Oxidovanadium(IV) acetylacetonate immobilized onto CMK-3 for heterogeneous epoxidation of geraniol

Heterogeneous catalysts based on oxidovanadium(IV) acetylacetonate ([VO(acac)2]) immobilized onto nanostructured ordered carbon material CMK-3 were prepared using two different strategies: (i) direct anchoring of the metal complex through the surface oxygen groups of the pristine support (CAT I) and (ii) immobilization via 3-aminopropyltriethoxysilane spacer previously grafted onto the support (CAT II). The metal complex immobilization through both methods was confirmed by X-ray photoelectron spectroscopy, elemental analysis, Fourier transform infrared spectroscopy and thermogravimetry. X-ray diffraction (XRD) analysis provided insights on the materials rod-like structure and suggested the existence of some expansion of the CMK-3 network upon the complex immobilization.The new materials were tested as heterogeneous catalysts in the epoxidation of geraniol using tert-butyl hydroperoxide as oxidant leading to substrate conversions higher than 98% after 2.5 h and 98–99% selectivity for the 2,3-epoxygeraniol product. The improved catalytic performance observed for the new materials when compared to other heterogenized [VO(acac)2] based catalysts was attributed to an efficient mass transfer provided by the rod-like structure of CMK-3 supports. When APTES was used as the linker for complex immobilization (CAT II), negligible catalyst leaching and higher substrate conversions were observed when compared to CAT I upon recycling and reuse. Furthermore, XRD provided evidence for the preservation of the rod-like structure of the support upon the catalytic reactions.

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► New catalysts were prepared by immobilization of [VO(acac)2] complex onto CMK-3.
► Direct complex immobilization and via 3-aminopropyltriethoxysilane were performed.
► The heterogeneous catalysts were active and selective in the geraniol epoxidation.
► The CMK-3 rod-like structure was kept upon complex grafting and catalytic reactions.
► Reduced reaction times were ascribed to low diffusion constraints.