A bifunctional catalyst for direct CO2 conversion to clean fuels: Mechanistic insights and a comprehensive kinetic model

Abstract

The escalating global concern over CO₂ emissions has spurred extensive research aimed at developing innovative solutions for capturing, storing, and utilizing CO₂, crucial for establishing a closed carbon loop. Thermo-catalytic CO₂ hydrogenation stands out as a promising approach, though challenged by CO₂'s high stability, hindering the production of heavy liquid hydrocarbons. This study explores the design and performance of a bifunctional cobalt-based catalyst, promoted by Ru and supported by multiple shells of carbon, mesoporous silica, and ceria for CO₂ hydrogenation in the Modified Fischer-Tropsch Synthesis (MFTS) route. Through meticulous characterization and evaluation, the catalyst demonstrates suitable textural properties, reducibility, and dispersion of active sites, promoting CO₂ conversion and selectivity towards heavier hydrocarbons, highlighting the significance of catalyst design and operating conditions. The catalyst exhibits notable stability across catalyst deactivation, attributed to its thermal conductivity provided by SiC matrices. SiC-supported catalysts play a pivotal role in enhancing the efficiency, selectivity, and stability of CO₂ hydrogenation catalysts. Moreover, in this study, through meticulous evaluation of elementary reactions based on molecular dynamic (MD) computations, a detailed mechanism for MFTS is presented. Key to this mechanism is the H-assisted CO₂ dissociation pathway, supported by computational analysis. The pathway involves sequential reactions starting from CO₂ adsorption on catalyst sites, followed by successive transformations leading to the formation of hydrocarbon building blocks. Ultimately, a developed MFTS kinetic model based on the MD-evaluated mechanism, which accurately predicts product selectivity across various operational conditions, indicating its robustness and reliability, is presented.