Co- or Ni-modified Sn-MnOx low-dimensional multi-oxides for high-efficient NH3-SCR De-NOx: Performance optimization and reaction mechanism

NH3-SCR performances were explored to the relationship between structure morphology and physio-chemical properties over low-dimensional ternary Mn-based catalysts prepared by one-step synthesis method. Due to its strong oxidation performance, Sn-MnOx was prone to side reactions between NO, NH3 and O2, resulting in the generation of more NO2 and N2O, here most of N2O was driven from the non-selective oxidation of NH3, while a small part generated from the side reaction between NH3 and NO2. Co or Ni doping into Sn-MnOx as solid solution components obviously stronged the electronic interaction for actively mobilization and weakened the oxidation performance for signally reducing the selective tendency of side reactions to N2O. The optimal modification resulted in improving the surface area and enhancing the strong interaction between polyvalent cations in Co/Ni-Mn-SnO2 to provide more surface adsorbed oxygen, active sites of Mn3+ and Mn4+, high-content Sn4+ and plentiful Lewis-acidity for more active intermediates, which significantly broadened the activity window of Sn-MnOx, improved the N2 selectivity by inhibiting N2O formation, and also contributed to an acceptable resistances to water and sulfur. At low reaction temperatures, the SCR reactions over three catalysts mainly obeyed the typical Elye-rideal (E-R) routs via the reactions of adsorbed l-NHx (x = 3, 2, 1) and B-NH4+ with the gaseous NO to generate N2 but also N2O by-products. Except for the above basic E-R reactions, as increasing the reaction temperature, the main adsorbed NOx-species were bidentate nitrates that were also active in the Langmuir-Hinshelwood reactions with adsorbed l-NHx species over Co/Ni modified Mn-SnO2 catalyst.