Solid-state NMR studies of the acidity of functionalized metal-organic framework UiO-66 materials
Jing Tang1,2, Shenhui Li1, Yueying Chu1
1State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, CAS Key Laboratory of Magnetic Resonance in Biological Systems, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan, 430071, PR China.
Abstract:
The acid strength of metal-organic frameworks plays a key role in their catalytic performance such as activity and selectivity during catalytic reactions. Solid-state nuclear magnetic resonance in combination with probe molecules including 2-13 C-acetone and pyridine-d5 was employed to characterize the acid strength of UiO-66-X (X = -H, -2COOH, -SO3 H). It was found that after introduction of the functional groups, the acid strength of UiO-66-2COOH and UiO-66-SO3 H is considerably enhanced compared with that of parent UiO-66, with that of the former being similar to that of zeolite H-ZSM-5, and with that of the latter being slightly stronger than that of the former. Even though the acid density can efficiently be modified through changing the relative ratio in multivariate functionalized UiO-66-X, no significant alternation for the acid strength could be discerned in the MTV-UiO-66-X compared with acidic same-link counterpart. Theoretical calculations were employed to further confirm the acid strength of UiO-66-SO3 H and UiO-66-2COOH.
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