Microwave-assisted Preparation Of Carbon Supported Metal Silicides As Catalysts For Hydrogenation

Transition metal silicides have been widely applied in the fields of semiconductor devices,thin-film coatings and thermoelectric materials for their unique physical and chemical properties.Due to the excellent thermostability,oxidation-resistivity and corrosion resistance,metal silicides have received extensive attention as novel catalytic materials and also showed good catalytic activity in some hydrogenation reactions recently.However,conventional preparation methods for silicides always need high energy consumption and long synthesis time,and form products with low surface areas,which restrict their further researches and applications as catalysts.Therefore,it is of great significance to develop a new method to prepare metal silicide nanomaterials with excellent catalytic performance and apply them in the hydrogenation reaction of fine chemicals.Microwave synthesis has the advantages of short synthesis time and low energy consumption,and is a green method for material synthesis.Therefore,this dissertation focuses on the preparation of carbon supported transition metal silicides by microwave method,and investigates the catalytic properties,reaction kinetic and cyclying stability in the hydrogenation of cinnamaldehyde,hydrodeoxygenation of phthalic anhydride and hydrodesulfurization of dibenzothiophene.The main conclusions are listed as follows.（1）Transition metal silicides encapsulated in porous carbon Co_xSi@C-N and M₂Si@C（M=Fe,Co,Ni）catalysts have been successfully prepared by microwave-assisted chemical vapor deposition with metal organic framework（ZIF-67and MOF-74）as the metal precursor.In the chemoselective hydeogenation of cinnamaldehyde,the prepared cobalt silicide based catalyst prefers to hydrogenate C=O bonds and nickel silicides based catalyst has high selectivity in the hydrogenation of C=C.（2）Cobalt silicide catalysts with different phases supported on carbon were successfully prepared by microwave method,and the phase transition was revealed as Co₂Si（orthorhombic）→CoSi（cubic）→CoSi₂（cubic）.In the hydrogenation of phthalic anhydride to phthalide,the activity of the prepared catalyst is gradually enhanced as the cobalt content in the silicides phase increases.（3）Cobalt-nickel bimetallic silicide catalysts have been successfully prepared by microwave-assisted chemical vapor deposition.Due to the bimetallic synergistic effect in the Co_1.5Ni_0.5Si@C catalysts in the hydrogenation of phthalic anhydride to phthalide,the yield of phthalide reaches 89.6%,which also showes superhigh acid stability.Ni₂Si@Ccatalystdisplaysexcellentcatalyticactivityinthe hydrodesulfurization of dibenzothiophene.The conversion of this reaction can be up to 84.0%and the direct hydrodesulfurization selectivity is 78.2%.At the same time,the catalyst has good stability.