Chemical vapor deposition of gold on Al2O3, SiO2, and TiO2 for the oxidation of CO and of H2
ABSTRACT In order to clarify the effect of metal oxide support on the catalytic activity of gold for CO oxidation, gold has been deposited on SiO2 with high dispersion by chemical vapor deposition (CVD) of an organo-gold complex. Comparison of Au/SiO2 with Au/Al2O3 and Au/TiO2, which were prepared by both CVD and liquid phase methods, showed that there were no appreciable differences in their catalytic activities as far as gold is deposited as nanoparticles with strong interaction. The perimeter interface around gold particles in contact with the metal oxide supports appears to be essential for the genesis of high catalytic activities at low temperatures.
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ABSTRACT: Uniform clusters of Pt have been deposited on the surface of capping-agent-free CeO2 nanooctahedra and nanorods using electron beam (e-beam) evaporation. The coverage of the Pt nanocluster layer can be controlled by adjusting the e-beam evaporation time. The resulting e-beam evaporated Pt nanocluster layers on the CeO2 surfaces have a clean surface and clean interface between Pt and CeO2. Different growth behaviors of Pt on the two types of CeO2 nanocrystals were observed, with epitaxial growth of Pt on CeO2 nanooctahedra and random growth of Pt on CeO2 nanorods. The structures of the Pt clusters on the two different types of CeO2 nanocrystals have been studied and compared by using them as catalysts for model reactions. The results of hydrogenation reactions clearly showed the clean and similar chemical surface of the Pt clusters in both catalysts. The support-dependent activity of these catalysts was demonstrated by CO oxidation. The Pt/CeO2 nanorods showed much higher activity compared with Pt/CeO2 nanooctahedra because of the higher concentration of oxygen vacancies in the CeO2 nanorods. The structure-dependent selectivity of dehydrogenation reactions indicates that the structures of the Pt on CeO2 nanorods and nanooctahedra are different. Thes differences arise because the metal deposition behaviors are modulated by the strong metal-metal oxide interactions.Nano Research 01/2011; 4(1):61-71. · 7.39 Impact Factor
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ABSTRACT: Since Haruta et al. discovered that small gold nanoparticles finely dispersed on certain metal oxide supports can exhibit surprisingly high activity in CO oxidation below room temperature, heterogeneous catalysis by supported gold nanoparticles has attracted tremendous attention. The majority of publications deal with the preparation and characterization of conventional gold catalysts (e.g., Au/TiO2), the use of gold catalysts in various catalytic reactions, as well as elucidation of the nature of the active sites and reaction mechanisms. In this overview, we highlight the development of novel supported gold catalysts from a materials perspective. Examples, mostly from those reported by our group, are given concerning the development of simple gold catalysts with single metal-support interfaces and heterostructured gold catalysts with complicated interfacial structures. Catalysts in the first category include active Au/SiO2 and Au/metal phosphate catalysts, and those in the second category include catalysts prepared by pre-modification of supports before loading gold, by post-modification of supported gold catalysts, or by simultaneous dispersion of gold and an inorganic component onto a support. CO oxidation has generally been employed as a probe reaction to screen the activities of these catalysts. These novel gold catalysts not only provide possibilities for applied catalysis, but also furnish grounds for fundamental research. KeywordsGold–nanoparticles–catalyst design–catalyst support–functionalization–promotion–CO oxidationNano Research 4(1):3-32. · 7.39 Impact Factor
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ABSTRACT: Bulk characteristics and deposition of gold nanoparticles on mica modified by (PAH) was studied by UV-visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS) and atomic force microscopy (AFM). The size of gold nanoparticles (AuNPs) was 15 nm as determined by TEM and AFM. The electrophoretic mobilities and electrokinetic charge of particles were quantitatively evaluated for a broad range of pH and ionic strength. Using Henry’s model, it was calculated that the zeta potential of particles varied between -50 mV and -80 mV for pH 2 and pH 11 respectively (at 10-2 M of NaCl). Measurements of nanoparticle deposition kinetics were performed for diffusion-controlled transport conditions using AFM and SEM imaging of particle monolayers. The influence of the bulk suspension concentration was systematically studied. Additionally, the maximum coverage of particle monolayers, which monotonically increased with ionic strength, was determined by SEM. The obtained data were in agreement with theoretical predictions derived from the random sequential adsorption (RSA) model. It was also confirmed that by varying the bulk suspension concentration and ionic strength one can prepare homogeneous gold particle monolayers of controlled coverage.Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2014; 441:204–210. · 2.11 Impact Factor