Heterogeneous structures in promoted chromia + alumina dehydrogenation catalysts
- 1 January 1977
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 73, 1471-1479
- https://doi.org/10.1039/f19777301471
Abstract
The catalytic activity and various physical–chemical properties (crystallographic phase, specific surface area, electric conductivity, e.p.r.) of alkali metal doped Al2O3+ Cr2O3 catalysts (7.5 mol % Cr2O3) have been compared before and after dissolution of the superficial layers in water. The active promoters (i.e. K, Rb and Cs) extensively segregate from the bulk to the outer layers. A substantial amount of chromium is simultaneously segregated. Some of the segregated alkali metal ions are associated with segregated chromium, and form a chromate in the regenerated (i.e. oxidized) catalyst. The additional activity brought about by the promoters can be explained by the formation of incompletely coordinated Cr3+ upon reduction in isobutane in the first minutes of the catalytic run.Keywords
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