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 COx 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.