Synthesis And Catalytic Properties Of Atomically Precise Gold-Based (Au_8n+4?AuRu?AuCd) Nanoclusters

In the last decade,with the rapid development of cluster chemistry,researchers have developed precision preparation methods to synthesize metal clusters with definite composition and precise structure.More and more attention has been paid to the catalytic properties of metal clusters,which show high catalytic activity and selectivity in many catalytic reactions.Because of the definite composition and structure of the metal clusters,the relationship between catalyst structure and catalytic performance can be established at the atomic scale.At the same time,compared with single metal clusters,bimetallic clusters not only have better thermal stability and catalytic activity,but also can be used to study the synergistic effect of bimetallic catalysts and guide the rational design of high-performance bimetallic catalysts.In this thesis,the catalytic properties of Au_8n+4(SR)_4n+8 homo-gold clusters,Au Ru and Au Cd bimetallic clusters were investigated in detail.The main contents are as follows:1.We prepared a series of Au_8n+4(TBBT)_4n+8(n=3,4,5)clusters.The core atoms of this series of clusters have a periodic geometric packing pattern,that is,the core structure grows layer by layer along the(001)direction,each layer has eight gold atoms,Au₂₈core structure has eight{100}planes,Au₃₆ core structure has twelve{100}planes,and Au₄₄ core structure has sixteen{100}planes.The catalytic hydration reaction of alkynes is studied,that is,the order of catalytic activity is:Au₂₈>Au₃₆>Au₄₄.The experimental results combined with theoretical calculations revealed that the core stacking structure of Au_8n+4(TBBT)_4n+8 clusters will affect the electronic properties of the gold atoms on the surface of the clusters,thereby changing the adsorption and activation behaviors of reactive molecules,and then realizing the modulation of the catalytic activity.2.We prepared two organic ligand-protected Au₄Ru₂ and Au₅Ru₂ new clusters.Structural analysis shows that Au₄Ru₂ has a twisted octahedral structure,in which Ru atom is regarded as Ru of the single site(i.e.,no Au-Ru and Ru-Ru bonds);The Au₅Ru₂cluster has a regular decahedron structure,in which Ru and Au atoms form two Ru-Ru and Ru-Au dual-sites with each other(i.e.,Au-Ru and Ru-Ru bonds exist).Therefore,Au₄Ru₂ and Au₅Ru₂ can be used to study single-site and dual-site catalysis.Au₅Ru₂exhibits superior catalytic performances to Au₄Ru₂ for N-methylation of N-methylaniline to N-methylformanili.Through comparative experiments and in-situ FT-IR spectroscopy experiments,it is proved that Au₅Ru₂ has better catalytic performance due to the dual-site cooperative catalysis.3.Nitrogen fixation reaction under mild conditions has important application value.It is difficult for N₂ molecules to adsorb on the gold clusters,which leads to the low photocatalytic nitrogen fixation activity of the gold clusters.In order to provide adsorption and activation sites for N₂ molecules,a supported bimetallic Au₄Ru₂/Ti O₂catalyst was designed.The experimental results show that Au₄Ru₂/Ti O₂ catalyst has good photocatalytic nitrogen fixation performance.Under light conditions,the electrons inside the Au₄Ru₂ clusters transition to Ru atoms,and N₂ can be adsorbed on Ru atoms.Ru donates electrons to N₂ molecules and activates N₂.At the same time,the Ti O₂ support photolysis water provides H source for nitrogen conversion,and finally N₂ and hydrogen react on the Au₄Ru₂ cluster to obtain ammonia,which realizes the nitrogen fixation reaction under mild conditions.4.The catalytic performance of heteroatomic doped Au Cd bimetallic clusters for CO₂ electroreduction was studied.Firstly,we investigated the singe-atom doping effect on CO₂ reduction by comparing mono-cadmium doped Au₂₄Cd₁ and homogold Au₂₅clusters that share an identical core structure.Experimental results show that single Cd substitution drastically improved the current density and the Faraday efficiency of the product.Furthermore,the effects of the doping number and location of Cd on the electroreduction of CO₂ were investigated,and it was found that Au₁₉Cd₃,Au₂₄Cd₁ and Au₃₈Cd₄ clusters showed significant differences in electrocatalytic activity and selectivity.During the reaction,the S site exposed by the S-C bond break is the active site of CO₂RR,while the M-S bond break exposes the Au atom and facilitates the generation of H₂.Under experimental conditions,Au₂₄Cd₁ exhibited a significant Faraday efficiency(97.0%,-0.5V)for CO and formate,because it undergoes only one S-C cleavage and its onset potential was low.Inspired by the two-stage mechanism,early S-C cleavage or blocking M-S cleavage by ligand modification can further improve the electrocatalytic CO₂RR performance of Au₂₄Cd₁ catalyst.