The Effect Of ZnO,CeO₂,or Iron-series Promoters On The Ag-based Catalyst For The Vapor-phase Synthesis Of 3-methylindole From Glycerol And Aniline

3-methylindole,a kind of important fine chemical raw materials,was widely applied in various fields of industry,agriculture and medicine,etc.How efficient,cheap and green synthesis of 3-methylindole is a matter of great concern to chemists.The synthesis of 3-methylindole from glycerol and aniline is the most promising route because it is green,cheap,and could meet the chemical reaction of the principle of atomic economy.In this paper,the effect of ZnO,CeO₂,or iron-series promoters on the performance of Ag-based catalyst for the vapor-phase synthesis of 3-methylindole from glycerol and aniline was investigated.The catalysts was prepared by incipient wetness impregnation and investigated by atmospheric gas-solid reactions,X-ray diffraction（XRD）,temperature programmed reduction of H₂（H₂-TPR）,temperature programmed desorption（TPD）of NH₃ and CO₂,and thermogravimetric and differential thermal analysis（TG-DTA）.The results showed that ZnO as a structural promoter could improve the dispersion of active component on the support and inhibit the sintering of silver particles during the reaction,as a result,the catalytic activity and selectivity improved remarkably.However,with the increase of ZnO content,the number of middle-strong acid sites increased,which led to the decline of catalyst stability.Over Ag/SiO₂-ZnO（Ag 1.0 mmol/g,ZnO 1.5 mmol/g）catalyst,the yield of 3-methylindole was 56%at the first hour of reaction.CeO₂ promoter was not conducive to the dispersion of silver particles on the support,but it could make Ag₂O easy to reduction and significantly decrease the number of middle-strong acid sites of catalyst,which inhibited carbon deposition and enhanced the stability of catalyst greatly.Over Ag/SiO₂-ZnO-CeO₂(CeO₂ 0.04 mmol/g),the yield of 3-methylindole was up to 66%.The iron-series promoters weakened the interaction between the support and the active component.Besides,the number of alkali sites on the Ag-based catalysts modified by iron series promotorsincreased and the acid sites reduced,which resulted in the catalyst stability,the conversion of glycerol and the yield of target product increased.Doped with appropriate amount of Fe₂O₃（0.02 mmol/g）,Co₃O₄（0.03 mmol/g）,NiO（0.05mmol/g）promoters,the yield of 3-methylindole reached 70%,67%and 68%,respectively in the first hour of reaction.After Ag/SiO₂-ZnO-CeO₂-Fe₂O₃ catalyst was regenerated 5 times,activity decreased rapidly,which the yield of 3-methylindole decreased to 12%.