Preparation And Selectivity Hydrogenation Properties Of Supported Metal Silicide Based On Strong Metal-Support Interaction

Transition metal silicides are widely used in high temperature coating,magnetic material,thermoelectric material and microelectronic materials because of their special physical and chemical properties.Particularly,its nanomaterials have broad application prospects in the fields of selective hydrogenation,hydrotreating,photocatalytic and electrocatalysis.However,the traditional preparation method cannot meet the preparation of transition metal silicide nanomaterials,which limits its research and application as a catalytic material.Therefore,it is of great significance to find a general,simple and controllable preparation method for the application of transition metal silicide nanomaterials in the field of catalysis.Based on the above purposes,this paper developed a synthesis strategy based on strong metal-support interaction,and successfully prepared supported Ni₂Si/SiCN and Pt₂Si/SiO₂ nano-catalyst materials by metal organic polymer pyrolysis method and high temperature reduction method.The catalytic hydrogenation performance of Ni₂Si/SiCN and Pt₂Si/SiO₂ catalysts were studied on nitrobenzene-benzaldehyde reduction coupling reaction and the selective hydrogenation of anthracene.The main research contents and results of this paper are as follows:The polysilazane is modified with nickel acetylacetonate.Under a reducing atmosphere,the high temperature causes a strong interaction between the metal Ni and the support SiCN,which gradually changes the active component of the catalyst from Ni to Ni₂Si.The method has the advantages of simple and safe operation,and can easily and accurately adjust the stoichiometric ratio of the product at the molecular level.In the"one-pot"method for preparing imines and secondary amines using nitrobenzene and benzaldehyde as raw materials,there is a repulsive force between the electronegative Si atoms in Ni₂Si and the O atoms in the C=O bond of benzaldehyde,which leads to lower activity of benzaldehyde hydrogenation to benzyl alcohol,so the Ni₂Si/SiCN catalyst can produce imines and secondary amines with high selectivity（≈92%）.The metal Ni-based catalyst catalyzes the hydrogenation of a large amount of benzaldehyde to form benzyl alcohol,which changes the reaction path.In addition,in a one-pot reduction coupling reaction,Ni₂Si/SiCN catalyst can not only efficiently catalyze the conversion of nitrobenzene（conversion rate>99%）,but also can be used for the reduction coupling of various aromatic aldehydes and nitroaromatic hydrocarbons,and showed excellent stability.This research work provides a new research idea for the design of catalysts involved in the reduction coupling reaction of aromatic aldehydes and nitroaromatics.The SiO₂-supported single-layer Pt salt pyrolysis precursor was successfully prepared by the strongest electrostatic adsorption method.Under 800 ^oC-15 h high temperature reduction conditions,a strong interaction occurs between the metal Pt and the non-reducing support SiO₂.And the non-reducing support SiO₂ is partially reduced under the strong interaction.The reduced Si atoms enter the lattice of the metal Pt,forming the corresponding intermetallic compounds Pt₂Si.After 30 h of reduction,part of the Si atoms in Pt₂Si were lost.Through characterization analysis,the metal nanoparticles are evenly distributed on the support SiO₂,with an average particle size of 2.34 nm.At the same time,the Pt₂Si/SiO₂ catalyst can achieve complete conversion of anthracene at 250 ^oC and 5 MPa,and generate symmetric octahydroanthracene with a high selectivity of 88%.Pt₂Si/SiO₂ catalyst is expected to open up the wide application of transition metal silicides in the selective hydrogenation of polycyclic aromatic hydrocarbons due to its excellent selectivity and stability.