Revealing the Role of MnO 2 Phase Structure for Efficient Oxidation of Formaldehyde at Room Temperature

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.