Chromium oxide nano-particles with an average diameter of 3 nm covered by amorphous carbon (CrOx/C) were successfully synthesized. The synthesized CrOx/C materials were used for the selective catalytic reduction of NOx by NH3 (NH3-SCR), which shows superb NH3-SCR activity and in particular, satisfactory regeneration ability in the presence of SO2 compared with Mn-based catalysts. The as-prepared catalysts were characterized by XRD, HRTEM, Raman, FTIR, BET, TPD, TPR, XPS and in situ FTIR techniques. The results indicated presence of certain amounts of unstable lattice oxygen exposed on the surface of CrOx nano-particles with an average size of 3 nm in the CrOx/C samples, which led to NO being conveniently oxidized to NO2. The formed NO2 participated in NH3-SCR activity, reacting with catalysts via a “fast NH3-SCR” pathway, which enhanced th NH3-SCR performance of the CrOx/C catalysts. Furthermore, the stable lattice of the CrOx species made the catalyst immune to the sulfation process, which was inferred to be the cause of its superior regeneration ability in the presence of SO2. This study provides a simple way to synthesize stable CrOx nano-particles with active oxygen, and sheds light on designing NH3-SCR catalysts with highly efficient low temperature activity, SO2 tolerance, and regeneration ability.
Jingjing Liu,Mengyuan Zhang,Diru Liu,Yunbo Yu,Guangyan Xu,Hong He
Ammonia selective catalytic reduction (NH 3 -SCR) of nitrogen oxides (NO x ) is a widely adopted method for controlling NO x emissions. However, achieving superior low-temperature activity while maintaining high N 2 selectivity over a broad temperature range remains a major challenge. In this study, a novel mesoporous manganese–titanium–aluminum (Mn-Ti-MA-S) composite oxide catalyst was synthesized by a modified evaporation-induced self-assembly method. The incorporation of Mn and Ti into mesoporous alumina (MA) framework significantly optimized the redox-acidic properties of the Mn-Ti-MA catalyst, with Mn in a highly dispersed state with fully exposed microcrystalline structures. Subsequent sulfur treatment further transformed the Lewis acid sites into Brønsted acid sites, shifting the reaction pathway from a Lewis acid site-dominated to Brønsted acid site-dominated mechanism. This strategy successfully overcame the conventional trade-off between low-temperature activity and high-temperature N 2 selectivity in NH 3 -SCR catalysts. Consequently, the optimized Mn-Ti-MA-S catalyst exhibited excellent catalytic performance, achieving both NO x conversion and N 2 selectivity above 90 % over a wide temperature range (104–400 °C). This work highlights a synergistic strategy that integrates redox and acid sites engineering with reaction pathway regulation, enabling the development of highly efficient NH 3 -SCR catalysts.
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