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.

SO2-Induced Alkali Resistance of FeVO4/TiO2 Catalysts for NOx Reduction

Selective catalytic reduction of nitrogen oxides with ammonia (NH₃-SCR) is an efficient NO_x abatement strategy, but deNO_x catalysts suffer from serious deactivation due to the coexistence of multiple poisoning substances such as K, SO₂, etc. in the flue gas. It is essential to understand the interaction among various poisons and their effects on NO_x abatement. Here, we unexpectedly identified the K migration behavior induced by SO₂ over K-poisoned FeVO₄/TiO₂ catalysts, which led to alkali-poisoning buffering and activity recovery. It has been demonstrated that the K would occupy both redox and acidic sites, which severely reduced the reactivity of FeVO₄/TiO₂ catalysts. After the sulfuration of the K-poisoned catalyst, SO₂ preferred to be combined with the surface K₂O, lengthened the K-O_Fe and K-O_V, and thus released the active sites poisoned by K₂O, thereby preserving an increase in the activity. As a result, for the K-poisoned catalyst, the conversion of NO_x increased from 21 to 97% at 270 °C after the sulfuration process. This work contributes to the understanding of the specific interaction between alkali metals and SO₂ on deNO_x catalysts and provides a novel strategy for the adaptive use of one poisoning substance to counter another for practical NO_x reduction.