Alkali Metal Poisoning and Regeneration of Selective Catalytic Reduction Denitration Catalysts: Recent Advances and Future Perspectives

NOx produced by various combustion devices can cause serious harm to the environment and human health. Selective catalytic reduction (SCR) denitration technology is the most widely used postcombustion denitrification technology due to its high denitration efficiency, mature technology, and no harmful products. However, the alkali metals (e.g., K, Na, Ca, Mg) in combustion flue gas can poison the SCR catalyst, resulting in catalyst deactivation and deterioration of the SCR denitration system. Therefore, studying the alkali metal poisoning mechanism and antipoisoning measures of the SCR catalyst is crucial for increasing the service life of a catalyst and reducing the operation cost of a SCR denitration system. In this review, the research advances in the poisoning mechanisms of alkali metals for SCR catalysts (mainly including vanadium-based catalysts, manganese-based catalysts, copper-based catalysts, cerium-based catalysts, iron-based catalysts) were reviewed systematically. Various antialkali metal poisoning measures and mechanisms (e.g., doping metals and nonmetals, using appropriate supports, designing novel structures) were summarized. In addition, some regeneration measures for alkali metal poisoning SCR catalysts were also commented on. The results demonstrate that the deposits of alkali metals on SCR catalysts can reduce the specific surface area and pore volume of the catalyst and also destroy the active sites on the catalyst surface, which eventually lead to poisoning of the catalyst. The doping of the catalyst with other elements, rational design of catalyst structures, and effective use of catalyst supports can effectively improve the antipoisoning ability of the SCR catalyst. Water washing, acid washing, and electrophoresis treatment are some common methods for the regeneration of alkali-poisoned catalysts.