The promoting effect of support pretreatment with sulfate acid on the Ca resistance of a CeO2/ZrO2 catalyst for NH3-SCR of NOx with NH3

In this paper, the effects of sulfuric acid treatment of a ZrO2 support (ZrO2-S) on the Ca resistance of CeO2 catalysts were investigated. The results showed that the CeO2/ZrO2-S catalyst exhibited much better SCR activity and Ca resistance compared with the CeO2/ZrO2 catalyst. To further reveal the Ca resistance mechanism, BET, XRD, Raman, XPS, H-2-TPR, NH3-TPD and in situ DRIFTS were used to characterize the changes in structure and properties of the CeO2/ZrO2 and CeO2/ZrO2-S catalysts before and after the Ca deactivation tests. The Ca poisoning of the CeO2/ZrO2 catalysts was mainly due to the decrease in specific surface area and surface acidity, the loss of reducibility and the enhanced stabilization of adsorbed nitrate/nitrite species. The treatment of ZrO2 with sulfate acid led to an increased specific surface area and highly-dispersed Ce species at the catalyst surface. It was also beneficial to inhibiting the transformation of ZrO2 from the tetragonal to the monoclinic phase. Moreover, it also enhanced the redox properties, Ce3+ species ratio, total surface acidity (especially Bronsted acid sites), and adsorption of NH3 species. The SCR reactions via both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms could proceed well even after the CeO2/ZrO2-S catalysts were subjected to Ca poisoning.

Automated summary

This study investigates the effect of sulfuric acid treatment on the Ca resistance of CeO2 catalysts supported by ZrO2. The results demonstrate that the CeO2/ZrO2-S catalyst displays significantly better SCR activity and Ca resistance compared to the CeO2/ZrO2 catalyst. Characterization techniques such as BET, XRD, Raman, XPS, H-2-TPR, NH3-TPD, and in situ DRIFTS were employed to analyze the changes in structure and properties of the catalysts before and after Ca deactivation tests. The results indicate that the Ca poisoning in CeO2/ZrO2 catalysts is mainly caused by the decrease in surface area and acidity, loss of reducibility, and enhanced stabilization of adsorbed nitrate/nitrite species. The treatment of ZrO2 with sulfuric acid leads to an increase in surface area, highly-dispersed Ce species, inhibition of tetragonal to monoclinic phase transformation, improved redox properties, Ce3+ species ratio, total surface acidity (especially Bronsted acid sites), and adsorption of NH3 species. Furthermore, the SCR reactions via both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms can still proceed effectively even after Ca poisoning in the CeO2/ZrO2-S catalysts.