Patent Application
20230372902
The invention relates to a catalyst composition, a catalyst article, an emission treatment system, a vehicle, a method of treating exhaust gas, as well as to a solid solution mixed oxide, a method of manufacturing the solid solution mixed oxide, a method of manufacturing the catalyst composition and a use of the catalyst composition or catalyst article.
A three-way catalyst (TWC) allows simultaneous conversions (˜98%) of CO, HCs and NOx from gasoline engine exhaust to innocuous compounds at stoichiometric air-to-fuel ratio. Specifically, the oxidation of CO and HCs to CO2 and steam (H2O) is mainly catalyzed by Pd, while the reduction of NOx to N2 is mainly catalyzed by Rh. Modern TWCs use supported platinum group metal (hereinafter “PGM”) catalysts (Pd, Rh, Pt, etc.) deposited on a single, double or multilayer support, with the support material consisting of metal oxides with high specific surface area, primarily stabilized alumina and ceria-containing oxygen storage materials. The supported catalyst is washcoated on a ceramic monolithic substrate.
Cerium oxide (CexOy), well known for its high oxygen storage capacity (OSC) due to the function of the Ce4+/Ce3+ redox pair, plays an important role in TWC performance. Besides providing high surface area for PGM metal dispersion, CexOy can also assist the feedback control of stoichiometric condition by uptaking or donating oxygen during fuel lean/rich perturbations. Further incorporation of zirconium oxide (ZrO2) into CexOy fluorite structure (denoted as CZO, i.e. a ceria-zirconia mixed oxide) improves the thermal stability of CexOy, and enhances the mobility of lattice oxygen through the formation of oxygen vacancies.
It is known that doping mixed oxides, such as ceria-zirconia mixed oxides, with tin may improve the OSC properties of the mixed oxides. For example, US 2021/0299647 A1 relates to doping ceria-zirconia mixed oxides with tin oxide. However, doping the mixed oxides with tin typically results in a crystal structure that may not be particularly stable to phase separation of the mixed oxide(s), particularly at higher temperatures.
There remains a need to provide tin-doped mixed oxides for use in TWC applications that provide for improved OSC properties yet remain more stable, particularly at the high temperatures experienced by TWCs in use, for example to treat the emissions from a gasoline engine.
One aspect of the present disclosure is directed to a catalyst composition comprising a mixed oxide support material and a platinum group metal supported on the mixed oxide support material, the mixed oxide support material comprising a solid solution mixed oxide having the formula CewZrxSnyMzOa, wherein: 0.05≤w≤0.90; 0.05≤x≤0.90; 0.001≤y≤0.25; 0.001≤z≤0.60; w+x+y+z=1.00; 1.0≤a≤2.0; and M is an element selected from one or more of sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, scandium, yttrium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, aluminium, gallium, thallium, silicon, germanium, lead, bismuth, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, erbium, lutetium, dysprosium, holmium, thulium and ytterbium.
Another aspect of the present disclosure is directed to a catalyst article comprising a substrate and the catalyst composition of the above aspect, wherein the catalyst composition is disposed on the substrate.
Another aspect of the present disclosure is directed to an emission treatment system comprising the catalyst article of the above aspect.
Another aspect of the present disclosure is directed to a vehicle comprising the emission treatment system of the above aspect.
Another aspect of the present disclosure is directed to a method of treating an exhaust gas, the method comprising: providing the catalyst article of the above aspect; and contacting the catalyst article with an exhaust gas.
Another aspect of the present disclosure is directed to a solid solution mixed oxide having the formula CewZrxSnyMzOa, wherein: 0.05≤w≤0.90; 0.05≤x≤0.90; 0.001≤y≤0.25; 0.001≤z≤0.60; w+x+y+z=1.00; 1.0≤a≤2.0; and M is an element selected from one or more of sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, scandium, yttrium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, aluminium, gallium, thallium, silicon, germanium, lead, bismuth, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, erbium, lutetium, dysprosium, holmium, thulium and ytterbium.
Another aspect of the present disclosure is directed to a method of manufacturing the solid solution mixed oxide of the above aspect, the method comprising: providing a solution comprising cations of each of Ce, Zr, Sn and M; contacting the solution with a base to provide a slurry; heating the slurry at a temperature of from 20 to 200° C. to provide a mixed-oxide precursor; and heating the mixed-oxide precursor at a temperature of greater than 450° C. to provide the solid solution mixed oxide.
Another aspect of the present disclosure is directed to a method of manufacturing the catalyst composition of the above aspect, the method comprising: providing a solid solution mixed oxide according to the above aspect or manufacturing a solid solution mixed oxide according to the method of the above aspect; and disposing the platinum group metal on the solid solution mixed oxide.
Another aspect of the present disclosure is directed to the use of the catalyst composition of the above aspect or the catalyst article of the above aspect in an emission treatment system.
