Hybridization of Ni-Cr, Cu-Cr, and Zn-Cr layered double hydroxides with polyoxometalates and their catalytic behavior

Abstract

Cr-based layered double hydroxides (LDHs) containing Ni, Zn, or Cu as the divalent cation were prepared with a divalent-to-trivalent cation molar ratio of 3. Then, LDH hybrids intercalated with polyanions ([PMo12O40]31(PMoO) or [H2W12O42]101 (HWO)) were prepared by ion exchange and hydrothermal processes. The shift of the diffraction line indicating interlayer space in the X-ray diffraction patterns confirmed the intercalation in the LDH. The fraction of PMoO and HWO anions incorporated was 3070 or 6090% of ion exchange capacity, respectively, by charge compensation for Cr3+. In the conversion of styrene by epoxidation and oxidation, the hybrid of the LDH composed of Zn and Cr with PMoO showed the maximum catalytic activity, with 70% conversion. For the LDH composed of Ni and Cr, hybridization with a polyanion enhanced the catalytic behavior by a synergistic effect resulting from the basicity of the LDH phase.