Oxides Supported Gold Catalysts In The Liquid Phase Oxidation Of Alcohols And Hydrogen Transfer Reaction In The Study

The unique character of gold catalysts has been extensively exploited since the discovery of its excellent catalytic behavior for CO oxidation in low temperature. Among the hot issues over gold catalysis,the organic reaction and chemicals synthesis through efficient methodology of oxidation and reduction under mild reaction condition is an interesting and challenging job.In this dissertation,metal oxides supported gold nanoparticles have been employed as heterogeneous catalysts in liquid-phase organic reaction,including alcohol oxidation, oxidative esterification and transfer hydrogenation.It was found that support played an important role in influencing the property of gold nanoparticles by support-metal interaction;supports with unique characteristics might function as co-catalysts for particular reactions by stabilizing gold nanoparticles and facilitating the proceeding of any step of these reactions.In the first part of alcohol oxidation,it was demonstrated the promising results of the gallia polymorphs as potentially attractive supports in the design of new type of supported gold catalysts highly active and selective for aerobic alcohol oxidation. Furthermore,different polymorphs of gallium oxides supported gold catalysts showed different catalytic performance,with theγ-Ga₂O₃-supported gold catalysts exhibiting the highest activity and selectivity.In the second part of alcohol oxidation,gold nanoparticles were deposited on different ratio of Ga-Al mixed-oxides and were then used as the catalysts in alcohol oxidation.An excellent linear correlation between the reaction rate and the dehydrogenation capability of catalysts was obtained,indicating that the dehydrogenation capability of gold catalyst was the key factor to get highly efficient materials for alcohol oxidation reactions.In addition,the TOF as high as 25000 h^-1 for the solvent-free oxidation of 1-phenylethanol could be obtained over Au/Ga₃Al₃O₉ catalyst.This catalyst was so active that it could catalyze the aerobic oxidation of benzyl alcohol and 1-phenylethanol at ambient temperature.Then,it was found that combination of gold nanoparticles and nanocrystallineβ-Ga₂O₃ can allow the devise of new versatile bifunctional gold catalyst highly effective for the aerobic oxidative esterification of alcohols,aldehydes or acetals under mild conditions.Nanocrystallineβ-Ga₂O₃ featured with unique surface Lewis acidity are far superior to conventional oxides(for example,TiO₂,Fe₂O₃,active carbon etc.) as supports for the rational devise of a novel bifunctional gold catalyst being able to catalyze at least two mechanistically distinct processes in a single reaction vessel under the same conditions.Inspired by the other metal catalysts'(Ru,Pd and Cu) successful application in hydrogen transfer reaction,gold catalysts were also tested in this reaction.Fortunately, we developed an exceedingly efficient and highly chemoselective approach to prepare aromatic alcohols from the corresponding aromatic carbonyl compounds under hydrogen transfer conditions using TiO₂ supported gold nanoparticles as an effective and reusable heterogeneous catalyst under the assistance of base.In addition,Au/ZnO catalyst,with particle size around 1 nm,was found to show high catalytic activity and selectivity for the transformation of aromatic nitro compounds to the corresponding amines in the absence of any base,while other noble catalysts(Pd,Pt and Ru) showed no activity under the identical catalytic reaction system.