Synthesis of MnO2 modified porous carbon spheres by preoxidation-assisted impregnation for catalytic oxidation of indoor formaldehyde

Resin-based porous carbon spheres with well dispersed MnO2 particles were sucessfully synthesised by steam activation and preoxidation-assisted impregnation of manganese nitrate salt. X-ray diffractometer (XRD), Fourier Transform Infrared spectroscopy (FT-IR), N2 adsorption–desorption, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), O2 temperature-programmed desorption (O2-TPD) and in-situ diffuse reflectance fourier transform spectrometry (DRIFTS) were applied to characterize the obtained porous carbon spheres, and the HCHO adsorption and stability performances were evaluated in a fixed bed reactor. The results demonstrated that surface chemical properties and HCHO removal performances were significantly enhanced after the modification of preoxidation-assisted impregnation. The optimal manganese nitrate loading value, and relative humidity were 6 and 50%, respectively. Moreover, the higher HCHO concentration showed a smaller breakthrough time. The HCHO removal efficiency of ACS–O-6% Mn remained 100% even after reaction for 20 h at room temperature, while the average HCHO removal efficiency only declines by 0.2% compared with the first adsorption after 10 regeneration cycles. The in-situ DRIFTS results showed the smaller accumulation and faster desorption of intermediate products over the ACS–O-6% Mn. The HCHO removal mechanism analysis indicated that the enriched Mn3+ and surface active chemisorbed oxygen accounted for the excellent catalytic oxidation activity and stability.