## 2 The Precursor (P)MCM-22 and MCM-22 Zeolites  
(P)MCM-22 was reported in 1990 by Mobil and is composed of individual lamellae with a thickness of 2.5 nm, with sinusoidal 10-ring channels (0.40 \(\times\) 0.50 nm) and 12-ring hemicavities (connected to each other by double 6-rings with an aperture of \(\sim\)0.3 nm) on the upper and lower surface of the lamella [12; 13]. The precursor contains hexamethyleneimine (HMI) molecules used as a structure directing agent (SDA) occluded in the sinusoidal channels, as shown in Figure 1a. The interaction between lamellae occurs via hydrogen bonds between silanol groups on the surface and the HMI molecules also present between the MWW lamellae [8]. After calcination, the organic content is removed and the silanol groups between lamellae are condensed to form three-dimensional MCM-22 zeolite, as shown in Figure 1a. Consequently, an additional two-directional 10-ring (0.40 \(\times\) 0.55 nm) channel, formed as the union of 12-ring hemicavities, generates internal super cages (free internal diameter of 0.71 nm and internal height of 1.82 nm), which are also connected to the aforementioned two-directional 10-ring channels [13]. In addition, it is possible to obtain a three-dimensional MCM-22 analog called MCM-49, which is obtained by direct crystallization by increasing the relative proportion of alkali in the gel composition [16]. Furthermore, another material called MCM-56 with a partial disorder of lamellar stacking is obtained when the reaction to form MCM-49 is stopped in the middle of the crystallization course [17; 18]. The MCM-22 zeolite with high crystallinity can be obtained with Si/Al molar ratios between 15 and 70 (usually 20). However, ferrierite competing phases are found when the amount of aluminum increases (Si/Al = 9), as shown in the microscopic analysis of Figure 2 (image a, white arrows). In contrast, the decrease in aluminum in the synthesis gel (Si/Al > 70) leads to MFI (Mobil Five) competing phases [19]. It is also possible to obtain a pure silica zeolite MCM-22 analog by direct  
Figure 1: The two-dimensional (2D) zeolitic precursor and three-dimensional (3D) MWW (Mobil twenty two) zeolitic structure (**a**); its eight different tetrahedral sites (**b**); HMI (hexamethyleneimine). Adapted from Reference [14; 15]. Copyright (1998), with the permission of the Royal Society of Chemistry, and Copyright (2006), with permission from Elsevier. synthesis using mixtures of trimethyladamantylammonium (TMAda\({}^{+}\)) and HMI as a second organic template, which is known as ITQ-1 [14]. The Si/Al ratio associated with the synthesis temperature and the static and dynamic (rotation of the autoclaves) conditions of the gel aging could interfere in the formation of MCM-22. It was reported that the use of 30 \(<\) Si/Al \(<\) 70 and temperatures above 150 \({}^{\circ}\)C results in the formation of ferrierite and/or mordenite competing phases. At temperatures below 150 \({}^{\circ}\)C with dynamic conditions, the MCM-22 phase is insignificant, while the formation of other phases increases with a decrease in the Si/Al ratio [20]. Other authors have reported that an MCM-22 formation with no other phase competitions was avoided using temperatures between 135 and 150 \({}^{\circ}\)C. Furthermore, dynamic conditions produce MCM-22 zeolite with good quality, while static conditions result in the nonsignificant formation of the desired phase or even the formation of pure ferrierite [20; 21]. In addition, it was reported that the previous aging of the gel at 180 \({}^{\circ}\)C for 4-12 h and static conditions produced pure MCM-22 with a reduced crystallization time [22]. MCM-22 presents distinct acid sites that reveal the homogeneity in acid strength.