Reverse Boudouard reaction: A key process for catalyst regeneration, biomass/waste valorization and clean energy production

The Reverse Boudouard Reaction (RBR) is a key chemical process with significant industrial relevance in various transformations such as gasification, coke removal, and smelting in blast furnaces. Although it is a highly endothermic reaction favored at elevated temperatures, RBR offers a promising pathway not only for mitigating atmospheric CO₂ emissions and producing clean fuels but also for waste/biomass valorization. Several factors can influence the rate of RBR. Typically, these factors are the carbon characteristics, oxygen transfer mechanism, the type of catalyst and its underlying mechanism and the reaction environment. Carbon with lower graphitic character and a high defect density is more easily gasified. In addition, the presence of dopants and oxygenated groups enhances the CO 2 gasification. For non-catalytic systems, RBR takes place via direct CO 2 dissociation at carbon surface, hence the reaction rate remains low. In the presence of alkali and alkaline earth metal oxides, in particular, K 2 O, Na 2 O, CaO and MgO are the most active catalysts for RBR owing to their ability to adsorb and activate CO 2 . In addition, Fe and Ni can catalyze RBR assigned to their ability to dissociate CO 2 and bind with oxygenated species resulting from CO 2 dissociation and hence mediate oxygen transfer through redox cycles. Mixed system comprised of transition metals/alkali or alkaline earth metal oxide can provide enhanced reactivity attributed to their dual function of CO₂ activation and oxygen transfer. In systems containing ceria, CO₂ can be activated at oxygen vacancies, producing CO and replenishing lattice oxygen, which is subsequently transferred to the carbon surface, oxidizing it to CO and regenerate vacant sites in a redox cycle. In metal-supported ceria, the metal phase facilitates CO₂ adsorption and dissociation, while the oxide support enhances oxygen mobility and storage capacity, enabling continuous oxygen supply to the carbon. Despite being investigated in diverse contexts, the reaction and its applications were not comprehensively reviewed or emphasized in previous studies. In this review, we highlighted the fundamental aspects of the RBR as a universal approach for CO₂ activation and valorization, which is mainly influenced by carbon structure, catalyst functionality, and oxygen transfer mechanisms. In addition, its practical applications were highlighted with special reference to catalyst regeneration, biomass valorization, and electricity generation via direct carbon fuel cells. Although, RBR is the main stream in these applications, however, they differ in terms of carbon characteristics, catalyst type and operating environment.