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

Abstract

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. 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.

In Situ Implanting of Single Tungsten Sites into Defective UiO‐66(Zr) by Solvent‐Free Route for Efficient Oxidative Desulfurization at Room Temperature

“…FT-IR was conducted to monitor the bonding characteristics of the samples.T he new emerging absorption band at 970 cm À1 in FT-IR spectra of W/ UiO-66(Zr) can be attributed to aW = Os tretching vibration (Figure 2a and S14 and S15). [38][39][40] Theb road Raman band of W/UiO-66(Zr) between 960-990 cm À1 can be assigned to the starching mode of terminal W=O bands. [41] Theemergent band at 910-950 cm À1 is related to the weak vibrations of Zr-O-W bonds.…”

Nanochannel-based {BaZn}–organic framework for catalytic activity on the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation

“…19,20 Creating heterometallic MOFs with micro-channels and highly exposed metal joints is a more challenging project, which can be realized by the elaborate design of organic ligands, the reasonable collocation of different metal ions and the subtle control of growth environments. [21][22][23] We have recently reported a series of heterometallic MOFs with excellent physicochemical properties including honeycomb channels, large specific surface area, coexisting Lewis acid-base sites, and high chemical stability. [24][25][26][27] However, the inherent laws regarding the arrangement and coordination number of the involved metal ions in cluster SBUs are still uncovered.…”

Ethylene polymerization with a crystallographically well-defined metal–organic framework supported catalyst

“…[31][32][33][34][35][36][37][38] Notably, MOFs are crystalline and thus can be characterized via single crystal X-ray diffraction (SC-XRD), even after post-synthetic modification. [39][40][41][42][43][44][45] This allows MOFs to be used as crystalline analogues capable of yielding information that is complementary to what can be learned structurally by anchoring catalysts on traditional materials such as amorphous oxides including silica, alumina, and zirconia. 46 Zr-Based MOFs, in particular, are desirable as catalyst supports due to high chemical and thermal stabilities, as well as providing uniform and spatially isolated catalyst deposition sites.…”