Promotional effect of fluorine on the selective catalytic reduction of NO with NH3 over CeO2-TiO2 catalyst at low temperature

In order to investigate the effect of F on CeO2-TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3, a series of F-doped CeO2-TiO2 catalysts were prepared by co-precipitation method. Compared with Ce0.3TiF0 catalyst, Ce0.3TiF1.5 catalyst exhibited the best catalytic activity, yielding 92.19% NO conversion at 180 °C. The catalysts were characterized by Brunauer–Emmett–Teller (BET) surface area, X-ray powder diffraction (XRD), photoluminescence (PL) spectra, Raman spectra, X-ray photoelectron spectroscopy (XPS) and Diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques. It was found that the enhanced catalytic activity was ascribed to several beneficial effects produced by the introduction of F: inhibition of the crystallization, decrease of the particle size, increase of the oxygen vacancies (F+ centers) and lattice defects. Raman measurements disclosed the formation of superoxide (O2−) ions in chemisorbed oxygen which was crucial for the formation of reaction intermediates (NO2−, NO3−). The study of DRIFTS proved that the addition of F could bring more ad-NOx and reaction intermediates. The NH3-TPD studies confirmed that the right amount of F could improve the number of acid sites over CeO2-TiO2 catalyst, especially the Lewis acid sites. These factors simultaneously enhanced the catalytic activity for NH3-SCR of NO. The effect of H2O and SO2 on the NO conversion was also investigated in our work.