this atmosphere was used in order to replicate those conditions. An atmosphere of 10%H2/90%Ar was used in order to replicate the reducing effect of the soot on the catalysts during the TGA testing.

The three CNA catalysts of Example 3 were each tested for soot oxidation by thermogravimetric analysis in the same manner as the three CNA catalysts of Example 2. The derivative plots are reproduced in Figs. 6A, 6B, and 6C, which respectively show the derivative of the TGA plot for CNA 750°C Static air, CNA 750°C Flowing air and CNA 750°C H2/Ar. In each of Figs. 6A, 6B and 6C, the solid line indicates the first test run and the dashed line indicates the second test run, with each of the graphs offset by 1%min-1 for ease of comparison. The soot oxidation data extracted from these dTG plots is reproduced in Table 3 below.

Testing revealed that the heat treatment conditions were highly influential in the soot oxidation activity of the CNA catalyst. As indicated in Table 3 below, the increase in heat treatment temperature under static air from 500°C to 750°C resulted in a decrease in activity, with the peak soot oxidation temperature rising to almost 560°C in the case of the latter. Interestingly, it was also observed that the activity of both these catalysts decreased after heat treatment, with the untreated material able to achieve peak soot oxidation at a considerably lower temperature than both. The catalysts heat treated under flowing air and an atmosphere of H2/Ar were considerably more active than the aforementioned "static air" catalysts, with the former being the most active of the two. The soot oxidation temperatures of these catalysts were similar to the rerun tests on the CNA catalysts of Example 2.

Table 3: Soot oxidation temperatures of soot mixed with CNA catalysts on their first and S second use Catalyst To (2C) Teo (2C) To (2C) Ti (2C) 15' run 2nd run lst run 2nd run 15' run 2nd run 151 run 2nd run Soot (no catalyst) 465 535 622 651 No heat treatment 428 455 523 592 5009C Static air 405 383 464 451 547 525 617 581 7509C Static air 457 411 472 454 559 533 623 578 7502C Flowing air 369 364 419 433 512 516 587 575 7502C H2/Ar 378 396 434 436 523 523 584 583 The heat treated catalysts were subjected to a second round of soot oxidation testing to determine their thermal durability, the results of which are also provided in Figs. 6A, 6B and 6C and in Table 3 above. As observed with the CNA catalysts of Example 2, "CNA 750°C Static" performed much better on its second run, decreasing the soot oxidation temperature at each marker by at least 25°C. The other two catalysts heat treated at 750°C were both able to maintain the high activity displayed during their first round of testing.

This suggested that a flowing atmosphere, either during heat treatment or soot oxidation testing, was essential to the improvement in activity observed. The higher activity of "CNA 7502C Flowing Air" suggested that an oxidative flowing atmosphere was more beneficial than a reductive atmosphere.

Example 4

The five catalytic materials prepared according to Example 1 above with the short names given in Table 1B above as CZA 7:3:10, CLA 7:3:10, CLZA 7:3:10, CPA 7:3:10 and CNA 7:3:10 were each impregnated with 5 % of copper by weight of the catalytic material acting as a support for the copper, using a wet impregnation method as follows. A copper nitrate solution (5% = 0.274g of copper for 1.5g of catalyst in each case) was impregnated onto the support by heating to 802C under constant magnetic stirring, until a viscous suspension remained. This suspension was then dried at 110°C for 16 hours, and heated to 500°C at a rate of 10°C min 1, dwelling at the final temperature for 5 hours. The resulting five materials are respectively referred to hereinafter as 5%Cu/CZA, 5%Cu/CLA, 5%Cu/CLZA, 5%Cu/CPA and 5%Cu/CNA. These catalysts are referred to collectively as 5%Cu/CMA.

