ABSTRACT The crystal‐phase‐dependent oxidation of formaldehyde (HCHO) over MnO 2 remains insufficiently understood in indoor air purification. Herein, the MnO 2 with different crystal phases (δ‐MnO 2 , α‐MnO 2 , and ε‐MnO 2 ) was synthesized to establish a phase–structure–activity relationship for efficient HCHO mineralization at room temperature. Correspondingly, the optimal 98.07% conversion of HCHO could be achieved, and the maximum mineralization rate for CO 2 reached 88% for δ‐MnO 2 in 30 min. Structural analyses confirmed their distinct architectures, with δ‐MnO 2 exhibiting the highest Mn 4+ /Mn 3+ ratio, the largest amount of chemisorbed oxygen, and the lowest oxygen desorption temperature, reflecting superior redox cycling and oxygen activation. The results of in situ DRIFTS tests revealed a minimized accumulation of dioxymethylene and formate intermediates on the surface of δ‐MnO 2 , consistent with accelerated oxidation kinetics. Besides, DFT calculations further indicated the strongest HCHO adsorption and highest charge transfer over MnO 2 , which intrinsically promotes the deep oxidation of HCHO. This work elucidates the decisive role of crystal‐phase regulation in adjusting redox processes for room‐temperature formaldehyde mineralization.
Gan et al. (2026) studied this question.