Defects in metal–organic frameworks (MOFs) play important roles in MOF reactivity and catalysis. Now, we report evidence of the reactivity and the quantitative characterization of the missing linker defects on the Zr12O22 nodes in the MOF hcp UiO-66 (these are paired Zr6O8 nodes bridged by OH groups) and those on the Zr6O8 nodes of the MOF UiO-66. The defect sites catalyze the ring-opening reactions of epoxides with alcohols, and new sites formed by removal of bridging OH groups on the Zr12O22 nodes also participate in the catalysis. The hcp UiO-66 was synthesized from UiO-66 and from molecular precursors, and, under various synthesis conditions, the nodes incorporated acetate ligands, where linkers were missing, and the number of these ligands was controlled by the synthesis conditions. These ligands are inhibitors of the catalytic reactions, and their removal by reaction with, for example, methanol (to form, for example, methyl acetate) preceded catalysis on the defect sites. The former MOF incorporated more defect sites than the latter, correspondingly being a more active catalyst. The defect sites on the Zr12O22 nodes are 2–6 times more active per site than those on the isolated Zr6O8 nodes, with the node-bridging OH groups increasing the catalytic activity of the neighboring node defect sites because new sites are formed by their removal. The results help point the way to the design and control of catalytic sites on metal oxide-like MOF nodes by tuning of the number and reactivity of the defect sites.

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Hierarchical porous ZSM-5 (HP-ZSM-5) was constructed using organosilanes as the growth inhibitors for CO2 capture. The properties of adsorbents were characterized by X-ray diffraction, N2 adsorption/desorption, scanning electron microscopy, temperature-programmed desorption of carbon dioxide, and 27Al magic angle spinning nuclear magnetic resonance. It was found that HP-ZSM-5 samples synthesized by organosilanes had a significant effect on the microstructure and morphology. CO2 adsorption capacity of HP-ZSM-5 was up to 58.26 cm3 g–1 at 0 °C and 1 bar, significantly higher than that of the ZSM-5 sample. The effective improvement of CO2 adsorption performance mainly originated from the micro-/mesoporous composite structure and complex surface morphology, which can provide low-resistant pathways for CO2 through the porous network. Besides, in situ Fourier transform infrared spectroscopy was carried out to study the adsorption process on adsorbents, and the results indicated that a faster physical adsorption process was achieved as a result of the introduction of mesopores.

Ce x Zr 1-x O 2 oxides prepared by a soft reactive grinding (SRG) procedure have been investigated as the catalysts for HCl oxidation. The results show that the catalytic activities and stabilities of Ce x Zr 1-x O 2 oxides are remarkably dependent on the Ce/Zr ratio. A correlation between the physicochemical properties and catalytic performances of these samples reveals that the cubic phase in Ce x Zr 1-x O 2 with higher oxygen storage capacity (OSC) is more activity for HCl oxidation, but the tetragonal phase is crucial to the stability of catalysts. The Ce 0.5 Zr 0.5 O 2 catalyst with mixed phases and the highest OSC (80 µmol O2 ·g cat -1 ) exhibits an excellent activity (1.89 g Cl2 ·g cat -1 ·h -1 at 430 °C) and stability (300 h) in the target reaction. Kinetic studies show that both O 2 and HCl competed for the active sites rendering desorption of surface Cl is the rate-determining step. Accelerating the replacement of surface Cl by O 2 is the essence for the activity improvement of Ce 0.5 Zr 0.5 O 2 .