Adjusting the thickness of 2D zeolite platelet for efficient selective catalytic reduction of NOx with ammonia

Abstract

NOx emissions from diesel exhaust are subject to increasingly stringent regulations, and ammonia selective catalytic reduction (NH3-SCR) technology using Cu-based zeolites as the core material is one of the most effective solutions. Two-dimensional (2D) zeolites have a high external specific surface area, resulting in the advantages of high accessibility of active sites and low diffusion limit of molecules. Herein, 2D Cu-based zeolite catalysts, denoted as Cu-PST-mRb (m = 0.5, 0.7), were synthesized with different plate thicknesses and acidic properties by adjusting the alkali metal additions, where the thicker catalyst (Cu-PST-0.7Rb) exhibited superior activity, hydrothermal stability and N2 selectivity in the NH3-SCR reaction. By increasing the thickness of the plate layer, more microporous structures can be formed, and the thicker plate layers were able to encapsulate and stabilize more framework Al along c-axis direction, thereby forming more reactive Z2Cu2+ species, which facilitated massive adsorption and rapid activation of NH3. In-situ DRIFTS further revealed that the thickness of the plate layer also modulated the acidic properties and accessibility of the active site, leading to different NH3-SCR reaction pathways. This work sheds light on the special physicochemical properties of high efficiency 2D nanosheets zeolites catalysts for NH3-SCR reactions under harsh operating conditions.