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

In order to satisfy the characteristics of non-power plantflue gas emissions, the reaction mechanism for the simultaneous removalof 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, transmissionelectron microscopy, X-ray diffraction, hydrogen temperature-programedreduction, temperature-programed desorption experiment with NH3,X-ray photoelectron spectroscopy, and in situ diffuse reflectance infraredFourier transform spectroscopy were used to characterize these catalysts.The results show that the introduction of transition-metal oxidesimproved the texture and structural properties, supplied abundant activesites, and induced more reactive oxygen species formation. Also, theredox equilibrium of Mn++Cu+<-> M(n-1)++Cu2+and Mn++Ce3+<-> M(n-1)++Ce4+is important in promoting NO reduction and tolueneoxidation. For CuFeZrCe and CuMnZrCe, toluene exhibited a slightly inhibitive effect on NO conversion because toluene competeswith NO for adsorbing on the Cu2+sites, while the selective catalytic reduction (SCR) atmosphere facilitated toluene oxidationowing to NO consumption and new Bronsted acid site formation for toluene adsorption. For CuCoZrCe, toluene and SCRatmosphere showed mutual promoted effects, mainly attributed to Co addition that provided Co3+sites for toluene adsorption whichoffset the competitive adsorption on Cu2+sites between NO and toluene.