The single-layered morphology of supported MoS 2 -based catalysts—The role of the cobalt promoter and its effects in the hydrodesulfurization of dibenzothiophene Gilles Berhault a, *, Myriam Perez De la Rosa b , Apurva Mehta c , Miguel Jose ´ Ya ´ caman d , Russell R. Chianelli b a Institut de Recherches sur la Catalyse et l’Environnement de Lyon, UMR 5256 CNRS – Universite ´ de Lyon, 2 avenue Albert Einstein, 69626 Villeurbanne cedex, France b Materials Research Technology Institute, University of Texas at El Paso, 500 West University Avenue, El Paso, TX 79968, USA c Stanford Synchrotron Radiation Laboratory, Stanford University, Menlo Park, CA 94025, USA d Department of Chemical Engineering and Center for Nano and Molecular Science and Technology, University of Texas at Austin, Austin, TX 78712, USA 1. Introduction The drastic reduction of sulfur in refinery products has triggered an urgency to improve our knowledge of the intrinsic activity of MoS 2 -based catalysts. Therefore a thorough under- standing of the complex relationship in hydrodesulfurization (HDS) between the morphology of the (Co)/MoS 2 active phase and its catalytic properties is required. Up to now, structure–function relationships in HDS have been developed based on model catalysts only, i.e. non-promoted and non-supported MoS 2 . The anisotropic layered structure and the stacking degree of MoS 2 are two fundamental aspects to explain the observed HDS activity and/or selectivity variations. First, the anisotropic layered structure of MoS 2 significantly impacts the reactivity of the basal and edge planes. The basal planes are formed of completely coordinated sulfur atoms resulting in an almost absolute inertness, while the edge planes possess dangling bonds where the active sites are encountered [1–3]. Therefore, activity is only related to the particle size along the basal direction. Secondly, the stacking degree is known to affect the selectivity of the catalyst. Daage and Chianelli [4] initially developed a model correlating stacking degree and selectivity properties for non-promoted and non-supported MoS 2 catalysts. Two types of sites are distinguished based on their location on the layers: the ‘‘rim’’ sites on the top and bottom layers able to hydrogenate and to cleave C–S bonds, and the ‘‘edge’’ sites located on interior layers able only to cleave C–S bonds. The specific location of ‘‘rim’’ sites on exterior layers is responsible for their hydrogenating character by making possible the h 6 flat adsorption of dibenzothio- phene (DBT), a requirement for this hydrogenation step [5]. Recently, using scanning tunneling microscopy (STM), Lauritsen et al. [6] have proposed new interpretation based on the observation of new catalytic features called ‘‘brim sites’’ on MoS 2 nanoclusters. These so-called ‘‘brim’’ sites exhibiting a metallic character are present on sites immediately adjacent to the edges of the MoS 2 Applied Catalysis A: General 345 (2008) 80–88 ARTICLE INFO Article history: Received 10 January 2008 Received in revised form 17 April 2008 Accepted 20 April 2008 Available online 2 May 2008 Keywords: CoMo Hydrodesulfurization Cobalt promotion Hydrogenation Support interaction Selectivity ABSTRACT In order to completely resolve the morphology of supported hydrodesulfurization (HDS) catalysts, synchrotron X-ray scattering studies of silica- and alumina-supported MoS 2 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 MoS 2 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 MoS 2 layers are ‘‘rim’’ sites able to perform both hydrogenation and C–S bond cleavage steps. Moreover, the complete determination of the morphology of these catalysts allowed correlation of structural and catalytic properties for both supported MoS 2 and CoMo catalysts. This approach led us to examine the respective influences of the MoS 2 slab morphology and of support interactions on activity and selectivity properties of HDS MoS 2 -based catalysts. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +33 472 44 53 20; fax: +33 472 44 53 99. E-mail address: Gilles.Berhault@ircelyon.univ-lyon1.fr (G. Berhault). Contents lists available at ScienceDirect Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata 0926-860X/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2008.04.034