Laboratory Investigation of Selective Catalytic Reduction Catalysts:  Deactivation by Potassium Compounds and Catalyst Regeneration

The deactivation and regeneration of selective catalytic reduction (SCR) catalysts poisoned by potassium by a wet-impregnation method was investigated experimentally. Potassium in the form of both chloride and sulfate is a strong poison for the catalyst. The results indicate that potassium titrates the active sites for NH 3 adsorption. Simply increasing the operating temperature or the vanadium content in the catalyst cannot compensate the loss of catalyst activity: Increasing the temperature hardly increases the conversion of NO for the strongly poisoned catalysts, and catalysts with high vanadium content become active for oxidizing NH 3 to NO, causing a net NO formation. Deactivated catalysts can be regenerated by different methods. Sulfation by gaseous SO 2 is efficient provided the poison is first removed by washing. When regenerating by 0.5 M H 2 SO 4, the catalyst regains a higher activity than that of the fresh catalyst at temperatures higher than 300 °C. Heat treatment of the catalyst at 400 °C for 2 h after poisoning to simulate actual operation has no influence on the regeneration by 0.5 M H 2 SO 4 . Deactivated catalysts without the heat treatment step regain higher activities than that of the fresh catalyst at all temperatures when regenerated by 1 M NH 4 Cl. However, the heat treatment step has a negative effect on the regeneration by NH 4 Cl.