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

Carbon black-supported molybdenum sulfide catalysts

Four carbon black samples differing in surface area, pH and surface properties (oxygen functionality) were pore volume impregnated with aqueous molybdate solutions as to achieve a Mo loading of 0.5 Mo atoms per nm2 support surface area. Dispersion measurements obtained by means of X-ray photoelectron spectroscopy, dynamic oxygen chemisorption and transmission electron microscopy, indicated the presence of highly dispersed molybdate in all precursor samples, which upon sulfidation was converted into molybdenum sulfide with a particle size varying between 3.5 and 13.5 nm dependant on the type of carbon black support. To explain these dispersion differences the interaction between molybdate ions and the carbon surface was studied by means of FTIR and XPS. No major changes were observed in the oxygen functionality of the carbon black upon loading with molybdate. Some minor changes were, however, observed by means of FTIR which could point to a chemical reaction between an aryl ether functional group and the molybdate ions

The Structure of the Cobalt Sulfide Phase in Carbon-Supported Cobalt and Cobalt-Molybdenum Sulfide Catalysts as Studied by EXAFS and XANES.

An X-Ray absorption spectroscopy study has been carried out on a carbon-supported Co and Co-Mo sulfide catalyst, the latter consisting of a fully sulfided Co-Mo-S (type II) phase. Detailed information on the structure of the cobalt sulfide phase is obtained by comparing the EXAFS and XANES spectra of the catalysts with those of Co9S8 and CoS2 reference compounds. It is shown that the cobalt atoms in the Co-Mo-S phase have an octahedral-like sulfur coordination while the cobalt atoms in the sulfided Co/C catalyst have a larger fraction of octahedral cobalt than Co9S8. On the basis of these results, the high HDS activity of a sulfided Co/C catalyst can be understood since it appears that the structure of the cobalt sulfide phase in Co/C is in agreement with that in Co-Mo/C. In the Co-Mo-S phase, approximately one cobalt atom is in contact with one molybdenum atom at a distance of 2.85 Å

The structure of the cobalt sulfide phase in carbon-supported Co and Co-Mo sulfide catalysts as studied by EXAFS and XANES

An x-ray absorption spectroscopy study was carried out on a sulfided Co/C and a Co-Mo/C catalyst, consisting of a fully sulfided Co-Mo-S phase. By comparing the EXAFS and x-ray absorption near-edge structure spectra of the catalysts with those of pure Co9S8 and CoS2 ref. compds., the Co ions in the Co-Mo-S phase have an octahedral-like S coordination while the Co ions in the Co/C catalyst have a larger fraction of octahedral Co than Co9S8

Structure of Cobalt Sulfide Phase in Carbon-Supported Cobalt and Cobalt-Molybdenum Sulfide Catalysts

An X-Ray absorption spectroscopy study has been carried out on a carbon-supported Co and Co-Mo sulfide catalyst, the latter consisting of a fully sulfided Co-Mo-S (type II) phase. Detailed information on the structure of the cobalt sulfide phase is obtained by comparing the EXAFS and XANES spectra of the catalysts with those of Co9S8 and CoS2 reference compounds. It is shown that the cobalt atoms in the Co-Mo-S phase have an octahedral-like sulfur coordination while the cobalt atoms in the sulfided Co/C catalyst have a larger fraction of octahedral cobalt than Co9S8. On the basis of these results, the high HDS activity of a sulfided Co/C catalyst can be understood since it appears that the structure of the cobalt sulfide phase in Co/C is in agreement with that in Co-Mo/C. In the Co-Mo-S phase, approximately one cobalt atom is in contact with one molybdenum atom at a distance of 2.85 Å

Carbon black-supported molybdenum sulfide catalysts

Four carbon black samples differing in surface area, pH and surface properties (oxygen functionality) were pore volume impregnated with aqueous molybdate solutions as to achieve a Mo loading of 0.5 Mo atoms per nm2 support surface area. Dispersion measurements obtained by means of X-ray photoelectron spectroscopy, dynamic oxygen chemisorption and transmission electron microscopy, indicated the presence of highly dispersed molybdate in all precursor samples, which upon sulfidation was converted into molybdenum sulfide with a particle size varying between 3.5 and 13.5 nm dependant on the type of carbon black support. To explain these dispersion differences the interaction between molybdate ions and the carbon surface was studied by means of FTIR and XPS. No major changes were observed in the oxygen functionality of the carbon black upon loading with molybdate. Some minor changes were, however, observed by means of FTIR which could point to a chemical reaction between an aryl ether functional group and the molybdate ions