Oxidation of methanol to methyl formate over supported Pd nanoparticles: insights into the reaction mechanism at low temperature

Abstract

Pd nanoparticles supported on TiO₂ and SiO₂ (2 wt.%) were synthesized by the water-in-oil microemulsion method. The materials were characterized by standard physico-chemical methods (XRD, ICP, TEM, BET, XPS) and DRIFT in operando mode and tested in the gas-phase reaction of methanol oxidation. The direct formation of methyl formate (MF) from methanol was observed. Supported palladium catalysts produced methyl formate at low temperature (<100 °C) with high selectivity. At higher temperatures methyl formate is no longer formed and the total oxidation to CO₂ occurred. The DRIFT-operando study confirmed that methanol is adsorbed mainly in two forms, the undissociated gaseous methanol (via H bond) and dissociatively adsorbed methoxy species (CH₃O⁻) on the surface. Methyl formate is formed already at RT with the maximum at about 80 °C. The mechanism of the formation of methyl formate from methanol at low temperature is discussed.