**1. Introduction**

Zeolites, with high-crystalline three-dimensional (3D) frameworks composed of TO4 (T = Si or Al, etc.) tetrahedrons, have found their unique advantages in the field of adsorption, separation, and catalysis, owing to a large surface area, uniform pore channels of molecular size, strong acidity, and redox ability. According to the International Zeolite Association (IZA), 244 kinds of zeolites have been recognized up to date, most of which are hydrothermally synthesized [1]. In addition, the topotactic conversion from two-dimensional (2D) lamellar precursors to 3D rigid zeolite framework contributes ~10% of the whole zeolite family [2]. Rather than strong and rigid covalent bonds, relative weak and flexible hydrogen bonds are the interaction force between the neighboring layers in 2D lamellar precursors, which are also called layered zeolites. These hydrogen bonds are derived from the abundant silanol groups on the layer surface, which would condense to form Si▬O▬Si linkage upon calcination and then produce 3D zeolite frameworks.

In the very beginning, layered zeolites are occasionally obtained from the traditional synthetic gels that were designed to produce 3D zeolites. However, the formation mechanism of these layered zeolites is still a mystery, which prohibits the researchers to design and synthesize more novel-layered zeolites via the traditional hydrothermal synthesis. Recently, several novel strategies have been proposed to synthesize layered zeolite, including the usage of specially designed bifunctional structure-directing agents (SDA) [3] and the transformation of 3D germanosilicates to 2D lamellar zeolites by posttreatment [4]. The newly established methods expanded the layered zeolite family, and there are now nearly 30 kinds of layered zeolites available (**Table 1**).

The interlayer flexible hydrogen bonds endowed the layered zeolites with modifiable structural property. Post-modifications including swelling [29], delamination [30, 31], pillaring [32], silylation [33], and detemplating [34] have been reported to increase the interlayer space or to gain higher external surface area (**Figure 1**). The classical swelling process is achieved by the intercalation of layered zeolites with large-sized surfactant molecules in the alkaline organic ammonium solution, resulting in enlarged interlayer space [29]. An ultrasonic treatment over the swollen intermediate produces full delaminated materials, changing the original ordered stacking style to house-of-cards arrangement and greatly enhancing the external surface area [30, 31]. Again, based on the swollen intermediate, the enhanced interlayer space can be stabilized by rigid silica pillars, giving pillaring materials with interlayer mesopores and intralayer micropores [32]. In contrast, interlayer silylation is an atom-level accurate modification to produce interlayer-expanded structures [33]. Detemplating, including the full and partial removal of the interlayer SDA molecules, results in a 3D zeolite framework and partial delaminated


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**Figure 1.**

*New Trends in Layered Zeolites*

*DOI: http://dx.doi.org/10.5772/intechopen.86696*

materials, respectively [34]. Although these posttreatments have achieved a great success for most of the layered zeolites, the corrosion effect of the alkaline solution on intralayer structure in swelling process, the multistep procedure of delamination, and the failure of silylation over some special layered zeolites cannot be

This chapter will review the recently developed synthetic methods, including the usage of bifunctional surfactants and the selective degradation of germanosilicates, and the modification strategies of layered zeolites, such as mild delamination, interlayer expansion assisted by deconstruction-reconstruction, and layer-stacking reorganization by dissolution-recrystallization. One of the most important driving forces of novel-layered zeolite exploration and modification improvement is to design synthesis of more efficient catalysts, with better accessibility of active sites provided by enlarged pores and external surface areas. Thus, this chapter will also cover the catalytic performance of the newly developed layered zeolite and derivative materials in the solid acid<sup>−</sup>/base-catalyzed reactions and the liquid selective oxidation reactions. For the conventional synthesis, characterization, classical modifications, and applications of layered zeolites, the readers could find them in the published reviews [35–40]. In the end, the challenge and possible future

ignored, and new modification strategies are highly desired.

