Inorganic materials as supports for palladium nanoparticles: Application in the semi-hydrogenation of phenylacetylene

A series of palladium heterogeneous catalysts supported on different inorganic materials were prepared using a palladium colloid and four different supports: γ-alumina (Pd/Al2O3), zeolite Beta (Pd/Beta), MCM-41, and Al-MCM-41. The two last catalysts were synthesized by two different methods of deposition of the metallic nanoparticles: impregnation or in situ synthesis of MCM in the presence of the Pd colloid. These catalysts were evaluated in the partial hydrogenation of phenylacetylene, performed in liquid phase, under very mild conditions (323 K, H2 flow of 30 mL/min, 1 bar pressure). All of the catalysts had very high selectivity toward styrene (around 96%) after total conversion. The activity values were very close to those of the homogeneous catalysts, being much greater for the catalysts obtained by synthesis of the MCM materials in presence of the Pd colloid, for which, the TOF values were fourfold to sixfold greater. The catalysts proved to be reusable; neither the catalytic activity nor the selectivity decreased appreciably after five consecutive cycles of reaction. Moreover, inductively coupled plasma (ICP) analysis confirmed that no Pd leaching from the samples occurred during the catalytic reaction.