Low-temperature thermocatalytic removal of formaldehyde in air using copper manganite spinels

The removal of formaldehyde (FA) is vital for indoor air quality management in light of its carcinogenic propensity and adverse environmental impact. A series of copper manganite spinel structures (e.g., CuMn₂O₄) are prepared using the sol-gel combustion method and treated with reduction or oxidation pretreatment at 300 °C condition. Accordingly, CuMn₂O₄-O ("O" suffix for oxidation pre-treatment in air) is identified as the best performer to achieve 100% conversion (X_FA) of FA (50 ppm) at 90 °C; its performance, if assessed in terms of reaction kinetic rate (r) at X_FA = 10%, is 5.02E-03 mmol g^-1 h^-1. The FA removal performance increases systematically with decreases in flow rate, FA concentration, and relative humidity (RH) or with increases in bed mass. The reaction pathways and intermediates of FA catalytic oxidation on CuMn₂O₄-A are studied with density functional theory simulations, temperature-programmed characterization experiments, and in-situ diffuse reflectance infrared Fourier transform spectroscopy. The synergistic combination of large quantities of adsorbed oxygen (O_A) species and oxidized metal species (e.g., Cu²⁺) contribute to the enhanced catalytic performance of CuMn₂O₄-O to oxidize FA into CO₂ with the reaction intermediates of H₂CO₂ (DOM), HCOO^-, and CO. The present study is expected to provide valuable insights into the thermocatalytic oxidation of FA over spinel CuMn₂O₄ materials and their catalytic performances in relation to the key process variables.