Mesostructured silicas as supports for palladium-catalyzed hydrogenation of phenyl acetylene and 1-phenyl-1-hexyne to alkenes

Abstract

The stereoselective hydrogenation of phenyl acetylene and 1-phenyl-1-hexyne at 298 K and atmospheric pressure of H 2 over Pd catalysts supported on mesostructured silica was studied. The catalysts were prepared by the impregnation of HMS and MSU-X silicas with 3-D wormhole framework structures and MCM-41 silica with a 1-D hexagonal framework using a toluene solution of Pd(acac) 2 to obtain a metal content close to 1 wt.%. All the supports were characterised by nitrogen adsorption–desorption isotherms at 77 K and XRD. The catalysts were characterized by H 2 chemisorption and TEM measurements. The reactions were found to be zero order with respect to the phenyl acetylene and 1-phenyl-1-hexyne concentration. Each catalyst presented a different catalytic performance. The 1%Pd/HMS catalyst was the most active in comparison with the 1%Pd/MSU-X and 1%Pd/MCM-41 catalysts. This superior performance in the case of the HMS support was attributed to the presence of interconnected framework channels and textural mesoporosity that can increase the accessibility of the Pd centers to a greater extent than the more monolithic MSU-X and MCM-41 supports. All catalysts displayed high selectivity to styrene and cis-1-phenyl-1-hexene compounds.