C−C Bond Formation in Syngas Conversion over Zinc Sites Grafted on ZSM‐5 Zeolite

• Published in: Angewandte Chemie International Edition Vol. 59; no. 16; pp. 6529 - 6534
• Main Authors: Chen, Yuxiang, Gong, Ke, Jiao, Feng, Pan, Xiulian, Hou, Guangjin, Si, Rui, Bao, Xinhe
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 16.04.2020
• Edition: International ed. in English
• Subjects: Absorption spectroscopy; Aluminosilicates; Aluminum silicates; Carbon dioxide; Catalysts; Conversion; Ethane; Fischer-Tropsch process; Fluorescence; Hydrocarbons; Ion exchange; Magnetic resonance spectroscopy; NMR; NMR spectroscopy; Nuclear magnetic resonance; Selectivity; Spectrum analysis; Synthesis gas; Topology; Zeolites; Zinc; Zinc oxide; zeolites; NMR spectroscopy; hydrocarbons; zinc
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201912869

Despite significant progress achieved in Fischer–Tropsch synthesis (FTS) technology, control of product selectivity remains a challenge in syngas conversion. Herein, we demonstrate that Zn2+‐ion exchanged ZSM‐5 zeolite steers syngas conversion selectively to ethane with its selectivity reaching as high as 86 % among hydrocarbons (excluding CO2) at 20 % CO conversion. NMR spectroscopy, X‐ray absorption spectroscopy, and X‐ray fluorescence indicate that this is likely attributed to the highly dispersed Zn sites grafted on ZSM‐5. Quasi‐in‐situ solid‐state NMR, obtained by quenching the reaction in liquid N2, detects C2 species such as acetyl (‐COCH3) bonding with an oxygen, ethyl (‐CH2CH3) bonding with a Zn site, and epoxyethane molecules adsorbing on a Zn site and a Brønsted acid site of the catalyst, respectively. These species could provide insight into C−C bond formation during ethane formation. Interestingly, this selective reaction pathway toward ethane appears to be general because a series of other Zn2+‐ion exchanged aluminosilicate zeolites with different topologies (for example, SSZ‐13, MCM‐22, and ZSM‐12) all give ethane predominantly. By contrast, a physical mixture of ZnO‐ZSM‐5 favors formation of hydrocarbons beyond C3+. These results provide an important guide for tuning the product selectivity in syngas conversion. Highly dispersed zinc sites were grafted onto aluminosilicate ZSM‐5 zeolite by an ion‐exchange method as [O−‐Zn2+‐O−] and [Zn‐O‐Zn]2+. Such a zinc‐modified zeolite steers C−C coupling selectively toward ethane in direct syngas conversion with a selectivity reaching 86 %. Quasi‐in‐situ solid‐state NMR spectroscopy reveals the evolution of C1 species into the C2 species acetyl (−COCH3) and ethyl (−CH2CH3).