# Effects of Different Variables on the Formation of Mesopores in Y Zeolite by the Action of CTA+
## 1 Introduction  
Zeolites are a class of natural and synthetic minerals that have several structural characteristics in common based on three-dimensional combinations of tetrahedra (TO\({}_{4}\), where T represents atoms of silicon and aluminum) connected by oxygen atoms [1]. The microporous zeolite structure is responsible for the acidity, hydrothermal stability, and structural selectivity of these materials [2]. However, the exclusive presence of micropores limits diffusive mass transport and reduces the access of large molecules to the active sites [3, 4]. One method for resolving this problem is creating mesopores in the zeolite structure to combine the properties of microporous and mesoporous zeolites in a single material. Ultrastable USY is a synthetic zeolite is widely used in the petroleum industry. This zeolite is not directly obtained by hydrothermal synthesis, but instead by vapor treatment of Y zeolite. This process creates mesopores that do not significantly affect intra-crystalline diffusion, since they mainly exist as cavities that are connected to the surface by micropores [5, 6]. This means that the preparation of USY zeolite possessing secondary porosity has to be performed via post-synthesis modifications. Compared to conventional zeolites, zeolites with mesopores provide high molecular weight reagents greater access to the active sites. They have shorter retention times of reaction products inthe micropores, avoiding secondary reactions and improving selectivity toward the primary products of interest. Furthermore, relative to purely mesoporous materials, they exhibit better hydrothermal stability and higher acidity [7]. The strategies that have been developed to create mesoporous in zeolites can be grouped into constructive and destructive techniques. In the constructive approach (bottom-up), the mesopores are created during the synthesis of the zeolite, with or without the use of templates. In the destructive route (top-down), mesopores are produced by means of post-synthesis treatments, such as dealumination and desilication. The modification of zeolites using surfactants together with alkaline treatment for the formation of mesoporous is a highly attractive post-synthesis route, since it produces materials with controlled mesoporousity in terms of the shape, size, connectivity, and location of the mesopores [5; 8]. Different approaches have been described for the creation of mesoporous using surfactants. The recrystallization technique reported by [PERSON] et al. [9] involves two stages: the zeolite is first partially destroyed using an alkaline treatment, then the surfactant is added to the reaction mixture, and hydrothermal treatment is applied. This work investigated the creation of mesopores in mordenite (MOR) zeolite using the recrystallization method. Modification of MOR (Si/Al = 49) was performed by treatment with NaOH at room temperature, followed by hydrothermal treatment at 100 \({}^{\circ}\)C, in the presence of cetyltrimethylammonium bromide (CTAB). The materials obtained under the conditions used, which were classified as micro- and mesoporous composites, were tested in a transalkylation reaction of biphenyl (BP) with para-diisopropylbenzene (p-DIPB) and in the cracking reaction of 1,3,5-triisopropylbenzene (TIPB). Each of these reactions required a certain volume of mesopores to ensure enhanced performance. Another approach reported in the literature is alkaline treatment in the presence of a CTAB surfactant at room temperature, followed by heating of the mixture at 150 \({}^{\circ}\)C for several hours to rearrange the structure and create ordered mesopores in the zeolite [8; 10; 11]. The advantage of this technique, compared to the recrystallization method, is that it avoids complete amorphization of the zeolite by the surfactant, which can occur during more severe alkaline treatments [5]. The crystal rearrangement associated with the use of a surfactant during alkaline treatment was first reported in a patent published in 2005 by [PERSON] [12].