(683h) Influence of Carbonaceous Deposits on the Ferrierite Structure and Reactivity for the Skeletal 1-Butene Isomerization

Extending the catalyst lifetime can greatly reduce the costs of industrial processes. In this work, we focus on the deactivation of ferrierite (FER) during the butene isomerization of 1-butene to iso-butene. Butene isomerization inevitably experiences carbon deposition (“coking”), which is simultaneously beneficial, by potentially exhibiting a catalytic effect, and detrimental, by gradually deactivating the catalyst. While reactivity data have been reported extensively for high time on stream (TOS > 100 h), a rigorous study of structural catalyst transformation and deposit formation over a wide TOS range is lacking. Connecting these characterization results with reactivity data allows us to generate time-dependent structure-property relationships.

The change in the crystalline unit cell volume, captured by X-ray diffraction (XRD) and Rietveld refinement, correlates with the activity and selectivity behavior of FER. A rapid and significant expansion in the first 24 h on stream was observed, where the catalyst exhibits rather unselective behavior and most carbonaceous deposits form. This was followed by a slow, subtle contraction over the remaining 180 h, when the performance gradually decreased due to coking. To invert catalyst deactivation, oxidative and reductive regeneration will be addressed. The changing unit cell volume is explained by a temperature-induced phase transformation from a Pnnm phase to an Immm phase at ~130 °C, which is fully reversible upon cooling. In our samples however, the Immm phase remains observable at room temperature after the reaction, indicating that coke depositions at 420 °C “freezes” the zeolite in the high-temperature configuration. After coke combustion, the structure reverted to the original Pnnm phase. Interestingly, the kinetic data reveal an improved stability of regenerated FER compared to unreacted FER, indicating a promoting effect of certain carbonaceous species. A revised model for the reaction mechanism based on these new insights will be discussed.