CARBON GASIFICATION CATALYZED BY CALCIUM - A HIGH-VACUUM TEMPERATURE PROGRAMMED DESORPTION STUDY

High vacuum temperature programmed desorption (HVTPD) experiments after CO2 treatment on bulk CaO and calcium-carbon samples have been performed in order to obtain information about the working mechanism of calcium as a catalyst in the CO2 gasification of carbon. The main characteristics of these HVTPD spectra are two well-defined CO2 peaks (at almost-equal-to 675 K and almost-equal-to 800 K) and two CO peaks (at almost-equal-to 850 and almost-equal-to 1125 K) of similar size, independent of the calcium content. The HVTPD experiments are interpreted on the basis of the reversibility of the bulk CaCO3 decomposition reaction and the different kinetic behaviour of the steps involved in the mechanism of carbon gasification catalyzed by calcium. TPD experiments carried out under high vacuum conditions allow the two steps corresponding to the catalysis of carbon gasification by calcium to be differentiated, under conditions in which no secondary reactions occur.