Kinetic Modeling of Ethene Oligomerization on Bifunctional Nickel and Acid β Zeolites

Bifunctional catalysts are challenging to model because there are two active sites capable of unique intermediates and reaction types. Nevertheless, they are versatile catalysts because the relative number of both active sites can be tuned to alter rate and selectivity in response to variation in feed compositions. In this work, a microkinetic model of ethene oligomerization on a Ni-H-β zeolite catalyst was developed based on nickel and Brønsted acid reaction families, with kinetic parameters estimated using transition-state theory, Evans-Polanyi relationships, and thermodynamic data. Species lumping allowed for the formation of products of high molecular weight at high conversion to be captured in the model while avoiding network truncation effects. The reaction mechanism culminated in a complex model describing the formation of C2-C12 products that accurately predicted three published experimental investigations using Ni-H-β (10 unique experiments) up to about 30% conversion. The agreement between the experiment and model predictions demonstrates the model's broad applicability and robustness. Ni sites produce linear alkenes of even carbon number, while Brønsted acid sites catalyze further oligomerization, cracking, and isomerization to broaden the product distribution. The model was used to probe potential experimental conditions and catalyst properties, without extrapolation, allowing for a better understanding of the effect of common experimental parameters (space time, temperature, pressure, Ni wt %) on reaction flux and selectivity to desired products, demonstrating the model as a powerful tool in catalyst and process design.