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 (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.