VO_x/SiO₂ Catalysts Undoped And Doped For The Oxidative Dehydrogenation Of N-Butane

C₄ alkanes, which widely exist in liquefied petroleum gas, refinery gas and natural gas, are abundant but cheap, most of which are utilized as fuel leading to a immense waste of energy resources. Butenes (including 1-butene and 2-butene) were important chemical materials and were relatively insufficient. The catalytic dehydrogenation and oxidative dehydrogenation of light hydrocarbons into more valuable unsaturated hydrocarbons were significant theoretically and economically.The widely utilization of C₄ alkane is dependent on the development of catalysts for C₄ alkane dehydrogenation, which has become one of the challenging research subjects in the area of heterogeneous catalysis.VO_x/SiO₂ catalysts with different VO_x loading was prepared with the calcination temperature 550℃, using SiO₂ as support. The catalysts were all prepared by impregnation. The catalytic performance of catalysts was studied on a micro-fixed-bed reactor. The influence of reaction condition on the catalytic performance of catalyst was studied. Then VO_x/SiO₂ catalysts doped with Li₂O, K₂O, MgO, CaO, SrO, Al₂O₃, Fe₂O₃, NiO, ZnO were prepared and their catalytic performance were srudied. Last, the compose, configuration, reducing property, surface acidic property and other information of active species are characterized by means of XRD, FT-IR, TPD-NH3 and TPR-H₂.In chapter three, the VO_x/SiO₂ catalysts were studied in catalytic dehydrogenation of n-butane. The results showed that when VO_x loading was 3wt.%, the catalysts showed the best activation. When the reaction conditions were reaction temperature 550℃, n-butane/O₂/N₂=4/4/42, and WHSV=1.5×104 ml·h-1·gcat-1, the n-butane conversion and C₄ olefins yield were 45.1% and 18.6% correspondingly on 3%VO_x/SiO₂ catalyst. Then the catalyst lifetime was studied. N-butane conversion decreased from 45.9% to 42.3% when the reaction was carried out 3h, and the catalyst shows favorable stability. The catalysts were characterized by means of XRD, FT-IR, TPD-NH3 and TPR-H₂. The results show that the active VO_x species have relatively strong bonding effect with the support, leading the improvement of reducing property of the VO_x species. It also shows that VO_x is well-dispersing on the support at low VO_x loading, V_<sub>2O₅ crystalline forms on support when VO_x loading exceeds a certain range. FT-IR results show that Si—O—V, V=O, V—O—H bonds was existing on the surface of catalyst.In chapter four, 3%VO_x/SiO₂ catalysts doped with Li₂O, K₂O, MgO, CaO, SrO, Al₂O₃, Fe₂O₃, NiO, ZnO were investigated for n-butane oxidative dehydrogenation. Influence of the weight of Mg added on the catalytic performance was studied, and it show that VO_x/SiO₂ catalyst with proper weight of Mg could get higher C₄ olifins yield. VO_x/SiO₂ catalyst doped with Ni is favor of the formation of 1,3-butadiene, ethylene and propylene. VO_x/SiO₂ catalyst doped with K greatly aggravates the cracking reaction. The rest of the modifiers can be classified into two categories, one of which are Li₂O, CaO, SrO and Zn, which can decrease the activity of the catalyst, but increase the selectivity of C₄ olefins, the other are Al and Fe₂O₃, which not only decrease the activity of the catalyst, but also decrease the selectivity of C₄ olefins. TPR-H2 results show that the addition of Mg into VO_x/SiO₂ catalysts makes VO_x species more difficult to be reduced.