The present invention seeks to tackle at least some of the problems associated with the prior art or at least to provide a commercially acceptable alternative solution thereto.
In a first aspect, the present invention provides catalyst composition comprising a mixed oxide support material and a platinum group metal supported on the mixed oxide support material, the mixed oxide support material comprising a solid solution mixed oxide having the formula CewZrxSnyMzOa, wherein:
M is an element selected from one or more of sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, scandium, yttrium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, aluminium, gallium, thallium, silicon, germanium, lead, bismuth, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, erbium, lutetium, dysprosium, holmium, thulium and ytterbium.
Each aspect or embodiment as defined herein may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular, any features indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.
Surprisingly, in comparison with conventional catalyst compositions and in particular those comprising CZO support materials, the catalyst composition of the present invention may exhibit improved OSC properties, for example when used as a TWC, while also remaining more thermally stable to phase separation. The catalyst composition may therefore maintain its high OSC activity for longer in use.
Without wishing to be bound by theory, it is thought that the tin may provide the improved OSC properties by a similar mechanism to ceria, i.e. due to the function of a Sn2+/Sn4+ redox pair.
Moreover, without wishing to be bound by theory, it is thought that the lack of stability to phase separation of known tin-doped mixed oxides may be at least partially as a result of the small cationic radius of tin (i.e. Sn2+ or Sn4+) compared to the cationic radius of zirconium (i.e. Zr4+) and/or cerium (i.e. Ce3+ or Ce4+). As such, in a fluorite lattice structure, the distance between the tin and the oxygen ions, compared to that of zirconium and oxygen ions, for example, may be larger. Thus, this may create enthalpic bond strain. In other words, the Sn—O “bonds” may be weaker than would be for, for example, Zr—O “bonds” within the crystal lattice. Thus, due to the presence of tin in the lattice causing bond strain, the mixed oxide may be more likely to phase separate, due to the balance of the enthalpic contribution and the entropic contribution of the Gibbs Free Energy of the phase separation reaction moving in favour of phase separation.
However, the inventors of the present invention have surprisingly found that further co-doping tin-doped CZO with larger cations (i.e. larger than tin, typically larger than cerium and/or zirconium) may result in a more stable crystal lattice, while also benefiting from the improved OSC properties introduced by the tin. Thus, when the solid solution mixed oxide is used as a support material in a catalyst composition such as in the present invention, advantageous catalytic properties, particularly for TWC applications, may surprisingly be exhibited.
Without wishing to be bound by theory, it is thought that the introduction of these larger cations may provide at least the following two benefits: (i) the bond strain of the lattice may be reduced due to the balance of larger and smaller cations, reducing the impact that the inclusion of only tin would have on the enthalpic contribution to the Gibbs Free Energy, and (ii) the inclusion of one or more further cations may increase the disorder in the mixed oxide lattice, thereby causing the entropic contribution to the Gibbs Free Energy to be less favourable to phase separation. Thus, surprisingly, it may be possible to provide a more stable mixed oxide, particularly at high temperatures, while still providing the improved OSC properties. This is advantageous in emission treatment applications, particularly for TWC applications.
Thus, advantageously, the solid solution mixed oxide of the invention may be used in place of existing support materials, such as where CZO is used as a support material in a known catalyst composition, to provide further and/or improved OSC properties to the catalyst, while remaining relatively stable to phase separation in use. The mixed oxide may also provide high OSC across the full temperature range of typical operating temperatures.
The term “support material” as used herein may encompass any known support material that may be used to support PGMs in the field of the present invention, typically in powder form. However, the support material of the present invention is a mixed oxide support material according to the appended claims.
The term “mixed oxide” as used herein may encompass an oxide that contains cations of more than one chemical element, for example at least Ce, Zr, Sn and M in this case. The mixed oxide may be in a single phase, for example.
The CewZrxSnyMzOa of the invention is typically crystalline. Preferably, the mixed oxide is crystalline. The term “crystalline” as used herein is used within its normal meaning in the art and may encompass a solid material having long-range order, i.e. periodic translational ordering of atoms or molecules within the solid.
The term “platinum group metal” or “PGM” as used herein may encompass one or more elements selected from ruthenium, rhodium, palladium, osmium, iridium, and platinum. Preferably, the PGM comprises platinum, palladium, rhodium, or a mixture or alloy thereof. Such metals may be particularly suitable for carrying out three-way catalysis. The PGM may be in the form of an alloy.
The term “supported on” as used herein may encompass that the PGM is in direct contact with and stably disposed on the mixed oxide support material, either on the surface and/or within the pores of the mixed oxide support material.
