CO2 hydrogenation over ZnFe2O4–zeolite hybrid catalysts: Effects of pore structure and acid site distribution

Abstract

The hydrogenation of CO 2 to value-added hydrocarbons via tandem ZnFe 2 O 4 -zeolite hybrid catalysis represents a promising carbon-neutral strategy. However, the distinct roles of the zeolite pore topology and acid-site characteristics in shaping the product selectivity remain unclear. In this study, we systematically evaluate the hydrogenation performance of catalysts paired with three zeolites with 10-membered-rings (MFI, MEL, and MRE). Although the CO 2 conversion remains comparable (>30%), the product selectivity differs markedly across the examined zeolite frameworks. ZSM-48 (MRE) favors olefins (~54%) with low iso-paraffin (11.5%) and aromatic (15.2%) selectivities. ZSM-11 (MEL) shows a higher iso-paraffin selectivity (30.0%) than ZSM-48, whereas its aromatic selectivity remains near 16%, corresponding to a distinct hydrocarbon distribution within the examined catalyst set. ZSM-5 (MFI) exhibits the highest aromatic selectivity (26.8%) with balanced iso- and n-paraffin selectivities (~30% each). The higher aromatic fraction observed with the MFI-containing hybrid is consistent with a contribution from its asymmetric intersection environment, although framework topology cannot be independently isolated from the other zeolite properties in this cross-topology comparison. The effect of acid sites distributed at the asymmetric intersections of ZSM-5 is additionally examined using ZSM-5 synthesized in a Na-free medium (ZSM-5-NF), which exhibits a more intersection-enriched Al distribution as indicated by 27 Al MQ MAS NMR and Co 2+ -probed UV–Vis spectroscopy. The ZSM-5-NF catalyst, with enrichment of intersection-associated Al environments, exhibits an increased aromatic selectivity from 26.8% to 32.3%. Overall, these results indicate a topology-associated hydrocarbon-selectivity trend among the examined 10-MR zeolites under a common ZFO component and fixed reaction conditions, while intersection-associated Al enrichment in ZSM-5-NF is associated with a further increase in aromatic selectivity within a coupled set of acidic and textural changes.