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

Coke deposition is commonly identified as the main cause of deactivation for dehydrogenation (DH) catalysts. The VOx-K2O/gamma-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.