| Indole, which is an important raw organic material and fine chemical product, has many uses in the fields of industry, agriculture and medicine. There are many known methods to produce indole. One of the most promising routes, from an economic point of view, seems to be the direct catalytic synthesis from aniline and ethylene glycol. In this dissertation, the synthesis of indole from aniline and ethylene glycol catalyzed by Ag/SiO2 catalyst , prepared by impregnation-programm heating calcination-insitu reduction method, has been investigated by means of some characterizations such as XRD, TEM. TG. DSC and XPS. Copper-based catalyst was also studied for this reaction. The main results are summarised as follows:catalyst prepared by impregnation-programm heating calcination-insitu reduction method exhibits high activity and selectivity in the synthesis of indole when the silver crystallite size is smaller than 10 nm. And the yield of indole could reach 78%, which is as high as the best result in the literature reported for the industrialized silver catalyst prepared by co-deposition method.2 It has been found that the activity of Ag/SiOz catalyst declined with reaction time. The characterization of the catalyst by TG. XRD and TEM indicates that the main reasons for the deactivation are the carbon-deposition on the catalyst surface and the sintering of silver particle during the reaction. And the carbon-deposition could be decreased efficiently by introducing steam and hydrogen into the reaction system. The other effect of the steam in the reaction is that it could restrain glycol breaking up and enhance desorption of indole from the catalyst surface, therefore greatly increase the indole selectivity.3 As a structure promoter, ZnO in the catalyst could efficiently improve the dispersion of silver on the support and block the sintering of silver crystallite during the reaction process. Consequently the stability of the catalyst is increased. The addition of CeO2 and FeO to the silver-based catalyst could increase not only the yield of indole, but also the stability of theinABSTRACTcatalyst. For Ag-FeO/SiO2-ZnO-CeO2 catalyst prepared by step-by-step impregnation method. the yield of indole still keeps higher than 87% after the reaction for 10 h. This is about 10% higher than the best result in the literature for the industrialized silver catalyst.4 Based on the quantum chemistry calculation and the experimented results, the pathway of iodole synthesis from aniline and ethylene glycol on the silver catalyst supported on silica can be proposed schematically as follows:HO-H2C fcgUSlow] x0"20"20" Kg!. [Fast] HO.H2i -H2?First, Glycol and aniline reacts by dehydration and produce the intermediate product of (1) o-amino-phenylethanol. Then the intermediate 1 could produce the target product of indole by dehydration and dehydrogenation. Comparing the two steps, the first step for producing o-amino-phenylethanol from glycol and aniline is slow, namely, this step is the rate-determining step. And the step for producing indole from the intermediate 1 is the fast.5 It has been also found that Cu/SiC>2 catalyst prepared by incipient impregnation method shows very high activity with the yield of indole up to 88%, but this catalyst is also deactivated during the reaction. The main reason for the deactivation of Cu/SiCh catalyst is the carbon-deposition on the catalyst surface during the reaction. Introducing hydrogen and steam into the reaction system could decrease the carbon-deposition. Addition of Zn, Fe, Co and Ni oxides to Cu/SiC>2 catalyst negtively affects the performance of the catalyst. And CuO/SiC>2 is hard to be reduced when ZnO is added to it.
|
PDF Full Text Request