Efficient and Durable\nOxidation Removal of Formaldehyde\nover Layered Double Hydroxide Catalysts at Room Temperature

Abstract

Room temperature catalytic oxidation (RTCO) using non-noble\nmetals\nhas emerged as a highly promising technique for removal of formaldehyde\n(HCHO) under ambient conditions; however, non-noble catalysts still\nface the challenges related to poor water resistance and low stability\nunder harsh conditions. In this study, we synthesized a series of\nlayered double hydroxides (LDHs) incorporating various dual metals\n(MgAl, ZnAl, NiAl, NiFe, and NiTi) for formaldehyde oxidation at ambient\ntemperature. Among the synthesized catalysts, the NiTi-LDH catalyst\nshowed an HCHO removal efficiency and CO₂ yield close to\n100.0%, and exceptional water resistance and chemical stability on\nrunning 1300 min. The abundant hydroxyl groups in LDHs directly bonded\nwith HCHO, leading to the production of CO₂ and H₂O, thus inhibiting the formation of CO, even in the absence of O₂ and H₂O. The coexistence of O₂ effectively\nreduced the reaction barrier for H₂O molecule dissociation,\nfacilitating the formation of hydroxyl groups and their subsequent\nbackfill on the catalyst surface. The mechanisms underlying the involvement\nand regeneration of hydroxyl groups in room temperature oxidation\nof formaldehyde were elucidated with the combined in situ DRIFTS,\nHCHO-TPD-MS, and DFT calculations. This work not only demonstrates\nthe potential of LDH catalysts in environmental applications but also\nadvances the understanding of the fundamental processes involved in\nroom temperature oxidation of formaldehyde.