TRA and DRIFTS studies of the fast SCR reaction over CeO2/TiO2 catalyst at low temperatures

The CeO 2 /TiO 2 catalyst was prepared by a deposition-precipitation method, which exhibited high low-temperature activity under the fast SCR condition. By using transient reaction analysis (TRA), the steps in the fast SCR, including NO 2 adsorption and decomposition, reaction between nitrates and NO, ammonium nitrate formation and reduction by NO, were investigated. Diffuses reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments, via NO + O 2 or NO + NO 2 adsorption, ammonium species reaction with NO x and NO reaction with NH 4 NO 3 , were designed to identify the roles of NO, NO 2 and NH 3 in fast SCR. Based on L-H mechanism, the NH 4 NO 3 formation played an important role in low-temperature SCR reaction. Compared with the behavior in standard SCR, the higher activity in the presence of NO 2 was ascribed to the faster NH 4 NO 3 formation rate and larger amounts of nitrates/nitrites. This phenomenon provided a basis for developing Ce-based catalysts as SCR catalysts for diesel exhaust aftertreatment.