Synergistic effect between Pt and Ir in PtIr/TiO₂ bimetallic catalysts boosting methane combustion activity

Highly efficient catalysts for methane combustion have long been pursued due to the intrinsic inertness of CH₄. In this work, bimetallic PtIr/TiO₂ catalysts with varying Pt:Ir ratios were synthesized to modulate the electronic structures of the metals, thereby achieving bimetallic synergy to enhance CH₄ combustion activity. Among the series of monometallic and bimetallic catalysts, Pt_0.5Ir_0.5/TiO₂ exhibited the highest activity, achieving complete CH₄ conversion (T₁₀₀) at 370 °C after activation during the first reaction cycle. Combined experimental and computational studies elucidated that the incorporation of Ir facilitated electron transfer and the formation of partially oxidized Pt^δ+ (0 < δ < 2) species, which were coordinatively unsaturated and more conducive for CH₄ oxidation. The high affinity of Ir for oxygen enabled the Pt^δ+ species to be stabilized under CH₄ oxidation reaction conditions, instead of being overoxidized into Pt²⁺ species as in the monometallic Pt₁/TiO₂ catalyst. Simultaneously, Ir species in the bimetallic catalyst were oxidized into Ir^δ+ species during the reaction and ultimately formed the Pt^δ+-O-Ir^δ+ interface to further elevate the reaction activity. Moreover, the bimetallic catalysts integrated the merits of Ir for CH₄ adsorption and Pt for intermediates conversion, synergistically boosting the reaction activity. This work provides insight into designing effective CH₄ combustion catalysts through fine-tuning the metal electronic structures.