Layered double hydroxides pillared by macropolyoxometalates

Pillared derivatives of Mg(1-x)Al(x) layered double hydroxides (LDHs) were prepared by anion exchange reaction of a synthetic meixnerite precursor, [Mg(3)Al(OH)(2)](OH), with macromolecular polyoxometalate ions. The intercalated polyoxometalates included the lacunary Dawson ion (alpha-P(2)W(17)O(61))(10-), the Finke (Zn(4)(H(2)O)(2)(AsW(9)O(34))(2))(10-) and (WZn(3)(H(2)O)(2)(ZnW(9)O(34))(2))(12-) ions, the doubled Dawson (P(4)W(30)Zn(4)(H(2)O)(2)O(112))(16-) and the polyoxocryptates (NaSb(9)W(21)O(86))(18-) and (NaP(5)W(30)O(110))(14-). Anion exchange reaction of [Zn(2)Al(OH)(2)](NO(3)(-)) with (NaP(5)W(30)O(110))(14-) also resulted in a crystalline pillared product. The intercalates exhibited gallery heights up to 16.6 Angstrom and thermal stabilities to 200 degrees 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 Zn(2)Al-(NaP(5)W(30)O(110))(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. (C) 1998 Elsevier Science B.V. All rights reserved.