Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso Desilication of *BEA zeolites using different alkaline media: Impact on catalytic cracking of n-hexane H. Sammoury a,b , J. Toufaily b , K. Cherry b , T. Hamieh b , Y. Pouilloux a , L. Pinard a,* a Université de Poitiers, CNRS UMR7285, Institut de Chimie des Milieux et Matériaux de Poitiers, B27, TSA 51106, 4 rue Michel Brunet, 86073 Poitiers CEDEX 9, France b Université Libanaise, Laboratoire des matériaux, catalyse, environnement et méthodes analytiques (MCEMA), Hadath, Lebanon ARTICLE INFO Keywords: BEA zeolite Desilication Pore directing agent n-hexane cracking Coke ABSTRACT The desilication of two commercial nano- and one synthesized microcrystal *BEA zeolites via different alkaline solutions have led to several observations. In the nanocrystal *BEA zeolites, the use of NaOH alone reduced the crystallinity and microporosity, which was recovered after the use of pore directing agents as tetra- propylammonium bromide (TPABr). The use of tetrabutylammonium hydroxide (TBAOH) was not as much effective with NaOH as TPABr in terms of crystallinity and microporosity recovery, as it wasn't also as much effective as was NaOH alone in introducing intracrystalline mesopores to these nanocrystals. In the microcrystal series, the use of NaOH with TBAOH was seen to be more effective than NaOH alone or NaOH with TPABr. The increase of relative Brønsted acidity was observed at lower alkaline concentrations with a pronounced decrease at higher alkaline media. The company of the pore directing agents was seen to provoke the formation of new Lewis acid sites. In the cracking of n-hexane, the desilication treatments were not seen to improve the catalytic performance of the requested catalysts, as the slight deactivation of the catalysts was at the basis of coke for- mation. The activity was seen to drop due to even the diffusional limitations occurring or due to loss of acidity after desilication. More olefin and isomers products were produced despite of coke formed which was considered non-toxic being located inside the mesopores. 1. Introduction Being rich with unusual features, zeolites are used in wide range of applications especially in oil refining and petrochemical industries [1,2]. The success of these zeolites in the industrial catalytic reactions is surely due to their micropores in which most of the catalytic sites are located and where the reactions take place. Notwithstanding the posi- tive effect induced by these micropores with respect to shape selectivity [3], they may still provoke negative impacts by lowering the rate of access of molecules into the crystals of the zeolites [4], and favor un- wanted adsorption effects of the reactants or the products as they un- dergo the catalytic action [5]. Hence, it was of much importance to seek after materials that withstand the bulky molecules without distorting the main objective. Bulky molecules that cannot diffuse properly into the zeolite mi- cropores might induce negative impact on the efficiency and activity in the media containing such substrates. These limitations have stimulated the researchers to follow up after new zeolitic structures [6]. Various methodologies to minimize diffusion limitations and enhance catalyst effectiveness were followed. Synthesizing zeolites with larger micropores [7–9], and decreasing the zeolite crystal size to reduce the intracrystalline diffusion path length [10–13], were two of the strate- gies used to overcome diffusional limitations. However, a more gen- erally applied strategy to obtain materials with sufficient molecular transport properties is to synthesize hierarchical zeolites that combine the primary micropore system and a secondary one that consists of mesopores (2–50 nm) inside the microporous zeolite crystals [14–18]. These improved structures enhance diffusion of bulky reactants and products molecules into and out of the pores respectively which in turn facilitates the adsorptive and catalytic reactions. The synthesis of these zeolites can be achieved by destructive methods (top-down approaches) [19,20]. It is known as post-synthetic procedures that account to subject an already synthesized zeolite to treatments that target there pore structure thereby introducing meso- porosity. Due to its simplicity and efficiency, desilication by alkaline treatments, which is a controlled way to extract silicon species from the zeolite framework [21], is one of the most widely applied methods recently to induce mesoporosity [22–25]. Nonetheless, such post-syn- thetic procedure may affect not only the pore system of the zeolite, but also the structural, compositional, acidic and as well the final catalytic https://doi.org/10.1016/j.micromeso.2018.03.022 Received 12 January 2018; Received in revised form 13 March 2018; Accepted 17 March 2018 * Corresponding author. E-mail address: ludovic.pinard@univ-poitiers.fr (L. Pinard). Microporous and Mesoporous Materials 267 (2018) 150–163 Available online 22 March 2018 1387-1811/ © 2018 Elsevier Inc. All rights reserved. T