Tandem catalytic process for CO2 methanation using ketonization-derived hydrogen over TiOx

Abstract

Carbon dioxide (CO₂) hydrogenation technology has been identified as a promising strategy to mitigate global warming. However, its practical approach faces significant challenges, one of which is the requirement for an external hydrogen supply. One potential solution involves coupling biomass conversion with CO₂ hydrogenation, utilizing the derived hydrogen (H*) for converting CO₂ into value-added products. Ketonization is one of the effective biomass conversion techniques capable of producing ketones and potentially generating hydrogen through hydrogen abstraction from reactants, as proposed by reaction mechanisms. This study investigated the CO₂ hydrogenation utilizing in-situ generated H* from methyl palmitate ketonization over TiO_x catalysts with varying oxygen vacancies (O_v) levels. The results indicated that Bl.TiO_x, possessing the highest O_v level, exhibited superior ketonization activity (70 % conversion), leading to enhanced H* generation, resulting in production of H₂ (100 µmol.min⁻¹) and CH₄ production (357 µmol.min⁻¹). This enhancement is attributed to O_v in facilitating acid-base pairs formation, thereby promoting blue H₂, CH₄, and palmitone production. Interestingly, CO₂ co-feeding enhanced both CH₄ production to 210 μmol.min⁻¹ via CO₂ methanation and blue H₂ generation to 480 μmol.min⁻¹ through accelerated coke dehydrogenation on Bl.TiO_x catalyst, while having little impact on ketone formation. Another surprising advantage of CO₂ co-feeding was the enhanced stability of the catalyst for the ketonization reaction, potentially attributable to the filling of O_v sites with CO₂. The findings of this study highlighted that co-feeding CO₂ into the ketonization process provides a novel strategy for CO₂ methanation using biomass-derived hydrogen, simultaneously enhancing biofuel production and catalyst stability.