Transition-metal chelates are good catalysts for the electrochemical reduction of oxygen, and their activity can be further improved by heat treatment. The present EXAFS study of 5,10,15,20-tetra-(p-chlorophenyl)porphyrinatocobalt(III) supported on Norit BRX active carbon and heat-treated in dinitrogen at temperatures up to 850 "C shows (i) that upon adsorption the Co chelate remains intact, (ii) that after heating at 550 "C, when the oxygen-reduction activity is at its maximum, all Co is still present in its original (square-planar N4) environment and (iii) that at higher temperatures the CON, part decomposes to form, ultimately, metallic Co, with a concomitant decline in catalytic activity. Metallic Co dissolves in 4 mol dm-3 H,S04, but reacts in 4 mol dm-3 NaOH to give an oxyhydroxide, which is thought to have a capacity for reducing oxygen electrochemically.
The use of isotope dilution analysis (IDA) in combination with inductively coupled plasma mass spectrometry (ICP-MS) is discussed. In particular, theoretical calculations are presented on the precision and accuracy attainable in the relatively high elemental concentration range. The results of these calculations have been applied to the determination of the amount of Re and Pt on two types of catalysts, with the intention of validating high-precision wet-chemical analysis methods developed for these systems. Both for Re and for Pt the results of the IDA using ICP-MS and the wet-chemical methods were in excellent agreement. Furthermore, for Pt, different amounts of spike material were used to investigate whether the calculations correlate with the experimental data. The results show the value of the theory in predicting the precision and accuracy attainable for a specified amount of spike material.
Absolute experimental cross sections are presented for elastic differential scattering of electrons by molecular hydrogen at impact energies between 100 and 2000 eV and at scattering angles between 5 and 50 degrees . The results are compared with the relative experimental cross sections of previous experiments and with the data of different theoretical calculations. Total elastic cross sections are considered as well. The present absolute molecular hydrogen cross sections, together with the 100 and 200 eV ratio measurements of the differential elastic cross sections of H2 and H of Lloyd et al. (1974) were used to obtain a new set of absolute elastic cross sections for atomic hydrogen. These experimental data are compared with the absolute experimental sections obtained by Williams (1975) and with theory.
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