scholarly journals Effects of particle size on the catalytic properties of very small metal particles.

Hyomen Kagaku ◽  
1987 ◽  
Vol 8 (5) ◽  
pp. 365-371 ◽  
Author(s):  
Yoshio TAKASU
Keyword(s):  
Particle Size ◽  
Catalytic Properties ◽  
Metal Particles ◽  
Small Metal Particles

The Characterization of Thin Platinum Films on Alumina

1986 ◽  
Vol 83 ◽  
Author(s):  
E. I. Altman ◽  
R. J. Gorte
Keyword(s):  
Particle Size ◽  
Catalytic Properties ◽  
Metal Particles ◽  
Small Particles ◽  
Oxide Substrate ◽  
Porous Oxide ◽  
Temperature Programmed ◽  
Thin Platinum ◽  
Small Metal Particles

ABSTRACTIndustrial metal catalysts are usually in the form of small metal particles supported on a porous oxide. The typical size of these metal particles ranges between 1.0 and 10.0 nm and it is well known that the particle size and the oxide substrate can affect the catalytic properties of the metal for some important reactions[1]. Previous work with adsorption on small particles has indicated that desorption temperatures[2–4] and the ability to dissociate CO[5,6] can also be affected by the particle size. To further investigate these size and substrate effects, we have examined the adsorption properties of several simple gases on small Pt particles supported on alumina using temperature programmed desorption (TPD). We will show that the desorption curves for CO, H2, and NO on these particles are very similar to curves measured on single crystals.

Examination by Electron Microscopy of Osmium Catalysts Supported on Thin Aluminium-Oxide Films

1982 ◽  
Vol 40 ◽  
pp. 658-659
Author(s):  
B. Tesche ◽  
E. Zeitler ◽  
E. A. Delgado ◽  
H. Knözinger
Keyword(s):  
Electron Microscopy ◽  
Particle Size ◽  
Metal Atom ◽  
Supported Catalysts ◽  
Metal Particles ◽  
Transmission Electron ◽  
High Area ◽  
Instrumental Resolution ◽  
Electron Microscopes ◽  
Small Metal Particles

It is easy to obtain resolutions of atomic dimensions with current conventional transmission electron microscopes. Hence, in principle, the examination of small metal particles or metal atom ensembles (≤1 nra) in supported catalysts is not limited by the instrumental resolution. However, usually the metal is located on dispersed high-area supports such as silica or alumina and the characterization by electron microscopy of these systems down to the atomic dimension is not directly possible, since the contrast in the micrographs is an unknown combination of phase and amplitude contrast. This uncertainty can result in incorrect determinations of particle size, shape and distribution.

Electron Microscopy of the Shape of Small Metal Particles

1977 ◽  
Vol 35 ◽  
pp. 300-301
Author(s):  
M. Jose Yacaman
Keyword(s):  
Electron Microscopy ◽  
Metal Particle ◽  
Field Experiments ◽  
Size Range ◽  
Dark Field ◽  
Metal Particles ◽  
Bragg Condition ◽  
Crystal Particle ◽  
Small Metal Particle ◽  
Small Metal Particles

In the Study of small metal particles the shape is a very Important parameter. Using electron microscopy Ino and Owaga(l) have studied the shape of twinned particles of gold. In that work electron diffraction and contrast (dark field) experiments were used to produce models of a crystal particle. In this work we report a method which can give direct information about the shape of an small metal particle in the amstrong- size range with high resolution. The diffraction pattern of a sample containing small metal particles contains in general several systematic and non- systematic reflections and a two-beam condition can not be used in practice. However a N-beam condition produces a reduced extinction distance. On the other hand if a beam is out of the bragg condition the effective extinction distance is even more reduced.

Microstructure and reactivity of small metal particles: The role of Ce additives

1992 ◽  
Vol 50 (1) ◽  
pp. 318-319
Author(s):  
L.D. Schmidt ◽  
K. R. Krause ◽  
J. M. Schwartz ◽  
X. Chu
Keyword(s):  
Atmospheric Pressure ◽  
Noble Metals ◽  
Mixed Oxides ◽  
Catalytic Properties ◽  
Chemical Shifts ◽  
Catalytic Converter ◽  
Structural Evolution ◽  
Single Particles ◽  
Small Metal Particles

The evolution of microstructures of 10- to 100-Å diameter particles of Rh and Pt on SiO2 and Al2O3 following treatment in reducing, oxidizing, and reacting conditions have been characterized by TEM. We are able to transfer particles repeatedly between microscope and a reactor furnace so that the structural evolution of single particles can be examined following treatments in gases at atmospheric pressure. We are especially interested in the role of Ce additives on noble metals such as Pt and Rh. These systems are crucial in the automotive catalytic converter, and rare earths can significantly modify catalytic properties in many reactions. In particular, we are concerned with the oxidation state of Ce and its role in formation of mixed oxides with metals or with the support. For this we employ EELS in TEM, a technique uniquely suited to detect chemical shifts with ∼30Å resolution.

