Addition of H2S in the gasification gas stream has been found to improve naphthalene and ammonia conversion over ZrO2 and Y2O3-ZrO2 catalysts, whereas over SiO2-ZrO2 such effect has not been observed. The differences in the properties of the catalysts were studied by spectroscopic (MeOH-DRIFTS) and temperature-programmed methods (H2S-TPD and MeOH-TPSR). Methanol was also used to probe the changes after sulfidation of the catalysts. H2S adsorption sites were found to be different on the ZrO2 and Y2O3-ZrO2 catalysts compared with the ones on the SiO2-ZrO2 catalyst. Sulfur was also found to be more reactive on the ZrO2 and Y2O3-ZrO2 catalysts than on SiO2-ZrO2. It was suggested, that the positive effect of H2S on naphthalene conversion during gasification gas clean-up is connected with the reactions of adsorbed sulfur on their surface. In contrast, on SiO2-ZrO2 the lack of such an effect may be related to limited reactivity of sulfur on the surface. (C) 2011 Elsevier B.V. All rights reserved.