Alkali metal catalyzed CO2 gasification of carbon

The mechanisms for CO2 gasification of carbon with alkali metal catalysts were investigated with pulse reaction and temperature-programmed desorption techniques. Details of oxygen-transfer reactions between oxidant and alkali metal, and between alkali metal oxygen complex and carbon, were discussed. It is suggested that two processes are involved in both catalyst oxidation and catalyst reduction steps. The two active sites, alkali metal cluster (or aggregated metal) and dispersed alkali metal which is a precursor for the cluster, exist for all alkali metals. On these sites, fast and slow oxidation and reduction cycles proceed. However, the characteristics of these sites are quite different among the alkali metals. The stability of cluster oxide on carbon decreased in the following order: Li > Na > K > Rb, and the reverse order afforded the decrease in the degree of interaction between metal and carbon. The reactivity of catalyst oxidation is the same order as that of the stability of cluster oxide, and the reactivity of catalyst reduction is essentially the same order as that in the degree of interaction with carbon. The stability of cluster oxide and the degree of interaction between the alkali metal and carbon were reflected to the mechanism of the steady-state gasification. Both the fast and the slow paths proceeded in Na- or K-loaded carbon. However, the slow path was not seen in Li-loaded carbon.