Investigation of cluster layers of small netal particles by TEM, SEM, EELS and by photoacoustic spectroscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 250-251
Author(s):  
H. Seiler ◽  
U. Haas ◽  
K.H. Körtje
Keyword(s):  
Bulk Material ◽  
High Vacuum ◽  
Optical Methods ◽  
Metal Particles ◽  
Silver Particles ◽  
Low Loss ◽  
Plasmon Excitation ◽  
First Results ◽  
Diffraction Patterns ◽  
Small Metal Particles

The physical properties of small metal particles reveal an intermediate position between atomic and bulk material. Especially Ag has shown pronounced size effects. We compared silver layers evaporated in high vacuum with cluster layers of small silver particles, evaporated in N2 at a pressure of about 102 Pa. The investigations were performed by electron optical methods (TEM, SEM, EELS) and by Photoacoustic (PA) Spectroscopy (gas-microphone detection).The observation of cluster layers with TEM and high resolution SEM show small silver particles with diameters of about 50 nm (Fig. 1 and Figure 2, respectively). The electron diffraction patterns of homogeneous Ag layers and of cluster layers are similar, whereas the low loss EELS spectra due to plasmon excitation are quite different. Fig. 3 and Figure 4 show first results of EELS spectra of a cluster layer of small silver particles on carbon foil and of a homogeneous Ag layer, respectively.

Coherent electron nanodiffraction from clean silver nano particles in a UHV STEM

1993 ◽  
Vol 51 ◽  
pp. 1058-1059
Author(s):  
J. Liu ◽  
M. Pan ◽  
G. E. Spinnler
Keyword(s):  
Supported Catalysts ◽  
Imaging Techniques ◽  
Nano Particles ◽  
Metal Particles ◽  
Shape Structure ◽  
Dynamical Simulations ◽  
Small Metal Particles ◽  
Extract Information

Small metal particles have peculiar chemical and physical properties as compared to bulk materials. They are especially important in catalysis since metal particles are common constituents of supported catalysts. The structural characterization of small particles is of primary importance for the understanding of structure-catalytic activity relationships. The shape and size of metal particles larger than approximately 5 nm in diameter can be determined by several imaging techniques. It is difficult, however, to deduce the shape of smaller metal particles. Coherent electron nanodiffraction (CEND) patterns from nano particles contain information about the particle size, shape, structure and defects etc. As part of an on-going program of STEM characterization of supported catalysts we report some preliminary results of CEND study of Ag nano particles, deposited in situ in a UHV STEM instrument, and compare the experimental results with full dynamical simulations in order to extract information about the shape of Ag nano particles.

Analytical Electron Microscopy study of two vehicle-aged automotive exhaust catalysts having dissimilar activities

1989 ◽  
Vol 47 ◽  
pp. 272-273
Author(s):  
Sooho Kim ◽  
M. J. D’Aniello
Keyword(s):  
Electron Microscopy ◽  
Particle Size ◽  
Noble Metal ◽  
Catalyst Deactivation ◽  
Analytical Electron Microscopy ◽  
Microscopy Study ◽  
Metal Particles ◽  
Automotive Exhaust ◽  
Exhaust Catalysts ◽  
Analytical Electron

Automotive catalysts generally lose-agtivity during vehicle operation due to several well-known deactivation mechanisms. To gain a more fundamental understanding of catalyst deactivation, the microscopic details of fresh and vehicle-aged commercial pelleted automotive exhaust catalysts containing Pt, Pd and Rh were studied by employing Analytical Electron Microscopy (AEM). Two different vehicle-aged samples containing similar poison levels but having different catalytic activities (denoted better and poorer) were selected for this study.The general microstructure of the supports and the noble metal particles of the two catalysts looks similar; the noble metal particles were generally found to be spherical and often faceted. However, the average noble metal particle size on the poorer catalyst (21 nm) was larger than that on the better catalyst (16 nm). These sizes represent a significant increase over that found on the fresh catalyst (8 nm). The activity of these catalysts decreases as the observed particle size increases.

The optical kerr effect in small metal particles and metal colloids: The case of gold

1988 ◽  
Vol 47 (4) ◽  
pp. 347-357 ◽  
Author(s):  
F. Hache ◽  
D. Ricard ◽  
C. Flytzanis ◽  
U. Kreibig
Keyword(s):  
Kerr Effect ◽  
Metal Particles ◽  
Optical Kerr Effect ◽  
Metal Colloids ◽  
Small Metal Particles
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