Abstract
Hydrodeoxygenation (HDO) kinetics of phenol over Ag/TiO2 catalyst was investigated at 415-600 K and 1 atm. The use of oxophilic TiO2 support has improved phenol conversion due to its preferential activation of C-O bond. Product analysis confirmed the occurrence of direct deoxygenation (DDO) and hydrogenation-dehydration (HYD) pathways to produce benzene and cyclohexane, respectively. Both phenol hydrogenolysis and hydrogenation steps are the respective rate-limiting steps for DDO and HYD pathways of phenol HDO over Ag/TiO2. Based on the transition state theory, negative entropy changes of activation during HDO indicated that the HDO reactants formed activated complexes that had more orderly bonding configurations prior to the hydrogenolysis, hydrogenation, and dehydration steps. Under the present conditions, the catalyst was stable after 4 hr of HDO runs and able to be regenerated via H-2-activation and calcination in air at 553 K with at least 98.9% removal efficiency to remove coke deposits and reform Ag metal species after HDO.