A nanostructured form of molybdenum disulfide/dioxide was prepared by a two-step hydrothermal/gas phase reaction. The material was composed of a solid MoO2 core with MoS2+x, crystallites nucleating on its surface. Most of the MoS2+x, consisted of nanowires, which are 14 to 30 nm long and are about one MoS2 unit cell wide. High-resolution electron microscopy (HREM), electron diffraction, energy-dispersive X-ray spectroscopy (EDS), high-angle annular dark-field (HAADF) and X-ray diffraction were used to characterize the structure of the catalysts. The morphology does not depend strongly on the parent oxide, since both samples presented the oxide and sulfide phases; however, the abundance of nanowires depends on the thickness of the original oxide crystal. The catalytic activity and selectivity measurements of the resulting unsupported catalysts are also presented. In both samples, a higher selectivity for hydrogenation over sulfur removal was found. (c) 2005 Elsevier Inc. All rights reserved.