The 5%Cu/CMA catalysts were each tested for soot oxidation by thermogravimetric analysis in the same manner as the three CNA catalysts of Example 2. The derivative plots are reproduced in Figs. 7A to 7E, which respectively show the derivative of the TGA plot for 5%Cu/CZA, 5%Cu/CLA, 5%Cu/CLZA, 5%Cu/CPA and 5%Cu/CNA. In each of Figs. 7A to 7E, the solid line indicates the first test run and the dashed line indicates the second test run, with each of the graphs offset by 1%min-1 for ease of comparison. The soot oxidation data extracted from these dTG plots is reproduced in Table 4 below.

As may be seen from the graphs for the first test runs in Figs. 7A to 7E, the soot oxidation tests resulted in the appearance of a lower temperature oxidation between 400°C and 500°C prior to the main oxidation curve. This was attributed to the reduction of CuO as determined by temperature-programmed reduction (hereinafter referred to as TPR), which provided oxygen able to be utilised for the oxidation of the hydrocarbons present on the soot particles. Once this oxygen supply was depleted, the remaining soot was oxidised by the support. The peak temperatures for the lower-temperature minor oxidation curve are shown in Table 4, and which appear at a similar temperature to the reduction of CuO, reaffirming this hypothesis. This also greatly decreased the onset temperature of soot oxidation compared to the bare supports in each case. The peak temperature of the main soot oxidation curve was also lowered compared to the supports. This was attributed to the exotherm caused by the initial soot oxidation.

Table 4: Soot oxidation temperatures of soot mixed with 5%Cu/CMA on their first and second use Catalyst To (gC) Minor Tp (2C) Major Tp (2C) T, (gC) 15' run 2nd run 15' run 2nd run V run 2nd run 151 run 2nd run Soot (no catalyst) 465 622 651 5%Cu/CZA 359 372 422 409 521 538 583 591 5%Cu/CLA 353 413 428 498 533 592 579 5%Cu/CLZA 364 411 419 525 535 614 597 5%Cu/CPA 332 r 423 r 417 520 548 r 595 r 596 5%Cu/CNA 341 409 420 523 513 615 568 As may be seen from Fig. 7A, the 5%Cu/CZA provided evidence that it was able to partially oxidise soot particulates at a low temperature on repeated use and after exposure to high temperatures. Despite oxidation of the remaining soot taking place at the same temperature as with the bare support, this still represented an improvement to the overall catalyst.

However unlike 5%Cu/CZA, the remaining 5%Cu/CMA catalysts were unable to produce the lower temperature oxidation on repeated use, as seen in the dTG plots of the second test runs in Figs. 7B to 7E. With the exception of 5%Cu/CNA, this resulted in a regression in overall catalytic activity, with the peak soot oxidation temperature returning to a similar temperature as observed with the bare support for each of 5%Cu/CLA, 5%Cu/CLZA and 5%Cu/CPA. It was not possible to determine to what extent, if any, the presence of copper was a factor in maintaining a low soot oxidation temperature with 5%Cu/CNA. However, given the evidence of the deactivation of copper on 5%Cu/CLA, 5%Cu/CLZA and 5%Cu/CPA, it was deemed more likely that this was due to the improvement to the catalytic activity of the CNA support by its heat treatment in the first test run, as described in Example 2 above.

Example 5

The three CLA catalysts prepared according to Example 1 above with the short names given in Table 1B above as CLA 7:3:10, CLA 5:5:10 and CLA 3:7:10 were each tested for soot oxidation by thermogravimetric analysis in the same manner as the three CNA catalysts of Example 2. The derivative plots are reproduced in Figs. 8A, 8B, and 8C, which respectively show the derivative of the TGA plot for CLA 7:3:10, CLA 5:5:10 and CLA 3:7:10. In each of Figs. 8A, 8B, and 8C, the solid line indicates the first test run and the dashed line indicates the second test run, with each of the graphs offset by 1%min-1 for ease of comparison. The soot oxidation data extracted from these dTG plots is reproduced in Table 5 below.

