Layered manganese oxides for formaldehyde-oxidation at room temperature: the effect of interlayer cations

A series of K-, Mg-, Ca-, and Fe-containing birnessites were prepared by a facile comproportionation reaction of Mn2+ and MnO4− in the presence of different metal cations. The as-synthesized birnessite samples were characterized by FESEM, XRD, TG, and XPS. The catalytic activity toward decomposition of HCHO was evaluated under ambient temperature. Fe-birnessite showed the highest HCHO oxidation activity due to its highest content of surface hydroxyl groups. However, the CO2 generation by Fe-birnessite was relatively low due to the accumulation of formate species without further oxidation. The influence of different interlayer cations on the activity of birnessite was studied by H2-TPR, O2-TPD, and HCHO in situ DRIFTS. The result indicates that K+ leads to a considerable enhancement of surface oxygen activity which then facilitates the regeneration of surface hydroxyls by activating H2O, therefore K-birnessite showed the highest CO2 generation performance during HCHO removal at ambient temperature. HCHO of 0.5 mg m−3 and the gas hourly space velocity (GHSV) of 1 200 000 h−1 (the corresponding contact time is 0.003 s) were selected to check the stability of the samples. K-Bir still showed stable activity with the removal efficiency reaching 40% under these critical test conditions. Considering the effect of introducing different metal cations, this work provides new insight into designing high performance catalysts for indoor air purification.