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]³⁻(PMoO) or [H₂W₁₂O₄₂]¹⁰⁻ (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 30–70 or 60–90% 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.