Selective formation of aromatics through CO2 hydrogenation over HZSM-5 cladded FeK core–shell catalyst

Abstract

The selective hydrogenation of CO₂ to produce aromatics presents an intriguing approach for carbon utilization and the formation of high-value chemicals. This study presents a novel core–shell FeK@HZSM-5 catalyst, developed by cladding HZSM-5 zeolite onto a K-promoted Fe oxide core, to enable the direct conversion of CO₂ into aromatics. Under optimum reaction conditions (320 °C, 2.0 MPa, H₂/CO₂ = 3), the FeK@HZSM-5 catalyst accomplishes 43.2 % selectivity for aromatics at 31.1 % conversion of CO₂, outperforming the physically mixed FeK-HZSM-5 catalyst (aromatics selectivity: 31.8 %) while keeping CH₄ selectivity below 12 %. Mechanistic investigations reveal that the reaction follows a tandem RWGS-FTS pathway, with olefins serving as crucial intermediates. Robust interactions between Fe and zeolite enhance the stability of active Fe₅C₂ phases and graphitic carbon, promoting olefin chain growth while inhibiting methanation. The appropriate density of Brønsted acid sites facilitates efficient aromatization, whereas an excess of acidity and increased shell thickness result in over-hydrocracking. The FeK@HZSM-5 catalyst exhibits a notable improvement in CO₂ adsorption capacity, attributed to the occurrence of increased oxygen vacancies and higher surface basicity, which facilitates effective CO₂ activation. The confinement effect of the zeolite shell further modulates intermediate diffusion and water retention. A FeK-to-HZSM-5 wt ratio of 1:2 provides the optimal structural and chemical balance. The catalyst exhibits remarkable stability after 100 h of operation with minimal coke deposition, emphasizing its promise for industrial CO₂-to-aromatics conversion.