Carbides and nitrides are active for a variety of reactions including hydrodesulfurization and hydrodenitrogenation. In addition, some materials in this class have been reported to be tolerant to sulfur. The basis for their sulfur tolerance, however, is not well understood. In this work, we studied the interaction of a variety of organosulfur compounds with early transition metal carbides and nitrides as part of a more comprehensive investigation of the sulfur tolerance of these materials.
The materials were prepared from their corresponding oxide precursors using temperature program reaction methods. The carburization or nitridation was carried out using either a mixture containing 15% CH4 in H2 or NH3, respectively. Interactions of the carbides and nitrides with organosulfur compounds including thiophene, benzohiophene (BT), dibenzothiophene (DBT), and tetrahydrothiophene (THT) were investigated. In addition, solvent effects were examined for benzene, and isooctane. The interactions of carbides and nitrides with thiophene were investigated at different temperatures. Isotherms showed that the adsorption of sulfur compounds on Mo2C and Mo2N was Langmuirian, suggesting that the heat of adsorption did not vary significantly with coverage. The heats of adsorption for thiophene on Mo2N and Mo2C were 30 and 49 KJ/mol, respectively. Characterization indicated that the interaction with sulfur was limited to the surface. These materials showed more affinity to non-aromatic sulfur compounds (THT) as compared to aromatic sulfur compounds. Additional results regarding competitive adsorption and surface characterization of the carbides and nitrides will be described.