The Effects Of ZnO And Fe₂O₃ Promoters On The Performance Of Cu/SiO₂ For Liquid-Solid Phase Efficient Synthesis Of 3-Methylindole From Glycerol And Aniline

3-Methylindole,an important indole derivative,is widely used in agriculture,medicine and industry.A green,simple and efficient method for the preparation of 3-methylindole has always been the focus and difficulty research.And the most promising method is the synthesis of 3-methylindole from aniline and biomass-based glycerol.In this paper,ZnO and Fe₂O₃modified Cu/SiO₂were used as catalysts to synthesize3-methylindole from glycerol and aniline in a stainless steel autoclave.The effects of ZnO and Fe₂O₃promoters on the liquid-solid phase synthesis of 3-methylindole over Cu/SiO₂catalysts were studied.Cu/SiO₂-ZnO catalyst was prepared by a sequential impregnation method,and the effect of ZnO was investigated by X-ray diffraction(XRD),transmission electron microscopy(TEM),H₂-programmed temperature reduction(H₂-TPR),NH₃(CO₂)-programmed temperature desorption(NH₃-TPD or CO₂-TPD),thermogravimetric-differential thermal analysis(TG-DTA),inductively coupled plasma(ICP)and other characterization methods.The results showed that the introduction of ZnO could increase the force between the carrier and Cu,which not only improved the dispersion of Cu on the surface of SiO₂-ZnO,but also effectively inhibited the sintering of Cu particles on the surface of the carrier in the reaction process.However,the introduction of ZnO enhanced the acidity of the catalyst,resulting in the formation of a large amount of carbon deposition in the reaction process.By considering the Cu loadings,the ZnO contents,reduction temperature and reaction temperature,the optimal experimental conditions were as follows:1.000 mmol/g of Cu loading,0.100 mmol/g of ZnO content,250?of reduction temperature and 190?of reaction temperature,where the yield of 3-methylindole reached 64%at 22 h.The catalyst was recycled four times,and the yield of 3-methylindole was only reduced by 5%.The Fe₂O₃promoter was introduced into Cu/SiO₂-ZnO,and the effect of Fe₂O₃on the structure and properties of the catalyst was investigated by various characterizations.The results showed that the introduction of Fe₂O₃could weaken the interaction between Cu and the carrier,which made Cu O easily be reduced,but the dispersion of Cu particles on the surface of the carrier decreased.After the introduction of Fe₂O₃,the number of middle-strong acid centers of the catalyst decreased and the acidity weakened,thus inhibiting the formation of carbon deposition in the reaction process.When the content of Fe₂O₃is 0.030 mmol/g,the reduction temperature is 240?,and the reaction temperature is 190?,the yield of3-methylindole is up to 73%at 18 h.The catalyst was recycled four times and the yield of3-methylindole was still 64%.The reaction mechanism of liquid-solid phase synthesis of 3-methylindole from aniline and glycerol over Cu/SiO₂-ZnO-Fe₂O₃catalyst was proposed by GC-MS analysis of the reaction products of aniline with glycerol and hydrogenolysis of glycerol and gas chromatography analysis of the products of aniline with 1,2-propanediol or acetol and the catalytic conversion of acetol.