Alkali and Heavy Metal Copoisoning Resistant Catalytic Reduction of NOx via Liberating Lewis Acid Sites

The catalyst deactivation caused by the coexistence of alkali and heavy metals remains an obstacle for selective catalytic reduction of NO_x with NH₃. Moreover, the copoisoning mechanism of alkali and heavy metals is still unclear. Herein, the copoisoning mechanism of K and Cd was revealed from the adsorption and variation of reaction intermediates at a molecular level through time-resolved in situ spectroscopy combined with theoretical calculations. The alkali metal K mainly decreased the adsorption of NH₃ on Lewis acid sites and altered the reaction more depending on the formation of the NH₄NO₃ intermediate, which is highly related to NO_x adsorption and activation. However, Cd further inhibited the generation of active nitrate intermediates and thus decreased the NO_x abatement about 60% on potassium-poisoned CeTiO_x catalysts. Physically mixing with acid additives for CeTiO_x catalysts could significantly liberate the active Lewis acid sites from the occupation of alkali metals and relieve the high dependence on NO_x adsorption and activation, thus recovering the NO_x removal rate to the initial state. This work revealed the copoisoning mechanism of K and Cd on Ce-based de-NO_x catalysts and developed a facile anti-poisoning strategy, which paves a way for the development of durable catalysts among alkali and heavy metal copoisoning resistant catalytic reduction of NO_x.