Selective Hydrogenation Of Benzonitrile Over Nickel-based Nanocatalysts

Catalytic hydrogenation, as the representative of the atom economy reactions, conforms to the concept of green chemistry and is regarded as the most common method to prepare saturated compounds. Catalytic hydrogenation of nitriles preparing primary amines and imines is one of the most attractive research spots. Primary amines are commonly used as intermediates in the pharmaceutical, agrochemical and plastics industries. Imines and their derivatives are also versatile synthetic intermediates, extensively utilized for the synthesis of dyes, fragrances, fungicides and pharmaceuticals. At present, the catalysts used in nitriles hydrogenation have some disadvantages, such as high cost. Thus, transition metal nickel was selected as the active species in this paper. A series of nano nickel-based catalysts were prepared for hydrogenation of benzonitrile. And the structure-activity relationship between catalyst and reaction was studied.Firstly, two novel layered double hydroxide(LDH)/layered double oxide(LDO) coated nickel-based core-shell nanocomposites were prepared based on hydrotalcite-like precursors and Ni particles. It was found that Ni@mSiO2@LDO and Ni@mSiO2@LDH can be interconverted through calcination/reduction and hydration. The results reveal that water acts as a switch to tune their structures and acid-base properties, resulting in a chemoselective hydrogenation of benzonitrile to form N-benzylidenebenzylamine and benzylamine, respectively.Secondly, LDH used as carrier was prepared by urea decomposition method. Then Ni/LDH catalyst was prepared by impregnation-reduction method. The TEM image showed that Ni particles dispersed homogeneously on LDH. It was found that Ni/LDH exhibited good catalytic performance for benzonitrile hydrogenation in different solvents and the selectivity of benzylamine increased in the polarity solvent.Finally, highly dispersed supported Ni catalysts were prepared based on LDH precursors. The results showed that the catalyst has good catalytic activity and selectivity in benzonitrile hydrogenation reaction. The conversion of benzonitrile was almost 100% and the selectivity of benzylamine was over 80% after six runs. The TEM image showed Ni particles dispersed homogeneously on the support. Moreover, no significant aggregate and sinter of active species were observed by TEM, which revealed that catalyst had a good stability. The results demonstrated that the catalyst prepared in this work had a potential application in the benzonitrile hydrogenation reaction.