Rational Synthesis Of Gold-based Composite Nanoparticles And Their Catalytic Applications

Since the seminal discovery by Haruta in 1987 that Au-based catalysts were surprisingly active for CO oxidation,researchers have widely employed Au-based catalysts in many types of mild chemical processes,with special focus on selective reactions involving small molecules?for example O2 or H2?as a reactant,such as selective oxidation of alcohols and amines and selective hydrogenation of ?,?-unsaturated aldehydes.However,since that Au 4d electronic orbit is in full state,the capability of adsorption and activation of small molecules is weak,seriously hampering the catalytic activity of gold catalyst and therefore hindering its large scale application.The relationship between the catalytic properties of gold catalysis and its own structure is closely related.Understanding and utilization of these structure-activity relationships of gold catalysts are important subjects in the field of gold catalysis,and are of great significance to the structure optimization of gold-based catalysts.In this paper,a series of studies have been carried out on how to further improve the catalytic performance of gold catalysts and develop gold-based catalysts with high activity,high selectivity and long-time stability.On one hand,the catalytic activity and stability of gold catalyst areimproved mainly through the optimization of gold catalyst preparation method and the rational design of the structure.On the other hand,metal-metal or metal-oxide synergies is applied to reduce the amount of precious metals while improving its catalytic performance.At the same time,the relationship between the microstructure of the gold catalyst and the properties of the material is analyzed in detail,which lays a theoretical foundation for the practical application of the gold catalyst.The main contents in this thesis include the following aspects:1)A facile confined solid-state seed-mediated alloying strategy is applied for the rational synthesis of supported Au-Ni bimetallic nanoparticles?BMNPs?.The method sequentially deposits nickel salts and AuNP seeds into the ordered array of extra-large mesopores?EP-FDU-12 support?followed by a high-temperature annealing process.The size,structure and composition of the AuNi BMNPs can be well tuned by varying AuNP seeds,annealing temperature and feeding ratio of metal precursors.Kinetic studies and DFT calculations suggest that the introduction of Ni component can significantly prompt the O2 activation on AuNPs,which is critical for the selective alcohol oxidation using molecular O2 as the oxidant.The optimal Au-Ni BMNP catalyst showed the highest TOF(59000 h^-1,240 )and highest space time yield of benzyl aldehyde?BAD?productivity(9.23 kg-gAu-1·h^-1)in the gas-phase oxidation of benzyl alcohol?BA?,which is at least about 5-fold as high as other supported Au catalysts.2)The CoO_x/Au inverse catalyst was designed and synthesized.The loading of trace CoO_x on the surface of Au NPs can not only effectively improve the metal-oxide interface concentration,but also stabilize the nanoparticles and enhance its thermal stability.Catalytic results show that synergies effects between Au NPs and CoO_x enhanced the capacity of adsorption and activation of O2 molecules on Au NPs,effectively improve its catalytic performance in the gas-phase alcohol oxidation.3)A method for synthesizing small-sized single-atom alloy catalysts in mesoporous channels has been developed.The effects of preparation conditions such as calcination temperature,atomic ratio and precursor selection on the structure of the obtained materials were systematically studied with Au-Ni system as the research object.When the calcination temperature is higher than 700 ? and the Au/Ni ratio is less than 1/10,the highly dispersed Ni-alloyed Au catalyst can be well formed.The Ni alloyed monatomic Au catalyst?Au1Ni20-800 ??has the properties of inhibiting deactivation and less side reaction in the methane dry gas reforming reaction.4)It is found that the ·OH radicals produced by the Fenton's reagent can initiate the reaction between the metal particles and the acetonitrile molecules.Not only can the single metal cyanide such as AuCN and AgCN be obtained,but also the bimetallic cyanide compounds such as AuxCu1-xCN,AuxAg1-xCN,AuxNi1-xCN.The process does not produce any free toxic components such as CN" ions,but also avoids the use of UV light,which is a green synthetic method for metal cyanide.By simply calcinating these bimetallic cyanides,catalysts of a metal-oxide?such as Au-NiO?composite structure can be obtained.Benefiting from the strong interaction between the two components,composite catalysts show better performance than pure gold cataltst in the gas-phase selective oxidation of benzylalcohol.