title: Thermal Stabilization of Metal-Organic Framework-Derived Single-Site Catalytic Clusters through Nanocasting.
abstract: Metal-organic frameworks (MOFs) provide convenient systems for organizing high concentrations of single catalytic sites derived from metallic or oxo-metallic nodes. However, high-temperature processes cause agglomeration of these nodes, so that the single-site character and catalytic activity are lost. In this work, we present a simple nanocasting approach to provide a thermally stable secondary scaffold for MOF-based catalytic single sites, preventing their aggregation even after exposure to air at 600 °C. We describe the nanocasting of NU-1000, a MOF with 3 nm channels and Lewis-acidic oxozirconium clusters, with silica. By condensing tetramethylorthosilicate within the NU-1000 pores via a vapor-phase HCl treatment, a silica layer is created on the inner walls of NU-1000. This silica layer provides anchoring sites for the oxozirconium clusters in NU-1000 after the organic linkers are removed at high temperatures. Differential pair distribution functions obtained from synchrotron X-ray scattering confirmed that isolated oxozirconium clusters are maintained in the heated nanocast materials. Pyridine adsorption experiments and a glucose isomerization reaction demonstrate that the clusters remain accessible to reagents and maintain their acidic character and catalytic activity even after the nanocast materials have been heated to 500-600 °C in air. Density functional theory calculations show a correlation between the Lewis acidity of the oxozirconium clusters and their catalytic activity. The ability to produce MOF-derived materials that retain their catalytic properties after exposure to high temperatures makes nanocasting a useful technique for obtaining single-site catalysts suitable for high-temperature reactions.
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors: Camille D
authors: CD
authors: Malonzo
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors: Sammy M
authors: SM
authors: Shaker
authors: Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States.
authors: Limin
authors: L
authors: Ren
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.|Department of Chemistry, Austin College , 900 North Grand Avenue, Sherman, Texas 75090, United States.
authors: Steven D
authors: SD
authors: Prinslow
authors: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors: Ana E
authors: AE
authors: Platero-Prats
authors: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors: Leighanne C
authors: LC
authors: Gallington
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors: Joshua
authors: J
authors: Borycz
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors: Anthony B
authors: AB
authors: Thompson
authors: Department of Chemistry and Chemical and Biological Engineering, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors: Timothy C
authors: TC
authors: Wang
authors: Department of Chemistry and Chemical and Biological Engineering, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.|Department of Chemistry, Faculty of Science, King Abdulaziz University , Jeddah, Saudi Arabia.
authors: Omar K
authors: OK
authors: Farha
authors: Department of Chemistry and Chemical and Biological Engineering, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
authors: Joseph T
authors: JT
authors: Hupp
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors: Connie C
authors: CC
authors: Lu
authors: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors: Karena W
authors: KW
authors: Chapman
authors: College of Science and Engineering Characterization Facility, University of Minnesota , 100 Union Street SE, Minneapolis, Minnesota 55455, United States.
authors: Jason C
authors: JC
authors: Myers
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors: R Lee
authors: RL
authors: Penn
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors: Laura
authors: L
authors: Gagliardi
authors: Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States.
authors: Michael
authors: M
authors: Tsapatsis
authors: Department of Chemistry, University of Minnesota , 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
authors: Andreas
authors: A
authors: Stein