Characterization of active sites for methane decomposition on carbon black through acetylene chemisorption

The use of carbon black as a stable catalyst for methane decomposition for the production of hydrogen without CO_x emissions has recently been reported. In order to characterize the catalytically active sites on carbon black, acetylene adsorption was examined at 773 and 873 K by using a pulse technique. As the injection was repeated at 773 K, the adsorbed amount gradually decreased and eventually the adsorption ceased. At 873 K a constant amount of C₂H₂ was consumed repeatedly after several injections. Good relationships were obtained between the methane decomposition rate at 1123 or 1173 K and the cumulative acetylene adsorption at 773 K or the constant acetylene consumption at 873 K. Acetylene adsorption at 773 K can be used for quantitative determination of the number of active sites on the carbon black and the constant consumption at 873 K can be utilized as a probe reaction for comparison of activities of different carbon catalysts. Different physicochemical processes taking place at 773 and 873 K were discussed and a model for these adsorption processes was proposed.