Table 5: Soot oxidation temperatures of soot mixed with CLA catalysts on their first and second use Catalyst To (gC) T" (2C) To (9C) T, (9C) Soot (no catalyst) 1st run 2nd run 1s1 run 2nd run 1st run 2nd run 1s1 run 2nd run 465 535 622 651 7:3:10 415 380 448 430 541 539 615 598 5:5:10 396 391 444 437 533 528 604 579 3:7:10 391 389 426 449 520 520 591 583 It was observed that an increase in the lanthanum content of these catalysts resulted in an increase in soot oxidation activity. As can be seen from Table 5, the onset, peak and final temperatures all followed this trend, with CLA 3:7:10 decreasing the peak soot oxidation temperature 20°C further than CLA 7:3:10.

The thermal stability of these catalysts was tested by rerunning the soot oxidation tests on the same samples. As the dashed lines in each of Figs. 8A, 8B and 8C and the data extracted from them in Table 5 show, these catalysts were able to maintain their activity after subjection to high temperatures, confirming the thermal stability of these catalysts.

X-ray diffractograms of the three CLA catalysts of Example 5 indicated the presence of two distinct crystalline phases, the intensities of which varied corresponding to the cerium/lanthanum ratio. It was observed that as the cerium content decreased in favour of lanthanum, the cubic fluorite reflections of ceria diminished in intensity. The second phase was identified as lanthanum dioxycarbonate, La202CO3* It was observed that the x-ray reflections due to this second phase were sharp, indicating a highly crystalline phase, and increased in intensity from CLA 7:3:10 through to CLA 3:7:10, corresponding to the increase in the lanthanum content. The presence of this second phase suggested that lanthanum carbonate formed during co-precipitation was not fully decomposed to lanthanum oxide during the heat treatment process. This indicated that the catalysts with higher lanthanum concentrations did not contain a homogenous mixed metal oxide crystalline phase, but was a composite metal oxide having more than one phase instead.

Example 6

The three CLZA catalysts prepared according to Example 1 above with the short names given in Table 1B above as CLZA 7:3:10, CLZA 5:5:10 and CLZA 3:7:10 were each tested for soot oxidation by thermogravimetric analysis in the same manner as the three CNA catalysts of Example 2. The derivative plots are reproduced in Figs. 9A, 9B, and 9C, which respectively show the derivative of the TGA plot for CLZA 7:3:10, CLZA 5:5:10 and CLZA 3:7:10. In each of Figs. 9A, 9B, and 9C, the solid line indicates the first test run and the dashed line indicates the second test run, with each of the graphs offset by 1%min-1 for ease of comparison. The soot oxidation data extracted from these dTG plots is reproduced in

Table 6 below.

Table 6: Soot oxidation temperatures of soot mixed with CLZA catalysts on their first and second use Catalyst T. (2C) Tee (2C) T. (2C) Ti (2C) 1st run 2nd run 15' run 2nd run 15' run 2nd run 15' run 2nd run Soot (no 465 535 622 651 catalyst) 7:3:10 399 391 439 449 531 534 607 603 5:5:10 400 416 440 467 528 539 600 579 3:7:10 393 377 449 438 528 527 603 585 The dTG plots show that the change in Ce:(Zr,La) ratio has little effect on the soot oxidation activity of the catalysts. The data presented in Table 6 shows that peak soot oxidation on first use takes place at similar temperatures for each of the catalysts, at around 530°C. The onset and extrapolated onset temperatures were also comparable for each of the catalysts.

Upon second use, it was found that CLZA 7:3:10 and CLZA 3:7:10 both showed comparable soot oxidation activity to their first use, showing a decrease in onset temperatures and maintaining the peak soot oxidation temperature. However CLZA 5:5:10 demonstrated some loss of activity on second use. The onset, extrapolated onset and peak temperatures all increased by at least 10°C compared to the first use with this catalyst.

