Nb-Modified Mn–Fe–PILC Catalyst with Improved Resistance to Alkali Metals for the NH3–Selective Catalytic Reduction Reaction

Sodium (Na) and potassium (K) are frequently encountered alkali metals in industrial exhaust gases, and their presence can significantly diminish the catalytic performance of the catalyst during the NH3–SCR reaction. Here, we prepared a catalyst using layered montmorillonite clay pillared with manganese and iron (termed Mn–Fe–PILC) as well as its niobium-modified counterpart (referred to as Nb/Mn–Fe–PILC). Furthermore, additional samples denoted as Mn–Fe–PILC-M and Nb/Mn–Fe–PILC-M (where M = Na or K) were synthesized using the impregnation method with a nitrate aqueous solution of Na or K. The results revealed an obvious enhancement in the catalytic activity of NH3–SCR upon the inclusion of Nb, with the best catalyst achieving a NO x conversion rate of 95% at 300 °C. Moreover, the resistance of the Mn–Fe–PILC catalyst to alkali metals was notably increased. Subsequent characterization demonstrated that the introduction of Nb to Mn–Fe–PILC led to an increase in the quantity of tetravalent manganese species present on the catalyst, alteration in reducibility, and augmentation in the number of acid sites, thereby enhancing the catalyst’s resistance to alkali metals. Furthermore, in situ DRIFTS experiments revealed that the modification with Nb resulted in an amplified adsorption capacity for ammonia or nitric oxide, particularly influencing the formation of ammonia intermediates and nitrate species. These alterations proved beneficial in bolstering the alkali metal resistance of the catalyst.