Neighboring Zn–Zr Sites in a Metal–Organic Framework for CO 2 Hydrogenation

作者：Jingzheng Zhang, Bing An, Zhe Li, Yonghua Cao, Yiheng Dai, Wangyang Wang, Lingzhen Zeng, Wenbin Lin, Cheng Wang · 发表于：Journal of the American Chemical Society · 年份：2021 · DOI：10.1021/jacs.1c03283 · 被引用次数：204 · 研究领域：Metal-Organic Frameworks: Synthesis and Applications、Carbon dioxide utilization in catalysis、Catalysts for Methane Reforming

ZrZnO x is active in catalyzing carbon dioxide (CO 2 ) hydrogenation to methanol (MeOH) via a synergy between ZnO x and ZrO x . Here we report the construction of Zn 2+ –O–Zr 4+ sites in a metal–organic framework (MOF) to reveal insights into the structural requirement for MeOH production. The Zn 2+ –O–Zr 4+ sites are obtained by postsynthetic treatment of Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 nodes of MOF-808 by ZnEt 2 and a mild thermal treatment to remove capping ligands and afford exposed metal sites for catalysis. The resultant MOF-808-Zn catalyst exhibits >99% MeOH selectivity in CO 2 hydrogenation at 250 °C and a high space-time yield of up to 190.7 mg MeOH g Zn –1 h –1 . The catalytic activity is stable for at least 100 h. X-ray absorption spectroscopy (XAS) analyses indicate the presence of Zn 2+ –O–Zr 4+ centers instead of Zn m O n clusters. Temperature-programmed desorption (TPD) of hydrogen and H/D exchange tests show the activation of H 2 by Zn 2+ centers. Open Zr 4+ sites are also critical, as Zn 2+ centers supported on Zr-based nodes of other MOFs without open Zr 4+ sites fail to produce MeOH. TPD of CO 2 reveals the importance of bicarbonate decomposition under reaction conditions in generating open Zr 4+ sites for CO 2 activation. The well-defined local structures of metal-oxo nodes in MOFs provide a unique opportunity to elucidate structural details of bifunctional catalytic centers.