Enhancing Water Tolerance and N2 Selectivity in NH3–SCR Catalysts by Protecting Mn Oxide Nanoparticles in a Silicalite-1 Layer

Abstract

Mn-based catalysts are promising candidates for eliminating harmful nitrogen oxides (NO_x) via selective catalytic reduction with ammonia (NH₃–SCR) due to their inherent strong redox abilities. However, poor water tolerance and low N₂ selectivity are still the main limitations for practical applications. Herein, we succeeded in preparing an active catalyst for NH₃–SCR with improved water tolerance and N₂ selectivity based on protecting MnO_x with a secondary growth of a hydrophobic silicalite-1. This protection suppressed catalyst deactivation by water adsorption. Interestingly, impregnating MnO_x on MesoTS-1 followed by silicalite-1 protection allowed for a higher dispersion of MnO_x species, thus increasing the concentration of acid sites. Consequently, the level of N₂O formation is decreased. These improvements resulted in a broader operating temperature of NO_x conversion and a modification of the NH₃–SCR mechanism. Diffuse reflectance infrared Fourier transform spectroscopy analysis revealed that unprotected Mn/MesoTS-1 mainly followed the Eley–Rideal mechanism, while Mn/MesoTS-1@S1 followed both Langmuir–Hinshelwood and Eley–Rideal mechanisms.