The graphical abstract depicts ethylene oligomerization over isolated Ni²⁺ sites encapsulated in hollow ZSM 5, eliminating Brønsted acidity to study intrinsic microkinetics. The Cossee-Arlman mechanism is modeled, capturing coordination, insertion, isomerization, and termination steps. Experiments and simulations reveal high selectivity toward 1 butene, with temperature influencing double bond isomerization, while the hollow architecture enhances Ni site stability and suppresses side reactions.

Abstract

We encapsulated Ni nanoparticles in a hollow ZSM-5 zeolite catalyst using the dissolution-recrystallization method to catalyze ethylene oligomerization. Our aim is to engineer an idealized catalyst free of Brønsted acid contributions to kinetics or deactivation, having isolated and encapsulated Ni²⁺–zeolite species, to study the intrinsic oligomerization kinetics on Ni²⁺–zeolite through an experimental and microkinetic standpoint. We proved how the hollow architecture encapsulates both Ni²⁺ and NiO species, being the former significantly more active and selective toward dimerization. A comprehensive microkinetic model, grounded in the Cossee-Arlman mechanism and parameterized using experimental data, provides a detailed understanding of the reaction network on isolated Ni²⁺ sites. The model reveals that while linear butene formation dominates, its selectivity decreases with increasing ethylene conversion, temperature, and pressure, highlighting the contribution of isomerization pathways at elevated temperatures. This study focuses on the method to develop isolated oligomerization sites and then studies the intrinsic microkinetic pathways and rates.