Pd(ii) immobilized on mesoporous silica by N-heterocyclic carbeneionic liquids and catalysis for hydrogenation

Abstract

In this work we synthesized Pd(II) immobilized on mesoporous silica by N-heterocyclic carbene (NHC) ionic liquids (ILs) with different alkyl chain lengths. The catalysts were characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), low-angle X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and nitrogen sorption. The catalysts were used for the hydrogenation of alkenes and allyl alcohol. The results indicated that the catalysts were very active, selective, and stable. The selectivity for the hydrogenation of allyl alcohol to 1-propanol increased with the increase of the alkyl chain length of the ILs. The effect of supercritical CO₂ (scCO₂) on the hydrogenation of allyl alcohol was also studied, and it was demonstrated that scCO₂ could enhance the selectivity of the reaction considerably. The XPS study showed that the valence of Pd(II) remained unchanged under hydrogenation conditions.