The term “solid solution” as used herein may encompass a mixture of two crystalline solids that coexist as a new crystalline solid, or crystal lattice, for example. In other words, the mixed oxide is typically substantially one phase, rather than a mixture of different phases. Preferably, the solid solution mixed oxide is at least 95% phase pure, more preferably at least 97% phase pure, even more preferably at least 99% phase pure, still more preferably completely phase pure, allowing for the presence of unavoidable impurities. The term “phase pure” as used herein encompasses that the solid solution mixed oxide comprises only one type of crystal structure. The level of phase purity may be measured by X-ray diffraction, for example. The skilled person is aware of suitable techniques, for example by the use of Rietveld refinement of the X-ray powder diffraction pattern. Preferably, the major phase of the solid solution mixed oxide is fluorite. The skilled person would be able to identify a fluorite X-ray diffraction pattern.
In the catalyst composition of the invention, 1.0≤a≤2.0, preferably 1.3≤a≤2.0, more preferably 1.5≤a≤2.0, more preferably 1.6≤a≤2.0, most preferably ‘a’ is about 2. Although ‘a’ may typically be about 2, the amount of oxygen present in the solid solution mixed oxide may vary between these amounts due to changes in oxidation states of the cations, for example. As described herein, cerium may vary between the CeIII and CeIV oxidation states and the tin may vary between the SnII and SnIV oxidation states, for example. The relative amount of oxygen may therefore vary as a result. Without wishing to be bound by theory, it is thought that the variation in oxygen and oxidation states should not substantially affect the crystal structure of the mixed oxide.
Where b is the mole fraction of cations in the 3+ oxidation state excepting the molar contribution of O, c is the mole fraction of cations in the 2+ oxidation state excepting the molar contribution of O, and d is the mole fraction of cations in the 1+ oxidation state excepting the molar contribution of O.
M is an element selected from one or more of sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, scandium, yttrium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, aluminium, gallium, thallium, silicon, germanium, lead, bismuth, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, erbium, lutetium, dysprosium, holmium, thulium and ytterbium. When M is more than one of the recited elements, it should be understood that the total amount of M is encompassed by the ‘z’ parameter. In other words, if Mz is Az1Bz2Cz3, for example, where A, B and C are each one of the recited elements, then the parameter ‘z’ encompasses z1+z2+z3, i.e. z=z1+z2+z3 in this case. Each of the recited elements may contribute to the stabilisation of the mixed oxide, as hypothesised above, for example due to their large cations.
Preferably, the catalyst composition is for three way catalysis. In other words, the catalyst composition is preferably capable of catalysing at least one of the target reactions of a TWC. Preferably, the catalyst composition is a TWC.
In some preferred embodiments, y+z is less than 0.15, preferably less than or equal to 0.13, more preferably less than or equal to 0.11, even more preferably less than or equal to 0.10, still more preferably about 0.10. Such a balance of components of the mixed oxide may provide catalyst compositions that are particularly stable and have excellent OSC properties.
In alternative preferred embodiments, 0.05≤y≤0.15, more preferably 0.07≤y≤0.13, even more preferably 0.08≤y≤0.12. In an alternative preferred embodiment, 0.05≤y≤0.10. In another alternative preferred embodiment, 0.10≤y≤0.15. Preferably, y is greater than or equal to 0.005, more preferably 0.01, even more preferably 0.02, still more preferably 0.05. Such amounts of tin doping may result in a catalyst composition that is particularly stable and has excellent catalytic properties.
In alternative preferred embodiments, 0.05≤z≤0.15, more preferably 0.07≤z≤0.13, even more preferably 0.08≤z≤0.12. In an alternative preferred embodiment, 0.05≤z≤0.10. In another alternative preferred embodiment, 0.10≤z≤0.15. Preferably, z is greater than or equal to 0.005, more preferably 0.01, even more preferably 0.02, still more preferably 0.05. Such amounts of tin doping may result in a catalyst composition that is particularly stable and has excellent catalytic properties.
Preferably, w+x is greater than or equal to 0.80, preferably greater than or equal to 0.85, more preferably greater than or equal to 0.90. For example, preferably 0.80≤w+x≤0.95, more preferably 0.85≤w+x≤0.95, even more preferably 0.85≤w+x≤0.90. Such a balance of components of the mixed oxide may provide catalyst compositions that are particularly stable and have excellent OSC properties.
Preferably, w+y is greater than 0.5, preferably greater than or equal to 0.51, even more preferably greater than or equal to 0.55, still more preferably greater than or equal to 0.60. Such a balance of components of the mixed oxide may provide catalyst compositions that are particularly stable and have excellent OSC properties.
Preferably, 0.07≤y≤0.11, more preferably 0.07≤y+z≤0.11. Such a balance of components of the mixed oxide may provide catalyst compositions that are particularly stable and have excellent OSC properties.
Preferably, 0.20≤w≤0.80, more preferably 0.30≤w≤0.70, even more preferably 0.40≤w≤0.60, still more preferably 0.50≤w≤0.60. Such a balance of components of the mixed oxide may provide catalyst compositions that are particularly stable and have excellent OSC properties.
