Ceria-based mixed-metal oxide structure, including method of making and use

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 m<2>/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 m<2>/cm<3>, 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.

Description

[0001] This invention relates to mixed metal oxides, and more particularly to ceria-based mixed-metal oxide structures, for use as catalyst supports, as co-catalysts, as getters, and the like. The invention relates further to methods of preparing such ceria-based mixed-metal oxide structures, and further still to metal loading of such structures. The invention relates still further to the application of such mixed-metal oxide structures as catalyst supports, co-catalysts, and / or getters in, for instance, fuel processing systems.[0002] Various metal oxides have found use in chemically reactive systems as catalysts, supports for catalysts, gettering agents and the like. As used herein, a gettering agent, or getter, is a substance that sorbs or chemically binds with a deleterious or unwanted impurity, such as sulfur. In those usages, their chemical characteristics and morphologies may be important, as well as their ease and economy of manufacture. One area of usage that is of particula...

AI Technical Summary

Benefits of technology

0030] Following drying, the oxide, or the aforedescribed formed and dried mixed metal oxide may be calcined at 250.degree. C.-600.degree. C., and preferably about 350.degree. C. -500.degree. C., for an interval sufficient to remove adsorbed species and strengthen the structure against premature aging. Lower temperatures typically mean more physisorbed and chemisorbed solvent and/or carbonates, while higher t...

Problems solved by technology

However, if that value becomes too small because of excessive pore size and/or volume, the effective number of sites pe...