In this paper, Cr/MnO2 catalysts were prepared by hydrothermal–calcination method and applied to the catalytic oxidation of formaldehyde (HCHO) at room temperature. The effects of calcination temperature on the physicochemical properties of Cr/MnO2 catalysts were investigated by means of N2 adsorption–desorption, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscope, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Based on this, the formaldehyde removal mechanism of Cr/MnO2 catalysts was proposed. The results showed that the specific surface area, OII/OI, Mn4+/Mn3+ and Cr6+/Cr3+ ratios of the Cr/MnO2 catalysts varied with the calcination temperature. The Cr/MnO2 catalyst calcined at 400 °C (CM400) has higher specific surface area (64.6 m2/g) and oxygen vacancy content, so it exhibits better formaldehyde removal performance, which could reach 92.1% within 22 h. It is concluded that the high specific surface area, abundant oxygen vacancy content, rich Mn4+ and Cr6+ species are primary reasons for the excellent formaldehyde removal performance of CM400 sample. The Cr/MnO2 catalysts reveal great application potential in indoor formaldehyde degradation, and will be promising industrial formaldehyde degradation catalyst.

The effects of the hydrothermal co-precipitation factors of hydrothermal temperature, hydrothermal time, calcination temperature and calcination time on the crystal structure, microstructure, lattice defect and formaldehyde removal properties at indoor temperature of MnO x -NiO composite oxide catalysts were investigated by using the X-ray diffactiono (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and the catalytic activity testing apparatus. The results showed that the formaldehyde removal rate of the catalysts would increase first and then decrease with increasing in the hydrothermal temperature, or hydrothermal time, calcination temperature, calcination time. The maximum formaldehyde removal rate at indoor temperature is 95.57% with the best technology of the catalysts is as the following: 0.0125 mol potassium permanganate, 0.005 mol nickel nitrate, 5 ml sodium oxalate solution, 0.5 ml ammonia solution, hydrothermal 5 h at 130 °C and then calcination 5 h at 200 °C, the loose spherical accumulation specimen was composed of amorphous and crystal, and existed abundant Mn 4+ species and lattice oxygen on the catalyst surface.