Synergistic effect of bimetallic RuPt/TiO₂ catalyst in methane combustion

Designing metal compounds based on their structure and chemical composition is essential in achieving desirable performance in methane oxidation, because of the synergistic effect between different metal elements. Herein, a bimetallic Ru–Pt catalyst on TiO₂ support (RuPt-O/TiO₂) was prepared by in situ reduction followed by calcination in air. Compared with monometallic catalysts (Ru-O/TiO₂ and Pt-O/TiO₂), the synergistic effect of mixed metals endowed bimetallic catalysts with excellent stability and outstanding performance in methane oxidation, with a reaction rate of 13.9 × 10^–5 \({\mathrm{mol}}_{{\mathrm{CH}}_{4}}^{-1}\cdot {\mathrm{g}}_{(\mathrm{Ru}+\mathrm{Pt})}^{-1}\cdot {\mathrm{s}}^{-1}\) at 303 °C. The varied characterization results revealed that among the bimetallic catalysts, RuO₂ was epitaxially grown on the TiO₂ substrate owing to lattice matching between them, and part of the PtO_x adhered to the RuO₂ surface, in addition to a single PtO_x nanoparticle with 4 nm in size. Consequently, Pt mainly existed in the form of Pt²⁺ and Pt⁴⁺ and a small amount of zero valence in the bimetallic catalyst, prompting the adsorption and activation of methane as the first and rate-controlling step for CH₄ oxidation. More importantly, the RuO₂ species provided additional oxygen species to facilitate the redox cycle of the PtO_x species. This study opens a new route for structurally designing promising catalysts for CH₄ oxidation.