In-situ infrared spectroscopic study of the mechanism of the low temperature selective catalytic reduction of NO surface by Mn/ bastnaesite concentrate

The Mn/bastnaesite concentrate and Mn/Al2O3 catalysts were prepared by impregnation method, and their NH3-SCR denitrification performance was tested. The results showed that the Mn/bastnaesite concentrate catalyst achieved up to 95% NO conversion rate at 150 degrees C, and the Mn/Al2O3 catalyst reached 76% at 300 degrees C. A series of characterisation results showed that the bastnaesite concentrate can better interact with MnOx species and promote mutual dispersion compared to Al2O3. The Mn/bastnaesite concentrate has a stronger redox capacity, and good NH3 and NO adsorption capacity at low temperatures. The multi-element coexistence system of bastnaesite concentrate itself is a significant advantage of its use as a carrier. In-situ Fourier transform infrared (FTIR) results showed that the Mn/bastnaesite concentrate catalyst follows an L-H mechanism throughout the reaction, with NH4+ species in the Bronsted acidic site on the catalyst surface being the main reactant species. Most of NO is converted to monodentate nitrite, which is formed by bonding with (Mn)(3)+ provided by the supported Mn species, rare earth elements and transition metal ions contained in the carrier itself to form O-N-O-Mn3+ intermediates, which participate in the reaction together, and then combined with the adsorbed NH4+/NH3 species to produce N-2 and H2O. An E-R mechanism was also present on the catalyst surface, NO participates directly in the reaction in gaseous form, and the NO [NH2](ads) intermediate species produced by interaction with NH4+ species in the acidic position of Bronsted was further decomposed to N-2 and H2O. By comparing the reaction mechanism with the commonly used catalyst carrier Al2O3 for NH3-SCR, it can be concluded that bastnaesite concentrate as a carrier not only has the performance of conventional carriers, but also has certain catalytic activity and can interact with the active components to give it excellent performance, which provides a theoretical basis for rare earth minerals as denitrification catalysts. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The Mn/bastnaesite concentrate catalyst showed higher NO conversion rate, stronger redox capacity, and better adsorption performance at low temperatures. Bastnaesite concentrate can promote interaction between active components, making it an excellent carrier.