Volcano curves relationships between hydrodesulfurization (HDS) or hydrogenation (HYD) catalytic activities and the ab initio calculated sulfur-metal bond energy, E(M-S), descriptor of transition metal sulfides (TMS) have been recently established. Such correlations helping to rationalize and predict the design of heterogeneous catalysts can be intuitively understood in the spirit of Sabatier principle. Similar calculations have also revealed the primary importance to better control the influence of the reaction conditions (P-H2S, P-H2, T) on such periodic trends as well as nature of the active sites. If H2S is generally considered as an inhibitor of HDS or HYD reactions, the inhibiting effect may depend on the nature of the transition metal sulfide (TMS). The observed HDS or HYD activities may thus be affected by the H2S partial pressure. The purpose of the present work is to explore the effect of H2S on the experimental catalytic activities of five relevant gamma-alumina supported TMS in toluene hydrogenation. We have undertaken a systematic kinetic study on gamma-alumina supported Rh, Ru, NiMo, Mo and Cr sulfides catalysts. Two distinct effects of H2S are evidenced. Transition metal sulfides with high and intermediate E(M-S) such as Mo, Rh, Ru and NiMo are inhibited by H2S, whereas the Cr sulfide exhibiting a low E(M-S) reveals an original promoting effect of H2S. (C) 2004 Elsevier B.V. All rights reserved.