In some preferred embodiments, M comprises two or more different elements. In other words, in such preferred embodiments, in the solid solution mixed oxide there are five or more different cations. As described above, having a larger number of different cations may contribute to the entropic component of the Gibbs Free Energy for phase separation, making phase separation less favourable. Thus, catalyst compositions that are particularly stable and have excellent OSC properties may be provided.
In some preferred embodiments, 0.15≤w, x≤0.25 and 0.30≤y+z≤0.70. By the term “0.15≤w, x≤0.25” it is meant that both of 0.15≤w≤0.25 and 0.15≤x≤0.25 are fulfilled. In other words, in some embodiments it is preferred that the molar ratio of each cation in the solid solution mixed oxide is substantially equal. In this embodiment, it may also be preferred that 0.15≤y≤0.25 and/or 0.30≤z≤0.50. Preferably, 0.17≤w, x≤0.23, more preferably 0.19≤w, x≤0.21. Preferably, 0.40≤y+z≤0.60. Such a balance of components of the mixed oxide may provide catalyst compositions that are particularly stable and have excellent OSC properties. In the preferred embodiments of this paragraph, it is further preferred that Mz is M′z1M″z2, where:
Preferably, M′ is yttrium. In an alternative preferred embodiment, M′ is lanthanum. In an alternative preferred embodiment, M′ is neodymium. In an alternative preferred embodiment, M′ is strontium. Such mixed oxides may result in catalyst compositions that are particularly stable and have excellent OSC properties.
Preferably, M″ comprises only one element. Accordingly, the cations of the mixed oxide may preferably consist of five different elements.
Preferably, 0.17≤z1≤0.23 and/or 0.17≤z2≤0.23, more preferably 0.19≤z1≤0.21 and/or 0.19≤z2≤0.21. Such a balance of components of the mixed oxide may provide catalyst compositions that are particularly stable and have excellent OSC properties.
In some preferred embodiments, M does not comprise lanthanum. In some preferred embodiments, M does not comprise yttrium. In some preferred embodiments, M does not comprise either lanthanum or yttrium. In other words, in some preferred embodiments, M is an element selected from one or more of sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, scandium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, aluminium, gallium, thallium, silicon, germanium, lead, bismuth, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, erbium, lutetium, dysprosium, holmium, thulium and ytterbium; in some preferred embodiments M is an element selected from one or more of sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, scandium, yttrium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, aluminium, gallium, thallium, silicon, germanium, lead, bismuth, praseodymium, neodymium, samarium, europium, gadolinium, terbium, erbium, lutetium, dysprosium, holmium, thulium and ytterbium; or in some preferred embodiments M is an element selected from one or more of sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, scandium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, aluminium, gallium, thallium, silicon, germanium, lead, bismuth, praseodymium, neodymium, samarium, europium, gadolinium, terbium, erbium, lutetium, dysprosium, holmium, thulium and ytterbium.
In the preferred embodiments where 0.15≤w, x≤0.25 and 0.30≤y+z≤0.70 described herein, the mean cationic radius of Ce, Zr, Sn and M in the solid solution mixed oxide is preferably from 90 to 106 pm. However, this preferred feature may also be applicable to all aspects described herein. The mean cationic radius may be determined by the 8-coordinate effective ionic radius (as defined in R. D. Shannon, Acta Cryst., 1976, A32, 751). Such a determination of cationic radius is well known in the field. It should be noted that the mean cationic radius of the Ce, Zr, Sn and M cations in the solid solution mixed oxide is weighted relative to the molar amounts of the cations in the solid solution mixed oxide. In other words, the “mean cationic radius of Ce, Zr, Sn and M in the solid solution mixed oxide” as defined may be defined as wRCe+xRZr+yRSn+zRM, where RA is the 8-coordinate effective ionic radius of element A in the oxidation state it is present in the solid solution mixed oxide. Preferably, the mean cationic radius of Ce, Zr, Sn and M in the solid solution mixed oxide is from 92 to 98 pm, more preferably 93 to 97 pm. Alternatively, the mean cationic radius of Ce, Zr, Sn and M in the solid solution mixed oxide is preferably from 90 to 106 pm; more preferably from 90 to 100 pm; even more preferably, 92 to 98 pm or 93 to 97 pm. Such a balance of components of the mixed oxide may provide catalyst compositions that are particularly stable and have excellent OSC properties.
Preferably, M is an element selected from one or more of calcium, strontium, barium, scandium, yttrium, hafnium, lanthanum, praseodymium, neodymium, samarium, europium and gadolinium, more preferably M is an element selected from one or more of calcium, strontium, barium, yttrium, lanthanum, neodymium and gadolinium. Such mixed oxides may provide catalyst compositions that are particularly stable and have excellent OSC properties.
