M. Breysse

Influence of sulphidation conditions on the properties of NiW/Al2O3 hydrotreating catalysts

Abstract The sulphidation of a nickel-tungsten catalyst has been studied by XPS and electron microscopy. These features are related to catalytic properties in test reactions characteristic of hydrotreatment (HDS, HDN, HN of aromatics) and to chemisorption measurements. It was observed that for a sulphidation temperature of 400°C, only 70% of the tungsten atoms are in a WS 2 - like form; this proportion increases to 95% at 650°C. High-resolution microscopy results indicate that a slight lateral growth of the WS 2 -like crystals occurs above 500°C. The activity in the HN of biphenyl does not vary with the sulphidation temperature in the same way as HDS reactions. These variations of catalytic activities support the existence of two different catalytic sites for hydrogenolysis and hydrogenation reactions. The crystallite length increase observed above 500°C leads to a decrease in the number of edge positions necessary for mixed site formation and therefore a decrease in the probe molecule uptake and HDS catalytic activity.

Ruthenium sulphide catalysts supported on alumina : physicochemical characterization and catalytic properties in hydrotreating reactions

Abstract Ruthenium sulphide catalysts supported on alumina were prepared using ruthenium III chloride trihydrate and they were sulphided under a N 2 /H 2 S(15%) flow at a number of temperatures. The properties of the catalysts in thiophene hydrodesulphurization, biphenyl hydrogenation and pyridine conversion have been investigated and interpreted in relation to their characterization by X-ray photoelectron spectroscopy, high resolution electron microscopic observations and temperature-programmed reduction data. The results show the importance of the sulphidation step in the genesis of different active RuS 2 particles. The relation between the activity and the nature of the exposed crystallographic planes is discussed.

Molten salt preparation of stabilized zirconia catalysts : characterization and catalytic properties

Abstract Supports of Mo and NiMo catalysts were prepared and tested in hydrotreatment model reactions. These supports, composed of zirconia and various amounts of yttria, were obtained by synthesis in molten salts. It was found that the distribution of yttrium in zirconium oxide was homogeneous. Moreover, it was shown that the crystalline structure as well as the textural properties (especially the porosity) were stabilized. These solids were then used as supports of Mo and NiMo sulphides and their activities were compared to those of a commercial NiMo alumina catalyst. In biphenyl hydrogenation, with the same coverage of Mo (2.8 at/nm 2 ), the activities per gram of both catalysts (supported on zirconia and alumina) were similar, while the activity per atom of Mo of the catalyst supported on ZrO 2 ue5f8Y 2 O 3 was twice the activity of the catalyst supported on alumina. For NiMo catalysts, a ratio r= Ni/(Ni+Mo)=0.4 with Mo = 2.8 at/nm 2 and a co-impregnation of the Mo and Ni were required to have a good synergetic effect. The activity per atom of Mo in biphenyl hydrogenation was then enhanced more than twofold when compared to the NiMo/alumina catalyst. In an HDN model reaction (conversion of diethylanyline in the presence of quinoline) the results obtained with zirconia were much better than with alumina.

Conversion of saturated cyclic and noncyclic amines over a sulphided NiMo/Al2O3 catalyst : mechanisms of carbon - nitrogen bond cleavage

Abstract The objective of this work was to provide comprehensive hypotheses concerning the mechanisms operative in the Cue5f8N bond cleavages occurring during the catalytic conversion of amines over a conventional hydrotreating catalyst, so as to account for experimental observations and to help in developing better hydrodenitrogenation catalysts. The approach consists in a study of the relations between the structure and the reactivity of two series of amines with different numbers of hydrogen atoms on the carbon atoms in the α and β positions with respect to their nitrogen atom. It was found that the hydrogen atoms on the carbon atom in the β position are involved in the formation of hydrocarbons, and that neither the hydrogen atoms on the carbons in the α position nor those on the carbon atoms in the β position are involved in the formation of condensation products. On the basis of these results, two mechanisms are proposed for the formation of the different reaction products.

