The effect of manganese vacancy in birnessite-type MnO2 on room-temperature oxidation of formaldehyde in air

Catalytic reaction active site tends to be the structural defects, such as edges, corners, ribs and other position that has low coordination number. Here, the potassium (K+) type birnessite (i.e. a layered-structure MnO2) was designed with different amounts of manganese vacancy (VMn) for catalytic oxidation of formaldehyde (HCHO). The content of VMn was determined by the ratio of Mn/O and coordination number of Mn–Mn edge-sharing structure. The VMn showed a dramatic promotion effect on the activity of birnessite for HCHO oxidation. The specific rate at 30 °C over the birnessite with the highest content of VMn was highest (0.052 μmol/m2 min) under 40 ppm of HCHO, 120,000 mL/g h of GHSV and ∼ 80% of relative humidity. The presence of VMn induced unsaturated oxygen species and K+ locating nearby VMn sites for charge balance facilitated the formation of active oxygen species, accordingly the activity for HCHO oxidation was greatly improved. This finding reveals a way to enhance the catalytic activity of metal oxides via adjusting metal vacancies.