Catalytic Properties of Single Crystal Metal Sulfides  

Metal sulfide materials are used extensively in the petroleum processing industry as catalysts for the removal of organosulfur compounds from sour crude oil. Although metal sulfide catalysts have been used for some time, there is still a great deal of uncertainty surrounding the catalytic mechanisms of organosulfur compounds on sulfide surfaces. The catalytically active material in these hydrodesulfurization catalysts is cobalt-promoted molybdenum disulfide (MoS2).  

A common way to investigate catalytic mechanisms on surfaces is to use surface science tools to probe the reaction pathways on clean surfaces in ultrahigh vacuum. Unfortunately, MoS2 preferentially grows large <0001> planes that have been reported to be unreactive towards aromatic organosulfur compounds. However, these surfaces are catalytically active towards nonaromatic organosulfur compounds. We have been examining the decomposition chemistry of selected thiols (R-CH2SH), dithiols (SH-R-SH), and cyclic sulfides on specially prepared, catalytically active single crystal surfaces of MoS2(0001).  
  

Organosulfur Decomposition Pathways on Carbon-Modified Molybdenum Surfaces  

Very high catalytic activity for the desulfurization of organosulfur molecules has been observed on molybdenum carbide-based materials. In this study, we are examining the decomposition of selected organosulfur molecules on selectively carbided Mo(110) surfaces. Surface science tools, such as TPD and HREELS, can be used to characterize the surface intermediates and reaction products occurring during decomposition reactions. This study should show the effects of small amounts of surface carbon on the types and yields of reaction products obtained.