In some preferred embodiments, M comprises only one element. In other words, in such preferred embodiments, in the solid solution mixed oxide there are four different cations only. Even though, as described above, having a larger number of different cations may contribute to the entropic component of the Gibbs Free Energy for phase separation, making phase separation less favourable, a stable solid solution mixed oxide having excellent OSC properties may still be provided with only four different cations, for example with the balance of cations described elsewhere herein. Thus, such mixed oxides may also be preferred.
Preferably, the platinum group metal comprises one or more of platinum, palladium and rhodium, preferably the platinum group metal comprises platinum. Such PGMs may result in a catalyst composition having particularly desirable catalytic properties, such as for TWC applications.
In a further aspect, the present invention provides a catalyst article comprising a substrate and the catalyst composition of any preceding claim, wherein the catalyst composition is disposed on the substrate.
The term “catalyst article” used herein may encompass an article in which a catalyst is supported thereon or therein. The article may take the form of, for example, a honeycomb monolith, or a filter, e.g. a wall flow filter or a flow-through filter.
The term “substrate” as used herein may encompass, for example, a ceramic or metallic honeycomb, or a filter block, e.g. a wall flow filter or flow-through filter. The substrate may comprise a ceramic monolithic substrate. The substrate may vary in its material composition, size and configuration, cell shape and density, and wall thickness. Suitable substrates are known in the art, such as cordierite.
The term “disposed on” in the context of this aspect may encompass both having the catalyst composition directly disposed on the substrate, i.e. with no intervening material, and/or indirectly disposed on the substrate, i.e. with intervening material. If the substrate is porous, then the term “disposed on” may also encompass having the catalyst composition disposed therein, for example within the pores of the substrate, i.e. wherein the catalyst composition is disposed thereon and/or therein. The catalyst composition is typically disposed on the substrate in the form of a washcoat. The term “washcoat” as used herein is well-known in the field and refers to an adherent coating that is applied to a substrate usually during the production of a catalyst.
The preferred features of the first aspect apply equally to this aspect. The advantages described above with reference to the first aspect may also be equally applicable to the resulting catalyst article comprising the catalyst composition.
Preferably, the catalyst article is a three way catalyst.
The catalyst article preferably has a washcoat loading of from 1 g/in3 to 3 g/in3. Preferably, the substrate comprises a wall flow filter substrate. In an alternative preferred embodiment, the substrate comprises a flow-through substrate.
The catalyst article preferably comprises two or more catalyst regions disposed on the substrate, the catalyst composition being present in one or more of the catalyst regions.
The term “catalyst region” as used herein may encompass an area on a substrate, typically obtained by drying and/or calcining a washcoat. A “region” can, for example, be disposed or supported on a substrate as a “layer” or a “zone”. The area or arrangement on a substrate is generally controlled during the process of applying the washcoat to the substrate. The “region” typically has distinct boundaries or edges (i.e. it is possible to distinguish one region from another region using conventional analytical techniques).
It is preferable that the “catalyst region” has a substantially uniform composition (i.e. there is no substantial difference in the composition of the washcoat when comparing one part of the region with another part of that region, on average). Substantially uniform composition in this context refers to a material (e.g., region) where the difference in composition when comparing one part of the region with another part of the region is 5% or less, usually 2.5% or less, and most commonly 1% or less.
The term “disposed on” in the context of this embodiment may encompass both having the catalyst region directly disposed on the substrate, i.e. with no intervening material, and/or indirectly disposed on the substrate, i.e. with intervening material. If the substrate is porous, then the term “disposed on” may also encompass having the catalyst region disposed therein, for example within the pores of the substrate, i.e. wherein the catalyst region is disposed thereon and/or therein. Preferably, the catalyst region is a washcoat layer.
Other support materials and catalysts other than those of the present invention may also be present on and/or in the catalyst article of this aspect.
When present, the catalyst article preferably comprises from 2 g/ft3 to 15 g/ft3 rhodium, more preferably from 3 g/ft3 to 10 g/ft3 rhodium. When present, the catalyst article preferably comprises from 20 g/ft3 to 200 g/ft3 palladium, more preferably from 30 g/ft3 to 150 g/ft3 palladium. When present, the catalyst article preferably comprises from 2 g/ft3 to 200 g/ft3 platinum, preferably from 10 g/ft3 to 100 g/ft3 platinum.
In a further aspect, the present invention provides an emission treatment system comprising the catalyst article described herein. Preferably, the emission treatment system is for a gasoline engine. Preferably, the gasoline engine operates under stoichiometric conditions.
In a further aspect, the present invention provides a vehicle comprising the emission treatment system described herein.
In a further aspect, the present invention provides a method of treating an exhaust gas, the method comprising: providing the catalyst article described herein; and contacting the catalyst article with an exhaust gas. Preferably, the exhaust gas is from a gasoline engine. Preferably, the gasoline engine operates under stoichiometric conditions.
In a further aspect, the present invention provides a solid solution mixed oxide having the formula CewZrxSnyMzOa, wherein:
The preferred features and advantages discussed herein with reference to the first aspect apply equally to this aspect. Such a solid solution mixed oxide may advantageously also be used in other applications which may require stable mixed oxides having excellent OSC properties.
