| 3-methylindole,an important indole derivative and intermediate,is widely used in the fields of medicine and spice. The paper reports the effect of Fe2O3, CoO and NiO on the performance of the catalysts of Ag/SiO2 and Ag/SiO2-ZnO for the vapor-phase synthesis of 3-methylindole from aniline and 1,2 propanediol. The catalysts of Ag/SiO2 and Ag/SiO2-ZnO doped with Fe2O3,NiO and CoO promoters have been characterized by means of XRD,H2-TPR and TG techniques. The effect of the loading sequence of Fe2O3, CoO or NiO on the performance of Ag/SiO2 and Ag/SiO2-ZnO was investigated.The Ag-based catalyst was prepared by incipient wetness impregnation. The results indicated that the addition of Fe2O3 or NiO was favorable for the increase of the selectivity of the catalyst. Among them, Fe2O3 could reinforce the interaction between active component silver and support and greatly promote the silver particles dispersing on the support, which resulted in the remarkable increase of the initial activity of the catalyst. The yield of 3-methylindole increased from 23.8% up to 33.1%. Adding CoO or NiO to Ag/SiO2 promoted the sintering of silver during the reaction, although it reduced the coking a little. As a result, the stability of the catalyst decreased. The effect of the sequence of the promoters added on the catalysts was investigated. For the Ag/SiO2, the best adding sequence of Fe2O3, CoO or NiO was Fe2O3-Ag/SiO2, CoO-Ag/SiO2 or NiO-Ag/SiO2 and the yield of 3-methylindole over the catalyst was 33.1%, 24.2% or 25.2% respectively.For the catalyst of Ag/SiO2-ZnO doped with Fe2O3, CoO or NiO, the best loading sequence was first ZnO, then Fe2O3, CoO or NiO, and last the active component Ag. Adding Fe2O3 to Ag/SiO2-ZnO could increase the initial activity of the catalyst and the yield of 3-methylindole increased from 43% to 52%. The addition of NiO to Ag/SiO2-ZnO could increase the initial activity of the catalyst to 49%. The stability of Ag/SiO2-ZnO doped with Fe2O3, CoO or NiO didn't be improved. |
