Vapor phase hydrogenation of phenol over palladium supported on mesoporous CeO2 and ZrO2 Original Research Article

Mesoporous CeO2 and ZrO2 were synthesized using hexadecyltrimethyl ammonium bromide (C16TMABr) as the template. Their physicochemical properties were investigated using X-ray diffraction (XRD) and N2 adsorption–desorption methods. Palladium (Pd) 1–10 wt.% was loaded on the mesoporous CeO2 and ZrO2 by deposition–precipitation method. The Pd metal surface area, dispersion and crystallite sizes were determined by room temperature H2 chemisorption on reduced samples. The catalytic activity of Pd supported mesoporous CeO2 (Pd/CeO2-MS) and ZrO2 (Pd/ZrO2-MS) were evaluated for the first time in the vapor phase hydrogenation of phenol in the temperature range between 160 and 230 °C at atmospheric pressure. The reaction over 3% Pd/CeO2-MS at 180 °C offered cyclohexanone as the major product (about 50%) along with some amounts of cyclohexanol (about 35%) and cyclohexane (about 15%). The influences of Pd loading, temperature, H2/phenol ratio, contact time, and nature of solvent on the catalytic performance were investigated systematically. A 3% Pd/ZrO2-MS offered slightly lower phenol conversion but very high selectivity of cyclohexanone (above 90%). The Pd/CeO2-MS exhibited a stable activity, while Pd/ZrO2-MS underwent deactivation during on-stream operation. Under similar operating conditions, the catalytic performance of Pd/CeO2-MS and Pd/ZrO2-MS was found to be far better than that obtained using MgO, Al2O3 and MgO-Al2O3 derived from hydrotalcites (MgAl-CHT) as supports. The benefit of using mesoporous oxide support to Pd was also demonstrated by comparing the catalytic activity with the activities of commercial oxide supports.