Ammonium heptamolybdate was dissolved in water or oxalic acid solution,and then compounded with TiO₂ to prepare MoO _x ?TiO₂ support,and the VO _x /MoO _x ?TiO₂ catalysts were obtained after loading vanadium by impregnation method.The structure and properties of the catalysts were characterized by XRD,SEM,BET,XPS,H₂?TPR and NH₃?TPD,and its denitration activity and high temperature aging performance were investigated.The results showed that the denitrification efficiency of VMoTiO?F prepared by oxalic acid?assisted dissolution of (NH₄)₆Mo₇O₂₄ was greater than 80.0% at 210 ~ 510 °C,which was better than that of VMoTiH?F prepared by water dissolution.Because there was more MoO _x on the surface of VMoTiO?F,the interaction with VO _x was enhanced,which promoted the production of more low?valence VO _x and surface chemisorbed oxygen (O_α) active species on the surface of the catalyst.At the same time,the interaction between VO _x and MoO _x could also improve the low?temperature redox performance and facilitate the electron transfer in the catalytic process.After high temperature aging,VMoTiH?F had more MoO _x into the TiO₂ lattice than VMoTiO?F,which was helpful to improve the thermal stability of TiO₂.However, anatase TiO₂ in VMoTiO?A was seriously sintered or even partially transformed into inert rutile crystal during high temperature aging,resulting in the loss of surface acid sites and the reduction of redox properties.Therefore,the denitrification performance of VMoTiH?A catalyst was significantly higher than that of VMoTiO?A.

A series of S, P, Si?doped TiO₂ supports and the corresponding VO_x/TiO₂ catalysts were prepared by sol?gel method and impregnation method for the purpose of enhancing SCR performance.Among them,the S?doped VO_x/TiO₂ catalyst exhibited the best low and medium temperature SCR performance and the widest active temperature window.According to the results of various analyses,the doping greatly influenced the agglomeration of vanadium species.As a result, numerous active polymeric VO_x species were emerged on the surface of catalysts.Meanwhile,S and Si was doped into TiO₂ lattice via the replacement of Ti⁴⁺ by S⁴⁺ and Si⁴⁺ to generate Ti-O-S and Ti-O-Si bonds,along with producing more surface V⁴⁺+V³⁺ and more chemisorbed oxygen species.The synergistic effect of the two active species can promote the oxidation of NO to NO₂,which can participate in the fast?SCR reaction by accelerating the reoxidation of VO_x species in the Redox process,and then improve the SCR performance of VO_x/TiO₂ catalyst at low and medium temperature range.The redox ability and activity of P?doped VO_x/TiO₂ catalyst are relatively low,because more phosphate is produced in the catalyst.Although doping S,P and Si has a significant effect on the acidity of the catalyst,it is not the dominate factor to determine the SCR activity.