Effect of chlorine on the performance of Cr-K/?-Al2O3 catalyst for n-hexane dehydrogenation

Dehydrogenation of n-hexane on Cr-K/?-Al2O3 catalyst can produce n-hexenes and benzene efficiently, while the catalyst deactivates rapidly. This work discovers that introducing an appropriate amount of Cl (NH4Cl) to the Cr-K/?-Al2O3 catalyst can significantly improve catalytic activity and enhance stability, which is caused by increased proportion of Cr6+ oxides and number of Lewis acid sites, improved dispersion of CrOx and depressed coke deposition. While excessive Cl further increases the acidity of the catalyst, accelerating the side reactions like cracking and isomerization, meanwhile the inactive Cr-Cl species are formed inevitably. Surprisingly, introducing Cl in the form of KCl can effectively avoid these negative influences owing to the strong interaction between Cl and K. For 13 wt%Cr-2.5 wt%KCl/?-Al2O3 catalyst, 61.2 wt% of n-hexane conversion, 93.1 wt% of selectivity to dehydrogenation products can be achieved, in which the selectivities to n-hexene and benzene are 20.4 wt% and 70.1 wt%, respectively.