Pathway regulation of carbon dioxide hydrogenation on iron-based-zeolite bifunctional catalysts

Selectively producing high-value chemicals through CO2 hydrogenation on metal-zeolite bifunctional catalysts has garnered significant attention. In this study, we synthesized a series of bifunctional catalysts consisting of an iron-based CO2-Fischer-Tropsch Synthesis (FTS) component and Na-modified H-SAPO-34 zeolite, We investigated the role of zeolite acidity, the proximity of two components, and catalyst bed configuration in tailoring the product distribution and reaction pathways. The highest C2-C4 olefins space-time yield (STY), reaching 18.87 mmol·g-1·h-1 (based on the quantity of iron-based component) was achieved by the physically mixed FeZnNa&Na-SAPO-2 catalyst over 100 hours time-on-stream. During the CO2 hydrogenation reaction, the strong acidity of zeolite effectively cracked C5+ products but also led to a decrease in O/P ratio of hydrocarbon products. The promotion of short-chain olefins, especially in the physically mixing configuration, was due to the enhanced adsorption CO intermediate on zeolite, which boosted the subsequent FTS reaction on the adjacent iron sites. In addition, Na in Na-SAPO-2 was found to be in a dynamic and active state, potentially improving the stability of the bifunctional catalyst. This study offers deep insights into designing bifunctional catalysts with a narrowed product distribution from CO2 hydrogenation. © 2024 Elsevier B.V.