Synthesis and Characterization of Supported Metal Cluster Catalysts with Well-Defined Structures

1994 ◽  
Vol 368 ◽  
Author(s):  
B. C. Gates
Keyword(s):  
Metal Clusters ◽  
Metal Cluster ◽  
X Ray ◽  
Coordination Numbers ◽  
Supported Clusters ◽  
Supported Metal Clusters ◽  
X Ray Absorption ◽  
Thermal Decarbonylation ◽  
Supported Metal

ABSTRACTNearly uniform supported metal clusters are the focus of this summary, which addresses their synthesis, characterization, and catalytic properties. Supported clusters represented as Ir4 and Ir6 were prepared on MgO powder by thermal decarbonylation of [HIr4(CO)11]− and [Ir6(CO)15]2−, respectively. The most useful characterization technique for supported clusters is extended X-ray absorption fine structure spectroscopy, but the structure data are limited by the precision of the coordination numbers (about ±20%). Ir4 and Ir6 clusters on supports catalyze hydrogenation of cyclohexene and of toluene, and they are catalytically distinct from larger iridium particles, although the reactions are structure insensitive (proceeding at about the same rate per exposed metal atom) when catalyzed by metal particles larger than about 1 nm. Thus the concept of structure insensitivity does not extend to supported metal clusters, which are regarded as quasi molecular.

Characterization of optical spectra of interacting systems: Application to oxide-supported metal clusters

2008 ◽  
Vol 108 (15) ◽  
pp. 2978-2990 ◽  
Author(s):  
Miquel Huix-Rotllant ◽  
Ajanta Deka ◽  
Alexei V. Matveev ◽  
Sergey I. Bosko ◽  
Lyudmila V. Moskaleva ◽  
...  
Keyword(s):  
Metal Clusters ◽  
Optical Spectra ◽  
Supported Metal Clusters ◽  
Interacting Systems ◽  
Supported Metal

Characterization of supported metal catalysts by X-ray absorption spectroscopy

1983 ◽  
Vol 20 (3) ◽  
pp. 389 ◽  
Author(s):  
FarrelW. Lytle ◽  
RobertB. Greegor ◽  
John Sinfelt ◽  
GraysonH. Via
Keyword(s):  
Absorption Spectroscopy ◽  
Metal Catalysts ◽  
Supported Metal Catalysts ◽  
X Ray ◽  
X Ray Absorption ◽  
Supported Metal

Characterization of large supported metal clusters by optical spectroscopy

1995 ◽  
Vol 33 (2) ◽  
pp. 133-141 ◽  
Author(s):  
T. G�tz ◽  
W. Hoheisel ◽  
M. Vollmer ◽  
F. Tr�ger
Keyword(s):  
Optical Spectroscopy ◽  
Metal Clusters ◽  
Supported Metal Clusters ◽  
Supported Metal

Synthesis and characterization of 1,2,3,4 tetrahydroquinoline intercalated into MoS2 in search of cleaner fuels

2007 ◽  
Vol 22 (10) ◽  
pp. 2747-2757 ◽  
Author(s):  
Karina Castillo ◽  
Felicia Manciu ◽  
J.G. Parsons ◽  
Russell R. Chianelli
Keyword(s):  
Fine Structure ◽  
Infrared Spectroscopy ◽  
Synthesis And Characterization ◽  
X Ray Diffraction ◽  
X Ray ◽  
Coordination Numbers ◽  
Absorption Fine ◽  
Diffraction Patterns ◽  
X Ray Absorption

Two different morphologies of MoS2 (short and long sheets) were utilized to elucidate the intercalation mechanism of 1,2,3,4 tetrahydroquinoline (THQ). MoS2 (short sheets) and molybdenite (MB) (long sheets) were exfoliated and restacked in the presence of THQ. The x-ray diffraction patterns of both samples show a new reflection in the 001 plane, which implies a lowering of symmetry and corresponds to an expansion of the layers by approximately 12.3 Å. In the MoS2-THQ sample, 80% of the MoS2 was intercalated and 20% remained stacked. In the MB-THQ sample, 30% of MB was intercalated while 70% remained stacked. X-ray absorption structure (XAS) studies showed changes in atomic geometry and coordination. The x-ray absorption near-edge spectra showed shifts in the geometry of the intercalated MoS2 and MB sample compared to the unintercalated samples. Extended x-ray absorption fine structure studies showed lower coordination numbers compared to the untreated samples. Infrared spectroscopy characterization of these same samples suggests intercalation and partial dehydrogenation of the THQ.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

EXELFS Studies of Carbon Fibers

1990 ◽  
Vol 48 (2) ◽  
pp. 72-73
Author(s):  
V. Serin ◽  
K. Hssein ◽  
G. Zanchi ◽  
J. Sévely
Keyword(s):  
Carbon Fibers ◽  
Energy Analysis ◽  
Electron Excitation ◽  
Complex Structures ◽  
High Modulus ◽  
Promising Technique ◽  
X Ray ◽  
Fine Structures ◽  
X Ray Absorption

The present developments of electron energy analysis in the microscopes by E.E.L.S. allow an accurate recording of the spectra and of their different complex structures associated with the inner shell electron excitation by the incident electrons (1). Among these structures, the Extended Energy Loss Fine Structures (EXELFS) are of particular interest. They are equivalent to the well known EXAFS oscillations in X-ray absorption spectroscopy. Due to the EELS characteristic, the Fourier analysis of EXELFS oscillations appears as a promising technique for the characterization of composite materials, the major constituents of which are low Z elements. Using EXELFS, we have developed a microstructural study of carbon fibers. This analysis concerns the carbon K edge, which appears in the spectra at 285 eV. The purpose of the paper is to compare the local short range order, determined by this way in the case of Courtauld HTS and P100 ex-polyacrylonitrile carbon fibers, which are high tensile strength (HTS) and high modulus (HM) fibers respectively.

scholarly journals Database of ab initio L-edge X-ray absorption near edge structure

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Yiming Chen ◽  
Chi Chen ◽  
Chen Zheng ◽  
Shyam Dwaraknath ◽  
Matthew K. Horton ◽  
...  
Keyword(s):  
High Throughput ◽  
Scattering Theory ◽  
Research Community ◽  
Metal Compounds ◽  
Edge Structure ◽  
X Ray ◽  
Initial Release ◽  
Computational Workflow ◽  
X Ray Absorption

AbstractThe L-edge X-ray Absorption Near Edge Structure (XANES) is widely used in the characterization of transition metal compounds. Here, we report the development of a database of computed L-edge XANES using the multiple scattering theory-based FEFF9 code. The initial release of the database contains more than 140,000 L-edge spectra for more than 22,000 structures generated using a high-throughput computational workflow. The data is disseminated through the Materials Project and addresses a critical need for L-edge XANES spectra among the research community.

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