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

• Lanthanide-based polyoxotungstates were incorporated into the porous MIL-101.
• Novel composite materials, Eu(PW11)2@MIL and Sm(PW11)2@MIL, were prepared.
• The two composites showed to be active for the oxidation of styrene with H2O2.
• Eu(PW11)2@MIL and Sm(PW11)2@MIL exhibited higher catalytic activities.
• Microwave-assisted oxidative reactions revealed higher selectivity.

The lanthanide-containing Keggin-type polyoxometalates (LnPOMs), [Ln(PW11O39)2]11− (Ln = Eu3+ and Sm3+), were incorporated for the first time into porous chromium terephthalate MIL-101(Cr) via an impregnation method, originating two unprecedented composite materials, Eu(PW11)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 LnPOMs 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 LnPOMs 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.

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