Synthesis Of Hierarchical Core-shell Magnetic Gold Nanoclusters Catalysts For Highly Efficient Alcohol Oxidation

In the present thesis, a series of hierarchical core-shell magnetic catalysts have been successfully synthesized by a modified electrostatic adsorption step of water-soluble atomic precise captopril-capped Au nanoclusters onto the preprepared magnetic supports followed by proper calcinations aiming at enhancing catalytic property and realizing green catalysis of supported nanogold catalysts in terms of facile recovery and efficiently recycling. The thesis focuses on:1) A series of honeycomb-like hierarchical core-shell magnetic catalysts γ-Fe2O3@M3Al-LDH@Au25-x (x refers to the mass of Au2s nanoclusters, wt%) and γ-Fe2O3@Mg3Al-LDH@Au24Pd1-0.2 have been successfully synthesized by a modified electrostatic adsorption step of water-soluble captopril-capped Au25 nanoclusters (Au25Capt18:1.6±0.5nm) and Au24Pd1 nanoclusters (Au24Pd1Capt18:1.5±0.5nm) onto the preprepared magnetic supports Fe3O4@M3Al-LDH ((M=Ni, Mg and Cu/Mg(0.5/2.5)), LDH:layered double hydroxide) followed by proper calcinations.2) Detailed characterizations show that the low Au loading samples γ-Fe2O3@Ni3Al-LDH@Au25-x (x～0.053,0.11) show nearly atomic precise Au25 clusters (Au25NCs)(ca. 1.4±0.3-1.9±0.6 nm) on the surface of shell Ni3Al-LDH, while the catalysts γ-Fe2O3@M3Al-LDH@Au25-x (x～0.2) display slightly aggregated Au25NCs on the surface of shell LDH with the size of Au25NCs ca. 3.0±.3,3.3±1.2 and 4.2±1.5nm for Ni-, Mg-, and CuMg-based catalysts, respectively, upon the sintering interaction of adjacent Au25NCs during the calcination and varied synergy between Au25NCs and M3Al-LDH at a little higher Au loading3) All the γ-Fe2O3@M3Al-LDH@Au25-x catalysts exhibit much higher catalytic performance for the oxidation of 1-phenylethanol under atmospheric O2 without basic additives in toluene than Fe3O4@Mg3AI-LDH@Au by traditional deposition-precipitation route. The y-Fe2O3@Ni3Al-LDH@ Au25-0.23 presents even higher alcohol oxidation activity than γ-Fe2O3@Mg3Al-LDH@Au25-0.21 and γ-Fe203@Cuo.5Mg2.5Al-LDH@Au25-0.2 ascribing to the large amount of Ni-OH sites and the strongest synergetic interaction between Au25NCs and magnetic support.4) Y-Fe2O3@Ni3Al-LDH@Au25-0.053 exhibits the highest activity (TOF: 112,498 h-1) for the aerobic oxidation of 1-phenylethanol under solvent-free conditions and can be applied for a varieties of alcohols in toluene, being mainly attributed to nearly atomic precise Au25NCs and the remarkable Au25NCs-LDH-magnetic core three-phase synergetic interaction. Moreover, the γ-Fe2O3@Ni3AI-LDH@Au25-0.053 can be easily separated by simply applying an external magnetic field and reused more than ten times without significant loss of activity, rendering the magnetic catalyst long-term stability.5) y-Fe2O3@Mg3Al-LDH@Au24Pd1-0.2 (2.7±1.0 nm) catalyst exhibits significantly enhanced activity of 1-phenylethanol oxidation compared to γ-Fe2O3@Mg3Al-LDH@Au25-0.21, mainly attribute to electron density transferred from Pd to Au leading to more electron-rich Au24Pd1 nanoclusters than Au25 nanoclusters in favor of the enhancement of alcohols oxidation activity.