197Au Mössbauer study of gold particles obtained by evaporation of metallic gold on Mylar

Stievano, Lorenzo; Santucci, S.; Lozzi, L.; Calogero, Sandro; Wagner, F. E.

doi:10.1016/s0022-3093(98)00434-7

Cited by 24 publications

(19 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Thus the invisible Au content of 82% (obtained by SIMS analyses) is very close to the 79 ± 9% of the Au assigned as metallic from the Mössbauer data. It was also suggested by Genkin et al (1998) that this metallic Au may in part represent submicroscopic gold, in particles as small as 2 nm, which yield Mössbauer spectra that are practically identical to pure gold (Santucci et al 1996, Stievano et al 1998. The XANES data with white lines, which provide evidence of chemical bonding of Au in arsenopyrite, may be interpreted in several ways (e.g., Simon et al 1999).…”

Section: Discussionmentioning

confidence: 98%

Chemical Speciation of Gold in Arsenopyrite

Cabri¹,

Newville

Gordon

et al. 2000

The Canadian Mineralogist

135

View full text Add to dashboard Cite

The speciation of Au in gold-bearing arsenopyrite (FeAsS) from four gold deposits (Olympiada, Sentachan, São Bento and Sheba) was determined by micro-X-ray absorption near-edge structure (XANES) on grains well characterized microscopically and by electron-microprobe and secondary-ion mass spectrometry analyses and images. "Invisible" gold in arsenopyrite occurs in two apparently mutually exclusive chemical forms: chemically bound and elemental. Arsenopyrite from the Sentachan, São Bento and Sheba deposits contains chemically bound gold. With comparable constituent electronegativities and a white-line feature in the XANES indicating unoccupied Au 5d-states, but absorption-edge positions comparable to Au 1+ species, the bonding is interpreted as being covalent rather than ionic. The invisible gold in arsenopyrite from the Olympiada deposit, on the other hand, occurs as very small particles of Au 0 , probably less than a few nanometers in diameter. Micro-XANES data for the Olympiada and Sentachan arsenopyrite support earlier results obtained by 197 Au Mössbauer spectroscopy on arsenopyrite concentrates. In some arsenopyrite crystals, the gold concentration is closely related to growth zoning. This feature represents conditions during crystallization and does not correlate with the chemical form of the gold. Similarly, selenium, where present, correlates with gold in some deposits and not in others, irrespective of the gold speciation. The finding of two types of invisible gold in arsenopyrite from different deposits has beneficial implications for extractive metallurgy.

show abstract

Section: Discussionmentioning

confidence: 98%

Chemical Speciation of Gold in Arsenopyrite

Cabri¹,

Newville

Gordon

et al. 2000

The Canadian Mineralogist

135

View full text Add to dashboard Cite

show abstract

“…The authors noted that this transition took place at the same point where a structural transition occurs, suggesting the two phenomena may be related (207). Stievano et al employed Mössbauer spectroscopy to observe changes in the electronic character of small gold particles supported on Mylar as the dimension was shrunk (327). Measurements revealed an asymmetry as the particle size decreased below a 1.5 nm diameter, due to the increased fraction of surface atoms.…”

Section: 2mentioning

confidence: 99%

Surface chemistry of catalysis by gold

et al. 2004

View full text Add to dashboard Cite

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)

show abstract

“…Mçssbauer spectra of pure Au colloids after heating (both in an air and hydrogen atmosphere) give narrower lines that indicate either a cluster shape phenomenon or a colloid agglomeration on annealing. [78][79][80] The results obtained for the mean isomer shifts and for the variance of the Gaussian distribution of isomer shifts are given in Table 3 for samples of Au, Au-Pd alloy colloids and for the arc-melted alloys used as reference materials. Electric-quadrupole interactions were not explicitly taken into account in the fitting procedure, but one should keep in mind that they should exist in random alloys, because the distribution of Au and Pd have different radii breaks and perfect local-cubic symmetry.…”

Section: Hydrogen Chemisorption Datamentioning

confidence: 99%

Characterization and Catalytic‐Hydrogenation Behavior of SiO₂‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids

Pârvulescu

Endruschat

et al. 2006

Chemistry A European J

View full text Add to dashboard Cite

Colloids embedded in a silica sol-gel matrix were prepared by using fully alloyed Pd-Au colloids, and pure Pd and Au colloids stabilized with tetraalkylammonium bromide following a modified sol-gel procedure with tetrahydrofuran (THF) as the solvent. Tetraethoxysilicate (TEOS) was used as the precursor for the silica support. The molar composition of the sol was TEOS/THF/H2O/HCl = 1:3.5:4:0.05 for the bimetallic Pd-Au and TEOS/THF/H2O/HCl = 1:4.5:4:0.02 for Pd and Au monometallic systems. After refluxing, the colloid was added as a 4.5 wt % solution in THF for Pd-Au, 10.2 wt % solution in THF for Pd and 8.4 wt % solution in THF for Au at room temperature. The gelation was carried out with vigorous stirring (4 days) under an Ar atmosphere. Following these procedures, bimetallic Pd-Au-SiO2 catalysts with 0.6 and 1 wt % metal, and monometallic Pd- and Au-SiO2 catalysts with 1 wt % metal were prepared. These materials were further treated following four different routes: 1) by simple drying, 2) in which the dried catalysts were calcined in air at 723 K and then reduced at the same temperature, 3) in which they were directly reduced in hydrogen at 723 K, and 4) in which the surfactant was extracted using an ethanol-heptane azeotropic mixture. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption measurements, solid-state 1H, 13C, 29Si-CP/MAS-NMR spectroscopy, powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and 197Au Mössbauer spectroscopy. The physical characterization by a combination of these techniques has shown that the size and the structural characteristics of the Pd-Au colloid precursor are preserved when embedded in an SiO2 matrix. Catalytic tests were carried out in selective hydrogenation of 3-hexyn-1-ol, cinnamaldehyde, and styrene. These data showed evidence that alloying Pd with Au in bimetallic colloids leads to enhanced activity and most importantly to improved selectivity. Also, the combination of the two metals resulted in catalysts that were very stable against poisoning, as was evidenced for the hydrogenation of styrene in the presence of thiophene.

show abstract

197Au Mössbauer study of gold particles obtained by evaporation of metallic gold on Mylar

Cited by 24 publications

References 17 publications

Chemical Speciation of Gold in Arsenopyrite

Chemical Speciation of Gold in Arsenopyrite

Surface chemistry of catalysis by gold

Characterization and Catalytic‐Hydrogenation Behavior of SiO₂‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids

Contact Info

Product

Resources

About

197Au Mössbauer study of gold particles obtained by evaporation of metallic gold on Mylar

Cited by 24 publications

References 17 publications

Chemical Speciation of Gold in Arsenopyrite

Chemical Speciation of Gold in Arsenopyrite

Surface chemistry of catalysis by gold

Characterization and Catalytic‐Hydrogenation Behavior of SiO2‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids

Contact Info

Product

Resources

About

Characterization and Catalytic‐Hydrogenation Behavior of SiO₂‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids