Study Of The Novel Preparation Methods Of Supported Metal Catalyst

Supported metal catalysts are extensively applied in petrochemical industry,fine chemistry and environmental catalysis owing to its high metal utilization ratio and good catalytic properties.Supported metal catalysts are usually prepared by impregnation and chemical reduction,and have been found wide application in industry.However,these preparation methods have the drawbacks of complicated procedure,too many influence factors,poor reproducibility,which affecting the catalytic properties,companying with severe environmental pollution.This thesis tries to produce supported metal catalyst with better catalytic properties by novel preparation methods.In this thesis,two novel methods were used for preparation of supported metal catalysts,laser vaporization deposition(LVD) and soluble metal nanoparticles direct-adsorption.At present,only three research goups around the world,Rousset's,Brenne's and ours',are to be employed in Laser vaporization deposition.A pulsed laser was focused on the bulk metal and a plasma was formed;Afterward,the plasma was oriented and deposited onto the surface of the support and nucleated to form metallic clusters.Laser vaporization deposition is a physical method,which is a simple and green approach for preparation of supported metal catalysts with few affecting factors on the catalytic properties.Soluble metal nanoparticles direct-adsorption is also a simple and green approach for preparation of supported metal catalysts.Soluble metal nanoparticles were extensively studied around the world,currently.Supported metal catalyst with small particles(＜5 nm) and high metal dispersion can be obtained by soluble metal nanoparticles direct-adsorption,exhibits good catalytic properties.The soluble metal nanoparticles were obtained by the decomposition of organometallic precursors such as Pd₂(dba)₃ using a reducing gas such as hydrogen gas in a solvent and stabilized by the solvent; Afterwards,the stable metal nanoparticles were adsorbed on the surface of support to produce the supported metal catalyst.There were few factors affecting the catalytic properties during the preparation process.In this thesis,Pt/Al₂O₃ catalyst and a series supported Pt,Pd catalyst were produced by laser vaporization deposition of bulk metals;Pd/Al₂O₃ and Pd/C catalysts were prepared by soluble metal nanoparticles direct-adsorption. The catalysts were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),inductive coupled plasma emission spectrometer (ICP) and X-ray photoelectron spectroscopy(XPS).The liquid phase hydrogenation of o-chloronitrobenzene(o-CNB) was used to test the catalytic properties of the catalysts obtained by laser vaporization deposition;Suzuki reaction and Heck reaction were used to test the catalytic properties of Pd/Al₂O₃ and Pd/C catalysts obtained by soluble metal nanoparticles direct-adsorption,respectively.The results are listed as follows:1.The characterization results show,the support temperature,the pressure of chamber and the voltage of laser have an impact on the properties of the Pt/Al₂O₃ catalyst obtained by laser vaporization deposition.The hydrogenation results show,the catalytic activity decreases with the support temperature,the pressure of chamber and the voltage of laser.The selectivity to o-chloroaniline(o-CAN) increases with the support temperature,the pressure of chamber,but decrease with the voltage of laser.The catalyst prepared under 300 Pa,600℃and 260 V exhibits the best catalytic properties, obtaining o-CAN with 99.4%selectivity at a conversion level of 99.8%.2.The characterization results show,the supports have a significant influence on the metal dispersion,the particles size and the electronic state of metal.The metal particles on CNTs are smaller than that onγ-Al₂O₃ and SiO₂; The metal-support interaction for the Pt-based catalysts is negligible,but the metal-support interaction for the Pd-based interaction is in order Pd/CNTs＞Pd/γ-Al₂O₃＞Pd/SiO₂.The hydrogenation results show the superiority of CNTs versus the high surface areaγ-Al₂O₃ and SiO₂ in terms of the catalytic activity and the selectivity to o-CAN.The effect of the supports may be interpreted by geometric effect and the textures and properties of the supports for the Pt-based catalysts.However,the effect of the supports may be interpreted by geometric effect,electronic effect and the textures and properties of the supports for the Pd-based catalysts.In addition, hydrogenolysis of the C-C1 bond in o-CAN is well inhibited over supported Pt, Pd catalysts obtained by laser vaporization deposition due to the metal particles deposited on the outer surface of the supports.3.The characterization results of the Pd/Al₂O₃ catalyst obtained by soluble metal nanoparticles direct-adsorption show,the Pd particles are evenly distributed over the surface ofγ-Al₂O₃,and the size range is 3-8 nm;The Pd particles size is invariant between pre-supported and Pd/Al₂O₃ catalyst.The electron is transferred fromγ-Al₂O₃ to Pd.The best Suzuki reaction results was obtained with K₂CO₃ as base,DMF/H₂O volume ratio 7/3 as solvent, reflux,and Pd loading 2.0 wt%,which provided the highest brornobenzene conversion of 100%and the highest biphenyl yield of 99%in 30 min.The substrates with electron-withdrawing groups or electron-donating groups were all achieved in good yields.The coupling reactions of aryl bromides containing electron-withdrawing groups proceeded more efficiently than that of bromobenzene,while aryl bromides containing electron-donating groups needed a longer reaction time for completion.4.The characterization results of the Pd/C catalyst obtained by soluble metal nanoparticles direct-adsorption show,the Pd particles are evenly distributed over the surface of active carbon,and the size range is 3-8 nm;The Pd 3d_5/2 and Pd 3d_3/2 level binding energies of Pd/C catalyst are higher than that of bulk Pd metal.The electron is transferred from Pd to active carbon. The best Heck reaction results was obtained with K₂CO₃ as base,DMF as solvent and reaction temperature 120℃,which provided the highest iodobenzene conversion of 100%and the highest coupling yield of 99%in 120 min.The coupling reactions of iodobenzene and aryl bromides containing electron-withdrawing groups proceeded efficiently,while aryl bromides containing electron-donating groups and aryl chlorides hardly proceeded.The catalyst can be reused for 3 times,exhibiting better stability than commercial Pd/C catalyst.In conclusion,it is clear that supported Pt,Pd catalysts obtained laser vaporization deposition exhibit good catalytic properties on the hydrogenation of o-CAN;Pd/Al₂O₃ catalyst obtained by soluble metal nanoparticles direct-adsorption exhibits good catalytic properties on Suzuki reaction of aryl bromides;Pd/C catalyst obtained by soluble metal particles supported method exhibits good catalytic properties on Heck reaction of iodobenzene and aryl bromides containing electron-withdrawing groups.Laser vaporization deposition and soluble metal particles supported method are novel,simple and green approaches for preparation of supported metal catalyst;Under suitable conditions,supported metal catalysts with metal particles and loading controllable can be produced;Other single component or multicomponents supported metal catalysts also can be produced by the two novel methods; These supported metal catalysts obtained by the two novel methods can be potentially applied in several mutil-phase reactions to produce the target products with high conversion and selectivity.In addition,the two novel methods can be potentially applied at the industrial scale.