Dealumination of Zeolite Beta Catalyst Under Controlled Conditions for Enhancing its Activity in Acylation and Esterific
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Dealumination of Zeolite Beta Catalyst Under Controlled Conditions for Enhancing its Activity in Acylation and Esterification Rajendra Srivastava Æ Nobuhiro Iwasa Æ Shin-ichiro Fujita Æ Masahiko Arai
Received: 6 March 2009 / Accepted: 17 April 2009 / Published online: 23 May 2009 Ó Springer Science+Business Media, LLC 2009
Abstract This work deals with the dealumination of zeolite beta under different conditions to optimize its catalytic performance. The dealumination was carried out either using oxalic or tartaric acid solution of different pH values or steaming up to 500 °C. The dealuminated zeolite samples were characterized using X-ray diffraction, N2-physisorption, ICP, 27Al NMR and NH3-TPD. Their catalytic activities were studied for acylation reaction of 2-methoxy naphthalene or naphthalene with acetic anhydride and esterification of benzyl alcohol with hexanoic acid. Among the dealuminated samples examined, those treated with oxalic acid or tartaric acid at pH 2 showed high activity. The high activity can be correlated with the relative increase in the amount of strong acid sites and with the enhanced accessibility of the reactants to the active sites, which are caused by removal of extra-framework Al species on the acid treatments. Keywords Zeolite beta Dealumination Acidity Acylation Esterification
R. Srivastava N. Iwasa S. Fujita M. Arai (&) Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan e-mail: [email protected] R. Srivastava e-mail: [email protected] R. Srivastava Department of Chemistry, National Institute of Technology, Tiruchirappalli, Tamilnadu 620015, India
1 Introduction The development of eco-friendly catalytic routes for various organic transformations is the ongoing interest of catalytic researchers [1, 2]. The acid catalyzed alkylation, acylation and esterification of aromatic hydrocarbons are most important reactions used in industrial scale for the production of pharmaceuticals and fine chemicals [3, 4]. These reactions are frequently carried out in liquid phases using metal halides or strong mineral acids. In spite of low selectivity and high corrosiveness, homogeneous acid catalysts (e.g. AlCl3, H2SO4, HF or H3PO4) are widely used [5]. Thus, there is a considerable interest for replacing strongly acidic, homogeneous, corrosive and polluting catalysts with environmentally clean heterogeneous solid acid catalysts [1–4]. A large number of zeolites such as MFI (ZSM-5), zeolite beta, zeolite Y, zeolite mordanite (MOR) have been described as active catalysts in these reactions [6]. Modification of as-synthesized zeolite samples is essential for obtaining stable and active catalysts for molecular transformations in fine chemicals synthesis. Dealumination, the removal of extra-framework Al species without destroying the microporous structure, is one of the modifications mainly utilized for improving the performance of zeolites. It has been achieved by hydrolysis of Al-O-Si bonds by mineral acids
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