Deactivation mechanism of Cu/Zeolite SCR catalyst under high-temperature rich operation condition

Selective catalytic reduction of NOx by urea (urea/SCR) and Lean NOx Trap (LNT) are two leading technologies for NOx reduction under lean condition. To quickly warm up SCR catalysts, considerable efforts have been made in integrating SCR onto a diesel particulate filter, so called SDPF. With the fact that the real driving emission test has taken effect, SDPF coupled with LNT might be one of most viable solutions to meet stringent emission regulations. However, desulfation process for LNT may result in a severe deactivation of SDPF in downstream. Here, we investigated the tolerance of Cu/zeolite SCR catalysts against periodic lean/rich operation condition simulating desulfation over LNT in front of SDPF. The lean/rich aging at 620 °C has led a severe deterioration of NOx conversion over Cu/SSZ-13 hydrothermally aged 800 °C, especially in high-temperature region above 400 °C. The accelerated NH₃ oxidation to NO was the primary cause for the poor NOx removal activity, originated from the alteration of Cu state. Cu ions turned out to be converted to CuOx cluster upon their exposure to rich condition, which could partly be re-dispersed as Cu²⁺ ion after the post-treatment at 700 °C under lean condition. Cu/SSZ-13 with low Cu content revealed better activity maintenance under the high-temperature rich condition compared to higher Cu loading counterpart. Cu/LTA recently developed showed superior tolerance against rich feed due to less reducible nature of Cu⁺ ion therein compared to that in Cu/SSZ-13 leading to less CuOx formation.