Gaseous CO and toluene co-oxidation over monolithic core–shell Co3O4-based hetero-structured catalysts

The inhibiting effects using Platinum-group metal (PGM) catalysts are universal problems for CO and hydrocarbons (HCs) co-oxidation, resulting in a higher temperature to handle CO and HCs pollutants. Herein, this work focuses on designing a series of Co-based catalysts whose catalytic activities in individual oxidation and co-oxidation of CO and toluene are comparable to Pt-based catalyst. The catalytic behaviors of CO and toluene oxidation over Pt/Al2O3 are mutually inhibited in the presence of CO and toluene, in which CO oxidation could improve catalytic toluene degradation over Co3O4-based catalysts, its CO oxidation is negatively affected by toluene oxidation. In addition, under the CO and toluene co-existence, light-off temperature of toluene oxidation on both Co3O4-based and Pt-based catalysts consistently followed that of CO oxidation. Among all monolithic core-shell Co3O4-based catalysts, these catalysts introduced into different elements (Co, Mn and Cu) show special promotions for CO and toluene oxidation, and the Co3O4@Co3O4 catalyst exhibits most outstanding catalytic performances for individual oxidation and co-oxidation of CO and toluene. In addition, the physicochemical properties of core-shell hetero-structured catalysts are further characterized in detail by XRD, BET, SEM, TEM, H2-TPR, XPS, O2-TPD and Raman spectrometry. It is confirmed that the excellent performance of Co3O4@Co3O4 catalyst is mainly associated with surface area, surface oxygen vacancies and low-temperature reducibility, whose prominent oxygen vacancy and low-temperature reducibility are induced by the synergistic effect of different Co3O4 structures. In-situ DRIFT spectroscopy confirms that bidentate carbonate species and benzoate species are considered as reaction intermediate species in the CO and toluene oxidation, respectively. Moreover, there is a competitive adsorption-reaction on the active sites of Co3O4-based catalysts for CO and toluene, but the reaction mechanism on the CO/toluene oxidation may be mutually independent in the CO and toluene co-existence.