Additive-Free Ethylene Dimerization Over Well-Defined Nickel-Zeolite Catalysts.

Ethylene dimerization is a crucial chemical process, which currently relies on organo-metallic catalysis with the assistance of overdosed additives as cocatalysts. Heterogeneous nickel catalysts have been investigated as alternatives for ethylene dimerization, however suffer from low catalytic activity and/or poor 1-butene selectivity. Herein, we report a simple two-step ion-exchange strategy for the preparation of Ni-Mg-Y zeolite containing well-defined coordinatively-unsaturated nickel centers as a promising catalyst for ethylene dimerization. Ni-Mg-Y shows unprecedent performance with 1-butene formation rate of 3.8 × 105 h-1 and 1-butene selectivity of 91.2 %, without the assistance of any cocatalysts. With the combination of advanced characterization techniques and comprehensive theoretical simulations, it has been demonstrated for the first time that the in-situ generated Ni-alkyl motif is the intrinsic active site and ethylene dimerization proceeds dominantly via the Cossee-Arlman pathway. The dynamic hydrogen transfer between ethylene/alkyl ligand and zeolite framework dedicates to the observed catalytic performance.