scholarly journals Influence of preparation method on the metal cluster size of platinum/ZSM-5 catalysts as studied with EXAFS

1990 ◽  
Vol 94 (23) ◽  
pp. 8574-8578 ◽  
Author(s):  
F. W. H. Kampers ◽  
C. W. R. Engelen ◽  
J. H. C. Van Hooff ◽  
D. C. Koningsberger
Keyword(s):  
Cluster Size ◽  
Preparation Method ◽  
Metal Cluster

Metal cluster size distributions during nozzle jet expansion

1986 ◽  
Vol 48 (17) ◽  
pp. 1122-1124 ◽  
Author(s):  
S.‐N. Yang ◽  
T.‐M. Lu
Keyword(s):  
Cluster Size ◽  
Metal Cluster ◽  
Size Distributions

scholarly journals Quantifying Enhancement of Metal-Supported Zeolites Due to Hydrogen Spillover

2018 ◽  
Vol 43 (2) ◽  
pp. 157-165
Author(s):  
Shrivanand M. Pai ◽  
Barat L. Newalkar ◽  
Parimal A. Parikh
Keyword(s):  
Cluster Size ◽  
Zeolite Y ◽  
Metal Cluster ◽  
Temperature Programmed Desorption ◽  
Acid Sites ◽  
Acid Strength ◽  
Hydrogen Spillover ◽  
Bifunctional Catalysts ◽  
Temperature Programmed

As bifunctional catalysts, metal-supported zeolites play an important role in refining and petrochemical processes, e.g. isomerisation, alkylation, etc. Reduction in acidity and acid strength of zeolites upon their impregnation with metals have been widely reported. Also hydrogen spillover vis-a-vis the closeness of two catalyst functions (acid and metal) has been discussed at length. Hydrogen spillover has been claimed to give rise to formation of additional acid sites on supports. Here quantification of acid sites for two zeolites, zeolite Y and ZSM-5, impregnated with different metals in various proportions after exposing them to hydrogen, has been attempted using ammonia temperature programmed desorption. The observed acidity values have been explained on the basis of metal cluster size.

Catalytic upgrading of biomass-derived vapors on carbon aerogel-supported Ni: Effect of temperature, metal cluster size and catalyst-to-biomass ratio

2018 ◽  
Vol 178 ◽  
pp. 251-261 ◽  
Author(s):  
Luis E. Arteaga-Pérez ◽  
Romel Jiménez ◽  
Nicolas Grob ◽  
Oscar Gómez ◽  
Romina Romero ◽  
...  
Keyword(s):  
Cluster Size ◽  
Metal Cluster ◽  
Carbon Aerogel ◽  
Effect Of Temperature ◽  
Catalytic Upgrading ◽  
Biomass Ratio ◽  
Supported Ni

Production and STEM examination of controlled-size silver clusters

1983 ◽  
Vol 41 ◽  
pp. 338-339
Author(s):  
M. A. Listvan ◽  
R. P. Andres
Keyword(s):  
Cluster Size ◽  
Metal Clusters ◽  
Experimental Parameter ◽  
Carbon Films ◽  
Metal Species ◽  
Silver Clusters ◽  
Free Jet ◽  
Size Dependent ◽  
Cluster Properties ◽  
Controllable Size

Knowledge of the function and structure of small metal clusters is one goal of research in catalysis. One important experimental parameter is cluster size. Ideally, one would like to produce metal clusters of regulated size in order to characterize size-dependent cluster properties.A source has been developed which is capable of producing microscopic metal clusters of controllable size (in the range 5-500 atoms) This source, the Multiple Expansion Cluster Source, with a Free Jet Deceleration Filter (MECS/FJDF) operates as follows. The bulk metal is heated in an oven to give controlled concentrations of monomer and dimer which were expanded sonically. These metal species were quenched and condensed in He and filtered to produce areosol particles of a controlled size as verified by mass spectrometer measurements. The clusters were caught on pre-mounted, clean carbon films. The grids were then transferred in air for microscopic examination. MECS/FJDF was used to produce two different sizes of silver clusters for this study: nominally Ag6 and Ag50.

Direct Observation of Heat Exchanger Deposits by Cross Sectioning

1967 ◽  
Vol 25 ◽  
pp. 364-365
Author(s):  
R. W. Anderson ◽  
D. L. Senecal
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Heat Exchanger ◽  
Direct Observation ◽  
Cross Sections ◽  
Preparation Method ◽  
Specimen Preparation ◽  
Flowing Water ◽  
Transmission Electron ◽  
Deposit Layer

A problem was presented to observe the packing densities of deposits of sub-micron corrosion product particles. The deposits were 5-100 mils thick and had formed on the inside surfaces of 3/8 inch diameter Zircaloy-2 heat exchanger tubes. The particles were iron oxides deposited from flowing water and consequently were only weakly bonded. Particular care was required during handling to preserve the original formations of the deposits. The specimen preparation method described below allowed direct observation of cross sections of the deposit layers by transmission electron microscopy.The specimens were short sections of the tubes (about 3 inches long) that were carefully cut from the systems. The insides of the tube sections were first coated with a thin layer of a fluid epoxy resin by dipping. This coating served to impregnate the deposit layer as well as to protect the layer if subsequent handling were required.

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.

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