Feature ArticleStudy of coke deposited on a VOx-K2O/γ-Al2O3 catalyst in the non-oxidative dehydrogenation of isobutane

- The coke on V-K/γ-Al2O3 catalyst in non-oxidative dehydrogenation was studied.
- The coke progressively transformed from aliphatic into polyaromatic species.
- A process for coke formation was proposed, containing consecutive side reactions.
- The coverage of VOx species by coke leads to decrease of dehydrogenation activity.
- The coke influences the acid content and distribution of V-K/γ-Al2O3 catalyst.

Coke deposition is commonly identified as the main cause of deactivation for dehydrogenation (DH) catalysts. The VOx-K2O/γ-Al2O3 catalysts for non-oxidative DH of isobutane were studied to better understand the formation and nature of coke. Coke deposition influenced VOx species and acid sites, leading to a deterioration of DH performances. The coke was identified as aliphatic and polyaromatic species. As the DH reaction proceeding, the deposited carbonaceous species progressively transformed from aliphatic into aromatic species, with aromaticity increasing. They continuously shift between metallic VOx species and acid sites. Of note is that the aromatic species eventually condense onto the support resulting in polyaromatic and graphitic carbon mixtures. A possible coke generation process was proposed, which contained consecutive reactions such as cracking, oligomerization, and aromatization. The establishment of the coke formation mechanisms and study of the nature of the deposited coke provide guidance for future DH catalyst optimization while reducing coke formation.

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