Effects Of TiO₂ Morphologies On The Activity Of Selective Catalytic Reduction Of No Over V₂O₅/TiO₂ Catalysts

As the one of the main air pollutants, nitrogen oxides（NO_x） have caused serious damages to the environment and human health. Selective catalytic reduction of NO_x by ammonia（NH₃-SCR） has been the main control technology for NO_x removal, which owned high-efficiency（>90 %） and operation stability. The V₂O₅-WO₃（MoO₃）/TiO₂ system is the most commonly used SCR catalyst. In this commercial SCR catalyst system, TiO₂ as the support plays an important role in the SCR reaction due to its excellent resistance ability to SO₂ poisoning and good dispersion of vanadium. Many investigations have shown that different morphologies or high exposure of crystal facets of TiO₂ may lead to the significant changes in the chemical and physical properties, such as surface energy, surface acidity, as well as the interaction between the carrir and the active component. It can be seen that TiO₂ crystals with specific morphology or surface configuration have exhibited distinct abilities in many applications like photocatalytic and dye-sensitized solar cells（DSSCs）. However, there is seldom in-depth study in regard to the effects of different morphologies or well-defined facets of TiO₂ on NO elimination by SCR reaction.In this work, the propersities of industrial TiO₂ from different suppliers were compared firstly, and then the effects of TiO₂ morphologies on the activities of seletive catalytic redution of NO over V₂O₅/TiO₂ catalysts were studied. The main results were as follows:1) The propersities of industrial TiO₂ powder were compared in the first part. The V₂O₅-MoO₃/TiO₂ catalysts were prepared with industrial TiO₂. SCR activity evaluation showed that the catalyst with TiO₂-J carrier, which owned neat ball morphology, had better NO conversion than the others. BET results showed the surface area of the catalyst increased significantly after loading of vanadium species to carrier TiO₂-J, which distinguished to the other carriers. From the TPR and TPD results, the catalyst with TiO₂-J as carrier showed higher reducibility and more acid sites than the other catalysts. The TiO₂-J was proved to own better chemical and physical properties, and it could be the good carrier to improve the SCR activity of the corresponding catalyst.2) The TiO₂ carriers with different morphologies were prepared in the second part. The samples were prepared by hydrothermal method. Through the adjusting the concentration of hydrazine hydrate, we got TiO₂ particles with regular morphology of octahedron, which was designated as TiO₂-O. The TiO₂-O particles were dominated by {101} planes in the whole surface. The end-capping agent HF was added to make TiO₂ particles with sheet morphology. This sample were dominated by high-energy {001} crystal surface, which was denoted as TiO₂-S.3) The effects of TiO₂ morphologies on the activiy of selective catalytic redution of NO over V₂O₅/TiO₂ catalysts were studied in the third part. The three 3 wt% V₂O₅/TiO₂ catalysts with TiO₂-O, TiO₂-S and the commercial TiO₂ P25 as the supports were prepared by impregnation method. The catalyst supported on the sheet TiO₂ with dominant {001} facets（V₂O₅/TiO₂-S） showed the highest catalytic activity among the three catalysts in the NH₃-SCR reaction. The V₂O₅/TiO₂ catalysts were also characterized by means of SEM, TEM, BET, H₂-TPR, Raman, NH₃-TPD, XPS, and in-situ DRIFTS technologies to explore their physical and chemical properties. It was found that the strong interaction between the sheet TiO₂ and active species due to the special structure of the high energy facet {001} of TiO₂ led to good dispersion of vanadium species on the TiO₂ surface, which resulted in the high reducibility and the high concentration of surface adsorbed oxygen of the V₂O₅/TiO₂-S catalyst. All these features could facilitate the achievement of the NH₃-SCR reaction that could be responsible for the high activity of V₂O₅/TiO₂-S catalyst in NH₃-SCR reaction.