Controlled Synthesis Of New Structured Nano Gold Supported Catalysts And Their Catalytic Performance

Catalysis is a research field with a long history and an eternal youthful vitality.Catalysts and catalysis have played an incomparable role in promoting the progress and civilization of human races.So it is an endless pursuit for human beings to produce high-quality catalysts efficiently and economically through reasonable design and controllable synthesis.In recent years,precious metal catalysts(especially gold)have attracted wide attention due to their unique physical and chemical properties.Surprisingly,gold,which was previously regarded to be catalytically inert in its bulk form,exhibits excellent activity,selectivity and stability for many kinds of catalytic reactions when its dimensions is downsized to a few nanometers.Therefore,since the 90s of last century,the field of catalysis has witnessed a "gold rush" to prepare nano gold catalysts which has lasted and grown for years till now.Among them,the researches on dispersion,support and structure of nano gold catalysts are the emphases and difficulties.In this thesis,we try to study and discuss the construction of supported nano gold catalyst by optimizing the composition,morphology and architecture to establish the intrinsic relationship between the structure and preformance of the catalyst.This thesis will focus on the preparation of nano gold catalysts with different supports,regulation of their kinds,components and architecture,and loading different forms of gold species on appropriate supports by different methods.Furthermore,through a series of characterization methods and performance tests,the synergistic catalytic performance between nano gold and support is revealed.And the essential requirements of the catalyst structure for different catalytic reactions are explored.The main results are as follows:(1)Through a simple one-step solventhermal method assisted by surfactant,the large scale and controllable synthesis of CeO2 nanotubes with uniform size,regular morphology and good crystallinity can be achieved.The mechanism of their formation was also studied,and the theoretical mechanism of "Oriented Attachment-Ostwald Ripening" was put forward.The supported Au/CeO2 nanotubes catalyst was prepared after loading the gold nanoparticles with CeO2 nanotubes as support.The catalyst showed high catalytic activity for the catalytic oxidation of carbon monoxide.The complete conversion temperature of carbon monoxide was about 73?,and its activity can retain for more than 100 hours.(2)A series of gold loaded metal organic frameworks(MOFs)pseudo single atom catalyst were prepared in large scale by a simple "one pot" method.The mechanism of "in situ reduction-room temperature conversion" was proposed for the formation mechanism of these materials.By adjusting the synthesis parameters,the size of gold particles can be reduced to the "pesudo single atom"level.According to the detailed characterization,the gold atoms were dispersed almost entirely atomically isolated except that a small amount of them clustered.Both the pores of MOFs supports and the surfaces of gold atoms were clean and neat,so the catalysts showed a good activity of the catalytic hydrogenation of p-nitrophenol.Compared with the literatures,the apparent first-order rate constant(2.49 min-1)and turnover frequency(581 min-1)of as-prepared pseudo single atom catalyt Au/FeBTC increased by one or two orders of magnitude.The catalyst showed excellent stability without decay in activity for 5 successive cycles.(3)Sandwich structured catalysts were designed and synthesized,which refered to novel catalysts with unique architecture that fill tiny noble metal nanoparticles between two layers of support materials.This unique structure provided confinement effect for the active species,which had a big impact on their catalytic preformance.A facile method was used to synthesize a series of catalysts with the sandwich structure,including MIL-100(Fe)@Au@MIL-100(Fe),ZIF-8@Au@ZIF-8 and UiO-66@Au@UiO-66 by firstly preparation of MOFs,followed by the adsorption of noble metal nanoparticles,and finally further coating of MOFs layer on the supported catalyst.This special sandwich structure had obviously improved the stability of the catalysts for carbon monoxide oxidation reaction.Compared with the traditional supported MIL-100(Fe)@Au catalyst,which completely deactivated after 30 hours of reaction at 140?,the sandwich structured MIL-100(Fe)@Au@MIL-100(Fe)restained its excellent catalytic performance for up to 120 hours without obvious activity loss.The research results of this thesis will provide a new insight into the design and synthesis of supported nano gold catalysts with new nanostructures,and also will be of great guiding significance for application of other high quality noble metal based catalyts.