Hydrodesulfurization by Reduced Molybdenum Sulfides: Activity and Selectivity of Chevrel Phase Catalysts

The hydrodesulfurization activity of reduced molybdenum sulfides was investigated with a series of Chevrel phase, ternary molybdenum sulfides-M_xMo₆S₈. Copper, iron, and cobalt Chevrel phase compounds were prepared at 1200°C by solid state synthesis procedures; the cobalt compounds which were prepared included a range of cobait-to-moiybdenum ratios. Hydrodesulfurization activities for thiophene conversion were measured at 400°C with both pulsed and continuous flow reactors. Hydrogenatlon activities were determined in a pulsed mode at 400°C with 1-butene. The hydrodesulfurization activities of all Chevrel phases were comparable to unpromoted and cobalt-promoted MoS2 model catalysts. However, the hydrogenation activities of the Chevrel phase catalysts were much lower. X-ray diffraction, laser Raman spectroscopy, and X-ray photoelectron spectroscopy were used to analyze the fresh and used catalysts. The bulk Chevrel phase structure was found to be stable under hydrodesulfurization conditions. Higher oxidation states for surface molybdenum atoms were believed to exist for some of the Chevrel phase catalysts after use.