DRIFTS investigation of methanol oxidation on CeO2 nanoparticles

Highlights: • Pseudo-flow and evacuated DRIFTS analysis of methanol reaction with CeO₂ compared. • Methanol chemisorption facilitated by monobound and bridged hydroxyls. • Only bridged methoxy groups found to lead to formate production. • Monobound methoxy species interact with adjacent hydroxyl and transform into bridged methoxy species. • Evacuated DRIFTS in tandem with temperature dependent peak height analysis found to add clarity to mechanism determination. • Mechanism for oxidation of methanol on surface of CeO₂ clarified and illustrated. The mechanism of the oxidation of methanol on the surface of heat treated CeO₂ nanoparticles was studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The study was carried out under high vacuum to ensure no interference from unreacted physisorbed methanol and compared to a similar analysis under pseudo-flow conditions. When methanol reacts with the CeO₂ surface, it either chemisorbs to a single cerium atom creating monobound (m) methoxy or to two neighboring cerium atoms forming bridged (b) methoxy groups. From the evacuated analysis, formate production depends directly on the presence and transformation of b-methoxy groups. Hydroxyls are found to facilitate the formation of the two surface methoxy groups, react with m-methoxy groups creating additional b-methoxy groups, and enable the transformation of b-methoxy groups to bidentate formate groups. The reaction mechanism is elucidated through the use of temperature dependent peak height analysis of the collected DRIFTS spectra which are correlated to the transforming surface bound species.