Crystallographically identified

The electronic interaction between the catalyst components is best exemplified by its color and optical spectra. For example, the very active binary catalyst Cu/ZnO = 30/70 has a pitch black color and although it is composed of crystallographically identifiable copper and zinc oxide, its optical spectrum is not a superposition of the spectrum of copper metal and zinc oxide, but rather comprises a very intense continuous absorption band in the visible part of the spectrum that contains no trace of the characteristic... 

Table II. Crystallographically identified cation sites and populations for K-A. The numbers in this table refer to the number of cations per pseudo-unit cell. Deh. is dehydrated, and Hyd. is hydrated. The last entry in the Table is for a. .Na A sample...

The progress on molecular uranium nitrido complexes has also been rather slow and the majority was formed on Nz elimination from suitable U—N3 precursors. " However, compounds 323 and 324 belong to the small class of uranium nitrido compounds actually derived from Nz reduction (Scheme 83). Treatment of the polypyrrolyl complex [(K(dme)][(Etg-calix[4]tetrapyrrolyl)U(dme)] with K[CioH8] under an Nz atmosphere resulted in a mixture of products, from which Gambarotta and coworkers isolated and crystallographically identified a mixed-valent U(V)/U(IV) nitrido... 

Microchemical or ultramicrochemical techniques are used extensively ia chemical studies of actinide elements (16). If extremely small volumes are used, microgram or lesser quantities of material can give relatively high concentrations in solution. Balances of sufficient sensitivity have been developed for quantitative measurements with these minute quantities of material. Since the amounts of material involved are too small to be seen with the unaided eye, the actual chemical work is usually done on the mechanical stage of a microscope, where all of the essential apparatus is in view. Compounds prepared on such a small scale are often identified by x-ray crystallographic methods. 

The crystallization of glassy Pd-Ni-P and Pd-Cu-P alloys is complicated by the formation of metastable crystalline phaf s [26]. The final (stable) crystallization product consists of a mixture of a (Pd,Ni) or (Pd,Cu) fee solid solution and more than one kind of metal phosphide of low crystallographic symmetry. Donovan et al. [27] used transmission electron microscopy (TEM) and X-ray microanalysis to study the microstructure of slowly cooled crystalline Pd4oNi4oP2o- They identified the compositions of the metal phosphides to be Pd34Ni45P2j and Pdg8Ni[4Pjg. 

Solid carbon materials are available in a variety of crystallographic forms, typically classified as diamond, graphite, and amorphous carbon. More recently another structure of carbon was identified—namely the fullerenes which resemble a soccer ball... 

Oldfield TJ. Pattern-recognition methods to identify secondary structure within X-ray crystallographic electron-density maps. Acta Cryst. 2002 058 487-93. 

In catalyst characterization, diffraction patterns are mainly used to identify the crystallographic phases that are present in the catalyst. Figure 4.5 gives an example where XRD readily reveals the Pd reflections in two Pd/Si02 catalysts. 

As illustrated by Eig. 4.13, an electron microscope offers additional possibilities for analyzing the sample. Diffraction patterns (spots from a single-crystal particle and rings from a collection of randomly oriented particles) enable one to identify crystallographic phases as in XRD. Emitted X-rays are characteristic for an element and allow for a determination of the chemical composition of a selected part of the sample. This technique is referred to as energy-dispersive X-ray analysis (EDX). 

With the arrival of new information on the amino acid sequence of various Ca " -ATPase isoforms [8,9,11,32,53-57,295] it became possible to identify the epitopes for the various antibodies, and to relate their positions to the three-dimensional structure of Ca -ATPase emerging from crystallographic studies [90,91,141,142,156,... 

In conclusion, therefore, at least for metal catalysts it will not be justihed to identify crystallographic defects emerging at the electrode surface with the active sites responsible for the catalytic activity of the electrode as a whole. 

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