Kinetic Modeling of Ethene Oligomerization on Bifunctional Nickeland Acid β Zeolites

Bifunctional catalysts are challenging to model becausethere are two active sites capable of unique intermediates and reactiontypes. Nevertheless, they are versatile catalysts because the relativenumber of both active sites can be tuned to alter rate and selectivity inresponse to variation in feed compositions. In this work, a microkineticmodel of ethene oligomerization on a Ni-H-beta zeolite catalyst wasdeveloped based on nickel and Bronsted acid reaction families, withkinetic parameters estimated using transition-state theory, Evans-Polanyi relationships, and thermodynamic data. Species lumpingallowed for the formation of products of high molecular weight athigh conversion to be captured in the model while avoiding networktruncation effects. The reaction mechanism culminated in a complexmodel describing the formation of C2-C12 products that accuratelypredicted three published experimental investigations using Ni-H-beta(10 unique experiments) up to about 30% conversion. Theagreement between the experiment and model predictions demonstrates the model's broad applicability and robustness. Ni sitesproduce linear alkenes of even carbon number, while Bronsted acid sites catalyze further oligomerization, cracking, and isomerizationto broaden the product distribution. The model was used to probe potential experimental conditions and catalyst properties, withoutextrapolation, allowing for a better understanding of the effect of common experimental parameters (space time, temperature,pressure, Ni wt %) on reactionflux and selectivity to desired products, demonstrating the model as a powerful tool in catalyst andprocess design.

Automated summary

In this study, a microkinetic model of ethene oligomerization on a Ni-H-beta zeolite catalyst was developed, allowing for the adjustment of relative numbers of active sites to alter reaction rate and selectivity. The model accurately predicted experimental results and demonstrated its significance in catalyst and process design.