Uniphase ruthenium–iridium alloy-based electronic regulation for electronic structure–function study in methane oxidation to methanol

Abstract

For the first time, we synthesize uniphase face-centered-cubic (fcc) structured Ru–Ir alloy nanoparticles (NPs) with a uniform size of ∼2 nm over the whole composition range, using RuCl₃ and IrCl₄ as precursors. The electronic structure of Ir is gradually tuned by varying the composition. The consistency of the fcc structure of Ru and Ir within the Ru_xIr_1−x alloys allows better study of the electronic structure–activity relationship without introducing unnecessary factors such as the lattice/phase effect in the case of the RuIr alloy composed of different structures of hcp-Ru and fcc-Ir. The obtained Ru_xIr_1−x alloys were further employed as precursors for the synthesis of their corresponding oxides, Ru_xIr_1−xO₂/CuO, to probe the electronic structure–activity relationship in the methane oxidation to methanol reaction. The electronic structure of Ir⁴⁺ was able to be regulated by tuning the composition of the Ru_xIr_1−x NP precursors. The optimum catalytic behavior was achieved over Ru_0.5Ir_0.5O₂/CuO, where both Ru and Ir reached the highest electrophilic state, at which point the C–H cleavage capacity also reached the maximum as observed by CH₄-TPR.