Oxidation of methane to methanol over Pd@Pt nanoparticles under mild conditions in water

Abstract

Direct methane oxidation into oxygen-containing chemicals under mild conditions has sparked increasing interest. Here, we report Pd@Pt core–shell nanoparticles that efficiently catalyse the direct oxidation of CH₄ to CH₃OH in water using H₂O₂ as an oxidant under mild conditions. The catalyst presents a methanol productivity of up to 89.3 mol kg_catalyst⁻¹ h⁻¹ with a high selectivity of 92.4% after 30 min at 50 °C, thus outperforming most of the previously reported catalysts. Electron-enriched Pt species in the Pd@Pt nanoparticles were identified by structural and electronic analysis. Pd in the core donates electrons to Pt, leading to higher rates of methane activation. Based on the results of control experiments and kinetic analysis, a consecutive oxidation pathway via a radical mechanism is proposed, which includes initial formation of CH₃OOH and CH₃OH followed by further oxidation of CH₃OH to HCHO, HCOOH, and CO₂.