Redox and catalytic properties of Ce–Zr mixed oxide nanopowders for fuel cell applications

Abstract

Ce x Zr 1− x O 2 mixed oxides nanopowders with x = 0.10, 0.25, 0.50, 0.75 and 0.90, and pure ceria, all prepared by a low temperature citrate complexion technique, were investigated using a range of temperature programmed (TP) techniques in order to evaluate their suitability for use as anode catalyst materials in solid oxide fuel cells operating on hydrocarbon fuels. In TP reduction experiments, reduction peak temperatures and peak areas were related to the activity and amount, respectively, of available catalyst oxygen. Mixed oxides with higher Ce contents ( x ≥ 0.50) were found to be reduced at significantly lower temperatures than samples with x < 0.50. The oxide with x = 0.75 supplied the largest amount of labile oxygen. TP reaction experiments performed in dry methane on two samples indicated that susceptibility of the oxides to carbon deposition was inversely related to availability of catalyst oxygen. Light-off experiments in a stoichiometric CH 4/O 2 mixture were performed to investigate the catalytic activity of the mixed oxide compositions for methane oxidation. Catalytic activity increased with cerium content to a maximum at x = 0.75 before decreasing at x = 0.90. All the mixed oxides were considerably more active for methane oxidation than pure CeO 2 prepared by the same citrate route.