NEW INSIGHT IN THE PREPARATION OF ALUMINA SUPPORTED HYDROTREATMENT OXIDIC PRECURSORS: A MOLECULAR APPROACH

The science on the preparation of the hydrodesulfurization oxidic precursors is coming of age, but the chemistry governing their preparation is not yet clearly understood. In this paper, the chemistry of alumina supported oxomolybdate preparation is revisited taking into account the dissolution/precipitation concept recently developed. Classical preparations with the ammonium heptamolybdate and Co nitrate salts will firstly be discussed. Then the use of new starting materials for the preparation of the impregnating solutions will be considered, showing that at high Mo loading the dispersion is strongly dependant on the nature of the starting salts. The use of phosphomolybdate cobalt salts will also be considered. Lastly we will discuss the improvement of the Co promoting effect using molybdocobaltate heteropolyanions as starting materials and complexing agents. This study shows that the maturation step is the determining step for the improvement of preparation of these alumina based oxidic precursor. I

Influence of operating conditions in a continuously stirred tank reactor on the formation of carbon species on alumina supported cobalt Fischer–Tropsch catalysts

International audienceThe paper focuses on the identification of carbon species using a wide range of ex situ characterization techniques (TPH/MS, TGA-DTA, XPS, TOF-SIMS) in spent 15 wt% Co/Al2O3 supported catalysts exposed to different conditions of Fischer–Tropsch synthesis in a continuously stirred tank reactor (CSTR) at 20 bar of total pressure, different gas-space velocities and H2/CO ratios. Three types of carbonaceous species were uncovered in the used catalysts: (i) hydrcarbobns (probably wax), (ii) strongly adsorbed hydrocarbons and (iii) amorphous polymeric carbon. The amounts of deposed carbon species strongly depend on the operating conditions. In agreement with the observed slow catalyst deactivation, only very small amounts of strongly adsorbed hydrocarbons and polymeric carbon were observed when the catalyst was exposed to a H2/CO = 2 syngas ratio and moderate carbon monoxide conversions. Lower gas space velocity and lower H2/CO ratio in syngas lead to larger amounts of deposed carbon species. Strongly adsorbed hydrocarbons and amorphous polymeric carbon seem to contribute to catalyst deactivation. Cobalt carbide and graphitic carbon were not detected in the used catalysts by ex situ methods

«Enhancing the performance of supported Co catalysts in Fischer-Tropsch synthesis by addition of cyclodextrins»

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«Cyclodextrin promotion of Co supported catalysts: effect on the catalyst structure and performance in Fischer-Tropsch synthesis»

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Molecular structure and localization of carbon species in alumina supported cobalt Fischer-Tropsch catalysts in a slurry reactor.

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Genesis of active phase in MoW/Al2O3 hydrotreating catalysts monitored by HAADF and in situ QEXAFS combined to MCR-ALS analysis

Alumina supported MoW hydrotreating catalyst was synthesized by using bimetallic H-4[SiMo3W9O40] Keggin heteropolyacid (HPA). Catalysts based on monometallic H-4[SiMo3W9O40] and H-4[SiMo3W9O40] and their mixture were also studied. Genesis of the active phase was studied during atmospheric gas sulfidation by H2S/H-2 of the catalysts by in-situ Quick X-ray absorption spectroscopy (XAS) and High-Angle Annular Dark-Field (HAADF) imaging. The combination of different chemometric tools such as Principal Component Analysis (PCA) and Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) allowed to determine the number of intermediate species, their chemical nature and concentration profiles during sulfidation. It was found that tungsten sulfidation using bimetallic HPA precursor started at lower temperature, compared to W sulfidation in the monometallic and in the mixture of monometallic HPA catalysts. Simultaneous sulfidation of Mo and W atoms in case of the bimetallic molecular precursor can govern the formation of mixed MoWS2 phase, which formation during activation was evidenced by HAADF

Fischer–Tropsch synthesis in milli-fixed bed reactor: Comparison with centimetric fixed bed and slurry stirred tank reactors

International audienceThis paper presents a comparative study of Fischer-Tropsch synthesis in single channel milli-fixed bed, conventional centimetric fixed bed and slurry stirred tank reactors. In the three reactors, the catalytic measurements were carried out with the same conventional platinum-promoted alumina supported cobalt catalyst at 493 K and 20 bar using a stoichiometric syngas ratio (H(2)/CO = 2). The single channel milli-fixed bed reactor displays a higher initial Fischer-Tropsch reaction rate than the conventional centimetric fixed bed reactor. This effect was assigned to a better temperature control and less significant catalyst deactivation during the startup of the single channel milli-fixed bed reactor. The slurry stirred tank reactor shows much lower hydrocarbon productivity than the milli- and centimetric fixed bed reactors, which is probably due to incomplete catalyst reduction. A considerable catalyst deactivation due to the uncontrolled temperature hike can occur during the reactor startup in the conventional centimetric fixed bed reactor. The slurry stirred tank and milli-fixed bed reactors show similar apparent deactivation behavior. (C) 2011 Elsevier B.V. All rights reserved

Identification of the active species in the working alumina-supported cobalt catalyst under various conditions of Fischer–Tropsch synthesis

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Bimetallic Fe-Ni/SiO2 catalysts for furfural hydrogenation: Identification of the interplay between Fe and Ni during deposition-precipitation and thermal treatments

Supported Fe-Ni catalysts have been reported for their activity and selectivity in the hydrogenation of unsaturated organic molecules. However, the control of the size and composition of the bimetallic nanoparticles remains a bottleneck when oxide-supported catalysts are prepared by impregnation, and alternative procedures should be investigated. Starting with Ni(II) and Fe(II) sulfates as precursor salts, deposition-precipitation with urea (DPU) on SiO2 in an inert atmosphere initially leads to the formation of an ill-crystallized Fe-containing Ni(II) 1:1 phyllosilicate, which reduces under hydrogen at 700°C into bimetallic fcc Fe-Ni nanoparticles of 5.4 nm in average. Compared with the composition of the DPU solution (50 Fe at %, 50 Ni at %), an excess of Ni is detected on the catalyst (32 Fe at %, 68 Ni at %), due to the preferential reaction of Ni2+ ions with silica. In situ X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy show that the reduction of Fe ions to the metallic state is triggered by the formation of reduced Ni centers above 350°C, and, from then, proceeds progressively, resulting in an excess of Fe in the outer shells of the bimetallic particles. The composition of individual Fe-Ni particles evidences a standard deviation of 8%. The bimetallic Fe-Ni/SiO2 catalyst gives high yields in furfuryl alcohol in the hydrogenation of furfural, in contrast with an analog Ni/SiO2 catalyst that favours side-reactions of etherification, hydrogenolysis and hydrogenation of the furan ring