Enhanced Performance of Ceria-Based NOx 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.