Oxidation mechanism of HCHO on copper-manganese composite oxides catalyst

Formaldehyde (HCHO) is a typical air pollutant that severely endangers human health. The Cu-Mn spinel-structure catalyst exhibits good catalytic oxidation activity for HCHO removal. Theoretical calculation study of density functional theory (DFT) was performed to provide an atomic-scale understanding for the oxidation mechanism of HCHO over CuMn₂O₄ surface. The results indicate that the (110) surface containing alternating three-coordinated Cu atom and three-coordinated Mn atom is more active for HCHO and O₂ adsorption than the (100) surface. The Mars-van-Krevelen mechanism is dominant for HCHO catalytic oxidation. This reaction pathway of MvK mechanism includes HCHO adsorption and dehydrogenation dissociation, CO₂ formation and desorption, O₂ adsorption, H₂O formation and surface restoration. In the complete catalytic cycle of HCHO oxidation, the second dehydrogenation (CHO* → CO* + H*) shows the highest energy barrier and is recognized as the rate-limiting step. The relationship of temperature and reaction rate constant is found to be positive by the kinetic analysis. The minimum activation energy of the MvK mechanism via the direct dehydrogenation pathway is 1.29 eV. This theoretical work provides an insight into the catalytic mechanism of HCHO oxidation over CuMn₂O₄ spinel.