预处理条件对一步法合成吲哚用Ag/SiO_2催化剂活性的影响

Effect of Pretreatment Conditions on Catalytic Activity of Ag/SiO_2 for Direct Synthesis of Indole

以简单浸渍法制备的Ag/SiO2 催化剂对苯胺和乙二醇一步法合成吲哚具有很高的催化活性.研究了预处理条件对催化剂活性的影响.结果表明,采用程序升温法将催化剂前体在5 0 0℃焙烧4h ,并在低于15 0℃时用H2 N2 混合气(H2 含量低于5 0 % )原位还原得到的Ag/SiO2 催化剂活性较高;TEM和XRD结果表明,预处理后催化剂表面银晶粒较小,结晶度较低.

Indole, an important organic raw material and fine chemical, is used in many fields such as industry, agriculture and medicine. There are many methods to produce indole, and one of the most promising routes, from the economic point of view, seems to be the direct catalytic synthesis from aniline and ethylene glycol. The Ag/SiO2 catalyst, prepared by the incipient impregnation method, exhibits very high activity. In this paper, the effect of pretreatment conditions on the activity of the Ag/SiO2 catalyst was investigated. The activity of Ag/SiO2 was influenced remarkably by the pretreatment conditions. The catalyst showed a high activity when it was calcined by temperature-programmed heating in air from room temperature to 500 degrees C at a rate of 3 degrees C/min and held at 500 degrees C for 4 h, and then reduced in-situ in a H-2-N-2 mixture gas with H-2 content less than 50% below 150 degrees C. The TEM and XRD results showed that the size of silver particles was small and the defects in silver crystals were more under the above pretreatment conditions.