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**Chapter 5**

**Abstract**

interlayer expansion

**1. Introduction**

*Hao Xu and Peng Wu*

New Trends in Layered Zeolites

Layered zeolites, with a flexible and changeable interlayer connection, can be modified to give a great number of derivative structures with enlarged pore sizes or enhanced external surface areas, via swelling, delamination, pillaring, or silylation. In recent years, great efforts have been devoted to the synthesis of novel-layered zeolite precursors, by using the specially designed bifunctional amphiphilic surfactants as the structure-directing agents or through the selective degradation of double four ring-containing germanosilicates. In addition, the novel modifications, such as mild delamination, interlayer expansion assisted by deconstruction-reconstruction, and layer-stacking reorganization by dissolution-recrystallization, have also been developed to create more derivatives while achieving better preservation of layer structures. Recent progresses in the field of layered zeolites are summarized

in this chapter, and the challenges for future development are also proposed.

**Keywords:** layered zeolite, design synthesis, structural modification, delamination,

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

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**).

calcination and then produce 3D zeolite frameworks.
