Enhanced oxidative ability, recyclability, water tolerance and aromatic resistance of α-MnO2 catalyst for room-temperature formaldehyde oxidation via simple oxalic acid treatment

To obtain a versatile formaldehyde oxidation material, simultaneously increasing the oxidative ability, recy-clability and deactivation repellence (e.g., enduring the interference from moisture and aromatic compound omnipresent in indoor air) is of great significance. Herein, the above properties of alpha-MnO2 were synchronously updated via one step treatment in oxalic acid (H2C2O4), and an in-depth understanding of the surface properties -performance relationship was provided by systematic characterizations and designed experiments. Compared with the pristine sample, XPS, ESR, O2-TPD, CO-TPR and pyridine-IR reveal that H2C2O4 created substantial Mn3+ species on surface, exposing a higher coverage of oxygen vacancies that actively participated in the dissociative activation of gas-phase O2 into reactive chemically adsorbed oxygen (OC), and the abundant Lewis acid sites further enabled the effective O2 activation process. The large amount of oxygen OC promoted the HCHO-to-CO2 conversion and inhibited the accumulation of formate that required a high temperature of 170 degrees C to be eliminated, thus conspicuously improving the alpha-MnO2's thermal recovery. The combined H2O-TPD, H2O-preadsorbed CO-TPR, C6H6-TPD and C6H6-preadsorbed CO-TPR investigations shed light on the H2C2O4-induced water and benzene resistance. The notably weakened water and benzene binding strength with the H2C2O4- modified surface together with the unrestrained oxygen OC accounted for the outstanding anti-deactivation performance.

Automated summary

Simultaneously increasing the oxidative ability, recy-clability and deactivation repellence of α-MnO2 was achieved through one step treatment in oxalic acid (H2C2O4), resulting in a versatile formaldehyde oxidation material.