Low-temperature synthesis of mixed NiMo sulfides: structural, textural and catalytic properties

Abstract

Unsupported NiMo sulfide catalysts are prepared by an original coprecipitation technique performed at low temperature. Studies by several surface investigation techniques (X-ray diffraction, electron microscopy, O 2-chemisorption, and X-ray photoelectron and ion-scattering spectroscopy) provide a good qualitative picture of these catalysts. The existence of an NiMoS mixed phase is observed over the whole range of composition. This MoS 2-like structure is supported on Ni x S y if Ni/(Ni+Mo) > 0.25, resulting in an enhancement of catalytic activities (on hydrogenolysis and hydrogenation). These results are discussed with respect to the geometrical model of hydrotreating catalysts. This work points out the extreme importance of the degree of exposure of active edges of the NiMoS phase on the overall activity.