V_2O_5负载量对VO_x/MgAl_2O_4催化异丁烷脱氢制异丁烯的影响

INFLUENCE OF V_2O_5 LOADING ON ISOBUTANE DEHYDROGENATION ON VO_x/MgAl_2O_4 CATALYST

采用浸渍法制备了不同V2O5负载量的VOx/MgAl2O4催化剂,考察了该系列催化剂对异丁烷脱氢反应的催化性能。利用XRD、低温氮气吸附-脱附、FT-IR和H2-TPR等手段对催化剂进行了表征,并分析了催化剂表面性质与催化性能的关系。结果表明:当V2O5负载量(w)低于5%时,催化剂表面以还原性能好、单层分散的孤立态和聚合态钒氧物种为主;当V2O5负载量(w)高于5%时,催化剂表面开始形成还原性能较差的镁钒酸盐物种。异丁烷脱氢反应评价结果表明,当V2O5负载量(w)为5%时,催化剂对异丁烷脱氢反应的催化性能最佳,在反应温度560℃、反应时间1.5h的条件下,异丁烷转化率和异丁烯收率可分别达到41.9%和31.4%。低价态钒氧物种为异丁烷脱氢反应的活性物种。

VOx/MgAl2 O4 catalysts with different V2O5 loadings were prepared by the incipient wet- ness impregnation and their isobutane dehydrogenation activities were investigated. X-ray diffraction （XRD）, nitrogen adsorption-desorption, Fourier transform infrared （FT-IR） spectroscopy and hydro- gen-temperature programmed reduction （H2-TPR） were used to characterize the structure and reduc- ibility of vanadium species on the surface of MgAl2 O4. The results show that the isolated and polymeric VOx species on the surface are present at low vanadium loading lower than 5 % and can he reduced more easily than samples with higher vanadium loading. With increase of V2O5 loadings, mixed magnesium vanadate compounds （Mg3V2O5, Mg2V2O7） appear, which are difficult to reduce by hydrogen. At the optimum V2O5 loading （5%）, yield of isobutylene was 31.4% with the corresponding isobutane conver- sion of about 41.9% at 560 ℃ ,reaction time 1.5 h. Based on the experimental results, it is suggested that low valence Vδ＋ （δ〈5） species on the surface are the active sites for this reaction.