Cascade Conversion of CO ₂ to Gasoline–Range Hydrocarbons over KFeZnO x and Zn/HZSM-5 Catalysts: Role of Zn as an Acidity Modifier

Zeolite catalysts play a pivotal role in determining the hydrocarbon product distributions in CO2-to-fuels conversion via a cascade process, consisting of (i) CO2 Fischer–Tropsch synthesis to light olefins in the first reactor and (ii) subsequent oligomerization of these olefins in the second reactor. Herein, we systematically investigated the relationship between the physicochemical properties and catalytic performances of Zn/HZSM-5 by varying the synthetic parameters, such as preparation method and drying temperature. The drying temperature after incipient wetness impregnation (IWI) determined the dispersion and chemical states of the Zn species; low-temperature favored the formation of Zn2+ species in both the micropores and external surface regions, whereas high-temperature led to the formation of ZnO particles on the external surface. Increasing the Zn content progressively decreased the Brønsted acid site/Lewis acid site ratio, indicating an interaction between Zn species and Brønsted acid site in the zeolite framework. These acidity modifications limit the formation of aromatics and heavy hydrocarbons. 3Zn/HZSM-5, prepared by IWI with low-temperature drying, achieved the highest C5–C12 hydrocarbon selectivity (97%) in the liquid products. This study demonstrates that controlling synthetic parameters for supported metal catalysts provides an effective strategy for optimizing catalytic performance and durability in CO2-to-fuels conversion.