Gasification of Radical Coke with Steam and Steam–Hydrogen Mixtures over Manganese–Chromium Oxides

The coke gasification performance of synthesized Mn–Cr–O catalysts, as well as MnOx, Cr2O3, and α-Al2O3, is evaluated in the presence of steam and steam–hydrogen mixtures. Radical coke is deposited in situonto the catalysts via ethylene pyrolysis at an elevated temperature. Raman spectroscopy analysis reveals that the coke deposited on the various catalysts is similar in nature across all catalysts. Rates of coke gasification are determined from thermogravimetric analysis (TGA) using different gas/vapor feeds including inert/steam and steam/hydrogen mixtures. Addition of hydrogen to a steam feed results in a considerable reduction in reaction rates, suggesting that hydrogen inhibits the production of surface oxygen that is needed for coke gasification. Active Mn3+species on the surface of Mn-rich spinel (Mn1.5Cr1.5O4) and MnO catalysts are hypothesized to be responsible for the significantly higher reaction rates and lower apparent activation barriers for coke gasification under mixed steam–hydrogen conditions.