Study On The Catalytic Effect Of Supported Metal Nickel Catalyst On MPV Reaction

The Meerwein-Ponndorf-Verley hydrogenation reduction of aldehydes and ketones is one such reaction which high selectivities are obtained with alcoholic compounds using catalysts.MPV reactions has been the most widely practised operations in the synthetic organic,fine and perfumery chemical industries.It was recently reported that raney nickel,urushibara nickel and nickel nanoparticles as the catalysts of carbonyl compounds hydrogenation reduction by' isopropyl alcohol have good catalytic activities,but there are some disadvantages in the preparation method of raney nickel and urushibara nickel,so Ni(0)-based catalyst which prepared by impregnation methd had been choosed to catalysis the MPV reaction.Ni/MgO and Ni/Al2O3 prepared by impregnation were inverstigated by different techniques such as BET,TPD,H2-TPR,XRD,XPS etc.First,catalytic activities of Ni/MgO and Ni/Al2O3 was tested for the MPV reduction of benzaldehyde,cyclohexyl aldehyde and cyclohexanone by contrasting with MgO and Al2O3.The MPV reaction of different aldehydes or ketones was studyed to investigate that the structure of substrates influence on conversion of the MPV reduction.The results showed that the conversion of different aldehydes or ketones was influenced by its own structure,conversion of benzaldehyde which a-C directly were connected to the benzene was higher than the compounds which carbon a-C were connected to the double bond or cyclohexyl.And saturated alkylaldehyde catalyzed by Ni/MgO was the condensation reaction,because the base sites of Ni/MgO could activate the ?-c of the substrates.Then,the mechanism of the MPV reaction catalyzed by the nickel-based catalyst was studyed.Zero-valent nickel which could easily adsorb H of alcohol,had goodeffect on the dehydrogenation of alcohol,due to the holes of its own atomic orbitals structure.Thus,Zero-valent nickel played an important role on the dehydrogenation of the MPV reaction.The mechanism of the MPV reaction catalyzed by Ni/MgO and.Ni/Al2O3 could be explained by the active sites of nickel and base.Alcohol had been adsorbed by the two kinds of active sites at the same time,hydrogen of hydroxy had been adsorbed by the active sites of base,and the active sites of nickel have adsorpt the hydrogen of a-c,the cleavage of O-H bond and C-H bone produces at the same time.Ni nanocatalyst supported on MgO or Al2O3 had two active sites and it has revealed an enhanced cooperative catalysis between Ni(0)and base sites;the same as hydrogenation of carbonyl.In summary,cooperation of Ni(0)and the base sites on MgO or Al2O3 enhances the catalytic activities.The conversions of benzaldehyde and hexahydrobenzaldehyde MPV reaction were more than 90%by optimizing reaction conditions that at 120?,in 3hs,with 0.1g Ni/MgO,0.5mmol of substrate and the ratio of substrate and isopropyl was 1:10.At the same conditions,the conversion of cyclohexanone was more than 96%in 6 hours.