Novel oligovanadate-pillared hydrotalcites

• Published in: Applied clay science Vol. 10; no. 1; pp. 57 - 67
• Main Authors: Bhattacharyya, Alak, Hall, Daniel B., Barnes, Tamila J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.1995
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/0169-1317(95)00016-W

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 Mg 5Al 2(OH) 14(V 20 7) 0.5·5H 2O, Mg 4Al 2(OH) 12(HV 2O 7) 0.67· xH 2O, Mg 5.3Al 2(OH) 14.6(V 4O 12) 0.5·2H 2O, and Mg 2Zn 2Al 2(OH) 12 (V 40 12) 0.5·2H 2O. The novel, 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, V 4O 4 −12, HV 20 7 3− and V 2O 7 4−. The pH ranges where these anions exist in highest concentrations are: 6.5 to 8.5 for V 4O 12 4− 8.5 to 10 for HV 2O 7 3−, and 10 to 13 for V 2O 7 4−. 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.