Nabil Allali

Niobium sulfides as catalysts for hydrotreating reactions

Abstract Hydrotreating properties of unsupported and supported niobium sulfides are compared to those of molybdenum sulfide catalysts. Niobium catalysts demonstrate higher activities than molybdenum sulfide ones and remarkable selectivity in cracking and isomerisation reactions.

Niobium sulfide as a dopant for hydrotreating NiMo catalysts

Niobium sulfide has been recently found to be an interesting new active phase for hydrodesulfurization. In this work, niobium was used as a dopant for a conventional hydrotreating catalyst. A NiMo hydrotreating catalyst in the oxide form was doped with various contents of Nb precursor salt (0<Nb wt.% <7). After drying, the activation of the catalyst was performed with CS 2 sulfiding agent in a high pressure vessel. The use of this new dopant increased the catalytic activity in both HDS and HYD model reactions. Highest activities were obtained with an optimum Nb content of 5 wt.%. The selectivity of the products was also modified since more isomerized compounds where produced. Various techniques were used to determine structural and morphological characteristics of the materials. TEM pictures only showed the presence of lamellar particles similar to MoS 2 . EDX analysis demonstrated the homogeneous distribution of the transition metal elements (Ni, Mo, Nb) even with small electron probes at high magnification. EXAFS was used to determine the local environment of Nb atoms and showed that Nb was present in the form of NbS 2 entities similar to the bulk phase.

Catalytic properties of pure and Ni doped niobium sulfide catalysts for hydrodesulfurization

Abstract New unsupported and carbon-supported niobium sulfide (pure or Ni doped) catalysts, characterized by EXAFS, demonstrate interesting properties for hydrodesulfurization.

Exafs characterisation and catalytic properties of supported niobium sulphide catalysts

Summary Niobium sulphide supported catalysts can reach catalytic activities higher than those of classical MoS2 based catalysts. However, the nature of the support and the sulfurizing agent are of prime importance. Depending on the preparation and the activation method, dispersed particles of different entities such as NbS3, NbS2 and Nb1−yS can be identified using the EXAFS technique. In this work, relations between structural arrangement and catalytic activity are discussed, species with cation clustering are showen to be particulary active.

Lithium intercalation-deintercalation reactions using matrixes with the sulvanite structure: Dimensionality lowering of the host-structure

Abstract Reaction of butyllithium with 3-D Cu 3 NbS 4 leads to redox extraction of copper and formation of 2-D LiNbS 2 . Action of iodine on the intercalated material allows NbS 2 (2H variety) to be obtained. For both Cu 3 NbS 4 and Cu 3 VS 4 , the electrochemical study shows an irreversible multi-phase transformation of the starting material during the first intercalation-deintercalation cycle. Cyclability is observed over a large composition domain (~5 Li per formula unit) corresponding to capacities larger than that of the Li-TiS 2 system.

Apports des phyllosilicates dans la différenciation entre altération hypogène et altération supergène dans le basalte triasique du Moyen Atlas (Maroc)

Abstract Triassic basalt of the Middle Atlas has been subject to metamorphic transformation then weathering. Occurrence in both metabasalt and saprolite of ubiquitous clay minerals, such as smectite and mixed layers chlorite–smectite, makes it difficult to distinguish between the two alteration facies and explains the interest of complementary sources of information. In the Bhallil weathering profile, petrographical and mineralogical analyses of primary igneous minerals and their alteration products coupled with Fe oxidation state determination in clay fractions allow to identify three alteration facies: ( i ) metamorphic basalt, where iron occurs mainly as the ferrous form; ( ii) the lower part of saprolite, where iron is partially oxidized to its ferric form; ( iii ) the upper part of saprolite, where iron is completely oxidized. To cite this article: A. Dekayir et al., C. R. Geoscience 334 (2002) 877–884.

Lithium intercalation into copper ferrite and copper chromite: Redox extraction of copper

Abstract From Mossbauer measurements we have shown that during lithium intercalation into copper ferrite no reduction of iron occurs, which means that the electronic transfer concerns copper. Copper chromite behaves in a similar way: the intercalation-induced reduction of copper results in its extraction from the structure as Cu 0 , which can then be removed from the powder by reaction with an iodine solution. Concomitantly a partial disintercalation of lithium occurs so that a compound with the formula Li 0.76 Cu 0.07 Cr 2 O 4 was obtained. During the intercalation-disintercalation reactions, the spinel framework is preserved but, contary to the pristine spinel, the intercalated and disintercalated compounds are cubic due to the elimination of the Jahn-Teller ion, Cu II .

Low-temperature reactions using potassium iron disulfide as a precursor

Abstract The chain structure of KFeS 2 allows exchange reactions to be performed. If potassium is replaced by calcium, the [FeS 2 ] structural framework is retained so that this reaction can be considered as a Soft Chemistry process. It is not the case of the silver exchange which induces a change to a chalcopyrite structure. Potassium can be extracted from KFeS 2 but the obtained FeS 2 is pyrite. This drastic structural change precludes this reaction to be considered as a Soft Chemistry process.