Molten salt-modified CaO catalyzed CO₂ gasification of biochar: reactivity and structural evolution

Biomass gasification technology has attracted significant interest for its capability to convert biomass into high-quality syngas. In this paper, molten salt-modified CaO catalysts (M/CaO) were produced by modifying conventional CaO with molten salt to catalyze the CO₂ gasification of waste biochar. The impact of CO₂ flow rate, molten salt loading, and gasification temperature on the gasification reaction was initially investigated. The results illustrated that the introduction of molten salt significantly enhanced the catalytic effect of CaO on the CO₂ gasification of biochar, and the maximum CO release rate increased from 134.7 mg/min (pure CaO) to 162.36 mg/min ((Li-Na–K)/CaO). The release rate of CO initially rose and once decreased as the increasing of flow rate of CO₂. The reactivity of CO₂ gasification was highly positively correlated with the reaction temperature. The physicochemical properties of the biochar before and after the reaction and the gasification reaction mechanism were analyzed by the characterization of XRD, XPS, BET, FTIR, and TG. The formation of a molten layer at elevated temperatures enhances the dispersion of CaO and prevents sintering, thus augmenting the contact between the sample and CaO. Furthermore, the existence of molten salt has the potential to mitigate the phenomenon of reactive inactivation in CaO, thus enhancing its catalytic stability. This study presents a possible solution for achieving negative carbon emissions.