Tuning e-fuel product distribution by combining a Na-promoted Fe-based catalyst with BETA zeolites in CO2-modified Fischer-Tropsch synthesis

The integration of acidic zeolites with Fe-based catalysts provides a promising strategy to overcome the broad hydrocarbon distribution of CO2-modified Fischer-Tropsch synthesis (FTS) through in situ product upgrading. In this work, a 5 wt.% Na-Fe3O4 catalyst is combined with commercial BETA zeolites having nominal SiO2/Al2O3 ratios of 25, 38, and 360 to investigate the effects of zeolite acidity and catalyst configuration at 360 °C and 2.3 MPa. CO2 conversion remains within 37-44%, whereas BETA markedly alters hydrocarbon selectivity by promoting cracking, isomerization, and H-transfer reactions. Mössbauer spectroscopy and STEM-EDS show that close contact between the catalytic functions modifies the iron-phase distribution and promotes Na migration toward the zeolite. Physical separation in the dual-bed configuration reduces the Na content detected on BETA-38 from 1.02 to 0.20 mmolNa gzeolite-1. NH3-TPD reveals a substantial loss of acidity after reaction, although the residual acid sites remained sufficient to sustain secondary upgrading. Detailed Hydrocarbon Analysis (DHA) and GC-MS show a strong depletion of linear olefins and enrichment in branched and cyclic hydrocarbons. For the layered BETA-38 system, the reconstructed liquid product contains 71.3 vol.% naphtha-range and 21.7 vol.% kerosene-range hydrocarbons, with only 7.0 vol.% gasoil and heavier residue. The dual-bed configuration promotes more extensive cracking and an almost entirely naphtha-range liquid. Despite the wide initial acidity range, product distributions are similar, identifying catalyst architecture as the dominant parameter for tuning CO2-derived fuel composition.