Effect of chromium addition on the behaviour of iron/activated carbon catalysts for carbon monoxide hydrogenation

Abstract

To study the effect of chromium addition to iron/active carbon catalysts in the carbon monoxide hydrogenation reaction at atmospheric pressure, five FeCr/C catalysts were prepared with a range of Cr/Fe atomic ratii. Three samples were prepared by coadsorption of the respective nitrates and the other two by successive adsorption. Catalysts were characterized by carbon monoxide chemisorption at 298 K and their catalytic activity was studied in differential conditions after reduction in hydrogen at 673 K. Both the irreversible carbon monoxide chemisorption and the catalytic activity of the samples decrease with increasing chromium content, this decrease being more important in the catalyst prepared by successive adsorption, with the chromium precursor added after adsorption of iron. Chromium favors methane production without modifying the selectivity towards alkenes. These results are interpreted on the basis of a diluent effect of chromium, which results in a decrease in the amount of surface-reduced iron sites.