In a further aspect, the present invention provides a method of manufacturing the solid solution mixed oxide described herein, the method comprising:
Providing a solution comprising cations of each of Ce, Zr, Sn and M typically comprises dissolving soluble salts of each of Ce, Zr, Sn and M in water. In other words, the solution is preferably an aqueous solution, i.e. an aqueous solution comprising the metal cations and their respective counterion(s). In the method of providing the solution, the order of addition of each cation salt is not particularly limited. Suitable salts can be in somewhat water soluble form, include but not limited to, nitrates, chlorides, ammonium nitrates, and oxynitrates, sulphates, carbonates, and any number of organic ligands, such as acetate or citrate.
Contacting the solution with a base may comprise adding a base, for example in powder form, to the solution and/or contacting the solution comprising the cations with a basic solution. Contacting the solution comprising the cations with a basic solution typically comprises adding the solution to the basic solution or vice versa. Preferably, contacting the solution with a base comprises raising the pH of the solution, preferably to a pH of from about 7 to about 9. Contacting the solution with a base typically causes precipitation of a hydrous oxide of the metal cations in the solution. In other words, the slurry may comprise a hydrous oxide of Ce, Zr, Sn and M. A suitable basic solution can contain a weak base, such as NH3, urea, or a quaternary ammonium hydroxide (e.g., tetraethyl ammonium hydroxide), or any strong base solution like NaOH, KOH, Ba(OH)2, Sr(OH)2, etc. The suitable basic solution may comprise a buffer solution comprising ammonium nitrate, ammonia and water, for example.
Heating the slurry at a temperature of from 20 to 200° C. typically leads to drying of the slurry, for example. In other words, heating the slurry preferably comprises at least partially drying the slurry. The mixed-oxide precursor may therefore comprise a hydrous oxide powder of Ce, Zr, Sn and M. The slurry is typically heated at a temperature of from 20 to 200° C. for from 1 hour to 24 hours. The slurry may be heated in multiple stages of heating.
Heating the mixed-oxide precursor at a temperature of greater than 450° C. typically comprises calcining the mixed-oxide precursor/hydrous oxide powder of Ce, Zr, Sn and M. The mixed-oxide precursor is typically heated in air for 30 mins or longer. This heating step typically causes formation of a crystalline mixed oxide.
Advantageously, such a method is a simple one-pot synthesis. The method may also be easily scalable to larger scale manufacture. The cations of the resulting mixed oxide are typically substantially evenly dispersed within the solid solution mixed oxide. This may not be achieved by a method of manufacture involving, for example, incipient wetness impregnation of tin into a CZO.
In a further aspect, the present invention provides a method of manufacturing the catalyst composition described herein, the method comprising:
Disposing the platinum group metal on the solid solution mixed oxide typically comprises contacting a PGM precursor, such as a PGM salt, for example a nitrate, acetate or chloride salt, with the solid solution mixed oxide and depositing the PGM onto the solid solution mixed oxide via incipient wetness impregnation or wet impregnation. Alternative methods involve the use of PGM complexes, such as PGM-polymer complexes. Suitable methods are known to the skilled person.
Preferably, after the step of contacting the solution with a base and prior to the step of heating the slurry, the method further comprises:
Washing the slurry preferably comprises washing the slurry with deionized (DI) water. Washing and/or filtering the slurry may advantageously remove any excess starting material that has not formed a hydrous oxide, for example. Thus, the resulting mixed oxide may have fewer impurities. The preferable embodiments in relation to contacting the solution with a base as described above apply equally to these further embodiments.
Modifying the pH of the slurry or further slurry using a base typically comprises contacting the slurry or further slurry with a basic solution. Modifying the pH of the slurry preferably comprising raising the pH of the slurry, preferably to a pH of from about 7 to about 9. Such modification can accelerate the formation of a porous network of particles which imparts thermal stability to high temperature aging.
The method preferably comprises washing and/or filtering the mixed-oxide precursor prior to heating the mixed-oxide precursor. This step may also advantageously remove any excess starting material that has not formed a hydrous oxide, for example. Thus, the resulting mixed oxide may have fewer impurities.
In a further aspect, the present invention provides the use of the catalyst composition of described herein or the catalyst article described herein in an emission treatment system. Such a use may have the advantages described herein with reference to the other aspects of the invention.
The invention will now be described in relation to the following non-limiting examples.
A solution of metal ions was prepared by dissolving appropriate metal salts (cerium ammonium nitrate, zirconium oxynitrate, tin (IV) chloride, lanthanum nitrate, neodymium nitrate, gadolinium nitrate, yttrium nitrate, barium nitrate, strontium nitrate, calcium chloride) in DI water as described in Table 1. A buffer solution was prepared by combining ammonium nitrate, ammonia, and water in a molar ratio of 1:10:89. The metal salt solution was then added to a mechanically stirred vessel containing the buffer solution. A precipitate formed upon mixing of the two solutions. The mixture was allowed to stir for an additional fifteen minutes. The hydrous oxide precipitate was then filtered in a filter press and washed with DI water.
