Alkali and Heavy Metal Copoisoning Resistant Catalytic Reduction of NO_<i>x</i> via Liberating Lewis Acid Sites

Abstract

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 <i>in situ</i> 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_<i>x</i> adsorption and activation. However, Cd further inhibited the generation of active nitrate intermediates and thus decreased the NO_<i>x</i> abatement about 60% on potassium-poisoned CeTiO_<i>x</i> catalysts. Physically mixing with acid additives for CeTiO_<i>x</i> catalysts could significantly liberate the active Lewis acid sites from the occupation of alkali metals and relieve the high dependence on NO_<i>x</i> adsorption and activation, thus recovering the NO_<i>x</i> removal rate to the initial state. This work revealed the copoisoning mechanism of K and Cd on Ce-based de-NO_<i>x</i> 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_<i>x</i>.