Browsing by Author "Angeletti, Carlo"

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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.