Ruthenium molybdenum sulphide catalysts : physicochemical characterization and catalytic properties in HDS, hydrogenation and HDN reactions

Alumina supported RuMo sulphide catalysts having different weights of metal content and atomic composition ratios r=Ru/(Ru+Mo) were prepared by using ammonium heptamolybdate dissolved in water or a 10% (NH4)2S-H2O solution and RuCl3.3H2O as precursor compounds. Their activities were studied in the hydrodesulphurization (HDS) of thiophene and in the hydrogenation (HYD) of biphenyl, and optimized in terms of the preparation method and the sulphidation process. Some hydrodenitrogenation (HDN) tests were also performed on these catalysts. Electron microscopy and XPS measurements were performed, and the nature of the active phase was discussed.

Inorganic-chemistry approach to the preparation of sulfided “mixed-phase” hydrotreating catalysts using thiometalates as precursors

The application of bisthiometalato complexes of the type [M′(MS4)2]n− (n = 2 or 3, M′ = Co or Ni, and M = Mo or W) as precursors for the preparation of hydrotreating catalysts was investigated. The thermal decomposition of the tetraethylammonium salts of these complexes in an H2ue5f8H2S atmosphere at 400°C leads to the formation of catalytically active materials which were characterized by physico-chemical methods and their catalytic activities in biphenyl hydrogenation. As the molecular structures of the starting complexes are known, the resulting catalysts can be discussed as “modified precursors”. Structural models of these catalysts have been developed on the basis of this assumption and the present results.

Preparation, characterization and catalytic properties of unsupported vanadium sulphides

Abstract This work concerns the preparation and the ability of unsupported vanadium sulphide to catalyze different reactions representative of hydrotreatment. Pure V2S3 was prepared by decomposition of ammonium thiovanadate at relatively low temperature. The reactivity of the decomposed solid towards oxygen confirms the high oxophilic character of this group V sulphide. The oxidation mechanism involves a superficial oxidation followed by an insertion of oxygen into the lacunar structure of the solid. The comparison of the catalytic properties of this chalcogenide with those of molybdenum or tungsten sulphides shows the superiority of vanadium sulphide for performing hydrogenation reaction of various cyclic molecules. In contrast, the hydrodesulphurization properties are of the same order.

Mechanism of carbon-nitrogen bond cleavage during amylamine hydrodenitrogenation over a sulphided NiMo/Al2O3 catalyst

By comparison of the hydrodenitrogenation rate of amylamine with those of neopentylamine and tert-amylamine over a conventional catalyst, it was evidenced that the hydrogen atoms of the carbon in the β position with respect to the nitrogen atom participate in the C-N bond cleavage. A detailed mechanism including the interaction with the catalyst is proposed for this reaction.

Use of CO as probe molecule for characterization of mixed Ru-Ni sulphide phases supported over alumina

Infrared spectroscopy was used to characterize mixed ruthenium-nickel sulphides prepared by step-wise impregnation over alumina and further sulphidation. The hydrogenation of biphenyl was compared over samples containing different amounts of nickel and ruthenium and a large increase was observed for a catalyst with an atomic Ni /(Ni + Ru) ratio near 0.4. Infrared spectra of adsorbed CO indicate that the increase in catalytic activity is ascribed to the presence of a very large number of Ru-Ni sites.

Optimization of the composition of Ni-W/A1203 hydrotreating catalysts using model molecules and real feedstock conversion studies

Abstract Alumina supported Ni-W catalysts with contents of components varying over a wide range were systematically studied in order to optimize a catalyst for further industrial use, mainly for HDN reactions. The catalytic activities were determined in different reactions representative of the hydrotreatment process, viz., piperidine HDN, biphenyl and pyridine hydrogenations, thiophene and dibenzothiphene HDS. The promoting effect of Ni is always observed but the amplitude of the synergy is greatly dependent on the type of molecule to be treated. The nature of the active sites responsible for the catalytic activities is discussed in terms of the mixed phase model. The selected most active catalyst for performing HDN reactions was tested in real feedstock conversions and compared with conventional nickel-tungsten catalysts.