Effect of the activation process on thiophene hydrodesulfurization activity of activated carbon-supported bimetallic carbides

PUELLO POLO, ESNEYDER; JOAQUÍN L. BRITO

CATALYSIS TODAY

ELSEVIER SCIENCE BV

Año: 2010 vol. 149 p. 316 - 320

0920-5861

The effect of passivation and presulfidation after carbiding of activated carbon-supported Fe–Mo, Co–Moand Ni–Mo catalysts on their thiophene HDS activity was evaluated. Catalytic precursors were preparedby co-impregnation of the support with solutions of ammonium heptamolybdate and the promotornitrates or sulfates. Carbiding was achieved by means of the carbothermal method, employing pure H2 asreductant and the support as the carbon source. Carbided samples were submitted to one out of threetypes of procedures before HDS tests: (a) passivation at room temperature followed by presulfiding; (b)presulfiding (no passivation); and (c) neither passivation nor sulfiding before HDS. Samples of passivatedcatalysts prepared from the sulfates of Fe, Co or Ni contained variable amounts of sulfur, as shown by XPSand elemental analysis, while XRD showed only metals andmixed Fe3Mo3Cor h-M6Mo6C2 (M55Co, or Ni)phases. The nitrate-derived catalysts only presented b-Mo2C and metals (XRD). Sulfur containingcatalysts showed high initial activities although deactivate strongly during the first 40 min on thereaction stream, while the unsulfided nitrate-derived samples showed a more stable behavior and loweractivities during the 2–3 h of testing. In general, samples submitted to passivation followed bypresulfiding showed the higher steady state activities and those neither passivated nor sulfided were theless active. The results show the benefits of a passivating treatment on these carbon-supported catalysts,and point out to the importance of sulfided surface phases in HDS on carbides of transition metalcatalysts.