Layered double hydroxides pillared by macropolyoxometalates

Pillared derivatives of Mg1−xAlx layered double hydroxides (LDHs) were prepared by anion exchange reaction of a synthetic meixnerite precursor, [Mg3Al(OH)2](OH), with macromolecular polyoxometalate ions. The intercalated polyoxometalates included the lacunary Dawson ion (α-P2W17O61)10−, the Finke (Zn4(H2O)2(AsW9O34)2)10− and (WZn3(H2O)2(ZnW9O34)2)12− ions, the doubled Dawson (P4W30Zn4(H2O)2O112)16− and the polyoxocryptates (NaSb9W21O86)18− and (NaP5W30O110)14−. Anion exchange reaction of [Zn2Al(OH)2](NO3−) with (NaP5W30O110)14− also resulted in a crystalline pillared product. The intercalates exhibited gallery heights up to 16.6 Å and thermal stabilities to 200°C. Nitrogen adsorption/desorption studies for the LDH intercalates showed that access to the gallery micropores was achieved upon POM intercalation. All of the intercalates contained a salt-like impurity phase, as indicated by XRD. The Zn2Al–(NaP5W30O110)14− LDH was investigated as a catalyst for the peroxide oxidation of cyclohexene. A comparison of the reactivities of three samples containing different fractions of the salt-like impurity suggested that the impurity phase contributes significantly to the observed activity.