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.

Keen interest is taken in zeolite-encapsulated metal nanoparticles (NPs) owing to their excellent performance and ultrastability in heterogeneous catalysis. Herein, we propose a simple and efficient method to contain Fe NPs within zeolite Y microcrystals. First, a lowpressure technique was developed to successfully synthesize the zeolite Y microcrystals. The technique was then invoked, using Fe NPs fixed in nanosized C spheres as a precursor, to prepare zeolite Y-embedded Fe composite catalysts. The C spheres served as a template that restricted Fe NP growth within zeolite Y. Above all, the successful confinement of small Fe NPs within the microcrystals of zeolite Y enhanced the catalyst activity with 36.2% selectivity for light olefins (C 2 −C 4 = ) at a CO conversion of 91.2% during evaluation in Fischer−Tropsch synthesis. The techniques presented in this work open up a new avenue worth exploiting for the synthesis of nano/microcrystalline materials and highly active metal− zeolite composites in heterogeneous catalysis.

Fischer-Tropsch synthesis (FTS) remains the technology of the future for sustainable production of hydrocarbon fuels. Till date, controlling the hydrocarbon selectivity is still a major challenge since it tends to...

No abstract

No abstract