Deep Hydrodesulphurization via Hydrogen Spillover
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Deep Hydrodesulphurization via Hydrogen Spillover C. Navarrete • R. Garcı´a • C. Sepulveda F. J. Gil-Llambias • J. L. G. Fierro • N. Escalona
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Received: 23 May 2011 / Accepted: 29 September 2011 / Published online: 21 October 2011 Ó Springer Science+Business Media, LLC 2011
Abstract The synergistic effect between Co//Mo and Co//W stacked bed systems in the hydrodesulphurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was studied. The reaction was carried out in a high-pressure continuous-flow microreactor at 3 MPa and 300 °C. The observed synergism can only be explained by the action of hydrogen spillover (HSO). The selectivity in hydrogenation over direct desulphurization pathways (HYD/DDS) of Mo/c-Al2O3 and W/c-Al2O3 catalysts increased when the reaction was carried out in Co//Mo and Co//W stacked bed systems, respectively. The changes in selectivity can be explained by the fact that hydrogen spillover does not only create more active sites, but it also modifies the sites, favouring the HYD pathway. Differences in synergistic effect between Co//Mo and Co//W stacked bed systems were related to the higher degree of sulphurization of the molybdenum compared to the tungsten phase, as detected by XPS.
C. Navarrete R. Garcı´a C. Sepulveda N. Escalona (&) Facultad de Ciencias Quı´micas, Universidad de Concepcio´n, Casilla 160c, Concepcio´n, Chile e-mail: [email protected] F. J. Gil-Llambias Facultad de Quı´mica y Biologı´a, Universidad de Santiago de Chile, Casilla 40, Correo 33, Santiago, Chile F. J. Gil-Llambias Universidad Cato´lica Silva Henrı´quez, Casilla 28, Correo 22, Santiago, Chile J. L. G. Fierro Instituto de Cata´lisis y Petroleoquı´mica, CSIC, Cantoblanco, 28049 Madrid, Spain
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Keywords Hydrodesulphurization Hydrogen spillover Synergism 4,6-DMDBT
1 Introduction Recent environmental laws require a drastic decrease of sulphur content in diesel, with a maximum level of 10 ppm expected to be enforced by 2012 in Europe. Consequently, in recent years there has been renewed interest in identifying new catalysts that might be more active and selective for refractory molecules than conventional hydrodesulphurization (HDS) catalysts. The development of new catalysts requires greater knowledge of the behaviour of the active phases and their effect on selectivity and activity. Currently, only two active phase models are used to explain the activity of HDS catalysts. In the first model the synergism is explained by the remote control (RC) model developed by Delmon et al. [1–3] working with mechanical mixtures of unsupported MoS2 and CoSx. The remote control model proposed that the hydrogen spillover (HSO) that occurred on the promoter, called the donor phase D (D = CoSx), migrated to the acceptor A (A = MoS2), increasing the active sites. The second model was developed by Topsøe et al. [4–6] and is called the ‘‘Co–Mo–S’’ phase. The authors explained the synergism between Co and Mo by the formation of Co–Mo–S like structures. In this model cobalt is atomically dispersed on the MoS2 edges. In
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