物理化学学报 >> 2000, Vol. 16 >> Issue (07): 601-607.doi: 10.3866/PKU.WHXB20000706

研究论文 上一篇    下一篇

激光促进甲醇氧化偶联表面反应的规律

钟顺和, 高峰, 叶文强, 肖秀芬   

  1. 天津大学化工学院,天津 300072
  • 收稿日期:1999-09-30 修回日期:2000-01-04 发布日期:2000-07-15
  • 通讯作者: 钟顺和

Study on Laser Stimulated Surface Reaction of Methanol Oxidative Coupling

Zhong Shun-He, Gao Feng, Ye Xiu-Qiang, Xiao Xiu-Fen   

  1. College of Chemical Engineering and Technology,Tianjin University,Tianjin 300072
  • Received:1999-09-30 Revised:2000-01-04 Published:2000-07-15
  • Contact: Zhong Shun-He

摘要:

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=O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附. 激光表面反应的机理为:用频率为1077cm-1的激光光子激发固体表面P=O键,可使其端氧活化,活化的氧与吸附态的甲醇分子作用使其脱氢,形成表面CH2OH负碳离子,进而在固体表面Lewis酸位上CH2OH负碳离子相互偶联生成乙二醇.反应温度的提高有助于补充激光能量密度的不足,同时促进产物的脱附,但温度升高会诱发热反应而生成副产物.在常压和120℃的反应条件下,用1077cm-1激光激发Li3PO4•BiPO4 表面1000次,甲醇的转化率达16 %,乙二醇的选择性达97.7 %.

关键词: 激光促进表面反应, 氧化偶联, 甲醇, 乙二醇, 复合磷酸盐

Abstract:

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℃.

Key words: Laser stimulated surface reaction, Oxidative coupling, Methanol, Ethanediol, Complex phosphates