(608b) Structural Change of Ferrierite during 1-Butene Isomerization at Extended Time on Stream

Understanding and preventing catalyst deactivation has the potential to reduce the costs of industrial processes by several billion dollars annually. In this study, we focus on the deactivation of ferrierite (FER) during the isomerization of 1- to iso-butene. Zeolite catalyzed butene isomerization suffers from gradual catalyst deactivation due to inevitable carbon deposition. This effect, increasingly relevant at higher times on stream (TOS), results in transient catalyst activity. While reactivity data have been reported extensively for high TOS (>100 h), a rigorous study of transformation of catalyst structure and deposits over a wide TOS range is lacking. Connecting these characterization results with reactivity data allows us to generate time-dependent structure-property relationships.

With increasing TOS, the conversion of 1-butene decreased, accompanied by a change in product distribution, most pronounced in the initial 24 h. The peak performance (i.e. highest isobutene yield and selectivity) over FER occurred between 60 and 90 h. The change in the crystalline unit cell volume, captured by XRD and Rietveld refinement, correlates with the activity behavior of FER. A rapid, significant expansion in the first 24 h was observed, followed by a slow, less prominent contraction. The FER structure exhibited anisotropic behavior, with the a-axis the most affected. The interplay of strain on the FER structure and a phase change, both due to deposits, is expected to be responsible for the observed abrupt change. These structural distortions influence the catalyst activity, by altering the acidity, pore size, and pore shape. Combining this knowledge with future analysis of the coke structure will provide critical understanding necessary to enhance the FER lifetime beyond the current limitation.