The Effect Of CeO₂ And Fe₂O₃ Promoters On The Performance Of Cu/MIL-101 Catalyst For The Vapor-phase Synthesis Of 3-methylindole From Glycerol And Aniline

3-Methylindole,an important fine chemical and synthetic intermediate,has been widely used in the fields of industry,agriculture and medicine.How to synthesize3-methylindole in a simple,efficient and green manner has always been the focus and difficult task.The synthesis of 3-methylindole from aniline and biomass-based glycerol on Cu-based catalysts is considered to be a potential method for development.In this paper,MIL-101,which was of excellent performance,was used as supporter and metal copper was the active component.The reaction about the synthesis of 3-methylindole from glycerol and aniline over Cu/MIL-101 and the catalyst modified with CeO₂ or Fe₂O₃ promoter were primarily studied.MIL-101 was synthesized by hydrothermal method.Copper based catalysts were prepared by sequential equal volume impregnation method.MIL-101 supporter and Cu-based catalysts were characterized by N₂ physical adsorption,fourier transform infrared（FT-IR）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）,thermogravimetry analysis（TG）,transmission electron microscopy（TEM）,temperature programmed reduction of hydrogen（H₂-TPR）,inductively coupled plasma（ICP）,,and temperature programmed desorption of ammonia（carbon dioxide）（NH₃-TPD or CO₂-TPD）techniques.The results showed that the MIL-101 supporter was successfully synthesized by hydrothermal method with a regular crystal shape,the main pores size was in 0.6².4nm,good thermal stability and the specific surface area was 1476.25 m²/g.Moreover,when the Cu loading was 3.000 mmol/g over Cu/MIL-101,the yield and selectivity of3-methylindole reached the best of 38%and 41%,respectively.An appropriate amount of CeO₂ promoter was added to Cu/MIL-101 catalyst and it was found by various characterization methods that CeO₂ could enhance the interaction between Cu and the supporter as well as the weak acid sites of the catalyst,which not only improved the dispersion of Cu particles,but also effectively inhibited the sintering of Cu particles during the reaction,as a result,the conversion of glycerol and the synthesis of 3-methylindole were improved.Under the optimum conditions of0.030 mmol/g of CeO₂ amount,the catalyst precursor reduced in situ reduction at280℃for 3 h（N₂:H₂=40:60 mL/min）,and the catalytic reaction carried out under the temperature of 260℃with the reaction gas ratio of N₂:steam:H₂=1:17:22（mL/min）,the catalytic activity and selectivity reached the best,which the yield and selectivity of 3-methylindole were 59%and 61%,respectively.Fe₂O₃ promoter was added to the Cu/MIL-101 catalyst and it can be obtained from various characterizations that Fe₂O₃ could weaken the interaction between Cu and the supporter,which made CuO particles be reduced easily although the dispersion of Cu nanoparticles decreased.The addition of Fe₂O₃ decreased the medium-strong acid sites of the catalyst,thereby the carbon deposition formed during the reaction could be inhibited.Under the optimum conditions of 0.030 mmol/g of Fe₂O₃ amount,the catalyst precursor reduced in situ reduction at 270℃for 3 h（N₂:H₂=40:60 mL/min）,260℃of reaction temperature and the reaction gas ratio of N₂:steam:H₂=3:17:20（mL/min）,the catalyst activity and selectivity reached the best,which the yield and selectivity of 3-methylindole were up to 60%and 65%,respectively.The catalytic mechanism of vapor-phase catalytic synthesis of 3-methyindole over MIL-101 supported Cu-based catalyst was proposed base on the investigation on the catalytic hydrogenolysis of glycerol,the catalytic conversion of acetol as well as the catalytic reaction of glycerol,acetol or 1,2-propanediol with aniline.