Zeolites have been widely used as adsorbents and catalysts in many chemical and petro-chemical processes due to their excellent properties such as higher acidity, hydrothermal stability, and form selectivity [1, 2]. However, the own presence of micropores in zeolites often imposes diffusion restrictions related to the intracrystalline transport of the reactants to reach the active sites and of products to move away from these sites. In addition, the large compound cannot access in many cases the internal surface area of zeolite, which limits their use as catalysts in important chemical processes [3, 4].
An alternative solution to deal with bulky substrates has been the synthesis of ordered mesoporous materials which possess uniform mesopores that can be varied in a wide range [5, 6], the synthesis of nanosized zeolites [7] and ultra large-pore zeolites [8].
Nevertheless, the application of these materials is fairly limited because of the difficult separation of nanosized zeolite crystals from the synthesis medium, the low acidity and hydrothermal stability of mesoporous molecular sieve materials and the need of employing Geranium, as well as the addition of special template in the synthesis of ultra-large-pore zeolite [9, 10].
One of the most successful strategies to overcome the above disadvantages is to prepare micro/mesoporous material. By this way, both advantages of large pore size of mesoporous materials and strong acidity and high hydrothermal stability of zeolites would be combined. Several successful routes for synthesizing composites with excellent catalytic performances have been reported in literatures [11, 12].
Omega zeolite or ZSM-4, the synthetic analog of mazzite is a large-pore (7.5Å) zeolite having hexagonal symmetry with a silica-alumina ratio (Si/Al) in the intermediate range (3–5). Omega framework contains gmelinite cages bridged by oxygen atoms to give a 12-membered cylindrical channel system along the crystallographic c-axis. Due to its high acidity and unique structural features, omega zeolite received much attention as catalyst and adsorbent [13–18]. To date, to improve the textural properties of the omega zeolite, researchers have turned to dealumination of this zeolite. However, it has been shown in several studies that this method leads to a decrease in the acidity strength, which subsequently influences on its catalytic performance.
In this work, and for the first time, the micro-mesoporous omega zeolite was prepared by assembling the precursors of the omega zeolite obtained at different stages of crystallization and then modified with a CTABr surfactant to form the mesoporous phase. The textural and structural properties of the materials obtained have been correlated and discussed.