Monovacant polyoxometalates incorporated into MIL-101(Cr): novel heterogeneous catalysts for liquid phase oxidation

Authors: Carlos M. Granadeiro, André D.S. Barbosa, Patrícia Silva, Filipe A. Almeida Paz, Vipin K. Saini, João Pires, Baltazar de Castro, Salete S. Balula, Luís Cunha-Silva

Abstract:
Two novel hybrid composite materials, PW11@MIL-101 and SiW11@MIL-101, were prepared by the inclusion of the potassium salts of the monovacant polyoxotungstates, [PW11O39]7− (PW11) and [SiW11O39]8− (SiW11), into the porous Metal-Organic Framework MIL-101(Cr). Materials were characterized by a myriad of solid-state methods such as powder X-ray diffraction (XRD), vibrational (FT-IR and FT-Raman) and 31P solid-state NMR spectroscopies, elemental analysis, scanning electron microscopy (SEM) and energydispersive X-ray spectroscopy (EDX), and textural analysis confirming the incorporation of the POMs into MIL-101(Cr). PW11@MIL-101 and SiW11@MIL-101 revealed to be active, selective and recyclable catalysts for the oxidation of cis-cyclooctene, geraniol and R-(+)-limonene using the H2O2 as oxidant. Only one product was obtained from the epoxidation of cis-cyclooctene and geraniol: 1,2-epoxycylooctane and 2,3-epoxygeraniol, respectively. In the oxidation of R-(+)-limonene the main products were limonene1,2-epoxide and limonene-1,2-diol, however the diepoxide was also formed. Both composite materials, PW₁₁@MIL-101 and SiW₁₁@MIL-101, are recyclable for, at least, three consecutive cycles without significant loss of activity. The stability of the composites after the catalytic cycles was confirmed by several techniques. Remarkably, the MOF framework was found to play an important role in the stability of the PW₁₁ in the presence of H₂O₂.

Keywords:
Polyoxometalates
Metal organic-framework
Hybrid materials
Heterogeneous catalysis
Oxidation

Published in: Applied catalysis A: General  (Volume 453, Pages 1-402, 26 February 2013)

Publisher: Elsevier

ISSN Information: 0926-860X

Monovacant polyoxometalates incorporated into MIL-101(Cr): novel heterogeneous catalysts for liquid phase oxidation

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