Cobalt-Molybdenum Sulfide Hydrodesulfurization Catalysts

Catalysts based on molybdenum disulfide, M0S2, and cobalt or nickel as promoters are used for the hydrodesulfurization (HDS) and hydrodenitrogenadon (HDN) of heavy oil fractions [48,49]. The catalyst, containing at least five elements (Mo, S, Co or Ni, as well as O and A1 or Si of the support), is rather complex and represents a real challenge for the spectroscopist. Nevertheless, owing largely to research in the last twenty years, the sulfided C0-M0/AI2O3 system is one of the few industrial catalysts for which we know the structure in almost atomic detail [49, 50], 

Let us take 1978 as the starting point. Massoth [51] then published an extensive review of what was known about the structure of HDS catalysts. Characterization was essentially based on techniques such as X-ray diffraction, electron microscopy, photoelectron spectroscopy, electron spin resonance and magnetic methods. Massoth was rather unhappy with the state of affairs in 1978. He was struck by the ...diversity and apparent contradictions of results and interpretations... It almost seems as though everyone is working with a different catalyst . 

Indeed, several models existed for the acdve C0-M0/ALO3 catalyst. There were, for example, the monolayer models [52], which assumed that the HDS 

the first steps in the sulfidation of Mo03 include exchange of lattice 

At sulfidation temperatures above 125 °C, the Mo 3d XPS spectra shift to those characteristic of Mo4+, whereas at temperatures of 250 °C and higher the Mo and S XPS spectra become equal to those of MoS2. The S22 groups gradually disappear to leave S2 as the only state of sulfur the S/Mo atomic ratio as determined with RBS reaches values between 2 and 2.5, as expected for MoS2 (see Fig. 9.16). 

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Supported Rhodium Catalysts Alkali Promoters on Metal Surfaces Cobalt-Molybdenum Sulfide Hydrodesulfurization Catalysts Chromium Oxide Polymerization Catalysts... 

Cobalt-molybdenum sulfide hydrodesulfurization catalysts Chromium oxide polymerization catalysts... 

Another SIMS study on model systems concerns molybdenum sulfide catalysts. The removal of sulfur from heavy oil fractions is carried out over molybdenum catalysts promoted with cobalt or nickel, in processes called hydrodesulfurization (HDS) [17]. Catalysts are prepared in the oxidic state but have to be sulfided in a mixture of H2S and H2 in order to be active. SIMS sensitively reveals the conversion of Mo03 into MoSi, in model systems of MoCf supported on a thin layer of Si02 [21]. 

Hariita et al. (14) prepared spherical particles of molybdenum sulfide and cobalt sulfide with a narrow size distribution by reaction of dilute ammonium orthomolybdate or cobalt(II) acetate with sulfide ions liberated from thioacetamide as a reservoir of S2- ions in weakly acidic media. The compositions of these metal sulfides were estimated to be Mo S 0 = 1.0 1.7 3.0 and Co S 0 = 1,0 4.5 6.4 by chemical analysis. Figure 3.1.4 shows an SEM of a thus prepared uniform molybdenum sulfide particles sample. These sulfide particles were of no distinct crystal structure as shown by x-ray diffractometry. The isoelectric points of the Mo sulfide and Co sulfide particles in terms of pH were 1.9 and 3.1, respectively. Both of them are useful as hydrodesulfurization catalysts. 

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