Transmission electron microscopy particle size analysis

The catalysts were all calcined and prereduced. For the calcination/reduction, a sieve fraction (225 < dp < 450 im) was placed in a downflow fixed-bed reactor. The prereduced catalysts were stored in air. The Pt particle size was determined by H2 chemisorption, high resolution transmission electron microscopy and EXAFS analysis. Details of H2 chemisorption25, HRTEM26 and EXAFS25 are given elsewhere. 

Charged-Particle Optics Particle Size Analysis Positron Microscopy Scanning Probe Microscopy Transmission Electron Microscopy X-Ray Analysis X-Ray Photoelectron Spectroscopy... 

In this chapter, size classification refers to the separation of particles by size so that the resulting aerosol contains particles of a given size, whereas size characterization is the determination of the size distribution of the aerosol. Size characterization of nanoflbers and nanotubes is commonly performed by transmission electron microscopy (TEM). TEM analysis has proven invaluable for examining the structure and composition of individual particles and is also valuable for size characterization if immediate feedback is not needed. Inasmuch as the particles must first be collected and then analyzed, the process is slow and laborious. 

Transmission electron microscopy is one of the most often used techniques for the characterization of catalysts. Determination of particle sizes or of distributions therein has become a matter of routine, although it rests of course on the assumptions that the size of the imaged particle is truly proportional to the size of the actual particle and that the detection probability is the same for all particles, independently of their dimensions. In situ studies of catalysts are of special interest and are possible by coupling the instrument to an external reactor. After evacuation of the reactor, the catalyst can be transferred directly into the analysis position without seeing air [17-19J. Numerous applications of electron microscopy in catalysis have been described in the literature, and several excellent reviews are available [2-6],... 

Particle size distributions of both hydrosols determined using a statistical image analysis of transmission electron microscopy (Jeol TEM 120 CX) micrographs are presented in Fig. 13.7. These hydrosols were prepared at different neutralization levels (pH = 2 and 2.8). Both particle size distributions are centered around 18 to 19 A and are extremely sharp as shown by the low values of the standard deviation a. 

The sfabilify of Pf particles during the 1.2 V hold has also been investigated. At 1.2 V and 80°C in 1 M H2SO4, up to 35% of the ECA was lost after 24 h. Transmission electron microscopy analysis of the tested catalysts found a growth in the Pt particle size distribution, suggesting that small Pt particles (-2 nm) are particularly susceptible to dissolution/agglomeration xmder steady-state voltage holds at 1.2 V. 

The size and morphology are characteristic parameters of metal particles. It is possible to determine them by various techniques transmission electron microscopy (TEM) [105-107], X-ray photoelectron spectroscopy (XPS) [108], X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAES) [109, 110], thermoprogrammed oxidation, reduction or desorption (TPO, TPR or TPO) and chemisorption of probe molecules (H2, O2, CO, NO) are currently used. It is therefore possible to know the particles (i) size (by TEM) [105-107], extended X-ray absorption fine structure (EXAES) [109, 110]), (ii) structure (by XRD, TEM), (iii) chemical composition (by TEM-EDAX, elemental analysis), (iv) chemical state (surface and bulk metal atoms by XPS [108], TPD, TPR, TPO) and... 

Although a number of secondary minerals have been predicted to form in weathered CCB materials, few have been positively identified by physical characterization methods. Secondary phases in CCB materials may be difficult or impossible to characterize due to their low abundance and small particle size. Conventional mineral identification methods such as X-ray diffraction (XRD) analysis fail to identify secondary phases that are less than 1-5% by weight of the CCB or are X-ray amorphous. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), coupled with energy dispersive spectroscopy (EDS), can often identify phases not seen by XRD. Additional analytical methods used to characterize trace secondary phases include infrared (IR) spectroscopy, electron microprobe (EMP) analysis, differential thermal analysis (DTA), and various synchrotron radiation techniques (e.g., micro-XRD, X-ray absorption near-eidge spectroscopy [XANES], X-ray absorption fine-structure [XAFSJ). 

Figures 5 (a) and (b) show electron micrographs of the RuxSey particles in powder form, Fig. 5.5(a) and in colloidal form, Fig. 5.5(b). The generated particle size in both cases is ca.2 nm. It is, however, interesting that the colloidal route delivers particles with a narrow size distribution. After multiple analysis by EDX performed with transmission electron microscopy (TEM), and/or via Rut-herford backscattering spectroscopy (RBS) we concluded that the stoichiometry of the RuxSey compound corresponds to x 2 and y 1. This is another experimental evidence that the "real" chemical precursor is the intermediate...

The chemical composition can be measured by traditional wet and instrumental methods of analysis. Physical surface area is measured using the N2 adsorption method at liquid nitrogen temperature (BET method). Pore size is measured by Hg porosimetry for pores with diameters larger than about 3.0 nm (30 A) or for smaller pores by N2 adsorp-tion/desorption. Active catalytic surface area is measured by selective chemisorption techniques or by x-ray diffraction (XRD) line broadening. The morphology of the carrier is viewed by electron microscopy or its crystal structure by XRD. The active component can also be measured by XRD but there are certain limitations once its particle size is smaller than about 3.5 nm (35 A). For small crystallites transmission electron microscopy (TEM) is most often used. The location of active components or poisons within the catalyst is determined by electron microprobe. Surface contamination is observed directly by x-ray photoelectron spectroscopy (XPS). 

The 20 A diameter monodisperse crystallites isolated Ifom S. pombe and C. glabrata have been calculated to contain 85 CdS pairs in the lattice coated with approximately 30y-EC peptides (Figure 10). The particle size was determined using transmission electron microscopy and powder X-ray analysis. The analysis of the X-ray diffraction patterns was inconclusive in discriminating between a four-coordinate zinc blende and six-coordinate rock salt lattice structure. The presence of a short coherence length (8 A) can be attributed either to internal disorder or to deviation from pure crystallinity. The absorption red edge of the crystallites is located at about 320 inn. The other properties characteristic of semiconductor nanoparticulates such as luminescence with emission near 460 mn, and electron transfer to methyl viologen... 

Ag2S was also effectively stabilized by cysteinyl ligands. These clusters are synthesized using a molar ratio of 2 1 cysteine silver ions upon which stoichiometric amounts of inorganic sulfide were added to nucleate the nanoparticle, with subsequent size-selective precipitation. The resultant nanoparticles had an absorbance shoulder at 300 nm. Further analysis using high-resolution transmission electron microscopy (HRTEM) revealed a particle size of approximately 9.00 2.25 run in diameter. Selected area electron diffraction (SAED) analysis also demonstrates the highly crystalline natme of the product. ... 

For supported metal catalysts, no simple calculation is possible. A direct measurement of the metal crystallite size or a titration of surface metal atoms is required (see Example 1.3.1). TWo common methods to estimate the size of supported crystallites are transmission electron microscopy and X-ray diffraction line broadening analysis. Transmission electron microscopy is excellent for imaging the crystallites, as illustrated in Figure 5.1.5. However, depending on the contrast difference with the support, very small crystallites may not be detected. X-ray diffraction is usually ineffective for estimating the size of very small particles, smaller than about 2 nm. Perhaps the most common method for measuring the number density of exposed metal atoms is selective chemisorption of a probe molecule like H2, CO, or O2. 

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