Revealing the Synergy between Oxide and Alloy Phases on the Performance of Bimetallic In–Pd Catalysts for CO₂ Hydrogenation to Methanol

Abstract

In2O3 has recently emerged as a promising catalyst for methanol synthesis from CO2. In this work, we present the promotional effect of Pd on this catalyst and investigate structure–performance relationships using in situ X-ray spectroscopy, ex situ characterization, and microkinetic modeling. Catalysts were synthesized with varying In:Pd ratios (1:0, 2:1, 1:1, 1:2, 0:1) and tested for methanol synthesis from CO2/H2 at 40 bar and 300 °C. In:Pd(2:1)/SiO2 shows the highest activity (5.1 μmol MeOH/gInPds) and selectivity toward methanol (61%). While all bimetallic catalysts had enhanced catalytic performance, characterization reveals methanol synthesis was maximized when the catalyst contained both In–Pd intermetallic compounds and an indium oxide phase. Experimental results and density functional theory suggest the active phase arises from a synergy between the indium oxide phase and a bimetallic In–Pd particle with a surface enrichment of indium. We show that the promotion observed in the In–Pd system is extendable to non precious metal containing binary systems, in particular In–Ni, which displayed similar composition–activity trends to the In–Pd system. Both palladium and nickel were found to form bimetallic catalysts with enhanced methanol activity and selectivity relative to that of indium oxide.