TPR and SIMS studies of CaCO₃ catalyzed CO₂ gasification of carbon

Temperature-programmed reaction (TPR) combined with isotope labelling is used to probe the CaCO₃-catalyzed CO₂ gasification of carbon. The identity and reaction chemistry of the surface species are probed with secondary ion mass spectrometry (SIMS). As carbon gasification begins, most of the CaCO₃ decomposes to form CaO and CO₂. The CaO species, which are observed by SIMS, appear to catalyze gasification by an oxidation-reduction mechanism that is similar to the mechanisms for Na and K catalysts. The catalyst oxidation step is shown to be reversible and in equilibrium, while the catalyst reduction step is rate limiting and essentially irreversible.