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

• Oxidizing atmosphere converts PdPt particle to Pt-rich core-PdO shell structure. • PdO shell with underneath Pt core is highly effective for C–H activation of CH 4 . • Adsorption of H 2 O/SO 2 derived species increases effective CH 4 activation barriers. • Kinetically relevant C–H cleavage on Pt core-PdO shell with or without H 2 O/SO 2 . • Pt-rich core-PdO shell cluster is more resistant to H 2 O than SO 2 comparing to PdO. 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 Pd 0 Pt 0 nanoparticles distributed in sizes and Pt:Pd ratios. Oxidative treatments, including treatments in CH 4 -O 2 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 Pd 2+ -O 2− site pairs that are highly effective for C–H activation in methane—the CH 4 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. H 2 O and SO 2 impurities increase the effective barrier to 58 and 116 kJ mol −1 , respectively, but such effects remain much smaller than on unpromoted PdO.