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Publication costs assisted by the Centre National de la Recherche ScientlfiqueThe catalytic activity for isooctane cracking, the surface acidity (using colored indicators and ir spectra of chemisorbed pyridine), and the concentrations in various OH groups (by means of ir and ESR spectroscopies) have been measured for Mg-Y zeolites having various H+ and Mg2+ contents and the same Na+ content. The influence of Mg2+ cations on these properties are discussed in terms of cation location and polarizing field. On the basis of the influence of CO2 at 400 °C, it is suggested that a part of the protons giving rise to the ir band at 3640 cm-1 and the ESR line of 4.1-Oe width may be inhibited for the catalytic cracking by the basic Mg(OH)+ species associated with the 3685-cm-1 ir band. The role played by CO2 in the increase of catalytic properties has been cleared up.

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EPR and XPS have been used to study the redox reaction on CuTh oxide catalysts with different Cu/Th atomic ratios. Apart from the substitutional (S) sites occupied by Cu2+ ions both in the bulk and on the surface of thoria, other Cu2+ ions, occupying different sites on the surface were susceptible to H, and/or 0, treatment at different temperatures. In particular, copper(ii) ion pairs which can be obtained at high copper contents (Cu/Th > 0.01) are formed from one copper(i1) ion, reducible by hydrogen, and another, corresponding to substitutional surface sites (SJ, which remains stable towards hydrogen. The migration of some Cu2+ ions, from sites very susceptible to the cyclic redox treatment, is responsible for the growth of CuO crystallites on the surface of CuTh oxide catalysts.

The growing needs for energy combined with the will to reduce CO2 emissions lead to the increase of the demand for liquefied natural gas (LNG), which will be stably available for many decades to come. Cryogenic materials used for the manufacture of the inner tanks for LNG storage are composed of 9% Ni steel plates with excellent low-temperature toughness, great ductility and crack resistance for a high safety level. To guarantee the reliability and safe operation of large-scale metallic structures exposed to cryogenic temperatures for extended periods, it is important to evaluate structural and mechanical properties of the metal base as well as the welded zone in their own operating conditions in order to prevent damages that could occur.