Neighboring Zn–Zr Sites in a Metal–Organic Framework for CO2 Hydrogenation,Journal of the American Chemical Society

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Neighboring Zn–Zr Sites in a Metal–Organic Framework for CO2 Hydrogenation
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2021-06-07 , DOI: 10.1021/jacs.1c03283
Jingzheng Zhang ₁ , Bing An ₁ , Zhe Li ₁ , Yonghua Cao ₁ , Yiheng Dai ₁ , Wangyang Wang ₁ , Lingzhen Zeng ₁ , Wenbin Lin ₂ , Cheng Wang ₁

Affiliation

ZrZnO_x is active in catalyzing carbon dioxide (CO₂) hydrogenation to methanol (MeOH) via a synergy between ZnO_x and ZrO_x. Here we report the construction of Zn²⁺–O–Zr⁴⁺ sites in a metal–organic framework (MOF) to reveal insights into the structural requirement for MeOH production. The Zn²⁺–O–Zr⁴⁺ sites are obtained by postsynthetic treatment of Zr₆(μ₃-O)₄(μ₃-OH)₄ nodes of MOF-808 by ZnEt₂ 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 CO₂ 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 Zn²⁺–O–Zr⁴⁺ centers instead of Zn_mO_n clusters. Temperature-programmed desorption (TPD) of hydrogen and H/D exchange tests show the activation of H₂ by Zn²⁺ centers. Open Zr⁴⁺ sites are also critical, as Zn²⁺ centers supported on Zr-based nodes of other MOFs without open Zr⁴⁺ sites fail to produce MeOH. TPD of CO₂ reveals the importance of bicarbonate decomposition under reaction conditions in generating open Zr⁴⁺ sites for CO₂ activation. The well-defined local structures of metal-oxo nodes in MOFs provide a unique opportunity to elucidate structural details of bifunctional catalytic centers.

中文翻译：

用于 CO ₂加氢的金属-有机骨架中相邻的 Zn-Zr 位点

ZrZnO _x在通过ZnO _x和ZrO _x之间的协同作用催化二氧化碳(CO ₂ )加氢为甲醇(MeOH)方面具有活性。在这里，我们报告了金属有机框架 (MOF)中 Zn ²⁺ –O–Zr ⁴⁺位点的构建，以揭示对甲醇生产的结构要求的见解。Zn ²⁺ –O–Zr ⁴⁺位点是通过ZnEt ₂对MOF-808的Zr ₆ (μ ₃ -O) ₄ (μ ₃ -OH) ₄节点进行后合成处理获得的温和的热处理以去除封端配体并提供用于催化的暴露金属位点。所得 MOF-808-Zn 催化剂在 250 °C 下的CO ₂加氢反应中表现出 >99% 的 MeOH 选择性和高达 190.7 mg _MeOH g _Zn^–1 h ^–1的高时空产率。催化活性稳定至少 100 小时。X 射线吸收光谱 (XAS) 分析表明存在 Zn ²⁺ –O–Zr ⁴⁺中心而不是 Zn _m O _n簇。氢的程序升温解吸 (TPD) 和 H/D 交换测试表明 H ₂被 Zn ²⁺中心活化。打开锆石⁴⁺位点也很关键，因为在没有开放 Zr ⁴⁺位点的其他 MOF 的基于 Zr 的节点上支持的Zn ²⁺中心无法产生 MeOH。CO _{2 的}TPD揭示了反应条件下碳酸氢盐分解在生成用于 CO ₂活化的开放 Zr ⁴⁺位点的重要性。MOF 中金属氧节点的明确局部结构为阐明双功能催化中心的结构细节提供了独特的机会。

更新日期：2021-06-17

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