Study On Oxidative Dehydrogenation Of Ethane To Ethylene With Carbon Dioxide Over Supported V-Based Catalysts

The research and development of the effective catalysts for oxidative dehydrogenation of ethane to ethylene with carbon dioxide plays an important role in catalysis science field.In this work, supported V-based catalysts including supported V₂O₅ and supported MxOy-V₂O₅ were prepared by incipient wetness impregnation method. The effect of the supports, V₂O₅ loading and the addition of metal oxide on the surface structures, crystal lattice oxygen activity, surface acidic properties and catalytic behaviors of supported V-based catalysts were characterized by XRD, IR, UV-vis DRS, TPR, NH3-TPD and microreactor techniques.The experiment results show that vanadium was highly dispersed on SiO2 andγ-Al2O3 supports and V₂O₅ exists as isolated VOx and polymeric VOx with high active crystal lattice oxygen; the strong interaction between V₂O₅ and TiO₂ makes the formation of TiVO4 new phase; The dispersion of V₂O₅ on the surface of ZrO2 is bad and vanadium exists as crystal V₂O₅. V-based catalysts on different supports have an order of acidic properties as follows: V₂O₅/Al2O3>V₂O₅/TiO₂> V₂O₅/ZrO2>V₂O₅/SiO2. The increasing of vanadium oxide loading makes VOx on the surface changing from isolated VO4 and polymeric VOx to crystal V₂O₅. Accordingly, surface acidic centre on the surface changes from weak acid centre existing in isolated VOx to strong acid centre existing in polymeric VOx. Addition of different metal oxides has a distinct influence on VOx species and acidic properties on the surface of catalysts. The strong interaction between Bi3+ and VOx species improves the dispersion of VOx species and BiVO4 can be easily created. Though addition of CeO2/Mn3O4 can improve the dispersion of VOx species, the interaction between CeO2/Mn3O4 and VOx species is not strong as Bi3+ and they still exist mainly as metal oxides forms. Besides, all of different metal oxides can decrease acidity on the surface of the catalysts.There is a close relationship between the activity and selectivity of the dehydrogenation of ethane and many factors such as the surface dispersion of VOx species, crystal lattice oxygen activity, surface acidic properties, and so on. High dispersion can improve the reactive activity and strong acid can decrease reactive selectivity. V₂O₅/Al2O3 and V₂O₅/SiO2 have good reactive activity, but their selectivity is low. The addition of metal oxides can improve selectivity evidently, though they can decrease reactive activity a bit. The catalytic behaviors of oxidation dehydrogenation of ethane into ethylene with carbon dioxide were studied over Bi2O3-V₂O₅/SiO2 catalyst. Under the conditions of 700℃, 0.1MPa, mixed gas space velocity of 1440 h-1ml/(g cat) and V (CO2) / V (C2H6) =1, the ethane conversion of 47.1% and ethylene selectivity of 80.6% were achieved.