In situ loading of highly-dispersed CuO nanoparticles on hydroxyl-group-rich SiO2-AlOOH composite nanosheets for CO catalytic oxidation

Abstract

Emerging hierarchical porous SiO2-AlOOH (SA) composite nanosheets were synthesized via structural reorganization of natural layer kaolin clay (KC). CuO nanoparticles were further attached on SA by in-situ chemical precipitation method for CO catalytic oxidation. The results demonstrated the relationship between synthesis, structure and performance of the catalytic system. Hydroxyl-group-rich SA composite nanosheets with high specific surface area could ensure the well dispersion of CuO nanoparticles through in-situ loading method without high-temperature calcination, further increasing the Cu active sites and retaining adequate hydroxyl groups. Hierarchical porous structure resulting from self-assembly of nanostructures (varisized sheets and particles) showed excellent physical adsorption performance for reactant gases. DRIFTS and XPS results revealed the possible role of three main surface reactive sites in this CuO/SA catalytic system: the coordinatively unsaturated Cu2+ of Si(Al)OCu bonds adsorbed gaseous CO, the Cu2+ with anionic vacancies on highly-dispersed CuO nanoparticles adsorbed gaseous O2, and the surface hydroxyls could promote CO oxidation by the chemisorption of gaseous CO as a formation of formate species to increase the CO concentration around the Cu active sites. A Langmuir–Hinshelwood mechanism of the hydroxyl-assisted CuO/SA for enhancing CO catalytic oxidation was also proposed.