Porous materials are a family of excellent adsorbents, catalysts, supporting materials, ion-exchanging agents, and micro-reactors. Because of their open-framework structures and large surface areas (including internal and external surface areas), these porous materials have been widely used in the petroleum and chemical industries and in air separation [1, 2]. According to the definition of the pore size from the International Union of Pure and Applied Chemistry (IUPAC) , porous materials can be classified into three groups: microporous materials (<2 nm), mesoporous materials (2-50 nm), and macroporous materials (>50 nm). These three classes of materials can be included in the so-called nanoporous materials (1-100 nm), which are found to be more and more important in the applications of large molecular conversion, optic-electric devices, and other hightech industries [4, 5].
Nanoporous materials can be amorphous, quasi-crystalline, or crystalline. Methods such as X-ray diffraction (XRD) and electron diffraction (ED) can be used to characterize these materials [1, 2]. The pore structure is one of the most important parameters for nanoporous materials and can generally be characterized by use of physical adsorption of the gas (such as N2, Ar, organic molecules, etc.) or by a liquid pressure method (mercury extrusion). Amorphous and quasi-crystalline porous materials such as silica gels, aluminum oxides, and activated carbons have been widely used in industry as catalysts or the supports for catalysts. However, because these materials possess no long-range ordered structural regularity and they have disordered pore structures and widely distributed pore sizes, zeolite-type microporous materials have long been used as substitutes.
Nanoporous materials with long-range ordered structures are discussed in this chapter, and the focus is on the newly developed classes of mesoporous materials. Ordered macro-porous materials developed recently will also be involved. At the atomic level, most mesoporous and macroporous materials are amorphous, but they have properties similar to those of crystalline materials because their uniform pore structures possess long-range order at the meso- or macroscales, which can be reflected by well-defined XRD and ED patterns.
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