I. A mechanistic study of the hydrodesulfurization of methanethiol over tungsten disulfide; II. A survey of rare earth sulfides for hydrodesulfurization activity
I. Hydrodesulfurization is a process whereby sulfur bound in organic compounds is removed as hydrogen sulfide, and is important to the control of sulfur dioxide emissions in the combustion of petro- leum and coal fuels. It involves the cleavage of carbon sulfur bonds, and is catalyzed by layered disulfides such as molybdenum and tungsten disulfide. The simplest example is the reaction CH(,3)SH + H(,2) (--->) CH(,4) + H(,2)S. The mechanism of even this prototypical reaction is unclear. In an effort to clarify it, the kinetics of methanethiol hydro- desulfurization over tungsten disulfide at low pressures was established, with partial pressures of methanethiol and hydrogen varied over a hundred fold. The kinetic order in each reactant was positive when its partial pressure was low, negative when its partial pressure was high. The negative order in hydrogen had not been previously seen. The product gases, methane and hydrogen sulfide, each exhibited negative kinetic orders at high partial pressures, zero kinetic orders at low partial pressures. A dual site Langmuir-Hinshelwood type mechanism, which defines one active site as two adjacent edge sulfur vacancies and the second as a neighboring sulfur atom, describes these results quite well;II. Seventeen rare earth sulfides were surveyed for catalytic activity toward methanethiol hydrodesulfurization. These sulfides included both stoichiometric and nonstoichiometric compositions and four different morphologies. In general, nonconductors were inactive and conductors were active. This correlation extended to;the nonstoichiometric (gamma)-phase sesquisulfides which exhibit both insulating and conducting properties; ('1)DOE Report IS-T-1144. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.