Mechanochemical regulation of the nickel species coordination environment on Ni/Beta catalysts to enhance propylene dimerization

Abstract

Propylene oligomerization over nickel-based catalysts has been developed as an attractive route to produce high-value fine chemicals and clean fuels. In this work, the coordination environment of nickel species on high-loading Ni/Beta catalysts is successfully regulated by mechanochemistry, exhibiting a remarkable promotion in activity for propylene dimerization. The optimized ball-milled catalyst with rich four-coordinated nickel species exhibits a higher initial rate of 139.6 molC3=/(molNi·h) than the conventional impregnated catalyst (57.5 molC3=/(molNi·h)). Mechanochemistry induces a strong metal-support interaction by transforming more Ni species into the zeolite channel to generate four-coordinated Ni cations, boosting the adsorption and activation of propylene. Additionally, in-situ Fourier Transform Infrared experiments reveal that propylene dimerization complies with the Cossee-Arlman mechanism via the initial π-adsorption of propylene instead of σ-adsorption. The steric hindrance of the Ni-alkyl intermediate is critical for product selectivity, driving the dimer distribution away from thermodynamic equilibrium and resulting in preferential 1,2-insertion and 2,2-insertion products.