Influence of phosphorus on the structure and the catalytic activity of sulfided Co-Mo catalysts

The influence of phosphorus (added as phosphates) on the sulfiding rate of carbon-supported Co–Mo catalysts is studied by means of temperature-programmed sulfiding. Significant progress is made in understanding the influence of phosphates on the structure and thiophene hydrodesulfurization (HDS) activity (atmospheric pressure) of carbon-supported Co–Mo catalysts. The model compound Co3(PO4)2·8H2O is sulfided to minor extent below 800 K. Between 800 and 1000 K, instead of further sulfiding, this compound is reduced to a mixture of CoP and Co2P. Phosphates have a large influence on the structure and sulfiding rate of carbon-supported oxidic cobalt and Co–Mo catalysts. Addition of phosphates to these catalysts results in the formation of "Co–PO4" species which are, compared with other cobalt species, relatively difficult to sulfide. Between 650 and 800 K cobaltphosphate species are not sulfided but reduced to cobaltphosphides while disperse sulfided cobalt species react with P2O5 and hydrogen to phosphides, water and hydrogen sulfide. These cobalt sulfide species are formed upon sulfiding of CoO, Co3O4, cobalt nitrates or cobalt species surrounded by a small number of phosphates. The sulfiding of the Mo/C catalyst is hardly influenced by the presence of phosphates. The poisoning of the low-pressure thiophene HDS activity of carbon-supported cobalt and Co–Mo catalysts by phosphorus can be explained by either the formation of "Co–PO4" species or CoP and Co2P. Which of these explanations is valid depends on the reaction time and conditions. After short reaction times at 673 K, the major part of the cobalt species is present as "Co–PO4", whereas the amount present as phosphides increases with reaction time. The Mo/C catalysts are most likely poisoned by phosphorus due to chemisorption of elemental phosphorus (P or P4) on sulfur anion vacancies present on the edges of the MoS2 slabs

Hydrodesulfurization activity of zeolite-supported nickel and cobalt sulfide catalysts

Various zeolite (NaY or CaY) supported metal sulfide (Ni or Co) catalysts were prepared (impregnation or ion exchange) and characterized by means of thiophene HDS, Xe-129 NMR and TPS. Especially the acidic zeolites showed a very high initial activity. The observed activity differences are discussed in terms of sulfidation, dispersion, position of the metalsulfide relative to the zeolite pore system and acidity, the latter two being the most important. It is concluded that small Ni and Co sulfide clusters are very efficient thiophene desulfurization catalyst

Reply to the comment A.J. Kassman and D.B. Losee on the "Effect of gallium ions and of preparation methods on the structural properties of cobalt-molybdenum-alumina catalysts"

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Behavior of the resonant absorption area of a 57Fe-doped Ni/C catalyst during sulfidation

In-situ Moessbauer spectroscopy measurements down to 4.2 K were performed on a 57Fe-doped Ni/C catalyst after various successive sulfidation treatments. After exposure of the catalysts to the H2S/H2 gas mixt. at room temp., part of the 57Fe becomes sulfidic. The rest is present as a sulfate-like intermediate species. The interaction between this intermediate species and the carbon support material is influenced by water. A

Steenkoolliquefactie met behulp van ijzersulfide katalysatoren

Als alternatief op termijn voor olie en gas ligt hernieuwd grootschalige inzet van steenkool als fossiele brandstof voor de hand, zij het voornamelijk na omzetting in een gasvormige en/of vloeibare vorm. Eén van de wegen hiertoe is de gekatalyseerde directe liquefactieroute. Aan de Technische Universiteit Eindhoven is een aanzet gegeven tot de ontwikkeling van goedkope, op ijzersulfide gebaseerde, katalysatoren die voor de gewenste omzettihgen voldoende actiefzijn

Carbon-covered alumina as a support for sulfide catalysts

Carbon-covered alumina carrier materials (10–35 wt.% carbon deposited) were prepared via pyrolysis (873–973 K) of cyclohexene or ethene on the surface of a ¿-alumina and evaluated for their use as supports for cobalt sulfide hydrodesulfurization catalysts. Promising textural properties were obtained for the samples prepared: BET surface areas up to 334 m2 g-1, meso- and macropore surface areas reaching values of 190–270 m2 g-1, and narrow pore size distributions in the 2.5–10 nm pore radius range. XPS measurements showed that the alumina surface was not uniformly covered, probably due to diffusion limitations of the carbon forming hydrocarbons. The coverage could be improved (maximum value reached was 77%) by increasing the amount of carbon deposited as well as by an additional high-temperature (1073 K) treatment. The thiophene hydrodesulfurization activity of Co sulfide supported on the prepared carbon-covered aluminas was found to increase linearly with increasing alumina surface coverage by carbon. A threefold increase in activity compared to Co/Al2O3 catalysts was obtained, demonstrating the effective shielding by the carbon layer which reduces or eliminates the strong metal-alumina interactions. Oxidizing the carbon surface prior to the introduction of cobalt led to a further improvement of the catalytic activity

