Deeply revealing the deactivation and decomposition mechanism of ammonium bisulfate on nanotube structured SCR catalysts for the low-temperature NH3-SCR reaction

Abstract

Sulfates formed on the catalyst surface have been the main cause of its rapid deactivation during the NH₃-SCR reaction. Here, after loading ABS onto nanotube structured Ce–Mn-TNTs and nanoparticle CeMnTiO_x catalysts, the low-temperature activities of the catalysts deactivated rapidly. After in situ decomposition of ABS on the catalyst surface under the reaction atmosphere, it was found that the de-NO_x efficiency of the regenerated Ce–Mn-TNTs-R catalyst was significantly restored. This was mainly attributed to the lower vapor pressure inside the nanotube structure compared to nanoparticles, which promoted the rapid decomposition of ABS. In addition, the decomposition process of ABS was accompanied by the formation of metal sulfates, which disrupted the redox cycle between the active metals, causing a certain inhibitory effect on the recovery of catalytic activity. However, the presence of SO₄²⁻ improved the content of chemisorbed oxygen on the nanotube structured catalyst surface and increased the numbers of Brønsted acid sites on the catalyst surface, which enhanced the adsorption capacity of the Ce–Mn-TNTs catalyst for NH₃ and was favorable for the recovery of catalytic activity. Thus, the presence of sulfates on the surface of nanotube structured catalysts had contradictory effects in the NH₃-SCR reaction process. The surface interface of nanotube structured catalysts is extremely advantageous for the decomposition of ABS. The above findings provided reliable theoretical bases for the design of catalysts with good SO₂ tolerance.