Promoting Simultaneous Desulfurization and Denitrification Performance of Al2O3@TiO2 Core–Shell Structure Adsorbents by Enhancing Oxidation Performance: Modification by Rare Earth Elements (La, Ce, and Y), Reaction Temperature, and Oxygen Concentration

Low-Dose Element-Doped CeCrM/TiO2 (M = La, Cu, Fe, LaCu, LaFe) Catalyst for Low-Temperature NH3-SCR Process: Synergistic Effect of LaCu/LaFe

A series of CeCrM/TiO₂ (M = La, Cu, Fe, LaCu, LaFe) catalysts were prepared via impregnation method and are employed as low-temperature NH₃-SCR catalysts. The present study investigates the low-dose element doping on the TiO₂-supported catalyst to improve the NH₃-SCR performance. And CeCrLaCu/TiO₂ exhibited the best catalytic performance (NO conversion approaching 100% at 260-420 °C). The characterization results show that the synergistic effect of LaCu and LaFe on the catalytic performance was more obvious than that of Cu, Fe, and La alone. The doping of LaCu/LaFe decreased the specific surface area of the catalyst but increased the dispersion, surface acidity, and reducibility of the catalyst. Moreover, LaCu/LaFe promoted the formation of valence state distribution and oxygen vacancy content on the surface of the catalyst. There were more Ce³⁺, Cr⁶⁺, Cu⁺, and oxygen adsorbed on the surface of the CeCrLaCu/TiO₂ catalyst. H₂-TPR analysis showed that the synergistic effect of LaCu was more likely to promote the reduction of Cr and Cu and increase the reduction degree of metal oxides. However, Fe is easier to coordinate with La, thus improving the redox performance of the catalyst. Compared with CeCrLaFe/TiO₂, the ammonia adsorption capacity of CeCrLaCu/TiO₂ is better. Therefore, the synergistic effect of LaCu can promote the reaction performance of NH₃-SCR better.

Improvement of low-temperature NH3-SCR catalytic performance over nitrogen-doped MO x -Cr2O3-La2O3/TiO2-N (M = Cu, Fe, Ce) catalysts

A series of MO x -Cr2O3-La2O3/TiO2-N (M = Cu, Fe, Ce) catalysts with nitrogen doping were prepared via the impregnation method. Comparing the low-temperature NH3-SCR activity of the catalysts, CeCrLa/Ti-N (xCeO2-yCr2O3-zLa2O3/TiO2-N) exhibited the best catalytic performance (NO conversion approaching 100% at 220-460 °C). The physico-chemical properties of the catalysts were characterized by XRD, BET, SEM, XPS, H2-TPR, NH3-TPD and in situ DRIFTS. From the XRD and SEM results, N doping affects the crystalline growth of anatase TiO2 and MO x (M = Cu, Fe, Ce, Cr, La) which were well dispersed over the support. Moreover, the doping of N promotes the increase of the Cr6+/Cr ratio and Ce3+/Ce ratio, and the surface chemical adsorption oxygen content, which suggested the improvement of the redox properties of the catalyst. And the surface acid content of the catalyst increased with the doping of N, which is related to CeCrLa/TiO2-N having the best catalytic activity at high temperature. Therefore, the CeCrLa/TiO2-N catalyst exhibited the best NH3-SCR performance and the redox performance of the catalysts is the main factor affecting their activity. Furthermore, in situ DRIFTS analysis indicates that Lewis-acid sites are the main adsorption sites for ammonia onto CeCrLa/TiO2-N and the catalyst mainly follows the L-H mechanism.