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Coating of Pd/C catalysts with Lewis-acidic ionic liquids and liquid coordination complexes – SCILL induced activity enhancement in arene hydrogenation

Lijewski, Martin, Hogg, James M., Swadźba-Kwaśny, Małgorzata, Wasserscheid, Peter, Haumann, Marco
RSC advances 2017 v.7 no.44 pp. 27558-27563
activation energy, catalysts, coatings, coordination compounds, hydrogen, hydrogenation, ionic liquids, liquids, mass transfer, palladium, temperature, toluene
New solid catalysts with ionic liquid layer (SCILLs) were prepared by the coating of heterogeneous Pd/C catalysts with a thin film of acidic liquid: a known chloroaluminate ionic liquid (IL), [BMIM]Cl/AlCl₃, and a recently developed liquid coordination complex (LCC), urea/AlCl₃. Both coatings improved the activity of Pd/C catalyst against toluene hydrogenation; at lower temperatures (40 °C) the IL-SCILL performed better, whereas at 80 °C the LCC-SCILL gave higher conversion. A thin film of ionic liquid proved to be sufficient to increase activity, while larger volumes of ionic liquid resulted in a decrease in activity due to pore blocking and hence mass transport limitations. Kinetic investigations in batch mode revealed a zero order with respect to toluene concentration, a first order in hydrogen pressure, and activation energy of 64.7 kJ mol⁻¹ for the Pd/C catalyst. The SCILL catalysts had slightly lower values of 53.1 kJ mol⁻¹ for [BMIM]Cl/AlCl₃ and 61.4 kJ mol⁻¹ for urea/AlCl₃, respectively.