Highly selective gas-phase oxidation of ethanol to ethyl acetate over bi-functional Pd/zeolite catalysts

Biomass-based ethanol is a potentially promising feedstock and its transformation into value-added chemicals has attracted growing attention. Herein we reported that bi-functional zeolite supported Pd nanoparticle catalysts achieved superior performance in gas-phase selective aerobic oxidation of ethanol to acetaldehyde and ethyl acetate under mild conditions. The selectivity to ethyl acetate and the ethanol conversion remained at 94.7% and 98.6%, respectively, after a long-term reaction for 73 h over the 2Pd/HY catalyst, while acetaldehyde selectivity of 89.0% was obtained on 2PdO/HY at a low temperature of 150 °C. The reaction selectivity can be readily tuned by controlling the oxidation state of the Pd species, the type of zeolite support and the reaction conditions. The coexistence of the Pd⁰ and Pd²⁺ species and a moderate oxygen supply played critical roles in following the partial oxidation route to form ethyl acetate rather than formation of acetaldehyde or acetic acid. The specific interaction between metallic Pd nanoparticles and the acidic zeolite surface via the reverse hydrogen spillover process was also speculated to be responsible for the improved catalytic performances.