EFFECT OF SULFIDING TEMPERATURES ON THE FORMATION OF SULFIDES OF MO/AL2O3 AND COMO/AL2O3

The structures and activities of Mo/Al2O3 and CoMo/Al2O3 sulfided with hydrogen sulfide/hydrogen at various temperatures were studied in the range of temperatures between 573 and 1073 K. The sulfide structures were characterized by electron spin resonance, oxygen chemisorption, sulfur content analysis, temperature-programmed reduction and X-ray diffraction. The thiophene hydrodesulfurization reaction and the ethene hydrogenation reaction were used as probe reactions. As the sulfiding temperature increased, oxo-Mo5+ interacting with alumina in Mo/Al2O3 and CoMo/Al2O3 decreased and finally disappeared at 1073 K. The decrease in oxo-Mo5+ facilitates the formation of crystalline molybdenum sulfide. Cobalt facilitates the formation of molybdenum sulfide weakly interacting with alumina. Cobalt also retarded the aggregation and crystallization of molybdenum sulfide. Cobalt sulfide [spectroscopic splitting factor, g = 2.16, H(PP) (peak-to-peak width) = 200 Gs] was formed when sulfided at 1073 K in CoMo/Al2O3. The rapid decrease in the ratio of activity of CoMo/Al2O3 to Mo/Al2O3 in the thiophene hydrodesulfurization reaction when CoMo/Al2O3 and Mo/Al2O3 was sulfided above 873 K can be explained by the transformation of the sulfide structure.