Papers by Keyword: Gold Catalyst

Abstract: Amorphous silica gel was modified by titania via an impregnation-surface hydrolysis approach and used as the support for preparing gold catalysts through an direct anion exchange method. These supported gold catalysts were characterized by XRD and TEM, and applied for the catalytic cyclopentane oxidation to cyclopentanone using oxygen in the absence of any solvent and initiator. The catalyst with a loading of 0.1wt.% gold and 10wt.% TiO₂ exhibited 7.2% cyclopentane conversion and 77.4% selectivities (including cyclopentanone and cyclopentanol) under the reaction conditions of 145°C, 2.0 MPa and 3 h. All the gold catalysts studied are very active in selective cyclopentane oxidation, and their high activities can be attributed to well dispersion and nanometer effect of gold particles within the catalysts.

Abstract: Gold nanoparticles supported on mesoporous ZrO₂ were prepared and their performance for the selective reductions of nitrobenzene to azoxybenzene was investigated. It was found that azoxybenzene could be successfully synthesized over these catalysts. Furthermore, the catalytic activity of catalysts is dependent on the pore size of catalyst. The catalyst Au/ZrO₂-PEG-1000 with pore size of 2.2 showed higher activity than Au/ZrO₂-PEG-600 with pore size of 1.9nm.

Abstract: This paper reports on the effects of gold (Au) catalyst on the growth of zinc oxide (ZnO) nanostructures by thermal chemical vapor deposition (TCVD). The thickness of Au catalyst was varied from 5 to 15 nm. The Au catalyst was annealed at 500 °C prior to the deposition of ZnO nanostructures by thermal chemical vapor deposition (TCVD). The morphology of the Au catalyst at different thickness and also ZnO nanostructures were characterized by field emission scanning electron microscopy (FESEM). The material component and crystalline properties of ZnO nanostructures were determined using Energy Dispersive X-ray spectroscopy (EDX) and also Raman Spectroscopy respectively. We found that the shape of the deposited ZnO nanostructures were different on different thickness of Au catalyst. There was no growth of ZnO on the 5 nm thick Au observed by FESEM and supported by EDX due to very small amount of Zn. On the 10 and 15 nm thick Au, growth of ZnO nanostructures were clearly observed.

Abstract: Highly dispersed supported gold catalysts have been prepared by solution reduction method using L-lysine as protection agents, and their catalytic activity was evaluated by the liquid phase catalytic oxidation reaction of glucose to gluconic acid. The results suggested that the Au/ZrO₂ catalyst, exhibited high activity for the selective oxidation of glucose. At the reaction temperature of 323K, reaction time of 1h, with the NaCO₃-NaHCO₃ as buffer solution, the yield of gluconic acid was 100%.

Abstract: Impregnation and deposition-precipitation (DP) methods were employed for the preparation of Au nanoparticles supported on SBA-15, and the influences of various reductants were systematically surveyed. The dispersion and particle size of gold loaded on SBA-15 were determined by XRD, SEM and TEM. It has been found that reductants have effect on the size and dispersion of Au NPs, resulting in different catalytic properties for aerobic oxidation of glucose. The Au NPs on SBA-15 using KBH₄ as reductant was approximately 5-6 nm, which exhibited excellent catalytic activity.

Abstract: Au/C catalyst used for the liquid phase selective oxidation of glucose to gluconate was prepared by gold sol method that includes the preparation of metallic colloid by citrate reduction and subsequent immersion by carbon support. The influence of gold particles of different size on the activity of Au/C catalyst was studied. The results show that the catalyst with good dispersed spherical gold particles has higher catalytic activity. After 16 runs, the conversion of glucose selective oxidation can still achieve over 96% under mild reaction conditions.

Abstract: The reaction mechanism of 2-propynyl-aniline with propyne catalyzed by AuCl3 has been studied by the B3PW91 method with the LANL2DZ effective core potential and basis set for gold, and 6-31G* and 6-311++G** basis set for C,H,O,Cl. The calculated results show that the reaction occurred through eight steps. The hydrogen migration step with the highest activation free energy of 198.13 kJ/mol is the rate determining step. The catalyst is easy to detach from the product with an activation of free energy of 48.83 kJ/mol. In addition, although the reaction has a relative high activation free energy, it can smoothly yield the indole derivatives because it is a strong exothermic reaction of 418.60 kJ/mol.

Abstract: A new type of gold catalysts have been prepared by supporting gold colloids on layered double hydroxide (MgAl-LDHs) carrier at different pH values. CO oxidation reaction at room temperature was used as probe reaction to test the oxidation activity of the gold catalysts, and X-ray diffraction (XRD), X-ray fluorescence (XRF) and high resolution transmission election microscopy (HRTEM) techniques were used to characterize the physical phase, gold loading, morphology as well as mean diameter of gold particles and particle distribution of the represented gold catalyst samples. Influence of pH value during synthesis of the catalysts on the gold loading and oxidation activity of the gold catalysts was studied. Besides these, the stability of the gold catalysts was investigated by thermal treatment and exposure to air and natural light for a long time. The results indicated that gold colloids can be attached on the carrier easily when pH value was controlled between 6-7, and gold loading in the gold catalysts prepared in this condition was above 1.3wt.%. 100% conversion of CO at room temperature can be obtained when the fresh prepared catalysts had been calcined in the air for 2 h at 473 K. The HRTEM images of the gold catalyst showed that the gold particles were highly dispersed on the surface of the carrier, and the average size of the gold particles was 3.2 nm. After thermal treatment at 723 K or storage 4 weeks in air, gold particle size was still kept less than 5nm and the conversion of CO at room temperature over the aged catalysts achieved 100%.

Abstract: _{Subscript textSubscript text}A series of Au/CeO₂ catalysts were synthesized and evaluated for formaldehyde catalytic combustion oxidation. In Au/CeO₂ catalysts, CeO₂ supports with different structure,Au/Macroporous-CeO₂ is found to be superior catalyst for formaldehyde catalytic oxidation. According to the analysis of transmission electron microscopy (TEM), the pore size of Macroporous-CeO₂ is broader than that of mesoporous SBA-CeO₂ support, which could make the active species gold adequately disperse as small nanoparticles, furthermore, it is most noticed that macroporous CeO₂ support is benefit to mass transfer comparing with mesoporous SBA-CeO₂ and ordinary power CeO₂.

Abstract: ZnO nanowires were grown on Au-coated GaN layer on c-plane sapphire by chemical vapor deposition (CVD). As-prepared ZnO oxides were characterized by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The results show that the growth of ZnO nanowires strongly depends on the location of GaN/sapphire substrates. The diameters of the resulting nanowires were in the range 60 nm with typical length about 10μm. The formation of ZnO nanowires with different morphologies at various positions of the substrate is explained by the mechanisms of vapor-solid and vapor-liquid-solid, respectively.