Room temperature deposition of ¡«4 monolayer equivalents (MLEs) of In metal on Pd foil and subsequent annealing to 453 K in vacuum yields a ¡«1:1 Pd/In near-surface multilayer intermetallic phase. This Pd1In1 phase exhibits a similar ¡°Cu-like¡± electronic structure and indium depth distribution as its methanol steam reforming (MSR)-selective multilayer Pd1Zn1 counterpart.
Catalytic characterization of the multilayer Pd1In1 phase in MSR yielded a CO2-selectivity of almost 100 % between 493 and 550 K. In contrast to previously studied In2O3-supported PdIn nanoparticles and pure In2O3, intermediate formaldehyde is only partially converted to CO2 using this Pd1In1 phase. Strongly correlated with PdZn, on an In-diluted PdIn intermetallic phase with ¡°Pd-like¡± electronic structure, prepared by thermal annealing at 623 K, methanol steam reforming is suppressed and enhanced CO formation via full methanol dehydrogenation is observed.
To achieve CO2-TOF values on the isolated Pd1In1 intermetallic phase as high as on supported PdIn/In2O3, at least 593 K reaction temperature is required. A bimetal-oxide synergism, with both bimetallic and oxide synergistically contributing to the observed catalytic activity and selectivity, manifests itself by accelerated formaldehyde-to-CO2 conversion at markedly lowered temperatures as compared to separate oxide and bimetal. Combination of suppression of full methanol dehydrogenation to CO on Pd1In1 inhibited inverse water-gas-shift reaction on In2O3 and fast water activation/conversion of formaldehyde is the key to the low-temperature activity and high CO2-selectivity of the supported catalyst.