CeO₂ doping boosted low-temperature NH₃-SCR activity of FeTiO_x catalyst: A microstructure analysis and reaction mechanistic study

Abstract

• CeO₂ doping significantly improved low-temperature NH₃-SCR activity on FeTiO_x.

• The crystallinity of FeTiO_x was decreased dramatically after CeO₂ doping.

• Unique Ce-O-Fe structure in FeCe_0.2TiO_x accounted for its superior redox property.

• Facile activation of NH₃ to-NH₂ on FeCe_0.2TiO_x promoted the DeNO_x efficiency.

FeTiO_x has been recognized as an environmental-friendly and cost-effective catalyst for selective catalytic reduction (SCR) of NO_x with NH₃. Aimed at further improving the low-temperature DeNO_x efficiency of FeTiO_x catalyst, a simple strategy of CeO₂ doping was proposed. The low-temperature (<250℃) NH₃-SCR activity of FeTiO_x catalyst could be dramatically enhanced by CeO₂ doping, and the optimal composition of the catalyst was confirmed as FeCe_0.2TiO_x, which performed a NO_x conversion of 90% at ca. 200℃. According to X-ray diffraction (XRD), Raman spectra and X-ray absorption fine structure spectroscopy (XAFS) analysis, FeCe_0.2TiO_x showed low crystallinity, with Fe and Ce species well mixed with each other. Based on the fitting results of extended X-ray absorption fine structure (EXAFS), a unique Ce-O-Fe structure was formed in FeCe_0.2TiO_x catalyst. The well improved specific surface area and the newly formed Ce-O-Fe structure dramatically contributed to the improvement of the redox property of FeCe_0.2TiO_x catalyst, which was well confirmed by H₂-temperature-programmed reduction (H₂-TPR) and in situ XAFS experiments. Such enhanced redox capability could benefit the activation of NO and NH₃ at low temperatures for NO_x removal. The detailed reaction mechanism study further suggested that the facile oxidative dehydrogenation of NH₃ to highly reactive-NH₂ played a key role in enhancing the low-temperature NH₃-SCR performance of FeCe_0.2TiO_x catalyst.

Graphical abstract

Keywords

NH ₃-SCR / CeO ₂ doping / Low-temperature NO _x removal / Improved redox property / In situ XAFS analysis

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