Research On Catalytic Oxidation Of Formaldehyde Over MnO_x-Based Catalysts At Room Temperature

It is well known that formaldehyde(HCHO), the primary indoor pollutant today, is emitted from widely used building and decorative materials. A concentration of formaldehyde exceeded standard level could have a harmful effect on human health, and might even cause cancer. Catalytic oxidation of formaldehyde at room temperature is identified as one of the most effective methods for formaldehyde elimination. Due to its excellent catalytic performance, the research on formaldehyde oxidation over MnOx catalysts is attracting more and more attention.In our work, MnO2 microspheres with various microspheres and structures were prepared by the hydrothermal method, and the Au/MnO2 catalysts were synthesized by the sol-gel method. The catalytic activities of formaldehyde oxidation over MnO2 and Au/MnO2 catalysts at room temperature were investigated. The reaction mechanism of formaldehyde oxidation over Au/MnO2 catalysts was also studied. The results show that:(1) The catalytic activities of formaldehyde oxidation over MnO2 microspheres varied with their crystal structures, hierarchical hollow MnO2 microspheres composed of nanorods and disc-like nanoplatelets(MnO2-S3) showed the highest activities, HCHO conversion at room temperature was 30.6%. The γ-MnO2 phase and manganese species in high oxidation states on the catalyst surface could be responsible for the catalytic activity enhancement.(2) The catalytic activities of Au/MnO2 catalysts also varied with crystal structures of the supports. Au/MnO2-S3 exhibited the highest catalytic activities, 59.2% HCHO was converted into CO2 and H2 O at room temperature. The gold-supports interaction could improve manganese species in high oxidation states on the catalyst surface, and accelerate the transformation of surface oxygen species, which could contribute to the catalytic performance enhancement.(3) A proposed mechanism of HCHO oxidation over Au/MnO2 catalyst was obtained. In this reaction process, the adsorbed HCHO was activated by the lattice oxygen on the surface and quickly oxidized to dioxymethylene(DOM), and the chemisorbed hydroxyl groups played a major role in the formation and oxidation of formate species. The molecular oxygen was activated on the catalyst surface, which could provide the chemisorbed hydroxyl groups for this reaction process.