Sulfidation and activity of Co/C catalysts having extremely low cobalt-loading: A Moessbauer emission spectroscopy and thiophene hydrodesulfurization study

Up to a sulfiding temp. of 473 K, the behavior of Co/C catalysts with extremely low cobalt loadings (ppm range) agrees with the trend obsd. before in the Moessbauer emission spectroscopy (MES) spectra of Co/C catalysts with much higher cobalt loadings (0.04-43. wt.%). Sulfiding at 573 K results in a rather well-defined very highly dispersed (most likely monatomically) Co sulfide species which shows a doublet with the extremely large value Q.S. = 4.11 mm/s. In this species the cobalt atoms may be four-fold (square-planar) or five-fold (square-pyramid) coordinated by sulfur. Sulfiding at 673 K results in the disappearance of this highly dispersed Co sulfide species and the newly formed species are again similar to the one previously found for Co/C catalysts with higher cobalt loadings. This finally formed Co sulfide species does not exhibit the Co-Mo-S MES spectrum (Q.S. between 1.0 and 1.3 mm/s) whereas its intrinsic thiophene hydrodesulfurization (HDS) activity equals that of cobalt in the Co-Mo-S phase. Thus, there is no general relation between the thiophene HDS activity (measured at atm. pressure) and the amt. of cobalt exhibiting a Co-Mo-S MES spectrum. [on SciFinder (R)

Vanadium oxide monolayer catalysts. 3. A Raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports

Vanadium(V) oxide supported on 7-A1203, GO2, Cr2O3, Si02, Ti02, and Zr02 was studied by X-ray fluorescence, by X-ray diffraction, and especially by the combination of Raman spectroscopy and temperature-programmed reduction (TPR) for qualitative and quantitative structural analysis, respectively. Catalysts were prepared via ion-exchange and wet-impregnation methods. The V contents ranged from - 1 to 40 wt % V. At low surface concentrations only surface vanadate phases of two-dimensional character are observed for all carriers. According to Raman and TPR data the structure of these surface vanadate species is independent of the preparation technique. At medium and high surface concentrations, the webimpregnated samples already contain crystalline V20b At equal surface concentrations the ion-exchanged catalysts contain no V205 crystallites. An exception is Si02 on which also crystalline V206 is formed in both preparation techniques. Monolayer stability toward thermal treatment decreases in the order AZO>3 Ti02> Ce02,w hereas on heating ion-exchanged V/Si02 the crystalline V206 spreads out over the silica surface. The reducibilities of the ion-exchanged catalyats, as measured by TPR, can be used as a measure for the contact interaction between vanadia and the carrier oxides. At temperatures of 500-800 K, this interaction ranges from strong with titania to weak with silica as a carrier

Influence of water on the sulfidation of Co/NaY and Co/CaY prepared by impregnation, A. Mössbauer Emission spectroscopy and EXAFS Study

The influence of physisorbed water on the sulfidation of impregnation type Co/NaY(imp) and Co/CaY(imp) catalysts which contain about 4 wt % Co and are prepared via pore volume impregnation is studied by Mossbauer emission spectroscopy and extended X-ray absorption fine structure. It is found that in the absence as well as in the presence of water, sulfidation of the impregnated samples finally results in the formation of Co9S8-like species at the outer zeolite surface. In the presence of water, this process proceeds via the intermediate formation of a well-ordered ''CoS1+x'' phase (NiAs structure). Water removal prior to sulfidation retards the formation of Co9S8-like species. This retardation in Co9S8 formation is found to be more effective for CaY-zeolite than for NaY- zeolite, which means that a larger part of the formed ''Co- sulfide'' is preserved in highly dispersed ''Co-sulfide'' particles. These findings are clearly different from those obtained earlier with ion exchanged CoNaY(ion ex) samples, for which drying prior to sulfidation resulted in very small ''Co- sulfide'' species with no resemblance to ''Co9S8'