Ceria-based mixed-metal oxide structure, including method of making and use
First Claim
1. A homogeneous, nanocrystalline, mixed metal oxide of cerium and at least one other metal constituent from the group consisting of Zr, Hf, Nb, Ta, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Mo, W, Re, Rh, Sb, Bi, Ti, V, Mn, Co, Cu, Ga, Ca, Sr and Ba, said mixed metal oxide having a surface area of at least about 150 m2/g, an average crystallite size less than 4 nm and agglomerated to form a skeletal structure with pores, average pore diameters being greater than 4 nm and normally being greater than the average crystallite size, and wherein the surface area of the skeletal structure per volume of the material of the structure is greater than about 320 m2/cm3.
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Abstract
A homogeneous ceria-based mixed-metal oxide, useful as a catalyst support, a co-catalyst and/or a getter, is described. The mixed-metal oxide has a relatively large surface area per weight, typically exceeding 150 m2/g, a structure of nanocrystallites having diameters of less than 4 nm, and including pores larger than the nanocrystallites and having diameters in the range of 4 to about 9 nm. The ratio of the pore volumes, VP, to skeletal structure volumes, VS, is typically less than about 2.5, and the surface area per unit volume of the oxide material is greater than 320 m2/cm3, such that the structural morphology supports both a relatively low internal mass transfer resistance and large effective surface area for reaction activity of interest. The mixed metal oxide is made by co-precipitating a dilute metal salt solution containing the respective metals, which may include Zr, Hf, and/or other metal constituents in addition to Ce, replacing water in the co-precipitate with a water-miscible low surface-tension solvent, and relatively quickly drying and calcining the co-precipitate at moderate temperatures. A highly dispersive catalyst metal, such as Pt, may be loaded on the mixed metal oxide support from a catalyst-containing solution following a selected acid surface treatment of the oxide support. The mixed metal oxide, as catalyst support, co-catalyst or getter, is applied in various reactions, and particularly water gas shift and/or preferential oxidation reactions as associated with fuel processing systems, as for fuel cells and the like.
80 Citations
48 Claims
- 1. A homogeneous, nanocrystalline, mixed metal oxide of cerium and at least one other metal constituent from the group consisting of Zr, Hf, Nb, Ta, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Mo, W, Re, Rh, Sb, Bi, Ti, V, Mn, Co, Cu, Ga, Ca, Sr and Ba, said mixed metal oxide having a surface area of at least about 150 m2/g, an average crystallite size less than 4 nm and agglomerated to form a skeletal structure with pores, average pore diameters being greater than 4 nm and normally being greater than the average crystallite size, and wherein the surface area of the skeletal structure per volume of the material of the structure is greater than about 320 m2/cm3.
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33. A process for the preparation of a mixed metal oxide of cerium, Ce, and at least one other metal constituent, comprising:
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a. dissolving urea and salts of the Ce and the at least one other constituent in water to form a dilute metal salt solution;
b. heating the solution to near boiling and coprecipitating homogeneously an oxide of the Ce and the at least one other constituent as a nanocrystalline coprecipitate;
c. replacing water existing in the coprecipitate with a water miscible, low surface-tension solvent that displaces water;
d. drying the coprecipitate to remove substantially all of any remaining water and the solvent; and
e. calcining the dried coprecipitate at a moderate temperature for an interval sufficient to remove adsorbed impurities. - View Dependent Claims (34)
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47. A catalyst comprising a metal-loaded, ceria-based mixed metal oxide containing at least one other metal constituent, the catalyst made according to the process of:
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a. dissolving urea and salts of the Ce and the at least one other constituent in water to form a dilute metal salt solution;
b. heating the solution to near boiling and coprecipitating homogeneously an oxide of the Ce and the at least one other constituent as a nanocrystalline coprecipitate;
c. replacing water existing in the coprecipitate with a water miscible, low surface-tension solvent that displaces water;
d. drying the coprecipitate to remove substantially all of any remaining water and the solvent;
e. calcining the dried coprecipitate at a moderate temperature for an interval sufficient to remove adsorbed impurities to provide the mixed metal oxide;
f. contacting the mixed metal oxide with a solution containing an acid from the group consisting of amino acids, hydroxy dicarboxylic acids, hydroxy polycarboxylic acids, and keto polycarboxcylic acids to treat the surface of the mixed metal oxide; and
g. loading the surface-treated, mixed metal oxide with noble metal by contacting the surface-treated mixed metal oxide with a solution containing the noble metal. - View Dependent Claims (48)
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Specification