Ultrafine cobalt oxide nanoparticles embedded in porous SiO₂ matrix as efficient and stable catalysts for methane combustion

Ultrafine cobalt oxide nanoparticles embedded in porous SiO₂ matrix were facilely prepared by a spontaneous deposition method, which were applied to catalytic methane combustion. Among the serial of CoO_x@SiO₂-T catalysts, the CoO_x@SiO₂-400 catalyst with the smallest particle size (˜1.3 nm) has the highest activity, showing an obvious size-dependent activity. Based on the XPS, O₂-TPD and H₂-TPR analyses, it indicated that the CoO_x@SiO₂-400 catalyst possessed a higher ratio of surface absorbed oxygen and lattice oxygen (O_ads/O_latt) and more active sites, which enabled the enhancement of its catalytic activity. Compared with simply supported CoO_x/SiO₂-400 catalyst, the embedded CoO_x@SiO₂-400 catalyst show superior catalytic performance under dry/moisture conditions owing to silica encapsulation. As for possible CH₄ combustion mechanism, the intermediate of Co-formate is determined by in-situ DRIFTS.