Catalytic reaction mechanism of formaldehyde oxidation by oxygen species over Pt/TiO catalyst.

Theoretical calculations based on density functional theory (DFT) were employed to uncover the molecular-level oxidation mechanism of HCHO over Pt/TiO surface. All the three possible reaction mechanisms including Eley-Rideal mechanism, Langmuir-Hinshelwood mechanism and Mars-Van Krevelen mechanism were deeply investigated to determine the primary channel of HCHO oxidation on Pt/TiO catalyst. The adsorption energies and geometries show that HCHO and O are chemically adsorbed on Pt and Ti sites of the Pt/TiO catalyst surface, respectively. The adsorption energy of O (-141.91 kJ/mol) is higher than that of HCHO (-122.03 kJ/mol). HCHO oxidation reaction mainly occurs through the Eley-Rideal mechanism: gaseous HCHO reacts with activated O produced from the dissociation reaction of molecular oxygen on Pt/TiO surface by comparing the three possible mechanisms. HCHO oxidation reaction prefers the pathway of HCHO → HCO → HCO → CO. In the whole HCHO oxidation reaction, the elementary reaction of HCO dehydrogenation presents the highest activation energy barrier of 230.45 kJ/mol. Therefore, HCO dehydrogenation is recognized as the rate-determining step. The proposed skeletal reaction scheme can be used to well understand the microcosmic reaction process of HCHO oxidation on Pt/TiO catalyst.