Controllable Preparation And Application Of Noble Metal Nanoclusters And Immobilization

In recent years,the preparation of precious metal nanomaterials and theirresearch in the field of catalysis have attracted more and more attention.However,due to the limitations of the precious metal catalyst in the preparation method,the production cost and the like,to a certain extent,its large-scale commercial application is limited.In this paper,the controllable synthesis of noble metal nanoparticles and its catalytic performance are studied.The main contents are as follows:With a water or ethanol as a solvent,with PVA,PVP,dodecyl mercaptan and the like as a protective agent,NaBH₄ or other reducing agents?such as aminoborane,H₂,etc.?under the action of uniform dispersion of Au nanoclusters or more large size gold nanoparticles,particle size can be adjusted in the range of 0.7-5nm.The preparation method was extended to nanometer clusters such as Pd,Pt and Ag and controlled preparation of Au-Ag alloy nanoclusters.The colloidal Au particles were prepared by using PVP as the protective agent and ethanol as the solvent,NaBH₄ as the reducing agent,and then loaded onto?-Al₂O₃,ZnO,ZSM-5 molecular sieve and so on.After calcination at 450°C for 6hours,the particle size is still less than 2 nm.The Pd-Sn/TiO₂ composites prepared by the same method were maintained at 1.3nm after calcination at 300°C.The synthesis of Au/zeolite was investigated by combining the synthesis of Au nanoparticles with the synthesis process of molecular sieves.The Au/MTS-1,Au/MCM-41 and Au/MCM-48 composites were calcined at 500°C,and the particle size was kept at2 nm,which showed good stability.The results of XRD and TEM showed that the introduction of Au nanoparticles did not destroy the ordered structure of molecular sieves.In the selective hydrogenation of cinnamaldehyde,the nano-Au catalyst showed significant differences in the selectivity of cinnamyl alcohol.Au/Ni₂O₃ showed better C=C hydrogenation ability,selective formation of phenylpropionaldehyde,selectivity of 86%,catalyst Au/?-Al₂O₃ showed better C=O hydrogenation capacity,selective production of cinnamyl alcohol,the selectivity was 67%.The results of NH3-TPD and CO₂-TPD show that the selectivity of cinnamyl alcohol depends mainly on the acidity and alkalinity of nano-Au catalyst.The catalyst Au/?-Al₂O₃ possesses both the acid and alkali centers,and the synergistic effect of the acid-base center makes the C=O double bond preferentially adsorbed,activated and hydrogenated to achieve high selectivity of cinnamyl alcohol.