Molecular mechanics study of the interaction of molybdenum disulfide layers with a γ-alumina support in hydrotreating catalysts

Abstract

The non-bonded interactions of MoS₂ slabs supported on γ-Al₂O₃, which are the active phase of a hydrotreatment catalyst, have been modelled by molecular mechanics. Free MoS₂ sheets, containing 39 molybdenum atoms, have been used to test the reliability of the force field.

The edge MoS₂ planes and the support surfaces have been ideally modelled in order to investigate the influence on energy of geometrical parameters such as the orientation of the MoS₂ layered cluster on γ-Al₂O₃ or the distance between the support and the MoS₂ slabs. Whatever the support surface, a single MoS₂ slab lying flat on the support is more stable than a slab perpendicular to the support, however, the energy difference between these two configurations decreases as the number of stacked MoS₂ sheets increases.

The energy of the interactions between two contiguous layers or between a sheet and the exposed surface of the support shows that single sheets lying flat are favoured on the [111] plane whereas the [110] plane induces a stacking of several slabs. The intercalation of one layer between a slab and the support or between two contiguous MoS₂ slabs leads to a screen effect, characterized by a decrease of about two orders of magnitude in the interaction energy of the separated surfaces. This effect increases with the number of inserted sheets.