Application Of Cu-Zn System Catalyst In Aniline N-Methylation Reaction

N-methylation reaction is an excellent way to realize C-N bond coupling,which can be used to synthesize a variety of important compounds.However,the commonly used methylation reagents,such as iodomethane,diazomethane acid and formic acid,not only produce a large number of by-products,but also have a great negative impact on human health and environmental protection.Therefore,it is of great significance and great prospect to find a sustainable,atomic-economical and environmentally friendly catalyst to realize N-methylation reaction.In this work,the preparation of a new Cu-Zn system catalyst and its application in the catalytic N-methylation of aniline are presented,which provides a new idea for the design and construction of Cu-based multiphase catalyst.The specific contents are as follows:1.A series of composite metal oxides Cu Zn Al MO_x（M is metal）were prepared by doping different non-precious alkali metals（Mn,La,Ba,Mn La）in CuZnAlO_x.These metal oxide catalysts showed high activity against the N-methylation of aniline with methanol.Cu_6.5Zn₂Al₁Mn_0.5O_xat atmospheric pressure,the molar ratio of aniline to methanol is 1:1.7,the reaction temperature is 220^oC,the liquid air speed is 0.4m L·g^-1·h^-1,the conversion rate of aniline is 96%,and the selectivity of N-methaniline is99%.The catalyst has shown a good stability and no obvious deactivation occurred after144h of reaction.Through a series of characterization,the excellent catalytic performance of Cu_6.5Zn₂Al₁Mn_0.5O_xis attribute to the small amount of Mn doping,which is more conducive to improve the dispersion of copper.2.In order to investigate the influence of catalysts on N-methylation activity of aniline under different treatment method,Cu₇Zn₂Cr₁O_xand Cu_6.5Zn₂Al₁Mn_0.5O_xwere prepared by coprecipitate method and compared the activity:（a）Reduction furnace reduction,fixed bed in situ reduction reaction;（b）Reduction furnace reduction,fixed bed in-situ reduction,anhydrous methanol passivation reaction;（c）Reduction furnace reduction,anhydrous methanol passivation reaction;（d）Direct reaction without reduction.Through the four reaction performance tests,the same law was shown in the case of catalyst without significant deactivation:the reaction activity of catalyst was improved after reduction,but after the passivation of anhydrous methanol,the conversion rate of aniline was decreased,and N,N-dimethylaniline was generated in all of them.This can be explained when anhydrous methanol is passivated,some methanol molecules will dehydrogenate and decompose into formaldehyde,which adheres to the surface of the catalyst,as a result,the formed N-methylaniline will condense with another formaldehyde molecule to form imine ion,and then be reduced to form N-N dimethylamine.At the same time,the reaction activity of commercial Cu Zn Cr O_xunder these four conditions was also investigated.Through the reaction performance test and X-ray diffraction（XRD）characterization,it has been proved the commercial Cu Zn Cr O_xafter roasting has shown better activity and stability,and the reaction activity is mainly concentrated on Cu⁰.