Insight into the Oxidation Mechanism of Furanic Compounds on Pt(111)

Partial oxidation of multifunctional oxygenates is of interest for the production of high-value chemicals, but the understanding of the mechanism on Pt catalysts is lacking. To probe the effects of oxygen in the reaction of furanics on Pt(111), temperature-programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), electrochemical catalytic experiments, and density functional theory (DFT) calculations were conducted. The presence of oxygen on the Pt(111) surface significantly altered the reaction paths for furan and furfuryl alcohol oxidation. Although furan desorbed without reaction from clean Pt(111) during TPD, on the O precovered surface, extensive oxidation and decomposition reactions were observed. The main volatile products were H₂O, CO, and CO₂. HREEL spectra and DFT calculations indicated that furan initially reacted through oxygen addition to the ring to produce surface-adsorbed furanone intermediates. For furfuryl alcohol, the same desorption products were formed, but maleic anhydride was also detected as a trace product. HREELS and DFT calculations suggested that alcohol oxidation proceeded through dehydrogenation at the hydroxyl and methylene groups and subsequent oxidation to produce a carboxylate intermediate. The carboxylate intermediate underwent decarboxylation to form CO₂ and surface furyl intermediates, which then underwent deep oxidation and decomposition. Thus, the presence of the oxygenated side chain on the furan ring for furfuryl alcohol strongly influenced the oxidation chemistry. Comparison of furfural electrocatalytic oxidation results on Pd (collected here) and Pt (from previous work) indicated that Pt is less active for C-C activation but more active for insertion of oxygen atoms into the furan ring, in line with the current and previously published surface science results.