Molecular aspects of the H-2 activation on MoS2 based catalysts the role of dynamic surface arrangements

In order to model one of the key steps in hydrosulfurization (HDS), density functional calculations of the dissociation of H-2 on the edges of a Co pr omoted MoS2 (Co-Mo-S) slab have been performed. The results show that the h eterolytic dissociation of hydrogen is not favored, but there appears to ex ist different homolytic pathways with similar activation barriers. It is sh own that the dissociation process couples strongly to flexible sulfur atoms such that dynamic surface reconstructions occur during the adsorption proc ess. By calculating the minimum energy reaction path we find that S atoms a t the edge of the MoS2 slabs can move up to extract one of the Il atoms of the dissociating H-2 molecule and transport it to the other side of the sla b where it diffuses on. Transition metal sulfides constitute an important c lass of heterogeneous catalysts and the active part of many enzymes, and we suggest that the catalytic activity of these systems may be closely couple d to the flexibility of the sulfur ligands. (C) 2000 Elsevier Science B.V. All rights reserved.