The catalytic conversion of benzoic acid to phenol in the presence of water and oxygen was studied in the vapor phase over nickel oxide on various supports. NiO/SiO2 was the most selective, and the selectivity reached over 50% using iron oxide and sodium oxide modifiers. Ni-Fe oxide prepared by coprecipitation deactivated with time-on-stream, but that prepared using a cellulose templating method was more stable. Benzene was often a significant by-product. Some coupling products were formed, including xanthone, fluorenone, and biphenyl. From deuterium isotope labeling experiments, the hydroxyl group was found to be formed at the carbon next to the one with the carboxylic acid group. (C) 2003 Elsevier B.V. All rights reserved.