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.

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.

THE KUBO EFFECTS IN SMALL PARTICLES OF METALS

1996 ◽  
Vol 03 (01) ◽  
pp. 3-7 ◽  
Author(s):  
SHUN-ICHI KOBAYASHI
Keyword(s):  
Electronic Properties ◽  
Metal Particles ◽  
Small Particles ◽  
Mesoscopic Systems ◽  
Level Statistics ◽  
Theoretical Paper ◽  
Charging Energy ◽  
Level Quantization ◽  
Nmr Properties ◽  
Small Metal Particles

This talk is to commemorate Kubo’s pioneering theoretical paper in 1962 on the electronic properties of very small metal particles. We discuss mainly the NMR properties of the particles. Emphasis is placed on factors such as the level quantization, the level statistics, the finiteness of systems, and the single electron charging energy, which are current topics in the field of mesoscopic systems.

Characterization of the catalytic properties of ceria-zirconia mixed oxides by temperature-programmed techniques

2005 ◽  
Vol 80 (1) ◽  
pp. 225-228 ◽  
Author(s):  
J. I. Gutiérrez-Ortiz ◽  
B. de Rivas ◽  
R. López-Fonseca ◽  
J. R. González-Velasco
Keyword(s):  
Mixed Oxides ◽  
Catalytic Properties ◽  
Temperature Programmed

Spontaneous Formation of Ag and Au Particles in Alcohols

1994 ◽  
Vol 351 ◽  
Author(s):  
Z.-Y. Huang ◽  
M. Quinn ◽  
G. Mills ◽  
W. Galef
Keyword(s):  
Light Scattering ◽  
Metal Particles ◽  
Small Particles ◽  
Plasmon Band ◽  
Spontaneous Reduction ◽  
Silica Surfaces ◽  
Spontaneous Formation ◽  
Ag Particles ◽  
Solvent Molecules ◽  
Small Metal Particles

ABSTRACTMetal particles are generated via the spontaneous reduction of Ag+ and AuCl4− ions by solvent molecules that takes place in air-saturated alcoholic solutions containing hydroxide ions. Changes in the plasmon band of the Ag particles are observed when the metal particles are in contact with Ag20 particles. The optical changes are explained in terms of surface effects of the metal particles. Larger shifts of the Au plasmon band and light scattering were observed at the initial stages of the particle formation process. These effects are explained in terms of formation of networks consisting of small metal particles. It is proposed that generation of small Au particles occurs mainly on silica surfaces, and that particle-networks are formed when small particles desorb from the surfaces.

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.

Structure Studies of Supported Metal Catalyst Particles by Microdiffraction Technique

1987 ◽  
Vol 45 ◽  
pp. 202-203
Author(s):  
M. Pan ◽  
J.M. Cowley ◽  
I.Y. Chan ◽  
R. Garcia
Keyword(s):  
Metal Particles ◽  
Metal Catalyst ◽  
Supported Metal Catalysts ◽  
Small Particles ◽  
Structure Information ◽  
The Past ◽  
Transmission Electron ◽  
And Performance ◽  
Small Metal Particles ◽  
Supported Metal

Understanding the structures of the small metal particles (<5nm) in supported metal catalysts can provide some basis for understanding the properties and performance of these catalysts. High resolution transmission electron microscopy (HRTEM) has been extensively used to characterize the structures of small particles in the past few years. As a complement to HRTEM, microdiffraction technique has its unique advantage of being able to provide local structure information within regions of diameter 1-2nm.In our VG HB-5 STEM an electron beam with diameter of 1-1.5nm can be easily generated at the specimen level and microdiffraction patterns from such small regions are routinely observed with the help of the attached optical system. Two series of catalyst samples, Pt/γ-Al2 O3 and Rh/CeO2 with various metal loadings and reduction temperatures, have been studied. The series of Pt/γ-Al2 O3 catalyst included both calcined and reduced samples. Both series of catalysts contain high dispersions of metal particles (<5nm). In the case of Rh/CeO2 Rh particles usually have sizes of 2-3nm.

Synthesis and Characterization of Bimetallic Fe/Co Nanocatalyst on CNTs for Fischer-Tropsch Reaction

2012 ◽  
Vol 16 ◽  
pp. 9-14 ◽  
Author(s):  
Sardar Ali ◽  
Noor Asmawati Mohd Zabidi ◽  
Duvvuri Subbarao
Keyword(s):  
Particle Size ◽  
Physicochemical Properties ◽  
Average Particle Size ◽  
Xrd Analysis ◽  
Synthesis And Characterization ◽  
Average Particle ◽  
Impregnation Method ◽  
Fischer Tropsch ◽  
Temperature Programmed

Cobalt and iron are common catalysts used in the Fischer-Tropsch (FT) reaction. This paper presents the synthesis and characterization of monometallic and bimetallic cobalt and iron nanoparticles supported on carbon nanotubes (CNTs). The CNTs-supported nanocatalysts were synthesized by a wet impregnation method at various ratios of Fe:Co. The physicochemical properties of the samples were analyzed by H2-temperature programmed reduction (TPR), CO and H2-chemisorption analyses, transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis. The effects of incorporation of Fe into Co on the physicochemical properties of Co/CNTs in terms of degree of reduction, CO and H2 chemisorptions and morphologies were investigated. TEM showed that metal nanoparticles were well dispersed on the external surface and inside the CNTs. For monometallic Co/CNTs and Fe/CNTs, the average metal particle size was 5±1 nm and 6±1 nm, respectively. For the bimetallic 70Co30Fe/CNTs nanocatalysts, the average particle size was found to be 4±1 nm. Metal particles attached to the outer walls were bigger than the ones inside the CNTs. H2-TPR analysis of Co/CNTs indicated two temperature regions at 330°C (low temperature) and 491°C (high temperature). The incorporation of iron into cobalt nanocatalysts of up to 30 % of the total metal loading enhanced the catalyst’s H2 and CO chemisorptions capacities and reducibility.

Electron Beam Driven Disordering in Small Particles

1996 ◽  
Vol 439 ◽  
Author(s):  
Richard R. Vanfleet ◽  
Jack Mochel
Keyword(s):  
Electron Beam ◽  
Critical Size ◽  
Scanning Transmission Electron Microscope ◽  
Metal Particles ◽  
Small Particles ◽  
Transmission Electron ◽  
Platinum Clusters ◽  
Scanning Transmission ◽  
The Individual ◽  
Small Metal Particles

AbstractSmall metal particles in the range of a few nanometers in diameter are seen to progressively disorder when the 100 keV electron beam of a Scanning Transmission Electron Microscope (STEM) is held stationary on the particle. The diffraction pattern of the individual particle is seen to progress from an initial array of indexable diffraction spots to a mixture of diffraction spots and amorphous-like rings and finally to rings with no persistent diffraction spots. After the electron beam is removed, the particles will recrystallize after minutes or hours. Only particles below a critical size are seen to fully disorder. We have observed this in Platinum, Palladium, Rhodium, and Iridium and based on our model of disordering process believe it is a universal effect. It has also been observed with a Platinum Ruthenium alloy. We discuss the mechanism of this disordering and the structure of the resulting disordering particle for the case of Platinum clusters.

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