Catalytic formaldehyde removal by " storage-oxidation" cycling process over supported silver catalysts

Catalytic removal of indoor HCHO was proposed to proceed in a " storage-oxidation" cycling process. Two kinds of supported silver catalysts, namely Ag/HZSM-5 and Ag-MnO_x-CeO_2, were investigated as catalysts for this cycling process. Due to the highly dispersed silver clusters formed and its good redox properties, the Ag-MnO_x-CeO₂ catalyst showed better HCHO oxidation properties in both the storage phase (HCHO partial oxidation to HCOO^- at room temperature) and oxidation-regeneration phase (total oxidation of the formates into CO₂ and H₂O at elevated temperatures). The presence of H₂O (RH=50%, 25°C) was found to enhance the HCHO storage capacity for Ag-MnO_x-CeO₂ catalyst, while competitive adsorption of HCHO with H₂O was observed over Ag/HZ catalyst. The results of DRIFTS indicate that the partial oxidation of HCHO into HCOO^- is accelerated by the presence of H₂O over the Ag-MnO_x-CeO₂ catalyst. In addition, the catalyst saturated with HCHO can be in situ regenerated without production of secondary pollutants and can be used repeatly. It is suggested that this is a promising approach for indoor HCHO elimination.