| With the development of controllable synthesis methods of TiO2and the increasing usage of periodic models in the catalyst-related density functional theory studies, the role of different TiO2crystal facets in the catalytic reaction has received more and more attention. V2O5/TiO2-based catalyts performs well not only in the selective catalytic reduction of NOx, but also in the catalytic oxidation of certern kinds of hydrocarbon compounds, alcohols and elemental mercury. This work focused on the role of different TiO2crystal facets in mercury oxidation performance of V2O5/TiO2-based catalyts.Firstly, Mechanisums of mercury oxidation processes on V2O5/TiO2(001) and V2O5/(101) were studied by DFT calculation. V2O5/TiO2(001) and V2O5/(101) periodic slab models were constructed and optimized. Effects of different T1O2cryastal facets on the oxidation performance of V2O5were focused. Adsorption energies of Hg, HCl and HgCl on V2O5/HO2surfaces, charge transfer between the adsorbates and the catalyst surfaces and the surface electronic structures of the catalyst srufaces were analysised. The result showed that Hg and HCl would preferentially adsorb on V2O5/(101) surface. So reactions between Hg and the active Cl species are more likely to take place on this catalyst surface. HgCl adsorbed on this surface is more reactive to combine with the active Cl species to form the final product HgCl2. So V2O5/(101) catalyst is more suitable for mercury oxidation in the presense of HCl.The role of the oxygen sites present on the support was also studied. Oxygen sites present on V2O5/TiO2(101)’s support is proved to be more suitble for adsorption and activation of Hg and HCl than those on V2O5/TiO2(101).O(3) sites on both of the catalytic surface are the best adsorption sites for Hg, because Hg is actually interacted with both O(3) and O(1) when adsorbed on O(3). Moreover, HgCl formed on O(3) is more active for further reaction with the the active Cl species. Activation of HCl on the sites of V2O5/TiO2(001)’s support is much less prefered for the strong interaction of HCl with these sites. Situation on V2O5/TiO2(101)’s support is better for HCl,but still not good enough when compared with adsortion on O(1) site of this surface.Finally, relative experimental study was carried out in order to verify the conclusion of DFT calculations. TiO2(001) support was prepared by hydrothermal synthesis method. A kind of regular TiO2support, which is commercially named MC90and mainly exposes (101) crystal facet, is used as the counterpart of TiO2(001). According to the V2O5content in typical commercial SCR catalysts, V2O5/TiO2(001) and V2O5/TiO2(101) were prepared by incipient impregnation. TiO2(001) facet, whose surface energy is very high, was demonstrated to be stable under the experimental conditions of this work. Mercury oxidation experiment indicated that V2O5/TiO2(101) performed better than V2O5/TiO2(001), even if the affect of the specific surface area is excluded by comparing oxidaiton efficiency of a unit specific surface area. This results is consistent well with the conclusion of previous DFT caculations, which indicates rudimentary reliability of the DFT calculations. |
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