Regulatory Strategies For Catalytic Performance Of Noble-metal Nanoclusters Protected With Monolayer Ligands

Noble metal nanoclusters are bridges between atoms and molecules and have unique physical/chemical properties due to their small size.Therefore,metal nanoclusters have great potential applications in many fields,especially in catalysis and biomedicine.In recent years,many kinds of atomic precision metal nanoclusters protected by ligands have been studied and synthesized,including thiol ligands,phosphorus ligands,selenium alcohol ligands,acetylene ligands,etc.The number of nanocluster is increasing,including Au clusters,Ag clusters,Cu clusters,Pd clusters and doped polymetallic clusters.Its catalytic reaction also involves electro-catalysis,photo-catalysis,and organic chemistry and so on.On the basis of previous studies,there is a great significance to study the reaction mechanism of atomically accurate metal nanoclusters.In the past,high reactivity was always obtained by exposing the metal active sites by removing some protective ligands of noble metal nanoclusters through high-temperature calcination.However,this not only destroys the structure of metal nanoclusters,but also fails to effectively explore its catalytic mechanism at the atomic level.This paper focuses on how to improve the activity of metal nanoclusters catalytic without destroying its structure.It is divided into the following two aspects:1.Using Pd₃（PPh₂）₂（PPh₃）₃Cl nanoclusters（Pd₃Cl NCs）and Titanate nanotubes（TNT）,Pd₃Cl/TNT Nano-catalyst with MSI effect was designed and synthesized that has high catalytic activity and chemical selectivity.The nano-catalyst can maintain the integrity of Pd₃Cl NCs structure without remove some or all ligands by calcining.Both Pd₃Cl NCs and TNT were prepared by reference,and the synthesized Pd₃Cl NCs and TNT.The results of UV-Vis,TGA,MS,and XRD were consistent with those reported in literatures.In addition,TEM was used to observe that the Pd₃Cl NCs were uniformly dispersed and adsorbed on TNT,and there was no aggregation or growth of Pd₃CI NCs.When the benzyl alcohol was oxidized by Pd₃Cl/TNT nano-catalyst,the conversion of benzyl alcohol was 100%and the selectivity of benzene aldehyde was also 100%.However,the pure Pd₃Cl NCs and TNT support showed no reactivity,this just proves that there was a certain Metal-Support interaction between Pd₃Cl NCs and TNT support.There has an electron transfer from Pd to Ti in Pd₃Cl/TNT catalyst by X-ray photoelectron spectroscopy（XPS）.when Pd₃Cl NCs load on TNT support,the binding energy decreases of Pd on Pd₃Cl NCs,and the electron loss of Ti on TNT support leads to the binding energy increase,the peaks displacement of Pd 3d and Ti 2p is caused by the MSI effect.At the same time,the theoretical calculation of DFT also proved that Pd₃Cl/TNT catalyst can catalyze the aerobic oxidation of benzyl alcohol with high reactivity at room temperature.Finally,through a series of mechanism exploration experiments,the mechanism of the aerobic oxidation of benzyl alcohol catalyzed by Pd₃Cl/TNT catalyst was speculated and simulated.2.We adopt the strategy of "electrostatic attraction" design synthesis atomic accurate nanoclusters @ metal organic framework（APNCs@MOFs）composite material.The principle of experimental synthesis is to use negatively charged metal nanoclusters anions and positively charged inorganic metal cations on the MOF,APNCs were loaded into MOF（in situ synthesized）under mild conditions by electrostatic attraction.The composite was analyzed and tested by SEM,TEM,XRD,FT-IR,and XPS,etc.It was proved that the nanoclusters were uniformly monodispersed within the MOF without aggregation and growth,and the structure of the MOF was not destroyed by the entrance of the nanoclusters.In addition,the UV-vis spectra of the composites after acid digestion were the same as its pure nanocluster;this indicates that the strategy does not affect the structure of nanoclusters.The composite combines the double advantages of MOF and metal nanoclusters,and is expected to exert the metal-support cooperative effect in catalytic reactions.