Enhancing Water Tolerance and N 2 Selectivity in NH 3 -SCR Catalysts by Protecting Mn Oxide Nanoparticles in a Silicalite-1 Layer.

Mn-based catalysts are promising candidates for eliminating harmful nitrogen oxides (NO _x ) via selective catalytic reduction with ammonia (NH ₃ -SCR) due to their inherent strong redox abilities. However, poor water tolerance and low N ₂ selectivity are still the main limitations for practical applications. Herein, we succeeded in preparing an active catalyst for NH ₃ -SCR with improved water tolerance and N ₂ 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 N ₂ O formation is decreased. These improvements resulted in a broader operating temperature of NO _x conversion and a modification of the NH ₃ -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.