Insight into the mechanisms of activity promotion and SO2 resistance over Fe-doped Ce-W oxide catalyst for NOx reduction

Ceria-based catalysts for the selective catalytic reduction of NOx with NH3 (NH3-SCR) are always subject to deactivation by sulfur poisoning. In this study, Fe-doped Ce-W mixed oxides, which were synthesized by the co-precipitation method, improved the SCR activity and SO2 durability at low temperatures of undoped Ce-W oxides. The improved low-temperature activity was mainly due to the enhancement of redox properties at low temperatures and more active oxygen species, together with the adsorption and activation of more abundant NOx species, facilitating the "fast SCR" reaction. In the presence of SO2, doping with Fe species effectively prevented sulfate deposition on the CeW catalyst, due to the interaction between Fe, Ce, and W species inducing electron transfer among different metal sites and altering the electron distribution. The competitive adsorption behavior between NO and SO2 was changed by Fe doping, in which the adsorption and oxidation of SO2 were restrained. Besides, the elevated NO oxidation accelerated the decomposition of ammonium bisulfate, causing the SCR reaction to not be greatly suppressed. Hence, Fe-doped Ce-W oxides catalysts showed excellent sulfur resistance. This study provides an in-depth understanding of efficient Ce-based catalysts for SO2-tolerance strategies.

Remarkable enhancement in the N2 selectivity of NH3-SCR over the CeNb3Fe0.3/TiO2 catalyst in the presence of chlorobenzene

The simultaneous removal of NO_x and dioxins is the frontier of environmental catalysis, which is still in the initial stage and poses several challenges. In this study, a series of CeNb₃Fe_x/TiO₂ (x = 0, 0.3, 0.6, and 1.0) catalysts were prepared by the sol-gel method and examined for the synergistic removal of NO_x and CB. The CeNb₃Fe_0.3/TiO₂ catalyst exhibits an optimum catalytic performance, with an NO_x conversion greater than 95% at 260-380 °C. It also exhibits an optimal CB oxidation activity, in which CB promoted both the NO_x conversion and N₂ selectivity below 250 °C. Moreover, the more favorable ratios of Ce⁴⁺ to Ce³⁺ and plentiful surface-adsorbed oxygen species are the reasons why CeNb₃Fe_0.3/TiO₂ catalyst has better catalytic activity than other catalysts at the lower temperature. Simultaneously, owing to the modulation of Fe to the redox properties of Ce and Nb, the large number of oxygen vacancies and acid sites was generated, and the CeNb₃Fe_0.3/TiO₂ catalyst is beneficial to NO_x reduction and CB oxidation. Furthermore, the results of in situ DRIFTS study reveal the NH₃-SCR reactions over CeNb₃Fe_0.3/TiO₂ catalysts are mainly conformed to by the L-H mechanism (< 350 °C) and E-R mechanism (> 350 °C), respectively, and the multi-pollutant conversion mechanism in the synergistic reaction was systematically studied.

Ce-based catalysts used in advanced oxidation processes for organic wastewater treatment: A review

Refractory organic pollutants in water threaten human health and environmental safety, and advanced oxidation processes (AOPs) are effective for the degradation of these pollutants. Catalysts play vital role in AOPs, and Ce-based catalysts have exhibited excellent performance. Recently, the development and application of Ce-based catalysts in various AOPs have been reported. Our study conducts the first review in this rapid growing field. This paper clarifies the variety and properties of Ce-based catalysts. Their applications in different AOP systems (catalytic ozonation, photodegradation, Fenton-like reactions, sulfate radical-based AOPs, and catalytic sonochemistry) are discussed. Different Ce-based catalysts suit different reaction systems and produce different active radicals. Finally, future research directions of Ce-based catalysts in AOP systems are suggested.