Sulfur poisoning and regeneration of the Ag/γ-Al2O3 catalyst for H2-assisted SCR of NOx by ammonia

Sulfur poisoning and regeneration mechanisms for a 2% Ag/γ-Al2O3 catalyst for the H2-assisted selective catalytic reduction of NOx by NH3 are investigated. The catalyst has medium sulfur tolerance at low temperatures, however a good capability of regeneration at 670 °C under lean conditions when H2 is present. These heating conditions can easily be established during soot filter regeneration. Furthermore, two types of active sites could be identified with different regeneration capabilities, namely finely dispersed Ag and larger Ag nanoparticles. The most active sites are associated with the finely dispersed Ag. These sites are irreversibly poisoned and cannot be regenerated under driving conditions. On the other hand the larger Ag nanoparticles are reversibly poisoned by direct SOx adsorption. The interpretation of the data is supported by DFT calculations.

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► SO2 tolerance testing protocol is developed for NOx SCR catalysts.
► Catalyst lifecycle in automotive application is modeled in the test setup.
► Ag/Al2O3 can be regenerated from sulfur under DPF regeneration conditions.
► Al2O3 contain two types of active sites with different regeneration capabilities.