Highly Active Nano Nickel Catalysts For The Hydrogenation Of Lauronitrile

Amines are valuable products that have wide applications as surfactants,textile additives,dyeing aids,corrosion inhibitors,anti-caking agents for fertilizers,floating chemicals,and chemicals used in plastics,rubbers and daily life.The catalytic hydrogenation of nitriles is one of the most important methods for the preparation of amines.In addition,this is an atom-economic route.However,due to the high activity of reaction intermediates,condensation reactions of intermediates often occur during the hydrogenation of nitriles,leading to the formation of mixtures of primary,secondary and tertiary amines.Therefore,the control of selectivity becomes one of the most important issues in the hydrogenation of nitriles.Industrially,Raney Ni is probably the most frequently used catalyst for the hydrogenation of nitriles to primary amines.However,it suffers from some disadvantages.For instance,the preparation of Raney nickel usually consumes great amount of energies and causes environmental pollutions.In addition,it is not convenient to handle since it is highly pyrophoric.Thus,it is desirable to develop more active and selective catalysts for the hydrogenation of nitriles to amines.In this work,highly loaded and active nickel catalysts were prepared and used for the hydrogenation of lauronitrile in liquid phase.Moreover,the surface coating of reduced catalysts and recycling of used catalysts were studied.Following are the main results obtained from this study.1.A highly loaded and dispersed Ni/SiO2-B catalyst was prepared by the co-precipitation method with an n-butanol drying process.Drying with n-butanol significantly increased the surface area of the catalyst as well as the reducibility and dispersion of supported nickel,leading to the high active nickel surface area(66 m2/g).In addition,the surface acidity of the Ni/SiO2-B catalyst was significantly enhanced,as probed by the microcalorimetric adsorption of ammonia.Accordingly,this catalyst exhibited high activity in the hydrogenation of toluene to methyl cyclohexane.In addition,it was also highly active for the hydrogenation of lauronitrile to corresponding amines.However,the selectivity to primary amine was not high due to its strong surface acidity that catalyzed the condensation reactions for the formation of secondary and tertiary amines.2.A series of Ni/SiO2-B catalysts with various Ni loadings(60-90 wt%)were prepared by the co-precipitation method with an n-butanol drying process,among which,70%Ni/SiO2-B catalyst exhibited the highest active nickel surface area(82 m2/g).According to the microcalorimetric adsorption of ammonia,strong surface acidities were probed on the surfaces of these catalysts.In addition,the surface acidity decreased with the increase of nickel loading.Thus,these catalysts showed high activity for the hydrogenation of lauronitrile,but low selectivity to the primary amine.3.60 wt%Ni/MgO-B catalyst was prepared by the co-precipitation method with an n-butanol drying process,exhibiting a high active nickel surface area of 46 m2/g.Microcalorimetric adsorption of H2 and CO showed that the treatment with n-butanol increased the amount of active metal sites on the surface,without the change of electron densities of supported nickel surface.Due to the strong surface basicity revealed by the microcalorimetric adsorption of CO2,the Ni/MgO catalysts exhibited high selectivity to primary amine for the hydrogenation of lauronitrile.4.Ni/MgO-B catalysts with different Ni content(20-90 wt%)were prepared.With the increase of nickel loading,the reducibility of supported nickel increased,while the dispersion decreased,particularly when nickel loading was higher than 80%).Thus,the 60%Ni/MgO-B exhibited a balanced reducibility and dispersion,so that it possessed the highest active nickel surface area.All these reduced Ni/MgO-B catalysts showed strong surface basicity and weak surface acidity,leading to the high selectivity to primary amine for the hydrogenation of lauronitrile,while the activity varied remarkably with the nickel content.5.Catalysts with nickel supported on different supports(MgO,SiO2,Al2O3,MgAlO and SiAlO)were prepared by the co-precipitation method and dried in n-butanol.The Ni/MgAlO and Ni/SiAlO showed considerably high active nickel surface areas(75 m2/g).The strong surface basicity of Ni/MgO was found to favor the selectivity to the primary amine,but inhibited the conversion of lauronitrile.On the other hand,the conversion of lauronitrile was high over the Ni/SiO2,Ni/Al2O3 and Ni/SiAlO with strong surface acidity,but the selectivity to the primary amine was relatively low.The Ni/MgAlO with intermediate strengths of surface acidity and basicity exhibited the high conversion of lauronitrile and high selectivity to the primary amine.6.A reduced Ni/MgAlO catalyst was coated by an aliphatic amine(distearyl amine),so that it was protected from oxidation in air.Specifically,the reduced catalyst was soaked in the molten distearyl amine and mixed with it thoroughly.The melt was dropped onto a cold metal plate on which the drops became flattened semi-spherical particles with diameters of about 5 mm.The particles contained 30-40 wt%of the reduced catalyst.Compared to the uncoated one,the coated catalyst exhibited the similar activity and selectivity for the hydrogenation of lauronitrile.The used catalyst was washed with lauronitrile and then calcined at 673 K to remove organic residues.It was then dissolved in nitric acid and the solution could be used to prepare Ni/MgAlO catalysts again.In this way,the catalysts could be recycled.