Catalytic Epoxidation of cis-Cyclooctene over Vanadium-Exchanged Faujasite Zeolite Catalyst with Ionic Liquid as Cosolvent

Introducing ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][NTf₂]) into dimethylformamide (DMF) as a cosolvent remarkably promoted the catalytic epoxidation of cis-cyclooctene over vanadium-exchanged faujasite zeolite catalysts (V-X), using tert-butyl hydroperoxide (TBHP) as the oxidant. The XRD spectra and SEM images show a certain destructive effect of IL on the zeolite support, while the UV-vis and UV-Raman results revealed the preserved local coordination of vanadium sites of the V-X catalyst during the reaction. The ²⁹Si MAS NMR along with ICP and XPS characterizations further illustrated the specific interaction between [emim][NTf₂] and the zeolite support as well as the vanadium site. The enhanced catalytic performance was mainly attributed to the ability of [emim][NTf₂] to form hydrogen bonds with byproduct t-butanol and consequently free the vanadium active sites for substrate adsorption during the reaction. It was also proposed that the activation energy of the kinetically relevant step was decreased in the weak acidic environment offered by the imidazolium cation of [emim][NTf₂].