Preparation, Characterization And Study On Denitration Performance Of V₂O₅/TiO₂Nanotubes Catalyst

The pollution of nitrogen oxides (NOX) is a growing global problem. Selective catalytic reduction (SCR) by NH3is widely applied on the removal of NO in industry. V2O5/TiO2and V2O5-WO3/TiO2(anatase) catalysts operated at350～400℃, with less than1%V2O5loading, have been widely accepted as commercial catalysts, because they have advantages of mature technology, high selectivity and good resistance to water and sulfur, compared with other catalysts. Synthesized by hydrothermal method in alkaline solution, TiO2nanotubes (TiNTs) have uniform diameter, large specific surface area, and high adsorptive capacity. Herein, our work focuses on the modification of TiO2support with hydrothermal treatment, in order to improve the catalytic activity at low temperature, reduce cost in industry application, raise economy benefit.Titanic acid nanotubes (TANs) were prepared by hydrothermal method, and after calcination, TiNTs were obtained. TEM was applied to observe the morphology of namotubes; TG/DTA, EDX, BET, XRD and FT-IR were adopted to analyse the structure and properties. The results indicated that raw TiO2became multi-layered hollow TAN with two open ends after hydrothermal treatment in alkali solution. With increasing calcining temperature, amorphous TiNTs transformed to anatase phase gradually, the SBET of nanotubes dropped from365m2/g to176m2/g. Calcined at350℃, TiNTs still maintain hollow tubular structure. However, when calcined at450℃, layer structure of nanotubes disappeared, and TiNTs turned into nanoribbons with the increase of crystallinity. When the temperature reached700℃, these nanoribbons further raptured into nanoparticles.Subsequently, V2O5/TiNT (VTiNT) catalysts with lwt%loading of active component were obtained by impregnation in NH4VO3solution. NH3-TPD, NO-TPD, H2-TPR and EPR characterization revealed that the hollow tubular structure of amorphous TiNT-350benefited the dispersion of V2O5on the catalyst surface, which could promote the SCR reaction, raise the surface acidity of VTNT-350, be good for NH3adsorption and activation, and promote the formation of low valenceV and superoxide radical, resulting in improving de-NOx efficiency.Besides, when the reaction conditions was0.08%NO.0.08%NH3,4vol%O2, balanced with N2to reach150mL/min and18000h-1·g-1SV, the NOx conversion over VTiNT-350at210℃.240℃and270℃was1.8.1.8and1.5times of that over VTiO2. respectively. Once H2O was passed alone, the NOx conversion at240℃fell by5%or so. When H2O was cut off. it immediately recovered. It illustrated that there was physical adsorption of H2O competing with reactant gas that leaded to the reduction of NOx conversion. In the presence of SO2. the denitration efficiency gradually increased. It might be due to the formation of SO42-through SO2oxidation which improved catalyst surface acidity and boosted adsorption of NH3. When the feed stream contained H2O and SO2simultaneously, the conversion decreased sharply. Beacause the sulfate salts deposited so much that it covered active center and blocked catalyst channels, causing decreasing in the NOX conversion.Eventually, the catalysts synthetized by N-doped TiO2nanotube was also investigated. Through catalytic activity test, it declared that the removal of NOx over the N-doped catalyst decreased, because of the destruction of tubular structure by doping.