Heterogeneous selective oxidation catalysts based on coordination polymer MIL-101 and transition metal-substituted polyoxometalates

摘要

Titanium- and cobalt- monosubstituted Keggin heteropolyanions, [PW11CoO39](5-) and [PW11TiO40](5-), were electrostatically bound to the chromium terephthalate polymer matrix MIL-101. The MIL-supported polyoxometalate (POM) catalysts were characterized by elemental analysis, XRD, N-2 adsorption, and FT-IR-spectroscopy. The catalytic performance of both MIL-101 and the novel composite materials M-POM/MIL-101 was assessed in the oxidation of three representative alkenes-alpha-pinene, caryophyllene, and cyclohexene-using molecular oxygen and aqueous hydrogen peroxide as oxidants. Ti-POM/MIL-101 demonstrated fairly good catalytic activity and selectivity in alpha-pinene allylic oxidation and caryophyllene epoxidation with hydrogen peroxide, whereas Co-POM/MIL-101 catalyzed alpha-pinene allylic oxidation by molecular oxygen. Both composite materials are stable to POM leaching, behave as true heterogeneous catalysts, and can be used repeatedly without sustaining a loss of activity and selectivity in oxidations with O-2 and H2O2, provided that rather mild reaction conditions (T < 50 degrees C, [H2O2] < 0.2 M) are used with the latter oxidant. (c) 2008 Elsevier Inc. Alt rights reserved.