Template-free sol-gel synthesis of high surface area mesoporous silica based catalysts for esterification of di-carboxylic acids

摘要

High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/sol-gel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m(2)/g) mesoporous (pore size 67 angstrom and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis sol gel synthesis procedure. The catalysts showed very high acidity as determined by NH3-TPD with the presence of Lewis as well as Brensted acidity. These catalysts showed very high catalytic activity for esterification: a typical acid catalyzed organic transformation of various mono- and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost. (C) 2016 Published by Elsevier Masson SAS on behalf of Academie des sciences.