This work investigates the potentiality of the deoxygenation of benzoic acid in the presence of hydrogen as a probe of the reduction state of molybdenum oxide in catalytic processes. On one hand, a complicated hysteresis phenomenon is observed when measuring the conversion of benzoic acid and selectivities to benzene, toluene and benzaldehyde Of Mo8O23 along a cycle of temperatures between 628 and 723 K. On the other hand, Mo8O23 undergoes a reduction to Mo4O11 and MoO2 throughout the catalytic reaction. These results, together with the performances Of Mo4O11 and MoO2 under the same conditions, allow to understand the reduction pathway Of Mo8O23. The proposed pathway fits with that suggested in the literature, thus confirming the deoxygenation of benzoic acid as a promising probe reaction of the behavior of molybdenum based oxides at work. (C) 2004 Elsevier B.V. All rights reserved.