Unveiling the Promotion Effects of CoO on Low-Temperature NO Reduction with CO over an In-Situ-Established Co3O4–CoO Heterostructure

Co-based catalysts have been widely applied in NO reduction by CO but still suffer from the unsatisfactory low-temperature catalytic performance. Here, a series of catalysts with a Co3O4–CoO heterointerface were in-situ-prepared and first applied into NO reduction by CO. Compared with single-phase samples, the catalysts with the Co3O4–CoO heterointerface exhibited superior catalytic performance. The best CoOx-350-7 sample showed a lowest apparent active energy (54.2 kJ·mol–1) and achieved 100% NO conversion at 150 °C (gas hourly space velocity = 50 000 h–1). The role of CoO as well as the structure–activity relationship between the interfacial effect and catalytic activity were deeply investigated. Abundant oxygen vacancies were induced due to the introduction of CoO species, and thus, the reducibility and oxygen migration of Co3O4–CoO catalysts were enhanced. The introduction of CoO not only optimized the NO adsorption but also enhanced electron donation ability from the catalyst to adsorbed NO. Moreover, the presence of CoO coupled with oxygen vacancies regulated the CO adsorption/conversion on the catalysts and thus promoted the exposure and reactivation of active sites for the reaction cycles. Accordingly, the stimulated dissociation of NO and the formation of −NCO could enhance the NO conversion to N2 at lower and higher temperatures, respectively.