Reaction pathway investigation using in situ Fourier transform infrared technique over Pt/CuO and Pt/TiO2 for selective glycerol oxidation

In this work, we found the supports themself could participate in the reaction to improve the catalyst activity and influence the product selectivity. The Pt-sol, Pt/CuO and Pt/TiO2 were prepared for glycerol oxidation and a dual catalytic site formed by Pt species with the surface atoms of the supports. After doping Pt, the activity of the catalyst was enhanced 1.4 times for Pt/CuO catalyst and 11.1 times for Pt/TiO2 catalyst. Interestingly, Pt/CuO showed an exceptional oxidation selectivity of secondary glycerol compared with the selectivity of Pt-Sol and Pt/TiO2. In situ Fourier Transform Infrared (FTIR) spectra results were performed to confirm this specific selectivity of the catalysts. Moreover, we found that the hydrogen-bonding interaction was temperature-sensitive interaction associated with the secondary hydroxyl group adsorbed on surface O atoms (Osurf) of Pt/CuO catalyst. In Pt/TiO2 catalyst, the surface Ti species (Tisurf) involved in the bridging alkoxy interaction was temperature-sensitive interaction with the primary hydroxyl. Based on the kinetic study, we proposed three kinds of glycerol oxidation pathway. The Pt species could activate the dioxygen and realize the primary hydroxyl oxidation by themself. In Pt-based metal oxide catalyst, the dual Pt-Osurf site selectively oxidated the secondary hydroxyl (Pt/CuO) and the dual Pt-Tisurf site favored the oxidation of primary hydroxyl (Pt/TiO2).