THIOPHENE HYDRODESULFURIZATION OVER ALUMINA-SUPPORTED MOLYBDENUM CARBIDE AND NITRIDE CATALYSTS - ADSORPTION SITES, CATALYTIC ACTIVITIES, AND NATURE OF THE ACTIVE SURFACE

Mo2C/Al2O3 and Mo2N/Al2O3 catalysts have been synthesized and characte rized by X-ray diffraction, pulsed chemisorption (CO and O-2) and infr ared (IR) spectroscopy, and temperature programmed desorption (TPD) me asurements. Thiophene hydrodesulfurization (HDS) activities were measu red for alumina-supported Mo carbide and nitride catalysts as well as a sulfided Mo/Al2O3 catalyst, all with a 10 wt% Mo loading. The HDS ac tivities (mu mol Th/mol Mo/s) of the catalysts after 24 h at 693 K wer e found to increase according to the trend sulfided Mo < gamma-Mo2N < beta-Mo2C, and provide further evidence that carbide and nitride catal ysts have the potential to replace sulfided Mo catalysts in commercial HDS reactors. X-ray diffraction analysis of fresh and tested 30 wt% M o2C/Al2O3 and Mo2N/Al2O3 catalysts indicates that the bulk structure o f the carbide (beta-Mo2C) and nitride (gamma-Mo2N) particles is retain ed, while IR spectroscopy of adsorbed CO indicates that the surface of the carbide and nitride particles becomes sulfided under reaction con ditions. A model is proposed for the structure of the active catalytic surface of the alumina-supported Mo carbide and nitride catalysts in which a thin layer of highly dispersed sulfided Mo is present on the s urfaces of the carbide and nitride particles. (C) 1996 Academic Press, Inc.