Platinum Inhibits Low‐Temperature Dry Lean Methane Combustion through Palladium Reduction in Pd−Pt/Al2O3: An In Situ X‐ray Absorption Study

Abstract

Palladium–platinum bimetallic catalysts supported on alumina with palladium/platinum molar ratios ranging from 0.25 to 4 are studied in dry lean methane combustion in the temperature range of 200 to 500 °C. Platinum addition decreases the catalyst activity, which cannot be explained by the decrease in dispersion or the structure sensitivity of the reaction. In situ X‐ray absorption near‐edge structure and extended X‐ray absorption fine structure spectroscopy measurements have been conducted for monometallic Pd, Pt, and 2:1 Pd−Pt catalysts. Monometallic palladium is fully oxidized in the full temperature range, whereas platinum addition promotes palladium reduction, even in a reactive oxidizing environment. The Pd/PdO weight ratio in bimetallic Pd−Pt 2:1 catalysts decreases from 98/2 to 10/90 in the 200–500 °C temperature range under the reaction conditions. Thus, platinum promotes the formation of the reduced palladium phase with a significantly lower activity than that of oxidized palladium. The study sheds light on the effect of platinum on the state of the active palladium surface under low‐temperature dry lean methane combustion conditions, which is important for methane‐emission control devices.