Among a group of silica coformed binary oxide catalysts, the Fe/Mo/SiO2 catalyst performed best for the selective gas-phase nitric acid oxidation of benzene to phenol. The dual functions exhibited by the catalyst, the formation of nitrobenzene and phenol, can be controlled by the atomic ratio of Mo/Fe and the oxidation temperature. With the atomic ratio of Mo/Fe=2.3, nitrobenzene was selectively formed at the lower temperatures (<370 degrees C) and this function was altered to selective phenol formation at higher temperature (>400 degrees C). With the ratio of Mo/Fe = 1.5, phenol was selectively formed at 350-475 degrees C. With the ratio of Mo/Fe = 1.05, a mixture of phenol and nitrobenzene was produced at all temperatures. Blending of 1 mol-% nitrobenzene in benzene remarkably enhanced the phenol yield, and nitrobenzene functions as a promoter for the reaction.