CENTRO DE INVESTIGACION Y DESARROLLO EN CIENCIAS APLICADAS "DR. JORGE J. RONCO"
Unidad Ejecutora - UE
Relationship Between Sulfidation and HDS Catalytic Activity of Activated Carbon Supported Mo, FeMo, CoMo and NiMo Carbides
PUELLO POLO, ESNEYDER; AÍDA GUTIÉRREZ-ALEJANDRE; GEMA GONZA´LEZ; JOAQUÍN L. BRITO
Año: 2010 vol. 135 p. 212 - 212
Temperature-programmed sulfiding (TPS) and temperature-programmed reduction of the sulfided catalysts (TPR-S) have been employed to evaluate Mo, FeMo, CoMo and NiMo carbide catalysts supported on activated carbon (AC). The carbides were prepared by carbothermal hydrogen reduction from co-impregnated precursors, and submitted to presulfiding prior to HDS. Samples of passivated catalysts prepared from the sulfates of Fe and Co contained variable amounts of sulfur, as shown by XPS and elemental analysis, while all samples showed increased sulfur contents after HDS. The TPS traces (up to 400ºC) of the Mo and CoMo samples exhibited two H2S consumption peaks, the first one starting at 100 _C and the second within the 400 ºC isothermal region, located immediately after a H2S production peak centered at 400ºC for Mo and at 340ºC for CoMo. The FeMo and NiMo carbides exhibited a broad H2S consumption signal between 100 and 400ºC. The low temperature signals can be attributed to reduction of Mo(VI) oxide into Mo(V) or Mo(IV) sulfides, while the broad, higher temperature band is assigned to further reduction to the fully sulfided surface species. The TPR-S spectra showed three H2S evolution peaks, where the area of the first peak (assigned to reduction of sulfur species adsorbed on coordinatively unsaturated edge/corner sites) follows the order CoMo » NiMo ~ Mo > Fe Mo, which fully agrees with the order of HDS activities at steady state. Elemental analysis of the pre-sulfided AC support suggest that a large part of the sulfur consumed in sulfiding the catalysts is retained as elemental sulfur within the microporous structure of the support, although HRTEM observations confirm that MoS2-like structures are present in these samples. These results reinforce the importance of sulfided surface phases in HDS on carbides of transition metal catalysts.