ABSTRACT
After about 50 years of intensive research on the development of inorganic molecular sieves, the porous solids have now taken a firm position in materials science, finding important applications in the field of adsorption and catalysis. The longest-known molecular sieves are the natural zeolites, with a three-dimensional open-structure framework built up of very small micropores (pore diameter <2 nm). After the oil crisis of 1973, the main objective was to obtain materials with larger pores allowing more bulky molecules in their porous network. It was then that scientists started to create porosity in the interlayer space of layered clays, developing the first pillared clays with pores in the larger microporous region. Since the mid-1990s, however, there has been an industrial need for materials with even larger mesopores (pore diameter >2 nm) for the processing of heavy oil fractions and the synthesis of pharmaceuticals, fine chemicals, and bio-compounds. Therefore, based on these changing requirements of the catalytic industry, much effort has been expended in producing mesoporous solids. In 1995, then, the first clay-derived mesoporous material (named porous clay heterostructure) was developed based on a templated technique. Both pillared clay and porous clay heterostructures will be discussed in this chapter, with the focus on their synthesis and applications.
