Direct Synthesis of <i>para</i>-Xylene from CO<sub>2</sub> Hydrogenation with a Record-High Space-Time Yield
Lijun Zhang, Teng Li, Wenjie Xiang, Zhiwei Ye, Luyao Wu, Wei Xia, Hao Huang, Zhihao Liu, Xiuyun Jiang, Guangbo Liu, Zhiliang Jin, Weizhe Gao, Hongliang Li, Jie Zeng, Noritatsu Tsubaki
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.