Beneficial role of manganese on the HDS and HDO properties of Ni-promoted MoS2/Al2O3 catalysts - CNRS - Centre national de la recherche scientifique Accéder directement au contenu
Communication Dans Un Congrès Année : 2018

Beneficial role of manganese on the HDS and HDO properties of Ni-promoted MoS2/Al2O3 catalysts

A. Lopez-Benitez
  • Fonction : Auteur
I. Vazquez-Garrido
  • Fonction : Auteur
A. Guevara-Lara

Résumé

Different options are generally envisaged to improve the HDS activity of nickel- or cobalt-promoted Mo(W)S2 catalysts including: 1) new methods for preparing promoted MoS2 or WS2 catalysts, 2) replacing the traditional -Al2O3 by new supports (ZrO2, TiO2, SBA-16, ..) or 3) modifying -Al2O3 by additives (P, F, B) or other oxides (TiO2-Al2O3 for ex.). Among the different oxides to be added to alumina, manganese oxide has been rarely considered since forming readily spinels when supported on Al2O3 or ZrO2. Chianelli et al. [1] have reported the periodic evolution in the HDS of DBT of different transition metal sulfides (TMS) showing that manganese sulfide has the lowest activity of the first TMS series. However, Ho et al. [2] emphasized in an industrial report that supported NiMnMo catalysts show high activity for the HDS of 4,6-DMDBT. Therefore, Mn seems to appear as poorly active if forming separate MnS phase but as an active promoter of NiMo catalysts. Interestingly, Mn also presents different oxidation degrees (mainly +2, +3, +4) and therefore it can markedly influence the Al2O3 support effect when preparing nickel-promoted catalysts. In the present study, NiMo/Al2O3 catalysts have been modified by adding different amounts of Mn (01-5.0 mol % as MnO) at several pHs of impregnation of the Ni and Mo precursors (5, 7, or 9) using either an impregnation technique for adding Mn to an existing Al2O3 support [3] or a sol-gel approach to form directly Mn-Al2O3 supports [4]. As-formed catalysts are characterized at each step of the preparation: after drying, after calcination and finally after sulfidation. Initial work was done by considering first the impregnation of a Mn precursor, manganese acetate on existing Al2O3 support. Both the pH of impregnation of the nickel nitrate and ammonium heptamolybdate precursors and the amount of Mn (1 or 5 mol%) strongly influence the dispersion of Mo and the final sulfide state. At a Mn content of 1.0 mol%, impregnation at pH 7 leads to well-dispersed molybdate species easily sulfided into a Ni-promoted MoS2 phase while impregnation at pH 9 favors more polymerized molybdate species and loss of Ni into NiMnO spinel. Increasing the Mn content to 5.0 mol% leads to the formation of MoO3 clusters and a severe loss of Ni into NiMnO spinels whatever the pH of impregnation. Optimized preparation of NiMo/Mn-Al2O3 leads to an HDS activity twice higher than without Mn. In a second step, manganese was added to the Al2O3 support using a sol-gel approach in a 0.1-5.0 mol% range. Impregnation of Ni and Mo precursors were carried out at pH 9 since leading to better final dispersion in this case. Results show a direct influence of the oxidation state of Mn on the nature of the Mo oxide species and their interaction with the Al2O3 support. A high proportion of Mn2+ (observed at low % of Mn:  0.5 mol %) leads to a weaker interaction with the support and to a very intrinsically active NiMo phase but in a lower proportion than without Mn. At too high amount in Mn ( 2.0 mol%), Mn3+ is mainly formed and reacts with Ni to form the NiMnO spinel phase leading to depleted HDS activity. Optimum activity is therefore reached at an intermediate loading of 1.0 mol % with weaker support interaction, higher sulfidation rate and highly active NiMo phase. Interestingly, whatever the method of preparation, adding Mn in optimized conditions leads to turnover frequencies twice higher for NiMo catalysts. Moreover, migration of Mn oxides to the surface of the support was observed during calcination of sol-gel prepared Mn-Al2O3 while sulfidation conditions leads to the formation of MnS showing a strong direct synergetic effect of Mn towards the NiMoS phase. Finally, results were also acquired during the HDO of a waste cooking oil showing once again a strong beneficial effect of Mn on the NiMo phase at a manganese content of 1.0 mol %. In conclusion, the present work shows undoubtedly for the first time a strong beneficial effect of manganese on the HDS and HDO properties of NiMo/Al2O3 catalysts confirming the presence of synergetic effects observed previously by Ho et al. [2] on NiMnMo systems.
Fichier non déposé

Dates et versions

hal-02018662 , version 1 (14-02-2019)

Identifiants

  • HAL Id : hal-02018662 , version 1

Citer

A. Lopez-Benitez, I. Vazquez-Garrido, A. Guevara-Lara, G. Berhault. Beneficial role of manganese on the HDS and HDO properties of Ni-promoted MoS2/Al2O3 catalysts. MACS VIII, May 2018, Cabourg, France. ⟨hal-02018662⟩
67 Consultations
0 Téléchargements

Partager

Gmail Facebook X LinkedIn More