The Contradictory Impact of Sulfation on a CeO<sub><i>x</i></sub>/TiO<sub>2</sub> NH<sub>3</sub>-SCR Catalyst: A Combined Experimental and DFT Study
Huaiping Liu, Shangchao Xiong, Hongjun Ou, Haohan Lei, Jianjun Li, Jianjun Li, Ling He, Junhua Li, Junhua Li
Abstract
The process of sulfation during SO 2 poisoning has been found to have a promoting effect on the selective catalytic reduction (SCR) activity of NO x by NH 3 over CeO 2, due to the generation of acid sites. However, sulfation generally tends to inhibit the SCR activity of Ce-based catalysts. This suggests that sulfation may have a dual character on Ce-based SCR catalysts. To investigate this, CeO x /TiO 2 (Ce/Ti) was employed in this study. The results show that sulfation suppressed the reducibility and O storage ability of Ce/Ti and reduced the content of surface Ce active sites, all of which suppressed the SCR activity of Ce/Ti. However, sulfation also generated new Brønsted acid sites on Ce/Ti, and the reactivity of NH 3 adsorbed on these Brønsted acid sites was almost equal to that on Lewis acid sites. Due to this contradictory impact of sulfation, Ce/Ti and S-Ce/Ti showed similar SCR activity at lower temperatures (150–300 °C). Furthermore, because of the relatively unstable nature of ionic NH 4 + adsorbed on the newly generated Brønsted acid sites, the SCR activity of S-Ce/Ti quickly decreased at higher temperatures (300–400 °C). Consequently, utilizing the advantages and bypassing the disadvantages of sulfation can be a new strategy for designing Ce-based SCR catalysts with excellent SCR performance.