Effect of the preparation of Ir-Mo/Al_2O_3 sulfide catalyst on activity and HDN/HDS selectivity

摘要

Two series of the mixed Ir-Mo/Al_2O_3 catalysts of different Ir loading (0.1-0.7wt.) were prepared by deposition of Ir_4(CO)_(12) on an oxidic and sulfidic Mo/Al_2O_3 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/Al_2O_3 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/Al_2O_3 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/Al_2O_3 probably protected the Mo phase agginst interaction with Ir_4 (CO)_(12),which could lead to partial formation of MoO_2.It is assumed that both factors improved the reducibility of the sulfur surface species of the MoS_2 phase and contributed in this way to higher catalytic activity.