Structure Control Of Ni/Al₂O₃ Catalyst And Its Hydrogenation Performance Of Adiponitrile

Catalytic hydrogenation of nitriles is of great industrial importance because the resulting amines and imines are versatile intermediates and precursors for the synthesis of various natural products,agrochemicals,pharmaceuticals,dyes,pigments,and polymers.The hydrogenation of adiponitrile to prepare amines is also widely used,and its hydrogenation products,6-aminocapronitrile and hexamethylenediamine,are very important chemical intermediates.The production capacity of adiponitrile hydrogenation in my country is far less than the demand.Therefore,it is very important to study the hydrogenation of adiponitrile.Understanding the important role in the hydrogenation of adiponitrile is an important factor in the design of promising nickel catalysts.In this work,a series of Ni/Mg_xAl₁O catalysts were first prepared,and catalysts with different specific surface areas and Ni particle sizes were obtained by adjusting different Mg/Al molar ratios.Using XPD,H₂-TPD,XPS and other characterization tests,it was further confirmed that doping with different Mg contents changes the content of Ni⁰ on the catalyst surface.In addition,the structure of the catalyst collapsed slightly,but the layered morphology remained basically unchanged even under high temperature treatment.Through the subsequent optimization of the pretreatment process and conditions,the primary amine selectivity of adiponitrile hydrogenation was as high as 86%.However,one of the primary amines produced by adiponitrile,hexamethylenediamine,has a very wide range of applications,so the catalyst was designed to improve the selectivity of a single primary amine.Since the nucleation and precipitation process of metal precursors can fine-tune the crystallization of Ni particles,a series of Ni/Al₂O₃ catalysts with Ni loading of 20wt%were synthesized by the deposition-precipitation method for the selective hydrogenation of adiponitrile.Hexanediamine.The formation of Ni particles and the chemical structure of the catalyst are regulated by the precipitant.XRD,N₂ adsorption-desorption,TEM,XPS,H₂-TPD and NH₃-TPD were characterized.In Ni/Al₂O₃-OH,smaller particles were obtained by rapidly depositing Ni²⁺using Na OH,and Ni/Al₂O₃-U using urea with uniformly dispersed Ni seeds.In the preparation process of the catalyst,the use of strong alkali Na OH leads to the formation of nickel hydroxide,which promotes the formation of Ni0 and has better H₂ activation ability.At the same time,a large number of nickel species with various oxidation states and strong acidity are simultaneously generated in Ni/Al₂O₃-U,which is more likely to produce cycloaddition by-products.Kinetic studies show that the hydrogenation of adiponitrile is a secondary reaction of adiponitrile.The number of Ni0 active sites and acid sites can be obtained by different precipitation and crystallization methods.The hydrogenation of adiponitrile with 20 wt%Ni/Al₂O₃-OH catalyzed the hydrogenation of adiponitrile in the absence of any bases and additives,and the yield of hexamethylenediamine was 75.0%.