Synergistic Effect over CeSnO_x Catalyst for the Selective Catalytic Oxidation of NH₃

The N2 selectivity of selective catalytic oxidation of NH3 (NH3-SCO) at high temperatures is a great challenge. CeSnOx catalysts were synthesized by the coprecipitation method and systematically investigated. CeSnOx catalysts exhibited excellent N2 selectivity at high temperatures compared to CeO2. The possible SCO reaction mechanism and synergistic effect over CeSnOx catalysts for NH3-SCO performance were investigated. X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption of ammonia (NH3-TPD) characterization manifested that the concentrations of Oads, Ce3+, and acid sites were increased. It is speculated that the reaction mechanism followed the internal-SCR (i-SCR) mechanism through in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments. Combined with density functional theory (DFT) calculations, it was verified that after doping Sn, the oxygen vacancy of CeSnOx catalysts possessed reduced formation energy, resulting from the shifting of electron density to Sn, redistribution of charge, and the smaller conduction band of O 2p, which also could be much easier to adsorb and stabilize oxygen as active sites. In addition, Sn doping succeeded in inhibiting the competitive adsorption of OH and NH3 on the Ce site because Sn could preferentially adsorb OH and then adsorb and activate NH3. This work reveals the synergistic effect over CeSnOx catalysts for NH3-SCO performance, which is conducive to the rational design of cheap SCO catalysts replacing noble-metal-based catalysts.