(570h) How Cu-SSZ-13 NH3 Selective Catalytic Reduction Catalyst’s Oxidation Activity Impacts on the Extent of Sulfur Poisoning

NH₃ selective catalytic reduction (NH₃-SCR) over Cu-zeolite catalysts is a catalytic after-treatment technology used to eliminate NO_x produced in a diesel engine. Cu-SSZ-13 in particular has high NO_x conversion in a wide temperature window, is hydrothermally stable, and is relatively resistance to hydrocarbon inhibition. Despite these positives, the catalyst deactivates from exposure to sulfur. Recent research has shown that the extent of catalyst deactivation from sulfur poisoning was less significant after a prior hydrothermal aging treatment [1]. Other research has shown that after the catalyst was hydrothermally aged below 750 °C, the zeolite structure was still intact, but the Cu active sites transformed from 1-Al binding Cu sites, ZCuOH, to 2-Al binding Cu sites, Z2Cu [2]. Our reactor data show that for a catalyst pretreated under mild hydrothermal aging conditions, there is a loss in oxidation activity and we correlate this to the distribution of ZCuOH and Z2Cu. Specifically, the results suggest that ZCuOH has higher NH₃, NO, CO and SO₂ oxidation activity than Z2Cu, under the conditions tested. These findings, along with those that show more oxidative conditions lead to greater extents of sulfur poisoning, lead to the hypothesis and the focus of this presentation: the extent of sulfur poisoning depends on the catalyst’s oxidation activity which is related to the distribution of the two copper species.

[1] Wei et al., Ind. Eng. Chem. Res. 2019, 58, 3949−3958

[2] Luo et al., Journal of Catalysis 348 (2017) 291–299