Study on the mechanism of NH₃-selective catalytic reduction over CuCe_xZr_{1--<?Pub Caret?>x}/TiO₂

Abstract

Copper--cerium--zirconium catalysts loaded on TiO₂ prepared by a wet impregnation method were investigated for NH₃-selective catalytic reduction (SCR) of NO_x. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy (DRIFT). When NH₃ is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe_0.25Zr_0.75/TiO₂ at high temperature, while Brønsted acid sites are more important than Lewis acid sites at low temperature. For the NH₃+NO+O₂ co-adsorption, NH₃ species occupy most of activity sites on CuCe_0.25Zr_0.75/TiO₂ catalyst, and mainly exist in the forms of NH₄⁺ (at low temperature) and NH₃ coordinated (at high temperature), playing a crucial role in the NH₃-SCR process. Two different reaction routes, the L-H mechanism at low temperature (<200°C) and the E-R mechanism at high temperature (>200°C), are presented for the SCR reaction over CuCe_0.25Zr_0.75/TiO₂ catalyst.

Keywords

CuCe_0.25Zr_0.75/TiO₂ / catalyst / selective catalytic reduction (SCR) / diffuse reflectance infrared transform spectroscopy (DRIFT) / reaction mechanism

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