A slurry was prepared by combining hydrous oxide (metals basis), ammonium nitrate, ammonia, and water in a molar ratio of 1:1:10:89 and mechanically stirred for 5 minutes. The slurry was then transferred to a Teflon sleeve and sealed in a Parr stainless-steel acid digestion vessel. The slurry was then heated to 150° C. and mixed for 2 h. Upon cooling to <60° C., the hydrous oxide was filtered and washed with DI water until the exiting filtrate reached a pH<7. The hydrous oxide was then dried at 90° C. for 16 h, ground to a powder, and further dried at 120° C. for 2 h. Upon drying, the hydrous oxide was calcined in air at 500° C. to form a crystalline solid oxide. The resulting solid metal oxide compositions are summarized in Table 2.
The XRD results of the powders of solid oxides after calcination are shown in
Powdered solid oxides prepared in Example 1 were subjected to high temperature redox conditions to simulate long-term operation on a vehicle. The powders were placed in a tube furnace and heated to 1050° C. at a rate of 10° C./minute under a stoichiometric gas mixture composed of: 1.2% CO, 0.4% H2, 0.8% O2, 10% H2O, 10% CO2, balance N2 flowing at 5 L/minute. The temperature was then held at 1050° C. for 40 hours while the flowing gas mixture was altered every 5 minutes in the order listed below:
After 40 h, the coated cores were cooled from 1050° C. to <400° C. under the rich gas mixture and then from 400° C. to room temperature under N2 only.
The XRD results of the powders of solid oxides after accelerated aging are shown in
After being subject to aging conditions described in Example 2, powdered solid oxides of Example 1 were characterized by an OSC test. In this test, samples were first pre-treated by heating to 600° C. and holding for 15 minutes in a 5% O2 (balance N2) atmosphere. While still holding at 600° C., the gas atmosphere was switched to pure N2 for 5 additional minutes. Then, the test began when a stream of 5000 ppm CO (balance N2) was passed through the powdered solid oxide while measuring the amount of CO2 generated for a period of 30 seconds. The OSC of the solid oxide was calculated using the following equation:
The results of the OSC test are depicted in
Catalysts were prepared by PGM addition to the Comparative Example 1 and JM-MO-2 to create Comparative Catalyst 1 and JM-MO-2 Catalyst, respectively, in order to demonstrate application in automotive emissions abatement. 10 g of calcined solid oxide (dry basis) was dispersed in 23 g DI water with mechanical mixing to form a slurry. 0.04 g of Rh was then added to the slurry in the form of a rhodium (III) nitrate solution. A solution of ammonium hydroxide was added to the slurry to re-adjust the pH to ˜7-8. The slurry was mixed for 2 hours, then transferred to an open crucible and dried overnight at 80° C. The resulting catalyst powder containing solid oxide and Rh was calcined in air at 500° C. for 4 hours.
Comparative Catalyst 1 and JM-MO-2 Catalyst were subject to a TWC light-off test. In this test, 0.05 g of powdered catalyst mixed with 0.25 g of ground cordierite was loaded into a reactor apparatus capable of heating and flowing a gas mixture designed to simulate gasoline exhaust conditions. The temperature was ramped from 150-600° C. at a rate of 5° C./min under a gas mixture flowing at 500 cm3/min. The gas composition by volume was: 1% CO, 1500 ppm propene (C3H6), 400 ppm NO, 0.65% O2, 6% H2O in a balance of N2. The conversions of NO, CO, and total hydrocarbons (THC, comprised of C3H6) as a function of temperature are reported in
A useful metric for quantifying performance of a catalyst is the T50 value which is herein defined as the minimum temperature at which 50% conversion is achieved. Lower T50 temperatures mark catalysts that demonstrate enhanced catalytic activity. In each case, the catalytic activity was greater for JM-MO-2 Catalyst than for Comparative Catalyst 1 as evinced by the T50 values achieved by each catalyst. JM-MO-2 Catalyst achieved T50 values for NO, CO, and THC conversions that were 40° C., 35° C., and 20° C. lower, respectively, than the Tso values of Comparative Catalyst 1. These results demonstrate that the materials of the present invention exhibit catalytic activity required for application as catalysts in automobile emissions systems.
A solution of metal ions was prepared by dissolving appropriate metal salts (cerium ammonium nitrate, zirconium oxynitrate, tin (IV) chloride, lanthanum nitrate, neodymium nitrate, yttrium nitrate, praseodymium nitrate, barium nitrate, strontium nitrate) in DI water as described in Table 3. A buffer solution was prepared by combining ammonium nitrate, ammonia, and water in a molar ratio of 1:10:89. The metal salt solution was then added to a mechanically stirred vessel containing the buffer solution. A precipitate formed upon mixing of the two solutions. The mixture was allowed to stir for an additional fifteen minutes. The hydrous oxide precipitate was then filtered in a filter press and washed with DI water.
