Catalytic features of new kappa-alumina immobilized thiazolium and imidazolium ionic liquids for esters production

The catalytic behavior of kappa-alumina heterogenized imidazolium hydrogen sulfate and 2-amino-thiazolium hydrogen sulfate sulfate monohydrate ionic liquids (ATHS/к-Al and ImHS/к-Al) were represented in this paper for the first time. For that purpose, acetic acid esterification with butanol (butyl acetate synthesis) was applied as a test reaction. To evaluate the textural properties, surface effects and thermal performance of ATHS/к-Al and ImHS/к-Al catalysts, a number of analytical methods were used: X-ray powder diffraction (XRD), nitrogen adsorption porosimetry (S_BET), X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis/differential scanning calorimetry (TGA/DSC). Important kinetic (activation energy, pre-exponential factor) and thermodynamic (enthalpy, entropy and Gibbs free energy) functions were determined as well. In addition, a plausible reaction mechanism for butyl acetate synthesis was assumed. Results revealed that the synthesized ATHS/к-Al and ImHS/к-Al are mesoporous materials with different nature of the surface active phase-support interaction. Stronger ImHS-carrier interaction than ATHS-carrier was responsible for higher thermal stability of ImHS/к-Al in comparison with ATHS/к-Al. However, kappa-alumina heterogenized ATHS ionic liquid possessed notably more pronounced catalytic activity with respect to ImHS/к-Al system.