LDH-Supported Atomic Precision Au Nanoclusters For Catalytic Oxidation And Hydrogenation

Atomically precise gold nanoclusters(NCs)are attracting extensive research interest in catalysis area due to their ultra-small size(<2 nm)and specific crystal structure.Generally,the catalytic performance of supported nano-gold catalysts mainly depends on the size of gold nanoparticles,active site structure,the type of support and metal-support interaction and so on.In the present thesis,the performance of supported Au nanocluster catalysts in catalytic oxidation of benzyl alcohol and reduction of 4-nitrophenol(4-NP)is effectively improved by adjusting the size and structure of metal nanoclusters and the type of support.The main research contents and innovations are as follows:(1)A series of Ni3Al-LDH-supported(LDH:layered double hydroxide)Aun NCs catalysts Aun/LDH(n=25,38,?127)by a modified electrostatic adsorption strategy,using atomically precise captopril(Capt)-protected Au25Capt18,Au38Capt24 and Au?127-Capt NCs as precursors.Detailed characterizations show that the catalysts Au25/LDH,Au38/LDH and Au?127/LDH possess ultrafine Au NCs size of 1.2 ± 0.2,1.4±0.3 and 1.8 ± 0.5 nm,respectively,which are majorly dispersed on the edge sites of the small-sized LDH nanosheets(20-40 nm).All the catalysts exhibit excellent catalytic activities in air oxidation of benzyl alcohol without external base additive associated with the remarkable size-and active site structure-dependence.The catalyst Au38LDH shows the highest activity with TOF of 1884 h-1,which can be attributable to the ultrafine bi-icosahedron structure Au38NCs and the strongest Au38 NCs-Ni-OH(LDH)synergistic effect facilitating the activation of ?-C-H bond of benzyl alcohol over more negatively charged Au sites.(2)Nanosheet array-like structure LDH/rGO hybrid supports with high specific surface area and high electron transport capacity was prepared by a citric acid assisted liquid phase co-precipitation method.A series of Au25/M3Al-LDH/rGO(M=Mg,Co,Ni)catalysts were prepared by loading Au25 NCs onto series M3Al-LDH/rGO supports using modified electrostatic adsorption method.The Au25 NCs are highly dispersed on LDH nanosheets and the junction sites between LDH and rGO.Upon the similar Au loading(?1.0 wt%),the Au25/Co3Al-LDH/rGO show the smallest Au NCs size(? 2.3 nm).The series of Au25/M3Al-LDH/rGO catalysts show excellent catalytic activity in the reduction of 4-nitrophenol and can completely reduce 4-NP within 180 s,of which the catalyst Au25/Co3Al-LDH/rGO shows the highest catalytic activity(only 90 s).The excellent catalytic activity of the series of catalysts can be attributed to the small size of Au25 NCs,possibly strong?-? stacking effect between 4-NP and catalysts and the strong Au25 NCs-LDH-rGO three-phase synergy.