Doping effect of cations (Zr4+, Al3+, and Si4+) on MnOx/CeO2 nano-rod catalyst for NH3-SCR reaction at low temperature

Abstract

Thermally stable Zr4+, Al3+, and Si4+ cations were incorporated into the lattice of CeO2 nano-rods (i.e., CeO2-NR) in order to improve the specific surface area. The undoped and Zr4+, Al3+, and Si4+ doped nano-rods were used as supports to prepare MnOx/CeO2-NR, MnOx/CZ-NR, MnOx/CA-NR, and MnOx/CS-NR catalysts, respectively. The prepared supports and catalysts were comprehensively characterized by transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction, Raman and N2-physisorption analyses, hydrogen temperature-programmed reduction, ammonia temperature-programmed desorption, in situ diffuse reflectance infrared Fourier-transform spectroscopic analysis of the NH3 adsorption, and X-ray photoelectron spectroscopy. Moreover, the catalytic performance and H2O+SO2 tolerance of these samples were evaluated through NH3-selective catalytic reduction (NH3-SCR) in the absence or presence of H2O and SO2. The obtained results show that the MnOx/CS-NR catalyst exhibits the highest NOx conversion and the lowest N2O concentration, which result from the largest number of oxygen vacancies and acid sites, the highest Mn4+ content, and the lowest redox ability. The MnOx/CS-NR catalyst also presents excellent resistance to H2O and SO2. All of these phenomena suggest that Si4+ is the optimal dopant for the MnOx/CeO2-NR catalyst.