N‑Hydroxyphthalimide Dissolved in Ionic Liquids Supported on Carbon Nanotubes as a Hybrid Catalytic System for Solvent-Free Aerobic Oxidation of Ethylbenzene.

Carbon nanotubes have gained significant interest in catalysis (as catalysts and catalyst supports) for hydrocarbon oxidation processes. In this study, pristine multiwalled carbon nanotubes and copper-(II) functionalized multiwalled carbon nanotubes were coated with [bmim] cationic ionic liquids (ILs) containing dissolved N-hydroxyphthalimide (NHPI) to produce novel SILP and SCILL-SILP hybrid catalytic systems, respectively (SILP: supported ionic liquid phase and SCILL: solid catalyst with an ionic liquid layer). The catalytic activities of the produced systems were investigated for the solvent-free oxidation of ethylbenzene (EB) (80 °C, 0.1 MPa, 6 h) using molecular oxygen as a green oxidant. Among the SILP systems, the 1-butyl-3-methylimidazolium chloride ([bmim]-[Cl])-based SILP system exhibited the highest conversion of EB (12.2 ± 3.1%) with enhanced selectivity (84.1 ± 11.4%) toward acetophenone (AcPO). The catalytic activity of the SILP system increased with increasing lipophilicity of the alkyl group in the IL cation. Conversely, among the SCILL-SILP systems, the highest conversion of EB (22.6 ± 1.2%) was achieved using 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)-imide ([bmim]-[NTf2]) as the IL phase. Recyclability and reusability studies showed that the catalytic activities of the SILP and SCILL-SILP hybrid systems generally decreased in the subsequent cycles, except for 1-butyl-3-methylimidazolium octyl sulfate ([bmim]-[OcOSO3])-based catalytic systems, which were relatively stable.