NH3-TPD methodology for quantifying hydrothermal aging of Cu/SSZ-13 SCR catalysts

We identified a new acidic feature in Cu/SSZ-13 catalysts, related to the presence of two distinct desorption peaks in the NH3-TPD profiles, and to the changes in their relative intensity in response to mild hydrothermal aging (Luo et al., 2017). In this work, we have translated those findings into a sensitive laboratory diagnostic methodology for quantifying cumulative aging exposure, based on the ratio of the two NH3-TPD peaks. We have also addressed some practical aspects of applying this methodology to real-world aged samples, by decoupling the effects of sulfur poisoning and of the catalyst loading variability. The developed method yielded a simple kinetic model of the Cu/SSZ-13 catalysts hydrothermal aging, and some useful insights into the practically relevant aspects of the aging process. In particular, we have shown that the aging is cumulative, and that the sequence of the exposure steps does not matter. One other important consequence of the developed model is related to the steep temperature dependence of the aging process (E-a approximate to 168 kJ/mol). As a result, the majority of the on-engine operation exposure, typically below similar to 400 degrees C, has no appreciable impact on the catalyst aging. In contrast, such aging is almost entirely induced by the periodic high-temperature events, such as those related to various system regeneration regimes. We have verified that observation by a 1000-h aging test at 400 degrees C. Finally, we expect that the developed method of diagnosing and quantifying cumulative hydrothermal age can be applicable to other types of catalysts which include Cu/SSZ-13 in their formulation, including ammonia oxidation catalysts (AMOX) and SCR on filter (SCRF), since it is based on the intrinsic properties of this metal-exchanged zeolite. (C) 2018 Elsevier Ltd. All rights reserved.