Chromium Oxide/Alumina Catalysts in Oxidative Dehydrogenation of Isobutane

doi:10.1006/jcat.1998.2203

Journal of Catalysis

Volume 178, Issue 2, 10 September 1998, Pages 687-700

https://doi.org/10.1006/jcat.1998.2203 Get rights and content

Abstract

The chromium oxide-alumina catalysts of the Cr loading varying between 1 and 50 Cr nm⁻²have been characterized by different physicochemical techniques and probe reactions of acido-basic properties and of the catalyst oxygen reactivity. They have been tested in oxidative dehydrogenation, ODH of isobutane. The characterization of the catalysts with chemical analysis, XRD, XPS, and Raman spectroscopy has confirmed the general model of the chromium-oxide/alumina catalysts proposed in the literature. The Cr⁶⁺species of two types: soluble and insoluble in water have been found at low Cr loading, and Cr₂O₃in amorphous and crystalline forms have been observed at higher Cr content. The densities of the Cr⁶⁺species increase with the increase in the total Cr content to constant values observed at 5–10 Cr nm⁻²for the water-soluble Cr⁶⁺species and at 2 Cr nm⁻²for the water-insoluble Cr⁶⁺. The highest densities of the Cr⁶⁺species are 1.6 Cr nm⁻²and 1.0 Cr nm⁻²for the water-soluble and insoluble species, respectively. The total initial activity in the ODH of isobutane and the selectivity to isobutene increase markedly with the increase in the Cr loading up to about 10 Cr nm⁻²and they change only slightly at higher loadings. TOF values referred to the content of Cr⁶⁺species (particularly to water soluble Cr⁶⁺) do not differ considerably, however, in the wide range of the Cr loading from 2–50 Cr nm⁻². This suggests that the dispersed Cr⁶⁺species are involved in the active centres of the ODH of IB. Unsupported chromia is more active and less selective (at comparable conversions) than the chromium oxide-alumina catalysts. The differences in catalytic performance between chromia and alumina supported chromium oxide catalysts are ascribed to lower acidity, higher oxygen bond energy, and lower rate of the oxygen chemisorption in the CrAl catalysts, as indicated by isopropanol decomposition probe reaction, oxygen TPD, TPR of hydrogen, and allyl iodide probe reaction.

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^☆: G. PonceletJ. MartensB. DelmonP. A. JacobsP. Grange

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Regular ArticleChromium Oxide/Alumina Catalysts in Oxidative Dehydrogenation of Isobutane☆

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