X-ray diffractograms of the three CLZA catalysts of Example 6 indicated the presence of only a single mixed metal oxide phase in the cases of CLZA 7:3:10 and CLZA 5:5:10. However, additional x-ray reflections were observed in the case of CLZA 3:7:10, which were matched with a reference for lanthanum oxide carbonate (La2O2CO3). This indicated that the lanthanum was present in a separate phase from ceria at higher lanthanum concentrations.

Example 7

The three CZA catalysts prepared according to Example 1 above with the short names given in Table 1B above as CZA 7:3:10, CZA 5:5:10 and CZA 3:7:10 were each tested for soot oxidation by thermogravimetric analysis in the same manner as the three CNA catalysts of Example 2. The derivative plots are reproduced in Figs. 10A, 10B, and 10C, which respectively show the derivative of the TGA plot for CZA 7:3:10, CZA 5:5:10 and CZA 3:7:10. In each of Figs. 10A, 10B, and 10C, the solid line indicates the first test run and the dashed line indicates the second test run, with each of the graphs offset by 1%min-1 for ease of comparison. The soot oxidation data extracted from these dTG plots is reproduced in Table 7 below.

Table 7: Soot oxidation temperatures of soot mixed with CZA catalysts on their first and second use Catalyst To (2C) Tee (2C) Tp (2C) Ti (2C) 15' run 2nd run 15' run 2nd run 15' run 2nd run P' run 2nd run Soot (no 465 535 622 651 catalyst) 7:3:10 410 389 461 436 542 538 605 597 5:5:10 396 400 452 456 532 532 607 597 3:7:10 415 408 465 474 542 543 601 594 The greatest decrease in soot oxidation temperature was observed in the case of CZA 5:5:10 which, as shown in Table 7, lowered the onset and peak temperatures by around 10°C further than CZA 7:3:10 and 3:7:10. CZA 5:5:10 therefore showed similar activity to all three of the CLZA catalysts of Example 6. This improvement in catalytic activity was attributed to the findings of TPR, which established that Ce4 ions on the surface of CZA 5:5:10 were able to reduce at lower temperatures and higher intensity than the other CZA catalysts.

The tests were repeated with fresh soot in order to determine the thermal durability of the catalysts on repeated use. Each of the catalysts showed good thermal stability, managing to maintain similar soot oxidation temperatures on their second test run as in their first, with the Teo of CZA 3:7:10 showing the only meaningful increase. This provided evidence that the higher activity of CZA 5:5:10 compared to the other catalysts could be sustained over multiple usage.

X-ray diffractograms of the three CZA catalysts revealed no evidence of any additional phases, indicating homogeneity of the ceria-zirconia structure in each case, and confirming that the catalytic material is a mixed metal oxide of Ce and Zr ions in solid solution in each case.

Example 8

The five catalytic materials prepared according to Example 1 above with the short names given in Table 1B above as CZA 7:3:10, CLA 7:3:10, CLZA 7:3:10, CPA 7:3:10 and CNA 7:3:10 were each impregnated with 2 % of silver and 10 % of potassium by weight of the catalytic material acting as a support for the silver and potassium, using a wet impregnation method as follows. A silver nitrate solution and potassium carbonate solution (2% = 0.047g and 10% = 0.265g respectively for 1.5g of the catalyst in each case) were impregnated onto the support by heating to 80°C under constant magnetic stirring, until a viscous suspension remained. This suspension was then dried at 110°C for 16 hours, and heated to 500°C at a rate of 10°C min-1, dwelling at the final temperature for 5 hours. The resulting five materials are respectively referred to hereinafter as 2%Ag,10%K/CZA, 2%Ag,10%K/CLA, 2%Ag,10%K/CLZA, 2%Ag,10%K/CPA and 2%Ag,10%K/CNA. These catalytic materials are referred to collectively as 2%Ag,10%K/CMA.

