Revealing the promotional effect of Ce doping on the low-temperature activity and SO2 tolerance of Ce/FeVO4 catalysts in NH3-SCR

Elimination of NOx from the non-electric industrial boilers has become priority under the effective implementation of ultra-low emissions. A series of Ce-promoted FeVO4 catalysts with improved acidity and reducibility have been synthesized in this work. Thereinto, 10Ce/FeVO4 exhibited an optimum low-temperature performance with 90% of NOx conversion and 95% of N2 selectivity at 200–300 °C which was kept nearly unchanged with different concentrations of SO2 ranging from 50 ppm to 200 ppm, showing a superior sulfur tolerance. An array of well-designed experiments has demonstrated that Ce mainly existed as CeVO4 under a low doping content (1 wt%) on FeVO4, which could efficiently increase the amount of acid sites. With more cerium (5–12 wt%) loading on FeVO4, the appearance of CeO2 further resulted in a strong interaction between cerium species and ion species, thus significantly improving the low-temperature catalytic activity. Therefore, the optimum coexistence of CeVO4 and CeO2 over 10Ce/FeVO4 modulated its Brønsted acid and enhanced its redox circulation of Fe3+ species. Moreover, the NH3-SCR reaction pathways of 10Ce/FeVO4 were broadened from only Eley-Rideal to both Eley-Rideal and Langmiur-Hinshelwood mechanisms after Ce loading on FeVO4 catalyst. With the presence of SO2, the SO/S-O deriving from the generated Ce2(SO4)3 and NH4HSO4 increased the Brønsted acid sites, inducing a satisfying SO2 tolerance of 10Ce/FeVO4 catalyst, although the Langmiur-Hinshelwood pathway of 10Ce/FeVO4 was immediately cut off due to the competitive adsorption of gaseous SO2 and NOx. This work exemplifies a promising strategy for developing an ideal low-temperature NH3-SCR catalyst with good SO2 resistance.