Activation of alumina-supported hydrotreating catalysts by organosulfides or H 2 S: Effect of the H 2 S partial pressure used during the activation process Samuel Texier a , Gilles Berhault b, * , Guy Pe ´rot a , Fabrice Diehl c a Laboratoire de Catalyse en Chimie Organique, UMR 6503 CNRS, Universite ´ de Poitiers, 40 avenue du Recteur Pineau, 86022 Poitiers Cedex, France b Institut de Recherches sur la Catalyse, UPR 5401 CNRS, 2 avenue Albert Einstein, 69100 Villeurbanne, France c Direction Catalyse et Se ´paration, IFP, IFP-Lyon, BP 3, 69390 Vernaison, France Received 31 March 2005; received in revised form 13 June 2005; accepted 3 July 2005 Available online 24 August 2005 Abstract The influence on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) of different activation procedures using H 2 S or dimethyldisulfide (DMDS) has been investigated on phosphorus-free and phosphorus-doped CoMo and NiMo industrial catalysts supported on alumina. The comparison of the two sulfiding agents was performed using strictly similar procedures of sulfidation to determine the origin of the well-known beneficial effect of organosulfides for the activation of hydrotreating catalysts. Partial pressures in H 2 and/or in sulfiding agents have been modified to observe activity variations among the different sulfiding agents used. Comparison between H 2 S and DMDS has also been performed on phosphorus-doped CoMoP/Al 2 O 3 and NiMoP/Al 2 O 3 catalysts. Results emphasized the importance of supplying H 2 S to the catalyst at low temperatures of activation (around 423 K) even in a low proportion (P H 2 S as low as 3.3 kPa) to sulfide correctly NiMo and CoMo catalysts. Indeed, through a low consumption of H 2 S, O–S exchange and intramolecular redox reactions can be initiated at low temperatures of activation leading to a level of sulfidation sufficiently advanced before reaching temperatures (above 573 K) at which a strong competition between reduction and sulfidation starts. DMDS appears less efficient than H 2 S for activating NiMo and CoMo catalyst due to its inability to provide H 2 S to the catalyst at these low temperatures of activation. At higher temperatures (T > 543 K), a good activation cannot be obtained if a high P H 2 =P H 2 S ratio is used whatever the sulfiding agent. Finally, the difficulty of activating the P-doped CoMoP/Al 2 O 3 and NiMoP/Al 2 O 3 catalysts was confirmed. This study confirms that the beneficial role of organosulfide compounds as activating agents is not related to a pure ‘‘chemical’’ phenomenon but more probably to a ‘‘thermal well’’ effect limiting the exothermic character of the oxide–sulfide transformation. # 2005 Elsevier B.V. All rights reserved. Keywords: Activation; Hydrodesulfurization; Sulfidation; Dimethyldisulfide; MoS 2 ; Phosphorus doping 1. Introduction In the last decades, environmental legislation has been tightened leading to a huge decrease of the sulfur amount authorized in vehicle transportation fuels. Therefore, research has been pushed up on better hydrodesulfurization (HDS) catalysts in order to respect these new regulations. Commercial hydrodesulfurization catalysts are generally made of alumina-supported MoS 2 promoted by Co or Ni [1]. These catalysts are usually sold in an inactive oxide form because of easier handling and loading compared to fully sulfided hydrotreating catalysts. Consequently, in order to be used in HDS processes, these solids must be first activated by a sulfiding agent either in situ, i.e. directly inside the hydrotreating reactor or ex situ by pre- impregnation with polysulfides. The experimental proce- dure used to in situ activate the catalyst has a major impact on the activity and stability of MoS 2 -based catalysts in the HDS process. www.elsevier.com/locate/apcata Applied Catalysis A: General 293 (2005) 105–119 * Corresponding author. Tel.: +33 472 44 53 20; fax: +33 472 44 53 99. E-mail address: Gilles.Berhault@catalyse.cnrs.fr (G. Berhault). 0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2005.07.026