Catalytic properties of nano-sized ZSM-5 aggregates N. Viswanadham *, Raviraj Kamble, Madhulika Singh, Manoj Kumar, G. Murali Dhar Catalysis and Conversion Process Division, Indian Institute of Petroleum, Dehradun 248005, India 1. Introduction Zeolites are finding more industrial applications by virtue of their properties such as thermal stability, shape selectivity, and the flexibility in tailor-making of catalyst for various reactions [1,2]. Presence of uniformly distributed micropores in the zeolites provides high surface area and excellent shape selectivity [3,4].Y zeolite in fluid catalytic cracking (FCC), mordenite in n-paraffin isomerization and ZSM-5 in light alkane aromatizaton are some of the well-known industrial applications of zeolites [5–7]. However, the hydrothermally synthesized zeolites need to be modified to improve their properties especially for thermal stability, porosity, and acidity before their use for catalytic applications. Steaming or acid treatment or combination of both treatments is generally used for the modification of zeolite properties [8–10]. The treatments facilitate removal of aluminum from the crystalline framework followed by its wash out by acid leaching to make more silicious zeolite. The type and severity of treatments needed for a zeolite depends on the zeolite types and the reaction to be catalyzed. In case of zeolite Y the steam dealumination is generally adopted for achieving the ultra stabilization [11]. In case of mordenite, the dealumination is used mainly for opening of the side pockets and for the creation of mesopores to improve the diffusion of bulky branched products [12,13]. For ZSM-5, the purpose is to improve its acidity as well as porosity [14]. Desilcation by post synthesis alkali treatment of silicious zeolites was also observed to create extra- porosity [15]. However, the materials obtained by such treatments may have limitations due to the presence of persistent extra- framework aluminum species in the narrow zeolite channels and structural damage of the framework at severe dealumination conditions [16,17]. The properties of the materials are also not reproducible at many times. Hence, it is recommended to tailor the zeolite properties during synthesis instead of its post synthesis modifications. Much work is done in the area of synthesizing large pore zeolites and high surface area mesoporous materials for obtaining the materials of improved porosity. But the industrial applications of these mesoporous materials are yet to be proven due to their lower thermal stability and weak acidity [18,19]. Creation of mesoporosity in zeolites such as ZSM-5 during hydrothermal synthesis is of much interest due to its wide applications in the petroleum, petrochemical, and fine chemical industries. More recently, a new carbon templating method has been introduced for creation of mesoporous voids in zeolites after the calcinations [20]. However, the method was reported to consume high amount of carbon material and limitations in incorporation of aluminum into the framework [21]. Grieken et al. reported the effect of synthesis parameters on the crystallinity and crystal size of the ZSM-5 [22]. Sorption isotherms, t-plots, cumulative pore volume curves, and pore size distribution data can provide useful information that can be used for tailor making of catalytic properties [23]. The present study is aimed to synthesize nanometer range ZSM- 5 crystals with improved porosity, where detailed characterization studies such as surface area, external surface area, pore volume, micropore volume, mesoporosity, and the detailed pore size distributions were conducted to understand the properties of the new material. The material exhibited a twofold increase in pore volume due to the mesopores created at inter-crystalline voids and the increase in volume of zeolitic pores. Catalysis Today 141 (2009) 182–186 ARTICLE INFO Article history: Available online 7 May 2008 Keywords: ZSM-5 Mesoporosity Micropore volume t-Plot and adsorption isotherms ABSTRACT Nano-ZSM-5 (NZ) with well-defined porosity was synthesized by organic silica method. The material exhibited more than a twofold increase in pore volume when compared to the normal ZSM-5 (HZ). The increase in pore volume is observed in the entire range of the pores with diameter from 5 A ˚ to 1500 A ˚ . The order of increase in volume is macropores (>500 A ˚ ) > micropores (up to 20 A ˚ ) > mesopores (20–500 A ˚ ). Although macropore and mesopore formation is responsible for the major increase in the pore volume, significant increase in zeolitic pore volume was also observed in NZ. Both the ZSM-5 materials were tested for esterification of cyclohexanol with acetic acid under autogeneous pressure conditions where NZ showed better activity (69% conversion). ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. E-mail addresses: nvish@iip.res.in, nviswanadham@india.com (N. Viswanadham). Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod 0920-5861/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2008.03.026