Size effect of Co–N–C-functionalized mesoporous silica hollow nanoreactors on the catalytic performance for the selective oxidation of ethylbenzene

Abstract

Mesoporous silica hollow nanoreactors have attracted significant attention owing to their controllable size, high specific surface area, and large pore volume. In this study, Co–N–C-functionalized mesoporous silica hollow nanoreactors with various void sizes were prepared via pyrolyzing mesoporous silica hollow spheres impregnated with cobalt porphyrin in an inert atmosphere. It was found that the size of the void in the hollow nanoreactors exerted a great influence on the catalytic performance for the selective oxidation of ethylbenzene. With the increase in void sizes in the range from 200 nm to 2900 nm, the catalytic performance of the nanoreactors displayed a volcanic-type trend. Among all the nanoreactors, the catalyst with 280 nm void size exhibited excellent catalytic performance due to its optimal size effect and presence of plenty of Co–N_X active sites. Actually, the size effect was closely related to void-confinement effect, which led to a reinforcement of the local concentration and long residence time of the reactant intermediates. Only the nanoreactor with suitable void size could exhibit the optimal void-confinement effect by achieving an ideal balance between enrichment and diffusion and display superior catalytic performance.