Browsing by Author "Pepe, Franco"

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    Structure and catalytic activity of CoxMg1–xAl2O4 spinel solid solutions. Part 2.—Decomposition of N2O
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Angeletti, Carlo; Pepe, Franco; Porta, Piero
    The catalytic decomposition of N2O was studied on spinel catalysts of general formula CoxMg1–xAl2O4(x= 0 → 1). The bulk distribution of Co2+ ions is predominantly tetrahedral with a small fraction of Co2+ in octahedral symmetry. It is shown that the octahedral coordination of Co2+ allows a catalytic activity larger than that attributable to tetrahedral coordination. The results also indicate that the surface Co2+ distribution is different from that found in the bulk by X-rays. The influence of the matrix on the activity is discussed in terms of surface—oxygen bond strength and a comparison is made with MgO- and ZnO- based catalysts.
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    Structure and Catalytic Activity of CoxMg1_YA12O4 Spinel Solid Solutions Part 1.—Cation Distribution of Co2+ Ions
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (12), 1977) Angeletti, Carlo; Pepe, Franco; Porta, Piero
    The cation distribution in CoAl2O4 and in several CoχMg1–χAl2O4 solid solutions with χ ranging from 0.05 to 0.5 has been studied by magnetic susceptibility, reflectance spectroscopy, lattice parameter variation and analysis of some X-ray reflections whose intensities are particularly sensitive to variation in cation positions. The results show that all specimens have the cobalt ions in a predominantly tetrahedral distribution and that there is a change towards a random cation distribution when the preparation temperature is increased from 1073 to 1473 K. The fraction of Co2+ ions in tetrahedral sites, α, is equal to 0.82 and 0.77 for the CoAl2O4 spinel prepared at 1073 and 1473 K, respectively. The X-ray results show, moreover, that α does not vary significantly with composition for χ varying from 1.0 to 0.1. For the most dilute cobalt solid solution (χ= 0.05), however, the value of α is lower; this trend is observed in both series of specimens prepared at different temperatures and may be explained in terms of anion–anion contact effects.
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    Structure and Catalytic Activity of Iron Oxide and Magnesium Oxide Solid Solutions: Part 3- E.S.R. Characterization
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (1), 1977) Cordischi, Dante; Pepe, Franco; Schiavello, Mario
    Magnesium oxide + iron oxide, fired both in air and in a reducing atmosphere, and magnesium oxide + iron oxide + lithium oxide (up to 1 % atomic Fe) were investigated by e.s.r. spectroscopy. The effects of outgassing at various temperatures and of N2O decomposition on the e.s.r. spectra are discussed in terms of surface redox processes. The incipient formation of the spinel phase, MgeFe2O4, and its precipitation, at the highest outgassing temperatures adopted, were readily studied by the e.s.r. technique. The hypotheses previously proposed on the modification of the catalyst solid state, occurring during N2O decomposition and/or in the vacuum treatment, are confirmed by the present study. Further details are also given.