Direct Synthesis of <i>para</i>-Xylene from CO₂ Hydrogenation with a Record-High Space-Time Yield

Abstract

The direct synthesis of para -xylene ( p -X) from CO 2 hydrogenation with high space-time yield (STY) remains a significant challenge due to two primary limitations: the Anderson–Schulz–Flory distribution, which restricts the C 8 selectivity to ∼6.8 C%, and the thermodynamic equilibrium, which confines the p -X content among xylene isomers to 15–25%. Herein, we report a composite catalyst, K-FeMn/Hollow ZSM-5, that enables the efficient hydrogenation of CO 2 to p -X by integrating two synergistic catalytic functions. The K-FeMn component facilitates the reverse water-gas shift reaction and Fischer–Tropsch synthesis to olefin processes, generating light olefin intermediates. These intermediates are subsequently transformed to p -X within the hollow ZSM-5 zeolite through oligomerization, cyclization, and aromatization. The hollow ZSM-5 features a suitable pore size to facilitate p -X diffusion only, while its passivated external acid sites effectively suppress isomerization and alkylation of p -X outside the zeolite. As a result, the K-FeMn/Hollow ZSM-5 catalyst achieves a p -X STY of 41.7 g kg cat –1 h –1 at a CO 2 conversion of 46.1%, surpassing all previously reported values. This work demonstrates a novel approach to overcome the local thermodynamic equilibria by specific catalyst design and the spatial separation of processes toward CO 2 hydrogenation into p -X.