Insights into the Structure–Activity Relationship in Aerobic Alcohol Oxidation over a Metal–Organic-Framework-Supported Molybdenum(VI) Catalyst

Journal Article · Thu Mar 11 00:00:00 EST 2021 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/jacs.0c12963· OSTI ID:1777839

Chen, Yongwei  ^[1]; Zhang, Xuan  ^[2]; Wang, Xingjie  ^[2]; Drout, Riki J.  ^[2]; Mian, Mohammad Rasel  ^[2]; Cao, Ran  ^[2]; Ma, Kaikai  ^[2]; Xia, Qibin  ^[3]; Li, Zhong  ^[3]; Farha, Omar K.  ^[2]

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1. South China Univ. of Technology, Guangdong (China); Northwestern Univ., Evanston, IL (United States)
2. Northwestern Univ., Evanston, IL (United States)
3. South China Univ. of Technology, Guangdong (China)

The understanding of structure–activity relationships at the atomic level has played a profound role in heterogeneous catalysis, providing valuable insights into designing suitable heterogeneous catalysts. However, uncovering the detailed roles of how such active species’ structures affect their catalytic performance remains a challenge owing to the lack of direct structural information on a specific active species. Herein, we deposited molybdenum(VI), an active species in oxidation reactions, on the Zr₆ node of a mesoporous zirconium-based metal–organic framework (MOF) NU-1200, using solvothermal deposition in MOFs (SIM). Due to the high crystallinity of the NU-1200 support, the precise structure of the resulting molybdenum catalyst, Mo-NU-1200, was characterized through single-crystal X-ray diffraction (SCXRD). Two distinct anchoring modes of the molybdenum species were observed: one mode (Mo1), displaying an octahedral geometry, coordinated to the node through one terminal oxygen atom and the other mode (Mo2) coordinated to two adjacent Zr₆ node oxygen atoms in a tetrahedral geometry. To investigate the role of base in the catalytic activity of these Mo centers, we assessed the activity of Mo-NU-1200 for the aerobic oxidation of 4-methoxybenzyl alcohol as a model reaction. The results revealed that Mo-NU-1200 exhibited remarkably higher catalytic reactivity under base-free conditions, while the presence of base inhibited the catalytic reactivity of this species. SCXRD studies revealed that the molybdenum binding motifs (structures of the supported metal on the Zr₆ node in the MOF) changed over the course of the reactions. Following the oxidation without base, both pristine coordination modes (Mo1 and Mo2) evolved into a new coordination mode (Mo3), in which the molybdenum atom coordinated to two adjacent oxygen atoms from the Zr₆ node in an octahedral geometry, while in the presence of base, the pristine Mo1 coordination mode evolved entirely into the pristine Mo2. Here, this study demonstrates the direct observation of an active species’ structural evolution from metal installation to subsequent catalytic reaction. As a result, these subtle structural changes in catalyst binding motifs led to distinct differences in catalytic activities, providing a compelling strategy for elucidating structure–activity relationships.

• Research Organization: Univ. of Minnesota, Minneapolis, MN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
• Grant/Contract Number: SC0012702; ECCS-1542205
• OSTI ID: 1777839
• Journal Information: Journal of the American Chemical Society, Vol. 143, Issue 11; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Oxidation reactions
Crystal structure
Metal organic frameworks
Catalysts
Molybdenum