SILCA – supported ionic liquid catalysts for fine chemicals

Various ionic liquids (ILs), together with Pd-metal species were immobilized on a high-surface area, structural active carbon cloth. The resulting SILCA (supported ionic liquid catalyst) catalysts were studied in the production of fine chemicals, i.e. in the hydrogenation of unsaturated aldehydes, citral and cinnamaldehyde. These model molecules are challenging ones, due to the possibility of several parallel and consecutive reactions that can occur, depending on the experimental conditions and the nature of the catalyst. In this paper we illustrate the feasibility of altering the selectivity profiles, not only by means of altered reaction conditions but also by variation of the nature of the IL present in the catalytic layer. The catalysts were characterized by means of, e.g. nitrogen physisorption, XPS as well as FESEM and EFTEM. The results revealed that Pd derived from a Pd(acac)₂-precursor, initially dissolved into the ionic liquid, undergoes a change of oxidation state from Pd²⁺ to Pd⁴⁺, regardless of the ionic liquid in question. However, upon decomposition of the precursor, at 373 K, under H2-flow, a transition to either Pd⁺ or Pd⁰ occurred, indicating the formation of catalytically active Pd complexes or nano particles, respectively.