Effect of the preparation of Ir-Mo/Al2O3 sulfide catalyst on activity and HDN/HDS selectivity

Two series of the mixed Ir-Mo/Al2O3 catalysts of different Ir loading (0.1-0.7 wt.%) were prepared by deposition of lr(4)(CO)(12) on an oxidic and sulfidic Mo/Al2O3 catalyst. The catalysts were tested in the hydrodesulfurization (HDS) of thiophene (TH) and hydrodenitrogenation (HDN) of pyridine (PY) and characterized by transmission electron microscopy (TEM), temperature-programmed reduction (TPR) and X-ray diffraction (XRD). It was found that Ir addition to a Mo/Al2O3 catalyst had positive effect on the activities in both reactions. A much larger effect was observed when Ir was deposited on the presulfided instead of oxidic Mo/Al2O3 catalyst. In the former case, the mixed catalysts displayed a synergism between Ir and Mo of about 3. We ascribe the higher activities of the catalysts prepared from the presulfided Mo sample to higher dispersion of the Ir sulfide phase. In addition, sulfidation of the Mo/Al2O3 probably protected the Mo phase against interaction with lr(4)(CO)(12), which could lead to partial formation of MoO2. It is assumed that both factors improved the reducibility of the sulfur surface species of the MoS2 phase and contributed in this way to higher catalytic activity. (C) 2003 Elsevier B.V. All rights reserved.