Effects of Pd precursors on the catalytic activity and deactivation of silica-supported Pd catalysts in liquid phase hydrogenation

Liquid phase hydrogenation of 1-hexene under mild conditions has been investigated on a series of silica (SiO2 and MCM-41)-supported Pd catalysts prepared from different Pd precursors such as Pd(NO3)2, PdCl2, and Pd(OOCCH3)2. For any silica support, use of PdCl2 as a precursor resulted in smaller Pd particles, higher dispersion, and consequently higher hydrogenation activities. Supported Pd catalysts prepared from PdCl2 showed greater metal sintering after 5-h batch reaction. However, leaching of Pd was found to occur to a significant degree for the catalysts prepared from Pd(NO3)2 and Pd(OOCCH3)2. The results suggest that deactivation of the silica-supported Pd catalysts in liquid phase hydrogenation is dependent on the palladium particle size with smaller Pd particles being more susceptible to sintering while larger particles are more likely to be leached. An optimum Pd particle size may be needed in order to minimize such loss and enhance Pd dispersion.