Redox Property and Reactivity of Pt/Ce_xZr_1-xO₂ (x = 0, 0.5, 1) for CO₂ Reforming of Methane

Abstract

Relationship between the redox property and the reactivity for CO₂ reforming of methane was investigated on 0.5 wt% platinum-impregnated CeO₂, Ce_0.5Zr_0.5O₂ and ZrO₂. Whereas CO-O₂ cyclic pulse experiment at 873K showed that the redox property was in the order of Pt/Ce_0.5Zr_0.5O₂ > Pt/CeO₂ >> Pt/ZrO₂, the reactivity for CO₂ reforming of methane was in the order of Pt/ZrO₂ > Pt/Ce_0.5Zr_0.5O₂ > Pt/CeO₂ by pulse experiments at 823-923K with stoichiometric mixture of the reactants. From the fact that relatively irreducible Pt/ZrO₂ exhibited higher reactivity than Pt/Ce_0.5Zr_0.5O₂ possessing more vigorous redox property, it could be deduced that Pt/ZrO₂ follows the reaction mechanism unequal to that for Pt/Ce_0.5Zr_0.5O₂ or Pt/CeO₂. While the reactivity of Pt/ZrO₂ reached a steady level from the beginning, the reactivity of Pt/Ce_0.5Zr_0.5O₂ and Pt/CeO₂ varied with the extent of catalyst reduction. Complete oxidation of methane was initially more dominant on Pt/Ce_0.5Zr_0.5O₂ due to its vigorous oxygen mobility, however, the selectivity toward CO₂ reforming of methane increased with the number of reactant pulses before it reached a steady level.