The 2%Ag,10%K/CMA catalysts were each tested for soot oxidation by thermogravimetric analysis in the same manner as the three CNA catalysts of Example 2. The derivative plots are reproduced in Figs. 11A to 11E, which respectively show the derivative of the TGA plot for 2%Ag,10%K/CZA, 2%Ag,10%K/CLA, 2%Ag,10%K/CLZA, 2%Ag,10%K/CPA and 2%Ag,10%K/CNA. In each of Figs. 11A to 11E, the solid line indicates the first test run and the dashed line indicates the second test run, with each of the graphs offset by 1%min-1 for ease of comparison. The soot oxidation data extracted from these dTG plots is reproduced

in Table 8 below.

Table 8 Soot oxidation temperatures of soot mixed with 2%Ag,10%K/CMA on their first and second use Catalyst To (2C) Too (2C) To (2C) Ti (2C) 15' run 2nd run 15' run 2nd run 15' run 2nd run 15' run 2nd run Soot (no catalyst) 465 535 622 651 2%Ag,10%K/CZA 363 376 388 442 450 535 564 589 2%Ag,10%1C/CLA 387 357 395 408 522 521 574 576 2%Ag,10%K/CLZA 388 370 396 409 514 508 586 575 2%Ag 10%K/CPA 396 402 410 435 527 522 603 579 2%Ag,10%1C/CNA 387 386 397 428 523 503 602 572 The soot oxidation testing showed that the presence of the supported metals enhanced the catalytic activity compared to the bare CMA supports. As may be seen from the solid lines in each of Figs. 11A to 11E, the dTG plots for the first run of testing all the samples of Example 8 showed a shoulder to the main soot oxidation curve at lower temperature, indicating the presence of a distinct second soot oxidation process attributed to the combustion of hydrocarbons. This was most pronounced in the case of 2)0Ag,10%K/CZA. However in the cases of 2%Ag,10%K with CLA, CLZA and CNA, the lower-temperature curve was not the dominant process, which meant the peak soot oxidation temperature occurred during the higher temperature process, hence the considerable difference seen in Table 8 in this regard between 2%Ag,10%K/CZA and the other catalysts. The shoulder peak observed in the case of 2%Ag,10%K/CPA was much less prominent even than the 2%Ag,10%K with CLA, CLZA and CNA. This is demonstrated by the onset and extrapolated onset temperatures for the first run of testing in Table 8, which were lowest in the case of 2%Ag,10%K/CZA and highest with 2%Ag,10%K/CPA, while the other three catalysts all displayed comparable temperatures in between.

The tests were repeated with fresh soot in order to determine the thermal stability of the catalysts on repeated use. As may be seen from the dashed lines in each of Figs. 11A to 11E, the shoulder to the soot oxidation curve observed during the first run of testing did not appear during the second run of any of the catalysts. This suggested the combustion of hydrocarbons at the lower-temperature did not occur on repeated use of the catalysts, and resulted in an increase in the extrapolated onset temperature in each case. In the case of 2%Ag,10%K/CZA, this resulted in significant increases in the onset, peak and final temperatures of soot oxidation. However, no such increases were observed during the second run of testing the remaining catalysts, which suggests that the impregnated metals retained their activity on these supports after subjection to high temperatures.

In the case of 2)0Ag,10%K/CNA a significant improvement was observed in the peak and final soot oxidation temperatures on the second run compared to the first run. This was attributed to the improvement to the catalytic activity of the support as described above in Example 2. However it is important to note that the activity of the used impregnated catalyst was greater than the activity of the used bare support, which suggests that the impregnated metals contribute to a further increase in activity after exposure to high temperatures.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features, whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings, whether or not particular emphasis has been placed thereon.

