One-Pass Hydrogenation of CO₂ to Multibranched Isoparaffins over Bifunctional Zeolite-Based Catalysts

Abstract

Direct hydrogenation of CO2 to high-valued fuels is a process that can be likened to the “Trapping two fishes with a single worm”. This win–win situation addresses the ever-increasing problems associated with excessive CO2 emission as well as renewable energy supply. In this contribution, a thorough study is realized on 10 MR zeolites with one-dimensional (1D) and three-dimensional (3D) structures for the direct hydrogenation of CO2 to gasoline (C5–C11), with a high fraction of multibranched isoparaffins. Emphasis is placed on identifying the factors that favor isomerization and increase the number of branches on the isomers. Zeolites SAPO-11 and ZSM-5 were configured with Na/Fe3O4 (NaFe) in single-, dual-, and various triple-bed arrangements for this investigation. A dual-bed reaction with SAPO-11 and ZSM-5 coupled individually with the NaFe catalyst showed relatively higher selectivity for low-branched isoparaffins and aromatics, respectively. In the event of combining both the zeolites with NaFe as a physical mix and triple-bed systems, isoparaffins selectivity increased with improved multibranched isomers and reduced aromatics at the same time. Among these different tactics, the triple-bed system comprising the NaFe catalyst followed sequentially with SAPO-11 and ZSM-5 maximizes the selectivity for isoparaffins with the enhanced formation of multibranched isomers. The selectivity of gasoline reached 71.7% in hydrocarbons (HCs) with a maximum of 38.2% isoparaffins possessing a RON value of 91.7 at CO2 conversion of 31.2%. Multibranched isomers accounted for 28.3% in all C5+ isoparaffins, much higher than that of the single zeolite. Purposefully, hypothetical knowledge obtained from the prior model reactions on the zeolites served as a strong foundation to support and give insight into the results from the CO2 hydrogenation reactions.