Jean-Pierre Deloume

ESCA studies of some copper and silver selenides

Abstract Photoelectron and Auger spectra have been obtained for the copper and silver selenides CuSe, Cu 2 Se, Ag 2 Se, and AgCuSe as well as from CuS, Ag 2 O, Ag 2 S, Cu, and Ag. Binding-energy values, chemical shifts, and peak-shapes are reported for the Cu 3 d , Ag 4 d and Se 3 p electrons. Absence of multiplet splitting and shake-up structure is discussed in relation to the magnetic properties. It is shown that chemical shifts are much better revealed in the Auger spectra (Cu L 3 M 4,5 M 4, 5 and Ag M 5 N 4, 5 N 4, 5 ) than in the direct photoelectron ones. In addition the use of the Auger parameter to characterize the series under study is emphasized. Finally the valence-band spectra have been examined and the electronic structures are interpreted.

Study of the redox behaviour of high surface area CeO2–SnO2 solid solutions

Abstract Molten alkali metal nitrites or nitrates and co-precipitation methods were used to prepare CeO2, SnO2 and Ce0.5Sn0.5O2 solid solutions with high surface areas. In the case of the single oxides prepared by the molten salt method, the use of KNO3 leads to better crystallised solids than with KNO2, but on the opposite with higher particle sizes and lower BET surface areas. The same effect was observed for the preparation of the mixed oxides with different resulting structures. With KNO3, the mixed oxide appears as a mechanical mixture of the single oxides, whereas with KNO2, a mixture of amorphous SnO2 and of solid solution with a specific surface area (SSA) of 100xa0m2xa0g−1 has been synthesised, but without evidence of Ce2Sn2O8 pyrochlore formation. The solid prepared by co-precipitation is also well dispersed. Its amorphous structure by X-ray diffraction (XRD) analysis does not allow to conclude to the formation of a solid solution. TPR experiments with hydrogen have shown a beginning of reduction at lower temperature in presence of the solid solution compared to the mechanical mixture of the single oxides. An improved reducibility was also observed with the oxide prepared by co-precipitation, which is in favour of a solid solution formation also in this case. Therefore, the resulting hydrogen consumption obtained when reducing the solid solutions at 450xa0°C is very high and the oxygen storage capacities (OSCs) reach about 1xa0mmol O2 g−1, value higher than those obtained with ceria-zirconia solid solutions. The OSC values were confirmed by oxygen chemisorption on the reduced solid between 25 and 450xa0°C. The full recovery of the initial solid solution was shown by XRD analysis and a second redox cycle has demonstrated the reversibility of the redox properties at this temperature.

X-ray photoelectron emission studies of mixed selenides AgGaSe2 and Ag9GaSe6

Abstract Auger and direct electron specta from crystalline AgGaSe 2 and Ag 9 GaSe 6 have been studied with X-ray photoelectron spectroscopy. It is shown that the AgM 5 N 4,5 N 4,5 and M 4 N 4,5 N 4,5 Auger spectra are more sensitive to the chemical environment than the Ag 3 d direct photoelectron spectra. Furthermore the Auger parameter as defined by Wagner is used in order to characterize the chemical state of these compounds. Last, the XPS spectra of the valence-band region are investigated and chalcogen s and p and noble-metal d bands are clearly identified. The electronic structure of these two selenides does not seem to be determined predominantly by the crystal structure. As a whole, the spectral features are discussed in connection with the character of the chemical bonding and the physical properties of these compounds.

Catalysis assisted characterizations of nanosized TiO2–Al2O3 mixtures obtained in molten alkali metal nitrates: Effect of the metal precursor

Abstract Mixtures of TiO 2 and Al 2 O 3 (0, 5, 10 and 20xa0mol% Al 2 O 3 ) were prepared by reaction of metal salts with molten alkali metal nitrates. The powders are constituted from nanosized anatase crystallites and amorphous alumina. Physico-chemical characterizations reveal the powders to be homogeneous. Ni–Mo sulphide catalysts were elaborated using these powders as supports and tested in the reaction of hydrogenation of tetralin. The decrease of the intrinsic catalytic activity per Mo atom, related to the alumina content, is higher than expected for a regular mixing of oxides, suggesting that alumina coats the anatase particles. On the contrary, it was found that changing the aluminium precursor salt leads to a metastable solid solution which increases significantly the intrinsic activity.

Un nouveau matériau, Ag9GaSe6: Etude structurale de la phase α

Abstract α-Ag9 GaSe6 is cubic, space group F 4 3m , with a = 11.126(2) A and Z = 4. The diffraction pattern at 20°C using Mo K α radiation was collected with an automatic four-circle diffractometer. The structure was determined by beginning from the low-temperature structure (βAg9GaSe6). An anisotropic full-matrix least-squares refinement was performed yielding a final R of 0.063 for the 103 reflections actually measured. The four Ga atoms and eight Se atoms are located on a 16(e) position. All the Gaue5f8Se bonds are 2.366(10) A. The Ag atoms are equally distributed on three sets of positions: two 48(h) and one 96(i). Among the 36 Ag atoms, 24 are bound to 3 Se atoms in an almost planar triangular arrangement (2.43(4)

Reactions of ruthenium(III) and -(IV) chlorocomplexes with nitrogen oxides NO and NO2

Ruthenium chlorocomplexes in the II, III and IV oxidation states are allowed to react with either NO or NO2. The reactions are followed by spectrophotometry and the products are characterized by IR spectra. In any condition the lower oxidation states oxidize to Ru(IV). The dinuclear complex [Ru2OCl10]4− reacts only when the conditions permit its depolymerization. In any case the product of the complexation is a complex of RuNO3+. n nThe reaction with NO2 in 0.5 mol/l HCl gives a complex which is identified as [RuNOCl4NO3]2− which is unstable (versus oxidation) in water. The solution containing HCl 3 mol/l represent a redox limit between Ru(III)/Ru(IV) and N(I), N(II), N(III) as Ru(III) is partially oxidized by NO and Ru(IV) is partially reduced by NO. The systematic oxidation of Ru(III) by NO and, as a consequence, the formation of RuNO3+ from Ru(IV) and NO lead to some reflexions on the electron repartition in this particular entity.

Determination of yttrium in zirconia matrices by atomic absorption spectrometry

A rapid method is described for determining yttrium in solutions containing a large excess of zirconium using atomic absorption spectrometry. Samples are analysed in nitric acid solution, using a spectrochemical buffer which consists of potassium-EDTA and lanthanum to effect maximum absorption. A standard additions technique, in which yttrium solution is added to the sample, is used to avoid the preparation of matrix matched standards. The yttrium absorbance is measured at 410.2 nm using a dinitrogen oxide-acetylene flame. Synthetic solutions show that the procedure is sufficiently accurate to be used for the routine determination of yttrium in refractory oxides containing up to 3 mol-% of Y2O3(5.7%m/m).