The single-layered morphology of supported MoS₂-based catalysts-The role of the cobalt promoter and its effects in the hydrodesulfurization of dibenzothiophene

In order to completely resolve the morphology of supported hydrodesulfurization (HDS) catalysts, synchrotron X-ray scattering studies of silica- and alumina-supported MoS₂ catalysts have been carried out and compared to results previously reported for their cobalt-promoted counterparts [J. Catal. 225 (2004) 288]. The present study is mainly centered on the structural role of cobalt and of support interactions and on their influence on the morphology and catalytic properties of these transition metal sulfide catalysts. Results showed that cobalt promoter strongly enhances the stacking height of MoS₂ layers. However this effect is counterbalanced by hydrodesulfurization conditions that favor in an opposite way the formation of single slabs. Single slab morphology suggests that the vast majority of the sites on MoS₂ layers are "rim" sites able to perform both hydrogenation and C{single bond}S bond cleavage steps. Moreover, the complete determination of the morphology of these catalysts allowed correlation of structural and catalytic properties for both supported MoS₂ and CoMo catalysts. This approach led us to examine the respective influences of the MoS₂ slab morphology and of support interactions on activity and selectivity properties of HDS MoS₂-based catalysts.