A mechanism for sodium oxide catalyzed CO 2 gasification of carbon

Abstract

Temperature-programmed reaction was used to study sodium oxide catalyzed CO 2 gasification of 13C. The stoichiometry of the reaction is CO 2 + a 13 C CO + (1 − a) 13 CO 2 + (2a − 1) 13CO, where the factor a is dependent on CO 2 conversion. This stoichiometry is consistent with a mechanism composed of a reversible catalyst oxidation step and an irreversible catalyst reduction step. On the surface the catalytic surface species is oxidized by CO 2 and forms CO; during the reduction reaction the oxidized species decomposes. The reversible oxidation step, which incorporates substrate carbon into gas-phase carbon dioxide, is at equilibrium. Carbon monoxide, via the reverse of the oxidation reaction, inhibits gasification of the substrate by decreasing the number of oxidized catalytic sites on the surface. The catalyst appears both to increase the amount of oxygen on the surface and to decrease the activation energy of the reduction reaction. Similar mechanisms describe potassium- and calcium-catalyzed gasification, but Na 2CO 3 does not interact with the carbon surface as readily as K 2CO 3 does. A similar mechanism is also consistent with steam gasification results reported by others and shows that a separate water-gas shift reaction is not required for CO 2 production.