Deactivation of Cu-SSZ-13 by SO2 exposure under SCR conditions

Abstract

A deactivation study of Cu-SSZ-13 has been conducted using SO₂ exposure under SCR conditions and examining its effect on different reactions involving NH₃-SCR. Several reactions, including NH₃ storage/TPD, NO/NH₃ oxidation, standard SCR, fast SCR and SCR with 75% NO₂, as well as NH₃–NO₂ storage/TPD, were investigated at a temperature range of 100–400 °C after exposing the catalyst to 30 ppm SO₂ under SCR conditions at 300 °C for 90 min. The catalyst was characterized using XRD, BET, ICP-SFMS and H₂-TPR. The BET surface area and pore volume decreased after the sulfur treatment presumably due to blocking by sulfur and/or ammonium–sulfur species. It was found that sulfur was not uniformly deposited along the monolith channel. The deposition occurred from the inlet towards the outlet, as evident from ICP-SFMS measurements. Part of the sulfur was removed after an SCR experiment up to 400 °C. However, this removal was observed only in the inlet half of the sample and not in the outlet. Ammonia TPD experiments revealed that the sulfur poisoning resulted in additional sites that were capable of adsorbing ammonia, resulting in increased ammonia storage. Moreover, standard SCR was significantly deactivated by SO₂ poisoning under SCR conditions. Due to the site-blocking effect of the ammonium–sulfur species, fewer copper sites are likely available for the redox SCR cycle. Furthermore, the effect of sulfur poisoning on NH₃ oxidation and NO₂-SCR as well as N₂O production in various SCR reactions were observed. Finally, it was found that the conditions for the sulfur poisoning were critical in which SO₂ deactivation under SCR conditions (NH₃ + NO + O₂ + H₂O) was more severe compared to SO₂ poisoning in O₂ + H₂O alone.