钒钼复合氧化物表面上激光促进异丁烷选择氧化制甲基丙烯酸

摘要

用共沉淀法制备了V和Mo的复合氧化物.运用XRD、IR、TPD和LSSR技术研究了其晶体结构、表面构造、化学吸附特性和激光促进异丁烷选择氧化反应性能.结果表明：V—Mo—O的主体物相为Mo4V6O24，它具有MoO3和V2O4交替排列的层状结构；其表面上存在着Lewis碱位Mo＝O和Mo—O—V键中的O2-及Lewis酸位V4+；异丁烷的2个甲基H分别吸附在2个相邻的Lewis碱位Mo＝O上形成双位分子吸附态；在常压和200℃条件下，用一定频率的激光激发Mo＝O键1000次，异丁烷的转化率为6.5%，其反应产物是异丁烯、甲基丙烯醛和甲基丙烯酸，其中甲基丙烯酸的选择性为78%.根据实验结果，探讨了激光促进异丁烷选择氧化为甲基丙烯酸的表面反应机理.%A Mo/V complex oxide was prepared from (NH4)6Mo7O26.4H2O andNH4VO3 by a coprecipitation method. The surface composition, structure, chemsorption and behavior of laser stimulated selective oxidation of isobutane have been investigated by XRD, IR, TPD and microreactor. The results showed that the main phase of the complex oxide is Mo4V6O24, which has a storeyed structure composed of MoO3 and V2O4. There are both Lewis base sites, O2- in the surface Mo＝O or Mo—O—V bonds, and Lewis acid site, V4+ appeared on the surface of complex oxide. Two methyl hydrogens in isobutane molecule can be chemisorbed on the terminal oxygen of the neibouring Mo＝O bonds on the surface of the complex oxide. Under the conditions of 0.1 MPa, 200 ℃ and 1000 times of laser excitation with 972 cm-1on the MoObonds, about 6.5% isobutane were converted to isobutene, methyl propenal and methacrylic aicd, among them 78% were the latter. A mechanism is proposed for isobutane selective oxidation.