Supported Pd is used as total oxidation catalyst in power generation, control of environmental emissions (i.e., automotive catalysts), and in combustible gas sensors that detect explosive hazards. Its catalytic chemistry is complex: methane oxidation is often viewed as occurring via a Mars van Krevelen cycle that takes place at a Pd-O/O-vacancy site pair. Activity depends on maintaining a high density of site pairs on the catalyst surface, which, in turn, can be influenced by the support. We prepared a series of Pd total oxidation catalysts on Al2O3, CeO2, and ZrO2-CeO2 supports, and characterized them by temperature programmed methane oxidation (TPRx), temperature programmed reduction (TPR) and x-ray diffraction. Pre-exponents of apparent rate constants, estimated by fitting a microkinetic model of oxidation (Fujimoto et al., Journal of Catalysis 179, 431-442 (1998)) to the TPRx results, suggest that the relatively low activity of Pd/CeO2 is due to a low density of active site pairs. Consistent with this observation are the relatively high temperatures of surface Pd-O reduction in TPR of pre-oxidized Pd/CeO2 catalysts: too-stable Pd-O are less likely to convert to vacancy sites to provide the site pairs required for reaction. Pd/Al2O3 and Pd/ZeO2-CeO2, which are more active for methane combustion, display lower reduction temperatures in TPR.

Pd catalysts for total oxidation of methane: Support effects

248th National Meeting (2014)

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