Electrothermal Effect in Formaldehyde Oxidation over a Nickel-Supported Nano δ-MnO₂ Catalyst

Catalytic oxidation over base metal oxides is widely studied for the abatement of indoor formaldehyde (HCHO), typically working at a higher temperature than the ambient. The conventional heating (CH) method has low heat-saving efficiency, often resulting in a significant increase in ambient temperature. In this work, the electric heating (EH) mode was used to generate electric current for catalyst heating and presented an increased heating efficiency at a lower power input in comparison to the CH mode. The typical nano δ-MnO2 was prepared via a hydrothermal method and deposited on the porous Ni foam (Mn/Ni) as a catalyst for the HCHO conversion. Under the EH mode, complete HCHO conversion was achieved at about 60 °C, which is much lower than that of the CH mode (95 °C). In addition, the Mn/Ni catalysts in the EH mode showed high water resistance and durability. Complementary characterizations indicated that the nano morphology and crystal structure of the δ-MnO2 had no change after being loaded on Ni foam, as well as that during the EH and CH reactions, but the release of lattice oxygen was enhanced by an electronic effect, leading to the rapid migration to the catalyst surface and an enhanced activity. Thus, the Mn/Ni catalyst achieved energy-efficient HCHO abatement under EH mode at a near-normal temperature of 60 °C, demonstrating the potential for practical applications in air purification devices.