The influence of surface functionality on the activity of carbon-supported catalysts

The aim of this research is to investigate how the presence of surface functional groups can influence the activity of carbon-supported MoS2 catalysts for coal asphaltene hydrogenation. Porous carbons were subjected to various chemical treatments in order to introduce oxygen and nitrogen surface functionalities prior to impregnation with ammonium tetrathiomolybdate. Supports and catalysts were examined by FTIR. Preoxidation of polymer-derived carbons lowered catalyst activity whereas preoxidation of a carbon black composite support increased it. Similar mixed results have been reported in the literature. The modified catalytic activity cannot be unequivocally attributed to surface oxygen. Qualitatively, it is considered that these groups exert some influence, but it is the structure of the carbon which is ultimately the controlling factor. In some cases, oxidation may introduce sites which promote interaction with metal species and, in others, oxidation may modify or destroy favourable sites which are already extant. Prenitriding was found to have a distinct influence in enhancing catalyst activity. The presence of nitrogen-containing surface groups may provide preferential sites for the adsorption of Mo species