Effect of Transition-Metal Oxide M (M = Co, Fe, and Mn) Modification on the Performance and Structure of Porous CuZrCe Catalysts for Simultaneous Removal of NO and Toluene at Low–Medium Temperatures
Jun Tang, Lingkui Zhao, Su Jiang, Yan Huang, Junfeng Zhang, Jiang Li
Abstract
In order to satisfy the characteristics of non-power plant flue gas emissions, the reaction mechanism for the simultaneous removal of NO and toluene over different transition-metal oxide M (M = Co, Fe, and Mn)-modified porous CuZrCe catalysts was investigated at low–medium temperatures. Brunauer–Emmett–Teller analysis, transmission electron microscopy, X-ray diffraction, hydrogen temperature-programed reduction, temperature-programed desorption experiment with NH3, X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy were used to characterize these catalysts. The results show that the introduction of transition-metal oxides improved the texture and structural properties, supplied abundant active sites, and induced more reactive oxygen species formation. Also, the redox equilibrium of Mn+ + Cu+ ↔ M(n–1)+ + Cu2+ and Mn+ + Ce3+ ↔ M(n–1)+ + Ce4+ is important in promoting NO reduction and toluene oxidation. For CuFeZrCe and CuMnZrCe, toluene exhibited a slightly inhibitive effect on NO conversion because toluene competes with NO for adsorbing on the Cu2+ sites, while the selective catalytic reduction (SCR) atmosphere facilitated toluene oxidation owing to NO consumption and new Brønsted acid site formation for toluene adsorption. For CuCoZrCe, toluene and SCR atmosphere showed mutual promoted effects, mainly attributed to Co addition that provided Co3+ sites for toluene adsorption which offset the competitive adsorption on Cu2+ sites between NO and toluene.