Highly Selective One-step Catalytic Full-hydrogenation Of Nitro-aromatics With Nitro-and Aromatic-ring Groups To Alicyclic Amines

Organic amines are produced by the reaction of organic hydrocarbon with ammonia,inchuding aliphatic amines,alcoholic amines,amides,alicyclic amines,aromatic amines,and other amines.Alicyclic amines are important organic chemicals and fine chemical intermediates,widely used in the manufacturing,of rubber chemicals,food additives,pharmaceuticals,plastics processing and textile fields.Conventionally,cyclohexylamine is produced via the following two steps,?)the reduction of nitrobenzene(NB)to aniline,?)the ring hydrogenation of aniline to CHA,which is a complicated process.However,the two-step reaction involving different reaction apparatus,different catalysts,different process conditions,and different separation processes,results in high cost of the reaction process and energy consumption and does not meet the requirements of "energy-saving" green chemistry.In this study,a series of supported catalysts have been prepared,in which oxides like SiO2,Al2O3,TiO2,and porous carbons like coconut shell charcoal,activated carbon,graphite are used as the carriers to support transition metals inclusive of Rh,Ru,Ni,Fe,Co,Cu,Mo and other transition metals.In the preparation of catalysts,two routes are adopted:(1)common impregnation method,(2)microwave-assisted impregnation method.These catalysts have been characterized by XRD,Raman,BET,EDX,SEM,TEM,XPS and H2-TPR analyses.Then,one-step catalytic full-hydrogenation of nitrobenzene to cyclohexylamine is conducted over supported catalysts.Clearly,the results show that the activity of the catalyst prepared by conventional impregnation method is significantly poorer than that by microwave-assisted heating impregnation.For the catalysts prepared by conventional impregnation method,high selectivity of fully-hydrogenated product cannot be achieved.In order to obtain high selectivity(90%)of cyclohexylamine,a small amount(‰)of precious metal must be added.However,coconut shell charcoal supported Ni catalyst prepared by microwave-assisted heating impregnation shows an excellent activity and selectivity for the full-hydrogenation of nitrobenzene,i.e.10%Ni/CSC catalyst can convert 100 mol%of nitrobenzene with 96.7%of cyclohexylamine(CHA)selectivity.More importantly,even if no any precious metal is added,the activity of only Ni-based catalyst is still very good.In addition,the catalytic hydrogenation of substituted nitrobenzene compounds inclusive of 2,4,5-trifluoro nitrobenzene,chlorinated nitrobenzene and methyl nitrobenzene are studied,in which some good reaction results are obtained.As a comparison,the catalytic hydrogenation of aromatic amines is investigated.In the hydrogenation of aniline,the most active catalyst is a mixed catalyst of 3%Rh/CSC and 10%Ni/CSC(3‰ Rh),which receives 91.2%selectivity of cyclohexylamine(CHA).The effects of various reaction conditions such as the type of supports,various metal species,the reaction temperature and time,the solvent and pressure,are explored.Also,the work discusses the catalytic hydrogenation of 4,4'-diaminodiphenyl methane(MDA).Among these catalysts tested,a particularly mixed catalyst of 2.2%Ru/Al2O3 + 10%Ni/Al2O3 shows the best activity,in which the conversion of MDA is up to 99.9mol%and the selecticity of targeted H12MDA is 96.5%.In the study of "one-step" catalytic full-hydrogenation of nitro-containing naphthalene to amino-decahydro naphthalene,the encouraging results are achieved.The present study is mainly focused on the catalytic full-hydrogenation of 1,5-dinitronaphathlene(1,5-DNN)or 1-nitronaphthalene(1-NNA)to 1,5-diaminodecahydronaphathlene(1,5-DADHN)or 1-aminodecahydronaphthalene(1-ADHN)over the supported Ni catalysts.Under optimal conditions,almost 100 mol%of 1,5-DNN conversion is obtained over 10%Ni/SiO2-la with a high selectivity of 1,5-DADHN up to 95.3%.However,for the hydrogenation of 1-NN only 81.0%selectivity of 1-ADHN is obtained.In addition,this work studies the catalytic hydrogenation of 1,5-aminonaphthalene(1,5-DAN)and 1,8-aminonaphthalene(1,8-DAN).For these two reactions,the catalyst 10%Ni/SiO2 is the most active.Under the pressure of 5.5 MPa H2,100 mol%of 1,5-DAN conversion is realized,with 94.7%selectivity of 1,5-DADHN.Similarly,100 mol%of 1,8-DAN can be converted over 10%Ni/SiO2,with 93.9%selectivity of 1,8-DADHN.Finally,the hydrogenation of other aromatic substrates is studied over supported Ni catalysts,inclusive of aromatic acids,pyridine and aromatic aldehydes.The catalytic hydrogenation of benzoic acid to cyclohexyl formate(CHF)is conducted over 3‰Rh-10%Ni/CSC bimetallic catalyst to achieve 96.8 mol%conversion,but only 76.2 mol%conversion over 10%Ni/CSC-II without precious metal,in which the selectivity of CHF is 100%.However,for the hydrogenation of pyridine(the substrate concentration<20 wt%)over 10%Ni/CSC catalyst,100 mol%conversion of substrate is achieved,with 100%selectivity of piperidine.As for the catalytic hydrogenation of vanillin,O-vanillin and phthalic aldehyde over 10%Ni/CSC,the observed conversions higher than 96 mol%,and the selectivities of fully-hydrogenated products are also higher than 96%,.Generally,the present work deeply investigates the preparation and application of the supported active catalysts for highly selective one-step catalytic full-hydrogenation of nitro-aromatics with nitro-and aromatic-ring groups to alicyclic amines.Some good results have been achieved.The studies have preliminarily revealed the hydrogenation route of bi-functional groups at one step.Hopefully,this investigation may provide a simple and efficient methodology for one-step full-hydrogenation of compounds with multi-functional groups over cheap Ni-based catalyst.