Hydrogenating Reduction Of Aromatic Ketones Catalysed By Skeletal Nickel In Water

Owing to good catalytic activity,high mechanical strength,non-sensitive to toxins,as well as good heat conductivity,skeletal nickel catalysts have been widely used in hydrogenation of unsaturated bond such as alkynes,alkenes,aromatic,nitrocellulose,carbonyl,nitrile,and dehydrogenation,desulfurization,dehalogenation in chemical industry.The reduction of aromatic ketones to obtain aromatic alcohols can be achieved through the conventional reduction processes by inorganic hydrides as reducing agents,as well as the catalytic hydrogenation reduction processes.Due to the advantages of environment-friendly and simple post-processing,the superiority of catalytic hydrogenation in industrial production is becoming more and more obvious.Organic solvents have been widely used in catalytic hydrogenation.However,skeletal nickel catalysts are pyrophoric and organic solvents have low boiling point,volatile and broad explosion limits.Therefore,the use of water as a reaction medium instead of organic solvents in catalytic hydrogenation has become a research focus.Herein,the catalytic hydrogenation of aromatic ketones to corresponding aromatic alcohol on skeletal nickel catalysts in water was studied.In the present work,twelve skeletal nickel catalysts were prepared in different ways.C-01 and C-02 catalysts were prepared by the traditional methods;C-03?C-A01?C-A04,C-B01?C-B04 and C-C01 catalysts were modified by Ni(OH)2 or Ni2O3 based on C-01 catalyst.It is noteworthy that we developed a novel way to prepare C-03 catalyst which is opposite to the traditional method.It has more nickel and aluminum in oxidation state on the surface of C-03 catalyst surface as a result of introducing HCl solution treatment.The C-01,C-02 and C-03 catalysts were characterized by means of XRD?N2-adsorption techniques?XRF?XPS?SEM?HRTEM and E2-TPD.Using H2 as hydrogen donor,hydrogenating reductions of acetophenone were conducted on the twelve skeletal nickel catalysts in water.The results showed that C-03 catalysts had the highest selectivity of 1-phenylethanol(99.23%).C-03x C-A01-C-A04,C-B01-C-B04 and C-C01 catalysts which were all modified by Ni(OH)2 or Ni2O3 had been shown the higher selectivity of 1-phenylethanol.From XPS analysis,the nickel was predominant in the metallic state in C-01 and C-02 catalysts,while that was the oxidation state in C-03 catalyst and amorphous 3Ni(OH)2·2H2O existed on the surface of C-03 catalyst.The catalytic hydrogenation of other aromatic ketones on C-03 catalyst were carried out in water,including 1-(4-methylphenyl)-ethanone,1-(4-ethylphenyl)-ethanone,propiophenone,1-(4-methylphenyl)-1-propanone and 1-(4-ethylphenyl)-1-propanone.The C-03 catalyst exhibited an excellent selectivity(>98%)to carbonyl bond in the hydrogenation of aromatic ketones,and the yields of corresponding aromatic alcohols also reached a high level(>91%).Therefore,the C-03 catalyst is a perfect catalyst for hydrogenation of aromatic ketones into the corresponding alcohol in water.Another focus of this paper is the investigation of the relationship between the structure of catalysts and selectivity.It was found that the novel method can produce nickel hydroxide on the surface of C-03 catalyst,which leaded to the unordered and dispersive chemical distribution of nickel and made the active sites more uniform on surface.These structure characteristics were beneficial to improve the reaction selectivity.HCl leaching process can dissolve more aluminum,which changed the pore structure from ink-bottle pore shape to sheet-like.The pore volume,pore diameter and specific surface area became lager,all those were benefited to the closer contact between raw material,hydrogen atoms and the rapid desorption of product,which increased conversion ratio of raw materials,and shorten the reaction time.In addition,a reaction mechanism for the hydrogenation of acetophenone over C-02 and C-03 catalysts has been proposed in this paper.The reaction system investigated favored C=O hydrogenation over C=C.So most of acetpohenone molecules are adsorbed on the catalyst surface via carbonyl bond and then hydrogenated.Acetpohenone molecules may interact through its C=O bond with the catalyst surface via ?(O)or ?~2(C,O)configuration over C-02 catalyst,but more likely absorbed through ?~1 species over C-03 catalyst because the nickel hydroxide had the effect that hinder the formation of ?~2 species.The ?~2(C,O)configuration can increase the possibility of C=C hydrogenation.Therefore,the selectivity of 1-phenylethanol was increased greatly by nickel hydroxide modified.