High-yield production of aromatics over CuFeO2/hierarchical HZSM-5 via CO2 Fischer–Tropsch synthesis

Abstract

The direct conversion of CO₂ to aromatics with the aid of renewable hydrogen sources is a promising way to mitigate the CO₂ emissions and simultaneously replace the dwindling fossil resources for the production of valuable chemicals. Even though some excellent results have been obtained for the direct conversion of CO₂ to aromatics via the methanol-mediated or modified Fischer–Tropsch synthesis (FTS) pathway, the low space–time yield (STY) of aromatics and the high selectivity of C₁ by-products (CO and CH₄) are the main bottlenecks. Herein, we demonstrate that the bifunctional catalyst (CuFeO₂/hierarchical HZSM-5) composed of defafossite-CuFeO₂ exhibits outstanding catalytic performance for producing olefins from CO₂ hydrogenation, and hierarchical HZSM-5 can catalyze the direct CO₂ conversion to aromatics with a high efficiency by single pass. Under the optimized reaction conditions, the CuFeO₂/hierarchical HZSM-5 bifunctional catalyst can suppress the total selectivity of CO and CH₄ to less than 12% with a high aromatics STY of 431.8 mgCH₂ gcat⁻¹ h⁻¹ at a CO₂ conversion of 52.8% and outperforms previously reported catalysts. In addition, upon the selective elimination of external surface acidity via epitaxial growth of a Silicalite-1 shell on the hierarchical HZSM-5 surface, the fraction of p-xylene in xylenes is improved from 27.8% to 66.9%. Furthermore, H recycling is realized via the intimate synergy between CuFeO₂ and hierarchical HZSM-5 and demonstrated to be significantly vital for improving the aromatics formation. The CO₂ adsorbed on CuFeO₂ also acts as an acceptor for H species produced from the olefin dehydrogenative aromatization in hierarchical HZSM-5, which in turn increases the aromatics STY by shifting the chemical thermodynamic equilibrium.