Active site structure and methane oxidation reactivity of bimetallic Pd and Pt nanoparticles

Abstract

Kinetic, oxygen uptake, microscopic, and spectroscopic studies shed light on the structural dynamics of PdPt bimetallic catalysts and their methane oxidation rates. Reductive treatments lead to Pd0Pt0 nanoparticles distributed in sizes and Pt:Pd ratios. Oxidative treatments, including treatments in CH4-O2 reaction mixture, lead the Pd, as the more oxophilic metal, to migrate onto the surfaces and undergo bulk oxidation, forming a thin PdO shell covering the underneath Pt-rich core. Residing on the PdO shell are Pd2+-O2− site pairs that are highly effective for C–H activation in methane—the CH4 turnover rates are the highest at 0.3 Pt:Pd ratio and the C–H activation barrier decreases from 64 to 37 kJ mol−1 as the Pt:Pd ratio increases from 0 to 1. H2O and SO2 impurities increase the effective barrier to 58 and 116 kJ mol−1, respectively, but such effects remain much smaller than on unpromoted PdO.