Pr: 0.2
La: 0.2
Sr: 0.2
La: 0.2
Sr: 0.2
A slurry was prepared by combining hydrous oxide (metals basis), ammonium nitrate, ammonia, and water in a molar ratio of 1:1:10:89 and mechanically stirred for 5 minutes. The slurry was then transferred to a Teflon sleeve and sealed in a Parr stainless-steel acid digestion vessel. The slurry was then heated to 150° C. and mixed via tumbling in an oven for 2 h. Upon cooling to <60° C., the hydrous oxide was filtered and washed with DI water until the exiting filtrate reached a pH<7. The hydrous oxide was then dried at 90° C. for 16 h, ground to a powder, and further dried at 120° C. for 2 h. Upon drying, the hydrous oxide was calcined in air at 500° C. to form a crystalline solid oxide.
The resulting solid metal oxide compositions and average cationic radii are summarized in Table 4. A commercially available mixed oxide containing similar Ce content to the samples of the present example and five total components without the presence of Sn was purchased from a supplier and utilized as Comparative Sample 2. The average cationic radius (ravg) is a useful metric for predicting stability of doped cerias of widely varying compositions. The average cationic radius of each doped ceria was calculated using the following equation:
r
avg=Σinniri
Wherein, ni is the mole fraction of each individual cationic component (excluding molar contribution of O) and ri is each individual cation radius. The method of ionic radius determination used in this work is the 8-coordinate effective ionic radius (as defined in R. D. Shannon, Acta Cryst., 1976, A32, 751). Cerium and tin are assumed to adopt an oxidation state of 4+. Lanthanum, neodymium, praseodymium, and yttrium are assumed to adopt a 3+ oxidation state. Strontium and barium are assumed to adopt a 2+ oxidation state.
Y: 0.09
Y: 0.2
Y: 0.2
La: 0.2
La: 0.2
The XRD results of the powders of solid oxides after calcination are shown in
Catalysts were prepared by PGM addition to the Comparative Example 2 and JM-MO-2 to create to create Comparative Catalyst 2 and JM-MO-10 Catalyst, respectively, to demonstrate application in automotive emissions abatement. 10 g of calcined solid oxide (dry basis) was dispersed in 23 g DI water with mechanical mixing to form a slurry. 0.3 g of Pt was then added to the slurry in the form of a platinum (II) nitrate solution. A solution of ammonium hydroxide was added to the slurry to re-adjust the pH to ˜7-8. The slurry was mixed for 2 hours, then transferred to an open crucible and dried overnight at 80° C. The resulting catalyst powder containing solid oxide and Pt was calcined in air at 500° C. for 4 hours. The powdered catalysts were then subjected to high temperature redox conditions to simulate long-term operation on a vehicle as described in Example 2.
The catalysts were then subject to a perturbed TWC light-off test. In this test, 0.3 g of powdered catalyst was loaded into a reactor apparatus capable of heating and flowing a gas mixture designed to simulate gasoline exhaust conditions. The temperature was ramped from 150-600° C. at a rate of 15° C./min under a gas mixture flowing at 3000 cm3/min. The flowing gas was perturbed between rich and lean conditions at a frequency of 1 Hz. The gas compositions by volume were as follows: rich=6% H2O, 14% CO2, 2000 ppm NO, 0.58% 02, 200 ppm propene (C3H6), 200 propane (C3H8), 2.5% CO, and 0.5% H2 in a balance of N2 and lean=6% H2O, 14% CO2, 2000 ppm NO, 1.93% O2, 200 ppm propene (C3H6), 200 propane (C3H8), 0.5% CO, and 0.5% H2 in a balance of N2. The temperatures at which a conversion of 20% of NO, CO, and total hydrocarbons (THC, comprised of C3H6 and C3H8) was reached (T20) are reported in
A useful metric for quantifying performance of a catalyst is the T20 value which is herein defined as the minimum temperature at which 20% conversion is achieved. Lower T20 temperatures mark catalysts that demonstrate enhanced catalytic activity. In each case, the catalytic activity was greater for the catalysts of the present invention than for Comparative Catalyst 2 as evinced by the T20 values achieved by each catalyst. JM-MO-10 Catalyst achieved T20 values for NO, CO, and THC conversions that were 14° C., 48° C., and 28° C. lower, respectively, than the T20 values of Comparative Catalyst 2. These results demonstrate that the materials of the present invention exhibit catalytic activity required for application as catalysts in automobile emissions systems.
The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art and remain within the scope of the appended claims and their equivalents.
| Number | Date | Country | |
|---|---|---|---|
| 63364987 | May 2022 | US |
