Pd Nanoparticles Immobilized on Molecular Sieves by Ionic Liquids: Heterogeneous Catalysts for Solvent-Free Hydrogenation

摘要

Ionic liquids (ILs) are attractive, environmentally acceptable solvents because they have a very low vapor pressure and can be used to replace volatile organic solvents. ILs are good solvents for a wide range of inorganic, organic, and polymeric molecules and have been successfully used as solvents in many reactions. Although the ability of biphasic catalysis in ILs has been successfully demonstrated, the chemical industry still prefers heterogeneous catalytic systems because of their ease of separation and the possibility of using a fixed-bed reactor. Furthermore, the use of a biphasic reaction system requires a large amount of IL, and on the basis of economic criteria and possible toxicological concerns, it is desirable to minimize the amount of utilized IL in reaction processes. Recently, Mehnert et al. reported a method for the immobilization of homogeneous Rh~+-based catalyst in an IL phase onto silica gel using a small amount of IL, which was used for hydrogenation and hydroformylation reactions. In their novel approach the IL layers on silica gel served as the reaction phase, in which the homogeneous Rh~+-based catalyst was dissolved.