(682h) Elucidating the Active Sites and Reaction Location during 1-Butene Isomerization

Extending catalyst lifetimes can greatly reduce downtime and cost of industrial processes. In this work, we focus on ferrierite deactivation during the isomerization of 1-butene to iso-butene. Iso-butene is a valuable intermediate to produce rubbers, solvents, and fuel additives. During this isomerization, the catalyst inevitably experiences carbon deposition (“coking”) which in this case is simultaneously beneficial and detrimental. While carbonaceous deposits contribute to catalytic activity for this reaction, they gradually deactivate the catalyst by blocking reactive sites. While consensus exists about the mechanism during reaction startup, the reaction mechanism at the peak catalyst performance is still contested.

Here, we demonstrate the presence of radical species on carbon deposits during 1-butene isomerization. The radical concentration increased as a function of reaction time, which was confirmed through EPR analysis. The addition of the radical scavenger 2,2,6,6-tetramethyl piperidine deactivated the catalyst (Figure 1) and accelerated coke formation. This finding suggest that unpaired electrons influence the catalyst activity.

Finally, we aim to locate the active sites. Nitrogen physisorption results indicate that the micropore volume of ferrierite rapidly decreases upon coking, while butene physisorption suggests that the micropores are inaccessible to small hydrocarbons at any time. Thus, the active sites must be located either on the surface of ferrierite or at the pore mouths. This observation is consistent with our hypothesis that coke-based radicals anchored in the pore mouths are the active catalytic species of butene isomerization. The knowledge gained here is likely applicable to other zeolite catalyzed hydrocarbon conversion reactions.