Novel oligovanadate-pillared hydrotalcites

Oligovanadate-pillared hydrotalcite-type layered materials are expected to be shape-selective oxidation catalysts with tunable acid-base character. The preparation and characterization of four oligovanadate-pillared clays are reported here. These are Mg5Al2(OH)14(V207)0.5·5H2O, Mg4Al2(OH)12(HV2O7)0.67·xH2O, Mg5.3Al2(OH)14.6(V4O12)0.5·2H2O, and Mg2Zn2Al2(OH)12 (V4012)0.5·2H2O. vel, one-step synthetic strategy used here was based on the fact that several oligovanadate anions are formed successively in aqueous solutions as a function of pH. For this particular study we focused our attention to the three anions, V4O4−12, HV2073− and V2O74−. The pH ranges where these anions exist in highest concentrations are: 6.5 to 8.5 for V4O124− 8.5 to 10 for HV2O73−, and 10 to 13 for V2O74−. These di- and tetravanadate-pillared clays are prepared in one step by carrying out the synthesis at a pH where the desired anion exists in highest concentration. The isolated clays were characterized by elemental analysis, X-ray diffraction, thermal analyses (TGA, DTA), and surface studies.