Hydrogenation of naphthalene to decalin at low temperatures (140-240 degrees C) was studied over highly loaded sulfided NiMo, NiW, and NiMoW catalysts with a supported NiMo/-gamma-Al2O3 catalyst as comparison. The NiMo, NiW, and NiMoW catalyst precursors were synthesized by hydrothermal reactions, and the corresponding highly-loaded catalysts were made by mixing the precursors with an alumina gel. The catalyst precursors, oxide and sulfided highly-loaded catalysts were characterized by XRD, N-2 adsorption desorption, SEM, and TPR techniques. A highly crystalline phase of ammonium nickel molybdate was detected on the NiMo precursor, and the NiW precursor exhibited sharp XRD peaks attributed to a phase of hydrated tungsten oxide. Typical Ni3S2 and MoS2/WS2 nanoparticles were observed over the sulfided highly-loaded catalysts, and a main reduction peak was detected due to nickel sulfide as revealed by TPR. Catalytic results showed that more than 99.0% of naphthalene was hydrogenated over the sulfided highly-loaded catalysts at 200 degrees C or higher temperatures, with a very high selectivity to decalin (more than 99.9%) during the same temperature regions over the NiMo and NiMoW catalysts. As a comparison, the reference NiMo/gamma-Al2O3 catalyst showed a moderate hydrogenation activity with a naphthalene conversion of 49.6% and a decalin selectivity of 40.1% at 300 degrees C. The ratios of trans- to cis-decalin on the highly-loaded catalysts and on the NiMo/-gamma-Al2O3 catalysts varied. (C) 2016 Elsevier B.V. All rights reserved.