Controllable Synthesis Of Gold Clusters And Their Catalytic Applications

In recent literatuers,well-defined gold nanoclusters with atomic precision(AunLm,where "L"represents organic ligands,n<200)have been demonstrated as a new and promising class of nanogold catalysts.The different sized AunLm catalysts possesses unique crystal frameworks and electronic structures,thereby providing an excellent opportunity to correlate the intrinsic catalytic performance with the catalysts' structures as well as to study mechanisms of chemical reactions catalyzed over gold nanoparticles.In this work,we investigate the important roles played by the gold nanoclusters for some catalytic reactions,including selective oxidation as well as carbon-carbon coupling reactions.Tailoring of the catalysts'functions is discussed in terms of size-specificity and doping effects(e.g.,copper,silver,and platinum).The proposed reactions' mechanisms and the structure-activity relationships at the atomic detail are presented.1.We here explore a kinetically controlled synthetic protocol for preparing solvent-solvable Au102(SPh)44 nanoclusters which are isolated from the polydispersed gold nanoclusters by solvent extraction and size exclusion chromatography(SEC).The as-obtained Au102(SPh)44 nanoclusters is determined by matrix-assisted laser desorption ionization(MADLI)and electrospray ionization(ESI)mass spectrometry,in conjunction with UV-vis spectroscopy and thermogravimetric analysis(TGA).Whereas,Au99(SPh)42,instead of Au102(SPh)44,is yielded when the polydispersed gold nanoclusters are etching in the presence of excess thiophenol under thermal conidtions(e.g.,80 0C).Interestingly,the Au102(SPh)44 nanoclusters also can convert to Au99(SPh)42 with equivalent thiophenol ligands,evidenced by the analysis of UV-vis and MADLI mass spectrometry.Finally,the TiO2-supported Au102(SPh)44 nanocluster catalyst is investigated in the selective oxidation of sulfides into sulfoxides by PhIO oxidant and gives rise to high catalytic activity(e.g.,80-99%conversion of R-S-R'sulfides with 96-99%selectivity for R-S(=O)-R' sulfoxides).2.We here report the catalytic effects of foreign atoms(Cu,Ag,and Pt)doped into well-defined 25-gold-atom nanoclusters.Compared to Au25(SR)18,the centrally doped Pt1Au24(SR)18 causes a drop in catalytic activity but with the selectivity retained,while the AgxAu25-x(SR)18 nanoclusters gave an overall performance comparable to Au25(SR)18.Interestingly,CuxAu25-x(SR)18 nanoclusters prefer the Ullmann homo-coupling pathway and give rise to product 4,4'-dimethoxy-1,1'-biphenyl,which is in opposite to the other three nanocluster catalysts.Our overall conclusion is that the conversion of p-iodoanisole is largely affected by the electronic effect in the bimetallic nanoclusters' 13-atom core(i.e.,Pt1Au12,CuxAu13-x,and Au13,with the exception of Ag doping),and that the selectivity is primarily determined by the type of atoms on the MxAu12-x shell(M=Ag,Cu,and Au)in the nanocluster catalysts.