Studies On The Effects Of Iron Promoters And Preferentially Exposed Facets Of Support In The Supported MnO_x/TiO₂ Catalyst For Low-temperature SCR

Selective catalytic reduction ?SCR? is one of the most effective methods for the elimination of NO_x in flue gases from stationary power plants and automobile sources, and the research and development of novel low-temperature SCR catalyst have attracted much attention because of its great theoretic and pratical significances. The structure-property relationship of supported MnO_x/TiO₂ catalysts, and the promotional effects of iron oxide in the FeO_x-MnO_x/TiO₂ catalysts and the titania supports with different preferentially exposed facets have been studied by using micro-reactor tests combined with various characterization methods. The research results obtained in this work provided important references for the development of high performance low temperature SCR catalysts. The experimental results have shown that:1. The MnO_x/TiO₂ catalysts with various MnO_x centents were prepared by sol-gel method, and the influences of catalyst composition and structure on their low-temperature SCR properties have been studied. Moreover, the N₂ and N₂O formation mechanisms over the MnO_x/TiO₂ catalysts have been investigated, and the results have indicated that the low-temperature SCR of NO by NH3 over the supported MnO_x/TiO₂ catalyst probably obey so-called "Eley-Rideal reaction mechanism", i.e. N₂ and N₂O were formed by reaction of gaseous NO with the adsorbed -NH2 and -NH species originated from the oxy-dehydrogenation of absorbed NH3, respectively. With increasing MnO_x loading, the NO conversion over MnO_x/TiO₂ catalyst increased significantly. However, the increase of MnO_x species polymerization degree resulted in the formation of -NH species through oxy-dehydrogenation of adsorbed NH3 by O₂- ions associated with MnO_x species, leading to the decrease of N₂ selectivity.2. The surface ineraction of Fe-MnO_x/Ti02 catalyst for the selective catalytic reduction of nitric oxide has been studied in detail. Addition of FeO_x increased the MnO_x dispersion and reduced their polymerization degree, leading to the increases of SCR activity and N₂ selectivity. Although addition of excessive FeO_x can further reduce the polymerzization degree of MnO_x species and thus increase N₂ selectivity, NO conversion decreases remarkablely. The optimum FeO_x content is c.a.0.5 molar ratio of Fe/Mn.3. The MnO_x/Ti02 ?NS? catalyst with preferentially exposed{001} facet exhibits higher activity than the MnO_x/TiO₂ ?NP? with preferentially exposed{101} facet for low-temperature SCR, and this effect of preferentially exposed facet is closely related to the surface structure of support. The MnO_x species in the MnO_x/TiO₂ ?NP? catalyst mainly exists as Mn4+ions incorporated into the tetrahedral vacancies on the preferentially exposed{101} facet with higher polymerization degree. In comparison, The MnO_x species in the MnO_x/TiO₂ ?NS? catalyst mainly exists as Mn³⁺ions incorporated into the octahedral vacancies on the preferentially exposed{001} facet with lower polymerization degree, leading to higher activity and N₂ selectivity for low-temperature SCR.