Transition metal-doped modification of lattice defects in formaldehyde catalysts − Controlling the specific surface area and mass transfer

This abstract presents a formaldehyde catalytic mechanism diagram, illustrating the formaldehyde in the reaction process of side reactions and providing a deeper understanding of its underlying mechanisms. [Display omitted] •The low crystallinity structure favors an increase in the concentration of oxygen defects, leading to an increase in the concentration of surface reactive oxygen species.•Cr doping results in an increase in the specific surface area and enhances mass transfer, facilitating diffusion and reaction of gas molecules.•The improvement of redox capacity and electron transport capacity accelerates the intermediate transformation and makes the reaction path more concise and efficient. Exploring room temperature treatment of formaldehyde (HCHO) is a crucial area of ongoing research, with transition metal catalysts showing promise for future development due to their cost-effectiveness. However, the challenge lies in the limited ability of these catalysts to activate oxygen efficiently and maintain stable catalytic oxidation of HCHO. The Mn3O4 catalyst doped with Cr, Cu, Zn, and Co was synthesized via hydrogen reduction in this study. Cr/Mn3O4 showed exceptional catalytic performance by completely converting HCHO at 30 °C and 200 ppm, while maintaining excellent stability during a 75-hour durability test. The characterization techniques revealed that the incorporation of transition metal Cr into the Mn3O4 lattice resulted in an increased number of oxygen vacancy defects on its surface, thereby significantly enhancing its ability to activate oxygen. Furthermore, Cr doping substantially augmented the specific surface area and abundance of mesoporous structures in the catalyst, which provided ample active sites and facilitated efficient mass transfer for substrate oxidation by promoting diffusion to these active sites. These enhancements ultimately led to a heightened activation of oxygen and H2O into reactive oxygen species, consequently reducing the dominance of side reaction pathways caused by intermediates occupying active sites.