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

The stereoselective hydrogenation of phenyl acetylene and 1-phenyl-1-hexyne at 298 K and atmospheric pressure of H2 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 H2 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.

Graphical abstractThe stereoselective hydrogenation of phenyl acetylene and 1-phenyl-hexyne at 298 K and atmospheric pressure of H2 over HMS, MSU-X, and MCM-41 supported Pd catalysts has been studied. The reactions were found to be zero order concerning the phenyl acetylene and 1-phenyl-1-hexyne concentration. The catalytic behaviour suggests an important effect produced by the differences in the characteristics of the supports. Thus, the 1%Pd/HMS catalyst was the most active compared to 1%Pd/MSU-X and 1%Pd/MCM-41 catalysts, which was attributed to the presence of interconnected channels which can increase the activity in a higher extent compared to straight channels observed in the others support. All catalysts displayed high selectivity to styrene and cis-1-phenyl-1-hexyne compounds. Figure optionsDownload full-size imageDownload as PowerPoint slide