ACTIVITY AND SELECTIVITY OF PALLADIUM CATALYSTS DURING THE LIQUID-PHASE HYDROGENATION OF PHENOL - INFLUENCE OF TEMPERATURE AND PRESSURE

Two series of highly dispersed palladium catalysts supported on alumina have been prepared by adsorption from solution, with palladium contents varying from 0.25 to 2.0 wt%. The first series was calcined at 773 K for 4 h in air, whereas the second series was just heated at 423 K for 1 h in nitrogen, before reduction. Complete dispersion of the metal has been found for the calcined catalysts, and metal dispersion was favored with low palladium contents for the noncalcined catalysts. The kinetic behavior of the catalysts has been analyzed for the liquid-phase hydrogenation of phenol in a stirred tank reactor, ensuring a chemically controlled regime for stirring speed above 750 rpm and catalyst particle below 0.08-0.16 mm in the studied conditions. Despite their higher metallic dispersion, the calcined catalysts presented lower activity than their corresponding noncalcined catalysts. The influence of hydrogen partial pressure on activity showed a reaction order of 2. The apparent activation energy resulted in 56.8 kJ mol-1. Selectivity to cyclohexanone was found to be very high for all experiments.