Diatomite-supported birnessite–type MnO2 catalytic oxidation of formaldehyde: Preparation, performance and mechanism

Abstract

Diatomite-supported birnessite–type MnO2 (δ-MnO2) with different loadings were synthesized through in-situ reduction method by methanol (Mnx/DM-MT) and hydrothermal reduction method by ammonium oxalate (Mnx/DM-AO), respectively. The as-synthesized catalysts were characterized by N2 adsorption-desorption, X-Ray diffraction, transmission electron microscope, scanning electron microscope, Raman, H2-temperature programmed reduction, thermogravimetric, X-ray photoelectron spectroscopy, and in-situ diffuse reflectance infrared Fourier transform spectrometry, and then utilized to catalytic oxidation of formaldehyde at ambient temperature and low temperature (50–250 °C). Compared with the Mnx/DM-MT catalyst, the Mnx/DM-AO catalyst exhibited superior catalytic activity in degrading HCHO at ambient temperature and low temperature. The highly defective structure, abundant hydroxyl groups, rich lattice oxygen and Mn3+ species were responsible for the excellent performance of Mnx/DM-AO. Meanwhile, the Mnx/DM-AO still exhibited good stability obtained from the cyclic testing. In-situ DRIFTS analysis indicated that δ-MnO2 provided the reactive site, while the diatomite carrier dispersed MnO2 and also provides a small number of active sites. The synergistic effect between diatomite and δ-MnO2 benefits the catalytic performance in removal HCHO. The advantages of high activity, low-cost and environment-friendly, suggested that Mn/DM-AO catalyst exhibits promising application foreground in catalytic oxidation of formaldehyde at the temperature from ambient to 250 °C.