EFFECT OF MO LOADING OF MOS2/GAMMA-AL2O3 ON DIENE HYDROGENATION - EVIDENCE OF AN ELEMENTARY ENSEMBLE SITE

Hydrogenation of alkadienes has been performed at relatively low temperature (323 K) and atmospheric pressure on a series of MoS2/γ-Al2O3 catalysts with contents ranging from 2.3 to 15.7 wt% Mo. After sulfidation the solids were treated at various temperatures under H2 for creating different degrees of unsaturation of the MoS2 slabs and then tested. The maximum of hydrogenating power is obtained for the same treatment temperature (823 K) under H2 whatever the Mo loading. As this treatment temperature has been correlated in a previous study on MoS2/γ-Al2O3 (9.2 wt% Mo) (A. Wambeke et al., J. Catal. 109, 320 (1988)) with-the presence of a maximum of three coordinatively unsaturated (CUS) Mo ions located in the (1010) edge plane of the MoS2 slab, this correlation applies well whatever the considered Mo loading. Moreover, the product distribution has been analyzed as a function of treatment temperature and Mo loading and attributed to different structures of sites corresponding to "elementary ensembles" constituted by at least two Mo ions with various S and anionic vacancy environments. © 1991.