Enhanced Performance of Ceria-Based NO_<i>x</i> Reduction Catalysts by Optimal Support Effect

Abstract

CeO₂-based catalysts have attracted widespread attention in environmental-protection applications, including selective catalytic reduction (SCR) of NO by NH₃, and their catalytic performance is often intimately associated with the supports used. However, the issue of how to choose the supports of such catalysts still remains unresolved. Herein, we systematically study the support effect in SCR over CeO₂-based catalysts by using three representative supports, Al₂O₃, TiO₂, and hexagonal WO₃ (HWO), with different acidic and redox properties. HWO, with both acidic and reducible properties, achieves an optimal support effect; that is, CeO₂/HWO exhibits higher catalytic activity than CeO₂ supported on acidic Al₂O₃ or reducible TiO₂. Transmission electron microscopy and X-ray diffraction techniques demonstrate that acidic supports (HWO and Al₂O₃) are favorable for the dispersion of CeO₂ on their surfaces. X-ray photoelectron spectroscopy coupled with theoretical calculations reveals that reducible supports (HWO and TiO₂) facilitate strong electronic CeO₂-support interactions. Hence, the excellent catalytic performance of CeO₂/HWO is mainly ascribed to the high dispersion of CeO₂ and the optimal electronic CeO₂-support interactions. This work shows that abundant Brønsted acid sites and excellent redox ability of supports are two critical requirements for the design of efficient CeO₂-based catalysts.