Study of Ca Catalysis on Carbon Gasification with ¹⁸O₂

Ca-loaded graphite was gasified with labeled O₂ and gas analysis during the O₂ gasification was carried out. CO₂ formation in the gasification was greatly enhanced by the addition of Ca. The surface oxygen compounds, C(O), formed by O₂ chemisorption during the gasification were analyzed by the subsequent temperature-programmed desorption. Furthermore, the surface analysis of Ca-loaded graphite after gasification was done with secondary ion mass spectrometer. From these data, the function of Ca on the C0₂ formation was explained as follows: (1) formation of C(O) by active oxygen from catalyst surface, CaO(O), (2) further reaction of the C(O) with active oxygen to form C(O-O), and (3) its desorption as CO₂. The essential point of this mechanism is that such CO₂ formation process intensively occurs only on the sites which are in contact with the catalyst particles. Many C(O) complexes are formed over the wide area apart from the catalyst, but they are not extensively involved in the CO₂ formation.