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

Mn-based catalysts are promising candidates for eliminating harmful nitrogen oxides (NO) via selective catalytic reduction with ammonia (NH-SCR) due to their inherent strong redox abilities. However, poor water tolerance and low N selectivity are still the main limitations for practical applications. Herein, we succeeded in preparing an active catalyst for NH-SCR with improved water tolerance and N selectivity based on protecting MnO with a secondary growth of a hydrophobic silicalite-1. This protection suppressed catalyst deactivation by water adsorption. Interestingly, impregnating MnO on MesoTS-1 followed by silicalite-1 protection allowed for a higher dispersion of MnO species, thus increasing the concentration of acid sites. Consequently, the level of NO formation is decreased. These improvements resulted in a broader operating temperature of NO conversion and a modification of the NH-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.