Insights into the role of Pt on Pd catalyst stabilized by magnesia-alumina spinel on gama-alumina for lean methane combustion: Enhancement of hydrothermal stability

Abstract

It is an urgent desire to decrease release of methane, a potential greenhouse gas, over methane-oxidation catalysts. However, the commonly used Pd-based catalysts normally suffer from poor hydrothermal stability. Here, we report a Pd-Pt bimetallic nano-catalyst stabilized by magnesia-alumina spinel via a facile doping strategy for lean methane combustion. The promoted effects of platinum on the hydrothermal stability of the catalyst are confirmed by XRD, HRTEM, STEM, XPS, CO-DRIFTS characterizations. Pd-Pt bimetallic catalyst can almost maintain its intrinsic catalytic activity (2.7 × 10−5 molCH4 gnoble metal-1s-1 at 260 °C) after harshly hydrothermal aging, while the aged analogous sample without Pt promotion presents remarkably reduced catalytic performance with an increment in CH4 light-off temperature of ca. 50 °C. Kinetic analysis further reveals a much higher turnover frequency (0.011 s-1 at 260 °C) and lower apparent activation energy (119 kJ/mol) of CH4 oxidation on the aged Pd-Pt bimetallic samples. Pt stabilized by magnesia-alumina spinel has a strong interaction with PdO. This interaction could stabilize Pd species in active PdO and also suppress the decomposition of active PdO to less reactive Pd°. Consequently, the sintering resistance of Pt and PdO crystallite and the electron interaction between them could be responsible for the enhanced hydrothermal stability.