Characterizations of alumina-supported gold with temperature-programmed reduction

Chang, Chao-Kang; Chen, Yeong-Jey; Yeh, C.L.

doi:10.1016/s0926-860x(98)00188-4

Cited by 78 publications

(25 citation statements)

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“…On the other hand, prereduced samples exhibited a high activity from the reaction onset. However, extensive reduction of catalysts has been shown to be detrimental to their activity in many cases (423,(466)(467)(468).…”

Section: Figure 27mentioning

confidence: 99%

“…First and foremost Haruta asserts strong contact is necessary between gold and the underlying support. Although calcinations at high temperatures generally leads to agglomeration of particles which is assumed to be undesirable (395,(421)(422)(423), Haruta and co-workers found an increase in activity with increasing calcination temperature between mechanically mixed Au colloid/TiO2 powder samples calcined at 573 K and 873 K (424). TEM results showed the more active catalyst, in spite of its larger particle size, had better contact with the support.…”

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confidence: 99%

“…The deposition precipitation method favored by Haruta (although many other methods have achieved at least limited success as well) relies upon an exchange between gold chloride and NaOH such that Au(OH)3 is formed and precipitates on the support. The dispersion and size of the particles, and therefore their catalytic activity, depend critically upon the pH used (typically 6-10) and the amount of gold in solution (423,(425)(426)(427)(428)(429)(430)(431)(432). After washing to remove Cl and Na ions, the catalyst is dried and calcined.…”

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confidence: 99%

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Surface chemistry of catalysis by gold

et al. 2004

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IntroductionGold has long been regarded as an "inert" surface and bulk gold surfaces do not chemisorb many molecules easily. However, in the last decade, largely through the efforts of Masatake Haruta, gold particles, particularly those below 5 nm in size, have begun to garner attention for unique catalytic properties (1-8). In recent years, supported gold particles have been shown to be effective as catalysts for low temperature CO oxidation (9), selective oxidation of propene to propene oxide (10), water gas shift (11), NO reduction (12), selective hydrogenation of acetylene (or butadiene) (13)

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Section: Figure 27mentioning

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Surface chemistry of catalysis by gold

et al. 2004

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“…Addition of base to a HAuCl4 solution hydrolyzes the chloroauric anion in the solution to form six major species with the general form of [Au(OH)xCl4-x] -, depending on the degree of hydrolysis 42 . Amongst these six gold species, [Au(OH)4] -is reported to have the lowest tendency of reduction even with a strong reducing agent 39 .…”

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Engineering the synthesis of silica–gold nano-urchin particles using continuous synthesis

2014

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Compared to freestanding nanoparticles, supported nanostructures typically show better mechanical stability as well as ease of handling. Unique shapes such as core-shells, raspberries and crescents have been developed on supported materials to gain improved chemical and optical properties along with versatility and tunability. We report the formation of hyperbranched gold structures on silica particles, silica-gold nano-urchin (SGNU) particles. Kinetic control of crystallization, fast mass transfer as well as a bumped surface morphology of the silica particles are important factors for the growth of gold branches on the silica support. Using a microfluidic platform, continuous synthesis of SGNUs is achieved with increased reaction rate (less than 12 min. of residence time), better controllability and reproducibility than that obtained in batch synthesis. The hyper-branched gold structures display surfaceenhanced Raman scattering (SERS). Introduction.Microfluidic systems offer excellent conditions for synthesis of nanomaterials by control of mixing, temperature, and pressure combined with fast heat and mass transfer. 1, 2 Moreover, they enable controlled synthesis under higher temperature and pressure conditions than typically feasible in batch with resulting faster synthesis. 1, 3 Herein, we report batch and microfluidic synthesis of hyper-branched gold structures on silica particles, silica-gold nano-urchin (SGNU) particles. The formed particles consist of a dielectric silica core decorated with densely packed gold nanobranches stretching outward. The morphology serves as an active substrate for tip-enhanced Raman scattering, 4 and could additional have applications in catalysis and bio-imaging. 5,6 Gold nanoparticles have been synthesized by a variety of approaches for diverse applications in catalysis, bio-imaging, drug delivery and photovoltaics. Their surface plasmon resonance (SPR) and surface enhanced Raman scattering (SERS) properties have been of particular interest for photothermal therapy and molecular sensing, respectively [7][8][9][10][11][12][13][14][15] . SERS active structures have been fabricated by complex with top-down methods, 4,12,16,17 but wet-chemical synthesis of gold nanoparticles offer potential advantages in simple, high yield, and limited scalable synthesis. 12,18,19,20,21,22 Gold nanostructures, such as nanorods, nanowires, tetrapods, nanoplates and star-shaped particles are particularly attractive for many applications because of their strong confinement of the electromagnetic field and high enhancement that can be tuned over a wide range of optical wave lengths in comparison with ordinary spherical structures. 11,[23][24][25][26][27] Combination of the metal nanostructure with a support material, such as in core-shells, raspberries, and crescents, affords additional advantages in tuning optical properties, improved chemical/mechanical stability, and ease of handling compared to free-standing nanoparticles.Batch methods, 20 specialized ligands 28 and additional electrochemical treat...

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“…Thus gold in the acidic or neutral pH occurs mainly in the form of negatively charged complexes [AuCl 4 ] − . Halogen ligands with increasing pH of the solution are replaced with hydroxyl groups, giving the dissolved complexes with general formula [Au(OH) n Cl 4−n ] − (n = 0-4) or Au(OH) 3 precipitate (Chang et al 1998). It has been stated that positive complexes of gold [Au(NH 3 ) 4 ] 3+ or [Au (NH 3 ) 2 (OH) 2 ] + can exist in the solution of ammonia (Cotton 1997).…”

Section: Resultsmentioning

confidence: 99%

The properties of gold catalysts precursors adsorbed on the MCM-41 materials modified with Mn and Fe oxides

et al. 2008

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Silica mesoporous materials modified with manganese and iron were obtained by the hydrothermal method. Gold was introduced to pure and modified silica materials by the direct hydrothermal and impregnation methods. Nitrogen adsorption/desorption studies evidenced formation of the materials with large total surface area and mesoporous structure. Unmodified silica materials showed regular pore arrangement. The uniform porous structure was distorted in the iron or manganese containing samples. XRD, UV-Vis/DRS spectroscopy and temperature programmed reduction studies revealed changes of the nature of transition metal oxide and gold species on the different preparation stages. The oxide species after drying were strongly dispersed and partially incorporated to the silica framework. High temperature treatment led to the formation of extraframework Mn and Fe oxide species. Complex processes of gold deposition were observed during hydrothermal synthesis and impregnation of modified silica materials. The increase of the size of gold species was observed during cal-W. Gac ( ) cination. The presence of transition metal oxides decreased sintering of gold crystallites.

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Characterizations of alumina-supported gold with temperature-programmed reduction

Cited by 78 publications

References 8 publications

Surface chemistry of catalysis by gold

Surface chemistry of catalysis by gold

Engineering the synthesis of silica–gold nano-urchin particles using continuous synthesis

The properties of gold catalysts precursors adsorbed on the MCM-41 materials modified with Mn and Fe oxides

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