Preparation Of Vanadium-based Catalysts And Its Nonoxidative Dehydrogenation Performance Of Isobutane

Turning the light alkanes into alkenes by dehydrogenation is one of the subjects having good economical and social benefit in petrochemical field,which can improve the added value for light alkanes and fit the increasing requirement for the demand of light alkenes.Nowadays,Pt-based and Cr-based catalysts are the most widely used industrial dehydrogenation catalysts.However,the former two kinds of dehydrogenation catalysts also have some disadvantages.Pt-based catalyst costs too much and gets deactivated easily due to the sintering of Pt species,which also need the high quality raw materials.As a result of the great toxicity,Cr-based catalyst is harmful to both human health and environment,with poor stability in dehydrogenation reaction.Therefore,environmental-friendly novel catalysts for dehydrogenation of light alkanes with high activity and good stability should be developed urgently.V-K/γ-Al₂O₃ catalyst was prepared with the methods of multiple impregnation and incipient impregnation after modifying the preparation process,the structure and performance of which was respectively characterized by different methods and evaluated through continuous fixed bed reactor.The information of physic-chemical structure was also associated with dehydrogenation performance.V-K/γ-Al₂O₃ showed bifunctional effect in the catalytic dehydrogenation of isobutane.The results implied that VO_x species are the catalytic active sites for dehydrogenation,of which the oligomeric VO_x species presented the maximum activity.At the same time,the acidity of V-K/γ-Al₂O₃ influenced the activation of isobutane and the selectivity of isobutene.The acidity and metallicity should be properly matched to improve the dehydrogenation performance of V-K/γ-Al₂O₃.In addition,a proposed reaction mechanism was brought up to show the reaction routine of dehydrogenation,catalytic dissociation and isomerization.Apparently,the dehydrogenation reaction is highly endothermic and thermodynamically limited.As a result,the reaction conditions were optimized to improve performance of vanadium-based catalysts,including temperature,pressure,GHSV and the ratio of paraffin to H2.The modified V-K/γ-Al₂O₃ represented the isobutene yield of 42.8% under the optimized conditions,which reached 39.2% after 10 h,with ideal activity and stability.The deactivation of V-K/γ-Al₂O₃ is caused by the coverage of carbon on active species,which can be removed by the calcination of catalysts in air,while the conditions of regeneration should be strictly controlled.After 15 cycles of dehydrogenation-regeneration,V-based catalysts still presented favorable reaction performance,indicating excellent regeneration performance.