Preparation of Keggin and Preyssler Heteropolyacid Catalysts on Amine-modified SBA-15 and Their Catalytic Performances i
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Preparation of Keggin and Preyssler Heteropolyacid Catalysts on Amine-modified SBA-15 and Their Catalytic Performances in Esterification of n-Butanol with Acetic Acid Shanshan Wu Æ Jun Wang Æ Weihong Zhang Æ Xiaoqian Ren
Received: 27 May 2008 / Accepted: 14 June 2008 / Published online: 16 July 2008 Ó Springer Science+Business Media, LLC 2008
Abstract The Keggin and Preyssler-structured tungstophosphoric acid catalysts anchored on the surface of modified SBA-15 (KNS and PNS) by grafting amine groups into system, and were characterized by infra-red spectroscopy, X-ray diffraction, N2-adsorption, Hammett indicator and UV-Vis spectroscopy. Their catalytic behaviors were investigated in the esterification of n-butanol with acetic acid. Characterization results for obtained catalysts verified the ordered hexagonal mesostructure of SBA-15 and preservation of the structures of heteropolyanions on aminemodified SBA-15. KNS and PNS catalysts with the 37 and 25% loadings of Keggin and Preyssler acids exhibited considerable conversions of n-butanol of 61.2 and 63.8% with both 100% selectivity for n-butyl acetate in the esterification reaction, respectively. Especially, tests of six-cycle reaction revealed good reusabilities of KNS and PNS due to their excellent water-resistance properties, and in contrast, the catalysts prepared by direct impregnation lost their high activities immediately at their second cycles. Active sites on the amine-modified SBA-15 retained the Keggin or Preyssler structure after reaction demonstrated by IR analysis. Also, reaction conditions such as the amount of catalyst, reaction time and temperature were explored. Keywords SBA-15 Preyssler Keggin Heteropolyacid Grafting Esterification
Electronic supplementary material The online version of this article (doi:10.1007/s10562-008-9559-5) contains supplementary material, which is available to authorized users. S. Wu J. Wang (&) W. Zhang X. Ren State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China e-mail: [email protected]
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1 Introduction Heteropolyacid (HPA) is a kind of significant catalytic material in both academic and industrial fields due to its unique properties such as strong Brønsted acidity, structure alterability, high proton mobility and environmental friendliness [1–3]. Keggin type heteropolyacid, for an example the tungstophosphoric acid (PW) with formula of H3PW12O40, has been widely studied and well known to be an efficient catalyst for a variety of organic reactions [4, 5]. Comparatively, the catalytic application of Preyssler’s anion has been largely overlooked. The Preyssler anion [NaP5W30O120]14- with an unusual doughnut-shaped structure consisting of a cyclic assembly of five PW6O22 units and with an approximate D5h symmetry, has gained more research attention in recent years owing to its exclusive physicochemical properties including large number of balanced protons, strong acidity, high hydrotherm
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