Preparation Of Mesoporous Metal-boron Alloy And Study On Its Catalytic Hydrogenation Performanc

Mesoporous materials contain uniform pores with the size range of 2-50 nm,which display high specific surface area,large pore volume,adjustable pore size,and surface active sites.The mesoporous structure can increase active sites,improve diffusion,and also enhance the adsorption capacity for reactant and intermediate molecules,leading to the enhanced catalytic activity and selectivity.Generally,mesoporous metals exhibit higher heat and electron conductivities than either oxides or carbon materials,showing good potential in catalysis.Compared with single-component metal catalysts,metal-metalloid（e.g.,B）alloy catalysts and multicomponent metal alloy catalysts often possess excellent catalytic properties owing to the unique metal-metal-like synergies and alloying effects.They are widely used in catalytic hydrogenation.Their catalytic efficiency mainly depends on the geometric and electronic effects.Firstly,the electronic state could be adjusted by introducing B,leading to the catalytic efficiency.Meanwhile,the catalytic performance strongly relates to the crystalline structure.Amorphous alloys received more attention due to their unique isotropic structure,flexible composition,and more highly coordinated unsaturated sites comparing to the crystal alloys.Metal-B is an important member in the family of metal-metalloid amorphous alloys.However,limited by harsh preparing conditions,the traditional metal-B amorphous alloys are mostly presented as ultrafine non-porous nanoparticles.There is still a challenge for preparing amorphous alloys with controllable morphologies and mesopores.This thesis aims at innovation of synthesizing method to prepare series of mesoporous metal-B crystalline or amorphous alloys with enhanced catalytic efficiencies.Those catalysts are used in different hydrogenation reactions.Based on the catalytic performance examination and materials characterizations,the geometric and electronic effects on the catalytic hydrogenation efficiency are explored.The main researching results are summarized into the following four parts.（1）A surfactant self-assembly method was developed to prepare Pd B alloy with ordered mesoporous structure using PS-b-PEO as structure guide agent.The as-prepared catalyst exhibited high activity and selectivity in hydrogenation of phenylacetylene to produce styrene with high efficiency at room temperature and pressure.The size of Pd B catalyst obtained by this method is uniform and the mesoporous size is continuously adjustable.The ordered mesoporous structure could increase the exposed active sites and enhance the adsorption of the reactant.At the same time,the B alloying with Pd could improve the Pd electronic state.The electron transfer between Pd and B made Pd in an electron-deficient state,optimizing the adsorption mode of the reactant phenylacetylene and also reducing the desorption energy barrier of the target product styrene,corresponding to the enhanced catalytic activity and selectivity.（2）The surfactant self-assembly method was further extended to prepare binary metal-metalloid alloy materials.A series of mesoporous Pd MB（M=Cu,Ni,Fe,Ru,etc.）alloys were achieved,showing good universality of the present method.The activity and selectivity of mesoporous Pd Cu_xB alloy catalysts was explored in phenol hydrogenation to cyclohexanone.The Pd Cu_3%B catalyst exhibited good activity and selectivity in water-medium phenol hydrogenation to cyclohexanone.The mesoporous structure was stable and there was no obvious deactivation after 5 runs.The introduction of Cu changed the electronic structure of surface Pd,which promoted the adsorption of reactants to the intermediate products.The advantages of mesoporous structure and composition synergically improved the hydrogenation activity.No precious metal was used,which reduced the cost.（3）Non-noble metal Co Fe_5%B amorphous alloy catalysts with mesoporous structure were prepared for the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol.The mesoporous structure enhanced exposed active sites and also facilitated the diffusion and adsorption of reactants,which promoted the reaction activity.Compared with the crystalline alloy,the unique electronic structure of the amorphous alloy more preferentially adsorbed the carbon-carbon double bonds rather than adsorbed the benzene cycloaddition in cinnamaldehyde molecules,leading to the high selectivity to the target product of cinnamyl alcohol.The Co Fe_5%B displayed excellent activity,selectivity and stability for the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol.Meanwhile,because of the ferromagnetic property,it could be easily recycled and separated in the applied magnetic field,leading to the recycling uses.（4）A magnetic Ru（Co,Ni）B bimetallic amorphous alloy catalyst with mesoporous structure was synthesized by means of surfactant self-assembly method.In the liquid-phase CO₂ hydrogenation process,the Ru_1%Co B showed 578μmol/g/h HCOOH yield with the selectivity up to 99%.The unique unsaturated coordination,riched electron and highly exposed active sites promoted the adsorption,activation,dissociation and surface reaction of CO₂ and H₂.In addition,the mesoporous channels favored the diffusion and adsorption of CO₂ and H₂,leading to the excellent catalytic performance.Both the Ru_1%Co B and the Ru_1%Ni B amorphous alloy catalysts exhibited strong stability against crystallization,mesopore collapse and active site leaching during CO₂ hydrogenation reaction,corresponding to the good durability for recycling uses.