Unraveling the Reaction Mechanism of HCHO Catalytic Oxidation on Pristine Co3O4 (110) Surface: A Theoretical Study

Various reaction mechanisms for the catalytic degradation of formaldehyde (HCHO) remain to be debated. Density functional theory (DFT) was applied to investigate whether the catalytic oxidation of HCHO on pristine Co3O4 (110) surface follows the Mars-van Krevelen (MvK) mechanism or the Langmuir-Hinshelwood (L-H) mechanism. Firstly, HCHO and O-2 co-adsorb on the surface and two H atoms from HCHO are peculiarly prone to transfer to O-2, forming CO and HOOH. For the MvK mechanism, CO2 is generated through CO grabbing a lattice oxygen. Meanwhile, the O-O bond of HOOH is broken into two OH groups. One OH fills the oxygen vacancy and its H atom moves to another OH group for H2O formation. For the L-H mechanism, CO directly obtains one OH group to generate COOH. Subsequently, the H atom of COOH transfers to another OH group along with CO2 and H2O generation. Both two mechanisms exhibit a similar maximum activation barrier. The lattice oxygen in the MvK mechanism and the surface-absorbed OH group in the L-H mechanism are the key reactive oxygen species. The small difference in energetic span further suggests that the catalytic cycle through the two mechanisms is feasible. This theoretical study provides new insight into the catalytic reaction path of HCHO oxidation on pristine Co3O4 surface.