On the role of co-cations in nickel exchanged LTA zeolite for butene dimerization

Partially Ni²⁺ exchanged Li⁺, Mg²⁺, Ca²⁺ and Na⁺ LTA zeolites were investigated for 1-butene dimerization, all showing selectivities higher than 90% into n-octenes and methylheptene isomers. The presence of the co-cations influences the rate of 1-butene double bond isomerization, while the Ni concentration determines the rates of dimerization. With higher electronegativity of the co-cation, the relative rate of isomerization increased, increasing so the selectivity to branched dimers. The higher Sanderson electronegativity of Li⁺ and Mg²⁺, with respect to Na⁺, is hypothesized to better stabilize the π-allyl Ni-complex-intermediate during butene isomerization. In consequence, the selectivity of alkene dimerization on Ni-exchanged zeolites can be tailored by acid-base properties of the alkali and alkali-earth cations.