铋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

A composite oxide catalyst containing Bi and Mo is prepared bycoprecipitation m ethod. Its surface composition and structure, chemisorption properties and behav iors in laser-stimulated isobutane selective oxidation are investigated by tech niques of XRD, IR, TPD and laser-stimulated surface reaction (LSSR). The main p hase component of Bi-Mo-O is α-Bi2Mo3O12. Lewis basic sites O2-, located at the surfaceMo＝O orMoOBibonds, and Lewis acid sites Bi3+ appear on the surface of the composite oxide. Two methyl hydrogen atoms in is obutane molecule can be chemisorbed on the terminal oxygen of neighboring Lewis basic sitesMo＝O bonds on the surface of the oxide. Using the laser photons of 984 cm-1 frequancy to excite the Mo＝O bond 1000 times under the conditions of 0.1 M Pa and 200 ℃, the conversion of isobutane obtained is about 11.2%, the reactio n products are isobutene, methylacrolein (MAL) and methacrylic acid (MAA), and t he selectivity for MAA is over 90%. Based on the experimental results above, apossible mechanism is proposed for the laser-stimulated isobatane selective oxid ation to MAA.%用共沉淀法制备了Bi和Mo的复合氧化物固体材料.运用XRD,IR,TPD和激光促进表面反应(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:Bi-Mo-O复合氧化物含有α-Bi2Mo3O12和少量γ-Bi2MoO6晶相;其表面上存在着Lewis碱位(MoO和Mo—O—Bi键中的O)及Lewis酸位(Bi3+);异丁烷的两个甲基H分别吸附在两个相邻的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,异丁烷的转化率可达11.2%,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90%.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.