Liquid-phase hydrogenation over palladium catalysts supported on sol-gel-derived silica

Abstract

The characteristic and catalytic properties of different silica supported palladium catalysts were investigated and compared in term of catalytic activities for liquid-phase hydrogenation of phenylacetylene, styrene selectivities and catalyst deactivation. Catalysts were prepared by two different methods, ion-exchange and impregnation. It was found that the sol-gel derived silica supported palladim catalyst prepared by ion-exchange method formed palladium silicade. From catalytic activities and selectivities study, the palladium catalysts supported on the sol-gel derived silica prepared by both methods exhibited better performances compared to those supported on commercial silica with the palladium silicide showed the best performance. Moreover, the effects of solvents on catalytic activity of Pd/SiO[subscript 2] catalysts in liquid-phase hydrogenation were investigated using cyclohexene as a model reactant. The solvents used were benzene, heptanol, n-methyl phrolidone (NMP) and supercritical CO[subscript 2]. In the cases of using organic solvents, the hydrogenation rates depended on polarity of the solvents in which the reaction rates in high polar solvents were lower. The use of high pressure CO[subscript 2] can probably enhance H[subscript 2] solubility in the substrate resulting in a higher hydrogenation activity. However, metal sintering and leaching in the presence of high pressure CO[subscript 2] were comparable to those in organic solvents