The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over V2O5/TiO2 and Mo-V-O/TiO2 catalysts. Ammonia reacted either with H2S or SO2, produced from the oxidation of H2S. Water vapor promoted the reaction of ammonia and SO2- Mo-V-O/TiO2 catalysts showed very high H2S conversion without any considerable emission Of SO2. Temperature-programmed studies [temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO)], X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses revealed that the high catalytic performance of Mo-V-O/TiO2 catalysts originated from the high redox capacity of vanadium molybdate phase. (C) 2004 Elsevier B.V. All rights reserved.