*Summary of the post-synthesis modifications over a typical MWW lamellar zeolite.*

development in the field of layered zeolites is prospected.

**2.1 Synthesis of layered zeolites with bifunctional amphiphilic SDAs**

Compared to the continuous expanding in the 3D directions for typical zeolite frameworks, the layered structures only spread in 2D directions, with the growth in

**2. Newly developed synthetic methods**

#### **Table 1.**

*Listing of existing layered zeolite.*

*Zeolites - New Challenges*

The interlayer flexible hydrogen bonds endowed the layered zeolites with modifiable structural property. Post-modifications including swelling [29], delamination [30, 31], pillaring [32], silylation [33], and detemplating [34] have been reported to increase the interlayer space or to gain higher external surface area (**Figure 1**). The classical swelling process is achieved by the intercalation of layered zeolites with large-sized surfactant molecules in the alkaline organic ammonium solution, resulting in enlarged interlayer space [29]. An ultrasonic treatment over the swollen intermediate produces full delaminated materials, changing the original ordered stacking style to house-of-cards arrangement and greatly enhancing the external surface area [30, 31]. Again, based on the swollen intermediate, the enhanced interlayer space can be stabilized by rigid silica pillars, giving pillaring materials with interlayer mesopores and intralayer micropores [32]. In contrast, interlayer silylation is an atom-level accurate modification to produce interlayer-expanded structures [33]. Detemplating, including the full and partial removal of the interlayer SDA molecules, results in a 3D zeolite framework and partial delaminated

**Layered precursors Structure codea Main pores for 3D structure Reference** MCM-22 MWW 10 × 10-R, 12R cages [5] PSH-3 [6] SSZ-25 [7] ITQ-1 [8] ERB-1 [9] EMM-10 [10] SSZ-70 [11] ECNU-5 [12] PREFER FER 10 × 8-R [13] PLS-3 [14] MCM-47 CDO 8 × 8-R [15] MCM-65 [16] PLS-1 [17] PLS-4 [14] RUB-36 [18] EU-19 CAS 8R [19] Nu-6(1) NSI 8 × 8-R [20] RUB-15 SOD 6R [21] RUB-18 RWR 8 × 8-R [22] RUB-39 RRO 10 × 8-R [23] PreAFO AFO 10R [24] Lamellar MFI MFI 10 × 10-R [3] IPC-1P PCR 10 × 8-R [4]

\*PCS 12 × 10-R, 10 × 8-R [25]

ECNU-21P — 10 × 6-R [26] MCM-69(P) — — [27] HUS-2 — — [28]

*The structure code for the 3D zeolite obtained from layered precursor upon calcination.*

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*a*

**Table 1.**

*Listing of existing layered zeolite.*

**Figure 1.** *Summary of the post-synthesis modifications over a typical MWW lamellar zeolite.*

materials, respectively [34]. Although these posttreatments have achieved a great success for most of the layered zeolites, the corrosion effect of the alkaline solution on intralayer structure in swelling process, the multistep procedure of delamination, and the failure of silylation over some special layered zeolites cannot be ignored, and new modification strategies are highly desired.

This chapter will review the recently developed synthetic methods, including the usage of bifunctional surfactants and the selective degradation of germanosilicates, and the modification strategies of layered zeolites, such as mild delamination, interlayer expansion assisted by deconstruction-reconstruction, and layer-stacking reorganization by dissolution-recrystallization. One of the most important driving forces of novel-layered zeolite exploration and modification improvement is to design synthesis of more efficient catalysts, with better accessibility of active sites provided by enlarged pores and external surface areas. Thus, this chapter will also cover the catalytic performance of the newly developed layered zeolite and derivative materials in the solid acid<sup>−</sup>/base-catalyzed reactions and the liquid selective oxidation reactions. For the conventional synthesis, characterization, classical modifications, and applications of layered zeolites, the readers could find them in the published reviews [35–40]. In the end, the challenge and possible future development in the field of layered zeolites is prospected.
