Preparation Of Nickel-based Nanocatalysts And Their Stabilities In Hydrogenation Reactions

Catalytic hydrogenation,as the representative of the atom economy reaction,conforms to the concept of green chemical engineering.It is one of the hot spot of research at home and abroad in recent years.Catalyst is the key of the catalytic reaction;therefore,the development of high efficiency catalyst is a significant role in the study of catalytic hydrogenation reaction.Aiming at the existing problem such as expensive of precious metal catalysts,cheap transition metal nickel was chosen as the main active component in this work.A series of nickel-based nanocatalysts were prepared and applied in catalytic hydrogenation,focusing on the solvent,carrier and structural effects on catalysts' activity and stability.First,a NiB amorphous alloy nanocatalyst was prepared by the chemical reduction method.The effect of solvents on the activity and stability of the nickel-based catalysts was studied in the hydrogenation of cinnamic acid.It was found that the conversion of cinnamic acid rate can reach 98.9% and the selectivity for hydrocinnamic acid can reach 100% while using methanol and chloroform as solvent.Meanwhile,the loss of the active component was lowest while using tertiary butyl alcohol in this hydrogenation reaction.Then,three supported Ni B amorphous alloy catalysts?Ni B/?-Al₂O₃,NiB/SiO2,NiB/TiO2?were prepared by the impregnation-reduction method and applied in the hydrogenation of cinnamic acid.The effect of carriers on the catalyst's activity and stability was investigated and found ?-Al₂O₃ can disperse the active species better.Ni B/?-Al₂O₃ catalyst showed good stability while using tertiary butyl alcohol as solvent.The conversion increased gradually with the increase of the cycles.The conversion of cinnamic acid can reach 75.0% after three cycles,together with 100% selectivity for hydrocinnamic acid.This was ascribed to the continuous exposure of the active species in the carrier channels during the reaction.Finally,a novel core-shell nanocomposite Ni-Ca@mSiO2 was first prepared by a modified St?ber method in this paper.It exhibited good catalytic performance in the selective hydrogenation of benzophenone,with 96.1% conversion and 94.9% selectivity for benzhydrol under relatively mild reaction conditions.TEM and CO2-TPD demonstrated that addition of small amounts of alkaline Ca can not only markedly improve the dispersion of the active species but also tune the acid-base property of this catalyst,resulting in the efficient suppression of benzhydrol dehydration to achieve a high selectivity.Furthermore,the used catalyst can be effectively separated by an external magnetic field and recycled four times without significant loss of its initial activity,indicating its good stability.