Experimental and theoretical study on thermal catalytic degradation of HCHO over Mn2O3 series catalysts

The utilization of manganese oxide catalysts in the thermal catalytic degradation of formaldehyde (HCHO) is widespread due to their beneficial catalytic activity, variable structure, and ease of preparation. This study delves into the oxidation reaction of HCHO on the surface of manganese(III) oxide(Mn2O3) series catalysts through a combination of experimental and theoretical simulation methods. The influence of alumina (Al2O3) loading and doping with Fe, Ce, Ni, Co, and Cu on the catalyst performance was investigated. Various methods such as X-ray diffraction (XRD), N2-adsorption-desorption, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to investigate the structure-activity relationship between the physical morphology and chemical state of catalyst activity and active components. In situ diffuse reflectance infrared Fourier transform spectra (in situ DRIFTS) was used to characterize the intermediates during the reaction and it was found that the major intermediates during formaldehyde oxidation include formate and dioxymethylene (DOM). Throughout the entire reaction process, H2O formation had the highest reaction energy barrier (Eb= 192.70 kJ/ mol), which acted as the rate-determining step of the reaction. The pore structure of the Al2O3-loaded catalysts was more complex, and the relative content of (O alpha+O gamma) increased, improving the conversion of HCHO. Still, the morphology changed from honeycomb to granular, and the agglomeration phenomenon was obvious, resulting in a decrease in the selectivity of CO2. In addition, Fe/Ce doping improved the agglomeration phenomenon of the catalyst and promoted the further oxidation of formaldehyde to CO2.