Heteropoly acid encapsulated SBA-15/TiO2 nanocomposites and their unusual performance in acid-catalysed organic transformations

Dhanashri P. Sawant, Josena Justus, Veerappan V. Balasubramanian, Katsuhiko Ariga, Pavuluri Srinivasu, Sivan Velmathi, Shivappa B. Halligudi, Ajayan Vinu

Research output: Contribution to journalArticlepeer-review

41 Scopus citations

Abstract

The preparation of SBA-15/ TiO2 nanocomposites with different loadings of Keggin-type 12-tungstophosphoric acid (TPA) nanocrystals in their mesochannels through a simple and effective vacuum impregnation method is reported for the first time. The catalysts have been characterised by various sophisticated techniques, including XRD, HRSEM, and TEM. It has been found that the acidity and the textural parameters of the nanocomposites can be controlled by simply changing the loadings of TPA and TiO2 or the calcination temperature. TPA and TiO2 loadings of 15 and 22.4 wt%, respectively, and a calcination temperature of 1123 K have proved to be optimal for obtaining mesoporous nanocomposite materials with the highest acidity. Moreover, the activities of these catalysts in promoting hydroamination as well as Mannich and Claisen rearrangement reactions have been extensively investigated. The results show that the amount of TPA has a great influence on the activity of the nanocomposites in all of the reactions studied. The effects of other reaction parameters, such as temperature and reaction time, on the conversion and product selectivity have also been studied in detail. A kinetic analysis of the formation of the products under various reaction conditions is presented. It has been found that the activity of the nanocomposite composed of 15wt% TPA deposited on 22.4 wt of TiO2 on SBA-15 in promoting the studied reaction is remarkably higher than the catalytic activities shown by pure TPA, TiO2-loaded SBA-15, or TPA-loaded SBA-15. The results obtained have indicated that the acidity and the structural control of the nanocomposite materials are highly critical for obtaining excellent catalytic activity, and the presented highly acidic nanocomposites are considered to show great potential for use as catalysts in promoting many acid-catalysed organic transformations.

Original languageEnglish (US)
Pages (from-to)3200-3212
Number of pages13
JournalChemistry - A European Journal
Volume14
Issue number10
DOIs
StatePublished - Mar 27 2008

Keywords

  • Brønsted acids
  • Mesoporous materials
  • Nanoreactors
  • Nanotechnology
  • Supported catalysts

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