Controlled porous hollow Co3O4 polyhedral nanocages derived from metal-organic frameworks (MOFs) for toluene catalytic oxidation

A series of hollow Co3O4 polyhedron with different sizes were successfully synthesized via pyrolysis of ZIF-67, which was applied to the catalytic oxidation of toluene. Notably, the size effect of hollow Co3O4 polyhedron on the catalytic oxidation of toluene was systematically investigated. It was worth mentioning that the samples still retained the nanosize and shapes of the MOF precursor according to SEM and TEM results. Especially, the Co3O4-400 catalyst with 400 nm size exhibited superior catalytic performance, and the complete conversion temperature of toluene (T100) was 280 °C. Through a series of characterizations, it was concluded that the particles size of hollow Co3O4 polyhedron could evidently alter their surface atomic ratio of Co3+/Co2+. Simultaneously, we discovered that the catalytic performance of hollow Co3O4 polyhedron was obviously improved with the increase of surface atomic ratio of Co3+/Co2+. In addition, lots of surface adsorbed oxygen would speed up the catalytic oxidation of toluene. Furthermore, no significant decrease in catalytic performance was observed over 30 h at 250 °C on the Co3O4-400 sample, which indicated that it exhibited excellent stability for toluene oxidation. Therefore, it showed potential as a metal-oxide catalyst in elimination of toluene.