Active Sites and Carbon Gasification Kinetics: Theoretical Treatment and Experimental Results

Abstract

Recent studies using transient kinetics (TK) and temperature programmed desorption (TPD) for the determination of (a) intermediate carbon oxygen surface complexes (at a steady-state gasification) and (b) intrinsic gasification or turn-over rates are critically discussed. Experimental results with transient kinetics and their simulation let conclude that temperature programmed desorption may exhibit some advantage. A further confirmation of this conclusion are the values of the activation energies of carbon dioxide gasification. Turn-over rates calculated on the basis of TK results yield values which are lower than the apparent activation energies, which again are lower than the activation energies calculated on the basis of TPD results. The latter ratio is more plausible, because it is equivalent to a decrease of the concentration of carbon-oxygen surface complexes with increasing gasification temperature.