Please cite this article in press as: D. Verboekend, et al., Acidity and accessibility studies on mesoporous ITQ-4 zeolite, Catal. Today (2010), doi:10.1016/j.cattod.2010.02.004 ARTICLE IN PRESS G Model CATTOD-6555; No. of Pages 6 Catalysis Today xxx (2010) xxx–xxx Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod Acidity and accessibility studies on mesoporous ITQ-4 zeolite Danny Verboekend a , Luis A. Villaescusa b , Karine Thomas c , Irina Stan c , Javier Pérez-Ramírez a,d,∗ a Institute of Chemical Research of Catalonia (ICIQ), Avinguda Països Catalans 16, 43007 Tarragona, Spain b Instituto de Reconocimiento Molecular y Desarrollo Tecnológico (IDM). Centro mixto Universidad Politécnica de Valencia-Universidad de Valencia. Departamento de Química, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022, Valencia, Spain c Laboratoire Catalyse et Spectrochimie, ENSICAEN, Université de Caen, CNRS, 6 Bd du Maréchal Juin, 14050 Caen, France d Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain article info Article history: Available online xxx Keywords: Hierarchical zeolites ITQ-4 Desilication Mesopores Acidity Accessibility abstract Desilication of ITQ-4 (IFR code, 1-dimensional 12-MR channel system of 0.62 nm × 0.72 nm) in aqueous NaOH solutions was practiced in order to produce the zeolite in the hierarchical form, i.e. combining the native micropores with a secondary network of intracrystalline mesopores. The parent material (Si/Al = 32) was synthesized using benzylquinuclidinium as the structure-directing agent in the pres- ence of fluoride anions. The samples were characterized by ICP-OES, XRD, TEM, N 2 adsorption, and FTIR spectroscopy. In a representative treatment, the mesopore surface area of the ITQ-4 experienced a seven- fold increase (from 29 to 206 m 2 g -1 ) upon optimized NaOH post-treatment, whereas the microporosity was reduced by 70% (from 0.20 to 0.06 cm 3 g -1 ). Chemical analysis and infrared spectroscopy of adsorbed pyridine showed that after alkaline treatment the amount of Brønsted acid sites remains practically con- stant whereas a significant increase in Lewis acid sites was obtained. Infrared studies with adsorbed 2,4,6-collidine concluded that the accessibility of acid sites in the hierarchical zeolite increased sub- stantially due to an increase in the available active sites at the pore mouths of the hierarchical zeolite. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The synthesis of new zeolitic materials is an important field of research due to the potential applications of new structures or compositions in catalysis, separation, and adsorption pro- cesses. In recent years, substantial efforts have been devoted to the design of zeolites with improved accessibility and molec- ular transport to/from the active sites. By doing this, diffusion limitations can be alleviated enabling improved catalytic perfor- mance in known as well as in novel reactions. Wide-pore zeolites with a multidirectional channel system and hierarchical zeolites combining the native microporosity with a secondary network of mesopores [1] comprise the two basic families of materials promising enhanced zeolite effectiveness in catalysis by increas- ing the diffusivity or by shortening the diffusion pathlength, respectively. The controlled extraction of framework silicon by treatment in aqueous NaOH is widely used to introduce mesoporosity in various zeolite frameworks: MFI [2], MTW [3], MOR [4], AST [5], BEA [6], ∗ Corresponding author at: Institute for Chemical and Bioengineering, Depart- ment of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland. Tel.: +41 44 633 7120; fax: +41 44 633 1405. E-mail address: jpr@chem.ethz.ch (J. Pérez-Ramírez). and FER [7]. Although the benefits of mesoporosity to the catalytic performance of the above zeolites have been unequivocally proven [1], there is a lack of detailed studies assessing the accessibility and diffusion of molecules in hierarchical zeolites, as well as changes in acidic properties induced by the post-synthesis treatment. The scarce literature available in this respect mainly deals with ZSM-5 [8–12]. Recently, some of us have shown that infrared spectroscopy of substituted alkylpyridines with different sizes (pyridine, 2,6- lutidine, and 2,4,6-collidine) enables to quantify the remarkably enhanced accessibility of acid sites in mesoporous ZSM-5 with respect to the purely microporous counterpart [11]. The derived accessibility index (ACI) can be used to standardize acid site acces- sibility in zeolites. It is relevant to expand the number of zeolite families that can be prepared in hierarchical form. Special attention should be placed on zeolites with small micropores and/or one-dimensional channel systems as they suffer to a more pronounced extent from diffusion constraints in catalytic applications. We have drawn our attention to ITQ-4 (IFR topology), which is isotypical with SSZ-42 and MCM- 58 [13]. The ITQ-4 structure comprises a monoclinic framework and is characterized by a high void volume and by its unique 1- dimensional sinusoidal 12-membered ring channel system (Fig. 1). Villaescusa et al. [14] reported the synthesis of ITQ-4 in the Si/Al range of 20-∞ and the physico-chemical characterization of the as-made and calcined materials. 0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2010.02.004