Nickel Cobalt Thiospinel Nanoparticles as Hydrodesulfurization Catalysts: Importance of Cation Position, Structural Stability, and Sulfur Vacancy

First-row transition metal-based thiospinels are prepared via a one-pot versatile strategy and for the first time investigated as hydrodesulfurization (HDS) catalysts. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy analysis confirm that these thiospinels consist of agglomerated nanoparticles (NPs) and contain multivalent metal cations. Among the sulfides synthesized at 230 degrees C, NiCo2S4 presents the highest thiophene conversion. This high intrinsic activity is found to be correlated with the normal spinel structure with Ni cations located on the tetrahedral sites and Co cations on the octahedral sites. However, the spent NiCo2S4 NPs experience phase transformation because of the relatively low synthetic temperature. Accordingly, six NiCo2S4 samples are prepared in the temperature range of 180-350 degrees C, and their HDS activity increases monotonically with the synthetic temperature, which is attributed to the higher structural stability and more surface sulfur vacancy of the NiCo2S4 NPs prepared at higher temperatures. Notably, the NiCo2S4 NPs synthesized at 350 degrees C exhibit a much higher thiophene conversation of 62.9% than the classic MoS2 catalyst (39.3%) as well as excellent reusability. Our study suggests that the NiCo2S4 thiospinels with high activity and stability can represent a new promising class of industrial HDS catalysts.