Operando synchronous DRIFTS/MS/XAS as a powerful tool for guiding the design of Pd catalysts for the selective oxidation of alcohols

The selective aerobic oxidation of crotyl alcohol to crotonaldehyde was investigated by time-resolved synchronous DRIFTS/MS/XAS over silica and alumina supported Pd nanoparticles. Alcohol and oxygen reactant feeds were cycled through the catalyst bed while dynamic measurements of the palladium oxidation state, molecular adsorbates and evolved product distribution were made simultaneously on a sub-second timescale. Highly dispersed palladium nanoparticles remained in a partially oxidised state <100 °C, independent of the redox environment, and were selective for crotonaldehyde formation. Higher temperatures facilitated rapid catalyst reduction on exposure to crotyl alcohol, with palladium metal driving crotonaldehyde decarbonylation to propene and CO, while slower (surface diffusion-limited) re-oxidation on exposure to oxygen re-opened selective oxidation pathways. Surface palladium oxide is identified as the desired active species.