激光促进甲醇氧化偶联表面反应的规律

用沉淀法制备了Ｌｉ３ＰＯ４、ＢｉＰＯ４和Ｌｉ３ＰＯ４、ＢｉＰＯ４三种固体表面材料，并用ＸＲＤ、ＩＲ、ＴＰＤ和激光促进表面反应（ＬＳＳＲ）等技术研究了这些固体表面上甲醇氧化偶联生成乙二醇的反应规律。实验结果表明：甲醇在固体材料表面的Ｐ＝９键上产生Ｃ－Ｈ端的分子态吸附，在表面的Ｌｅｗｉｓ酸位（金属离子）上产生解离态吸附。Ｌｉ３ＰＯ４和ＢｉＰＯ４的相互作用可促进甲醇在固体表面上的分子态吸附而抑制解离态吸

Study on Laser Stimulated Surface Reaction of Methanol Oxidative Coupling

Solid phosphates Li3PO4,BiPO4 and Li3PO4•BiPO4 prepared by precipitation were used as the surface materials. Their surface composition, structure and reaction behavior have been investigated by the techniques of XRD,IR,TPD and laser stimulated surface reaction (LSSR).In solid phosphates, there are surfaces Lewis base sites P=O and Lewis acid sites Mn+. Two types of methanol adsorption species have been found, the molecular type consists of the adsorption of the H of C-H bond on the Lewis base site P=O and the dissociative type that of O and H of O-H bond on the Lewis acid site Mn+ and Lewis base site P=O separately. Because of the interaction of Li+ and Bi3+,the introduction of Li3PO4 into BiPO4 can promote the molecular type adsorption and reduce the dissociative type adsorption. On the selective excitation of the surface P=O bond by 1077cm-1 laser photons, the activated terminal oxygen reacts with the adsorbed H of C-H bond forming CH2OH and P-OH. The former species then transfers to the Lewis acid site Mn+ and ethanediol is produced by the coupling reaction. The surface hydroxyl P-OH reacts with each other to form H2O and the surface oxygen defect. The Lewis acid sites Mn+ on the surface of solid materials can chemisorb gaseous molecular oxygen continuously and transform it into O2-to compensate the consumed surface lattice oxygen. Under atmospheric pressure and at the tempurature of 120℃,the methanol conversion of 16% and ethanediol selectivity of 97.7% can be obtained by using 1077 cm-1 laser exciting the surface P=O bond on Li3PO4•BiPO4 for 1000 illuminating times. Increase of temperature has the effects of compensating the energy density of laser photon and enhancing the desorption of reaction products. But it also causes the formation of dimethyl ether by thermal catalytic reaction while the temperature is over 120℃.