Claims (27)

1. CLAIMS1 A catalytic material comprising: ceria-metal oxide-alumina in a molar ratio of Ce:M:Al ions of from 75:25:100 to 25:75:100 inclusive, wherein M represents one of zirconium and zirconium at least partially substituted by a light lanthanide selected from the group consisting of lanthanum, praseodymium, neodymium and samarium.
2. 2. A catalytic material according to claim 1, wherein M represents neodymium and the catalytic material has been heat treated at more than 500 degrees Celsius and less than 1100 degrees Celsius.
3. 3. A catalytic material according to claim 2, wherein the catalytic material has been heat treated in a flowing atmosphere at more than 700 degrees Celsius and less than 1100 degrees Celsius.
4. 4. A catalytic material according to claim 3, wherein the flowing atmosphere is an oxidative atmosphere.
5. 5. A catalytic material according to claim 4, wherein the oxidative atmosphere is dry air.
6. 6. A catalytic material according to any one of claims 2 to 5, impregnated with from 0.1 to 7.5 % inclusive of copper by weight of the catalytic material.
7. 7. A catalytic material according to claim 1, wherein M represents lanthanum and the molar ratio of Ce:La ions is from 55:45 to 1:3 inclusive.
8. 8. A catalytic material according to claim 7, wherein the molar ratio of Ce:La ions is from 1:2 to 1:3 inclusive.
9. 9. A catalytic material according to claim 1, wherein M represents zirconium and lanthanum and the molar ratio of Zr:La ions is from 45:55 to 55:45 inclusive.
10. 10. A catalytic material according to any one of claims 2 to 9, wherein the catalytic material is a composite metal oxide having more than one phase.
11. 11. A catalytic material according to claim 10, comprising a carbonate phase.
12. 12. A catalytic material according to claim 1, wherein M represents one or more of praseodymium and samarium.
13. 13. A catalytic material according to claim 12, wherein M represents praseodymium and the catalytic material is a composite metal oxide having more than one phase.
14. 14. A catalytic material according to claim 13, comprising a phase of Pr6011.
15. 15. A catalytic material according to any one of claims 2 to 5 and 7 to 14, impregnated with from 0.1 to 5 % inclusive of silver by weight and from 2 to 15 % inclusive of potassium by weight of the catalytic material.
16. 16. A catalytic material according to claim 1, wherein M represents zirconium and the molar ratio of Ce:Zr ions is from 45:55 to 55:45 inclusive.
17. 17. A catalytic material according to claim 16, wherein the catalytic material is a mixed metal oxide of Ce and Zr ions in solid solution.
18. 18. A catalytic material according to claim 16 or claim 17, impregnated with from 0.1 to 7.5 % inclusive of copper by weight of the catalytic material.
19. 19. A catalytic composite for removing soot from an exhaust stream of an internal combustion engine, the catalytic composite comprising a catalytic material according to any one of claims 1 to 18 coated onto a substrate.
20. 20. A catalytic composite according to claim 19, comprising at least one additional component selected from the group consisting of platinum group metals, transition metals, refractory metal oxide supports, promoters, binders and stabilizers, coated onto the substrate in the same layer as or in a different layer from the catalytic material.
21. 21. An exhaust gas treatment system for treating an exhaust stream of an internal combustion engine, the system comprising: an exhaust conduit in fluid communication with the internal combustion engine via an exhaust manifold; and a particulate filter comprising a catalytic composite according to claim 19 or claim 20.
22. 22. A vehicle comprising an internal combustion engine and an exhaust gas treatment system according to claim 21.
23. 23. A method of removing soot from an exhaust stream of an internal combustion engine, the method comprising flowing the exhaust stream across a catalytic material according to any one of claims 1 to 17 or across a catalytic composite according to claim 19 or claim 20.
24. 24. A method of manufacturing a catalytic material, the method comprising: co-precipitating a ceria-zirconia-alumina catalytic material using potassium carbonate (K2003) or caesium carbonate (Cs2CO3) as a precipitating agent.
25. 25. A method of manufacturing a catalytic material according to claim 24, comprising washing the precipitate to remove potassium or caesium ions.
26. 26. A method of manufacturing a catalytic material according to claim 25, comprising washing the precipitate with at least one of deionised water and acetone.
27. 27. A method of manufacturing a catalytic material according to any one of claims 24 to 26, comprising heating the precipitate at more than 500 degrees Celsius and less than 1100 degrees Celsius.