Selective hydrogenation of cinnamaldehyde catalyzed by palladium nanoparticles immobilized on ionic liquids modified-silica gel

In this paper, preparations of supported Pd catalysts by immobilization of Pd(OAc)2 on silica gel that was modified by N-3-(-3-triethoxysilylepropyl)-3-methylimidazolium based ionic liquids ([(TESP)MIm][X], X = Cl−, NO3-, BF4-, and PF6-), and together with their catalytic applications for hydrogenation of cinnamaldehyde, were investigated. Depending on the ionic liquid involved, palladium can exist in the form as either palladium carbene complex (X = Cl−) or palladium nanoparticles with size less than 10 nm (X=NO3-, BF4-, and PF6-), which, in turn, lead to different catalytic activities in respect to hydrogenation of cinnamaldehyde. Supported Pd nanoparticles were demonstrated to be high active and reusable catalysts for selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde, due to the stabilization effect of ionic liquids. Keeping the yield of product as 100%, they can be reused for nine times with neither Pd leaching nor activity loss, and offer the value of TON as high as nearly 500,000.