Thermolyse de mélanges de chromates et d'oxalates de métaux alcalino-terreux II. Composés du magnésium |
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Authors: | EG Derouane Z Gabelica R Hubin |
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Institution: | Facultés Universitaires de Namur, Laboratoire de Catalyse, 61, rue de Bruxelles B-5000-Namur Belgique;Université de Liège au Sart-Tilman, Département de Chimie Générale et de Chimie Physique, B-4000-par Liège 1 Belgique |
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Abstract: | The thermolysis of mixtures of chromates and oxalates of magnesium has been studied combining thermal analysis and electron paramagnetic resonance. It is found that both the reduction of Cr(VI) to Cr(III) and that of Cr(VI) to Cr(V) are spontaneous and occur at about 600 and 250°C, respectively, under vacuum. Highly dispersed Cr(V) species are present after activation below 400°C while dispersed Cr(II) species, either as Cr2O3 or as Cr(III) in solid solution in the MgO lattice, are observed above 350 and 550°C, respectively. CO evolved during the decomposition of the oxalate is found to play a major role in the reduction of Cr(V) in Cr(III). Contrarily to the observation on the Ba and Sr homologues, no effect of the carbonate has been found. |
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