Novel heterogeneous catalysts based on lanthanopolyoxometalates supported on MIL-101(Cr)

Abstract

The lanthanide-containing Keggin-type polyoxometalates (LnPOMs), [Ln(PINi O-39)(2)](11)-(Ln=Eu3+ and Sm3+), were incorporated for the first ime into porous chromium terephthalate MIL-101(Cr) via an impregnation method, originating two unprecedented composite materials, Eu(PIN11)(2)@MIL and Sm(PW11)(2)@MIL, to be used as heterogeneous catalysts. The characterization of these new composites was performed by vibrational spectroscopy (FT-IR and FT-Raman), powder X-ray diffraction (XRD), elemental analysis, UV-vis spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and textural analysis. Ln(PW11)(2)@MIL materials were tested as heterogeneous catalysts in the oxidation of styrene using hydrogen peroxide as the oxidant and acetonitrile as the solvent. Their catalytic activity was also compared with the homogeneous LnPOM(5) catalysts in order to evaluate the effect of their incorporation on the catalytic activity. The composite materials exhibit higher catalytic activities toward the oxidation of styrene than the corresponding isolated LnPOM(5) with complete conversion of the substrate after 4 h and 5 h for the samarium and europium composites, respectively. Furthermore, microwave-assisted oxidative reactions were also performed showing an increase in the selectivity values while maintaining similar conversion values, especially in the heterogeneous reactions. (C) 2013 Elsevier B.V. All rights reserved.