Highly exposed metal atomic active sites in Al₂O₃/CoNC: Modify reaction pathways by coupling oxygen species

The catalytic oxidation of formaldehyde (HCHO) at ambient temperature is a highly efficient, cost-effective and environmentally friendly approach for formaldehyde removal. Reactive oxygen (O*) and reactive hydroxyl groups (OH*) are the main active species in the catalytic oxidation reaction of HCHO. Therefore, it is crucial to design catalysts that can simultaneously enhance the surface concentrations of O* and OH*, thereby improving their overall catalytic performance. The present study aimed to design an Al₂O₃/CoNC catalyst featuring layered carbon nitride coupled with metal oxides possessing domain-limited cobalt (Co) metal active sites, to efficiently remove HCHO (≈100 %, 100 ppm, RH=50 %, GSHV=20,000 mL/(g h)) and ensure stability (more than 90 % formaldehyde removal within 450 h) at ambient temperature. The characterization revealed that the interaction between Al₂O₃-supported metal and CoNC resulted in enhanced confinement of Co, leading to a higher abundance of edge structures exposing more active sites. Additionally, the presence of highly dispersed Co-N_X active sites and increased oxygen vacancies effectively facilitated the adsorption and activation processes of HCHO and O₂, as well as the adsorption and desorption dynamics of intermediates during the reaction. These factors collectively contributed to an improved catalytic activity. The results of in situ infrared spectroscopy revealed that the catalyst improved the adsorption and activation of O₂ and H₂O, leading to the rapid generation of substantial amounts of O* and OH*. This synergistic interaction between Al₂O₃ and CoNC plays a crucial role in the sustained production of O* and OH*, promoting efficient of intermediate decomposition, and ensuring excellent catalytic activity and stability for HCHO.