Dealumination of proton form mordenite with high aluminum content in atmosphere Naonobu Katada a,b, * , Takahide Kanai a,1 , Miki Niwa a a Department of Materials Science, Faculty of Engineering, Tottori University, 4-101 Koyama-cho Minami, Tottori 680-8552, Japan b PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan Received 3 February 2004; received in revised form 2 July 2004; accepted 6 July 2004 Available online 2 September 2004 Abstract AprotonformmordenitewithSi/Al 2 =10waspreparedbyheatingofanammoniumtypesampleat813Kinanitrogenflowand transferred into an NMR (nuclear magnetic resonance) cell in a dry box filled with a controlled atmosphere, and the framework aluminum content was measured by means of 29 Si NMR. It was estimated that almost all the aluminum atoms were located in the framework on the sample treated in helium which was purified by passing a liquid nitrogen trap. On the other hand, a consid- erable amount of extra-framework aluminum was estimated on the sample treated in commercially supplied nitrogen. After the cap of NMR cell was opened for several seconds in atmosphere, also the extra-framework aluminum was observed. These findings point out the readily dealumination of the proton form mordenite at room temperature. The dealumination resulted in the decrease of acidity and catalytic activity for cracking of octane and cumene [(1-methylethyl)benzene]. On the basis of the experiments using mordenite with Si/Al 2 = 15, the extent of dealumination was considered to decrease with decreasing the aluminum content and increasing the alkaline content. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Zeolite; Mordenite; Dealumination; Acid site; Nuclear magnetic resonance 1. Introduction Proton type zeolite is widely used as a solid acid cat- alyst for various petroleum and chemical processes. The acidity is generated by isomorphous substitution of Si by Al in the zeolite framework. Therefore a stoichiome- try should exist between the number of acid sites and aluminum atoms (or [Al]–[Na] in the case of sodium- containing sample). This stoichiometry is observed at low aluminum content [1]. In addition, it has widely been known that the activity for an acid-catalyzed reac- tion shows a linear relationship against the aluminum content [2–4]. However, a volcano shape relationship is observed between the acid amount and [Al]–[Na] gen- erally on such zeolites as Y (FAU) and mordenite (MOR), where high aluminum content is available, as shown in Fig. 1 (n, plotted based on the acid amount determined by the ammonia TPD in our previous study [5]). In other words, loss of the acidity is observed in the high [Al]–[Na] content region. The volcano shape relationship is widely observed between the catalytic activities for various acid-catalyzed reactions and the aluminum content [6]. The observed maximum is in agreement with the calculated composition where near- est next neighboring (NNN) aluminum pair (AlOSiOAl) 1387-1811/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2004.07.001 * Corresponding author. Address: Department of Materials Sci- ence, Faculty of Engineering, Tottori University, 4-101 Koyama-cho Minami, Tottori 680-8552, Japan. Tel./fax: +81 857 31 5684. E-mail address: katada@chem.tottori-u.ac.jp (N. Katada). 1 Present address: Department of Chemical Materials Science, School of Materials Science, Japan Advanced Institute of Science and Technology. www.elsevier.com/locate/micromeso Microporous and Mesoporous Materials 75 (2004) 61–67