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 γ-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 m 2 g −1, meso- and macropore surface areas reaching values of 190–270 m 2 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 Al 2O 3 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.