Mechanisms of CO2 gasification of carbon catalyzed with group VIII metals .1. Iron-catalyzed CO2 gasification

Mechanisms of iron-catalyzed CO2 gasification of various carbon materials were investigated. The investigation was conducted by using steady-state gasification with thermogravimetric analysis, (CO2)-C-13 pulsed reactions, temperature-programmed desorption (TPD), and powder X-ray diffraction (XRD) technique. Useful information obtained from the above techniques allowed us to elucidate reaction mechanisms. The activities and mechanisms of the iron catalyst were affected by carbon materials. Iron loaded on activated carbon or carbon black had high activity in the CO2 gasification showing ''rapid gasification''. It was elucidated from the responses to the pulsed reaction that both steps in the oxidation and reduction of iron species proceeded very fast and the key step for carbon gasification was the oxidation step of iron metal in the redox cycle. It was also clarified by the TPD spectra and XRD that the active species is highly dispersed iron metal and the deactivated species are sintered iron and highly oxidized iron. For coal chats, in addition to the iron active site showing fast reaction, another reaction site showing slow reaction giving ''satellite peaks'' exists and a larger amount of this site was contained on coal char. In the steady-state gasification, only the fast reaction on highly dispersed iron metal proceeds in all carbons. The amount of active site for the fast reaction determines the gasification rate.