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 PtOx adhered to the RuO2 surface, in addition to a single PtOx 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 PtOx species. This study opens a new route for structurally designing promising catalysts for CH4 oxidation.Graphical abstract