## 1 Introduction  
In the refining and chemical industry, most processes (above 80%) involve catalysis and catalysts. Catalysts are indispensable to many environmental procedures from automotive exhaust treatment to industrial effluent and municipal waste treatment, which contribute to reducing pollution and other adverse environmental impacts. Besides, catalysts are also key technologies in developing fuel cells and photovoltaic cells to replace conventional fossil fuels. Since most of the practical catalytic processes are so complicated that single component catalysts cannot easily meet the requirements for high performance such as high activity, remarkable selectivity and good resistance to deactivation, composite catalysts, which have two or more components combined together, are much more researched and used. According to the combination method of the components, there are several kinds of composite catalysts, as listed below:  
* Simple physical mixtures [1, 2, 3, 4]. * Crystalline composites obtained by intergrowth, overgrowth/core-shell growth or co-crystallization [5, 6, 7, 8]. * Composites with active components and/or promoters coated (attached, doped, loaded, supported or deposited) on the support [9, 10, 11, 12]. * _In-situ_ combinations prepared by sol-gel hydrolysis or co-precipitation followed by calcination [13, 14, 15, 16]
* Matrix materials modified with metal oxides, metal hydroxides, amorphous SiO\({}_{2}\), organic motifs, sulfonic acid groups, _etc._[17, 18, 19, 20]. * Host-guest composites, which are prepared by incorporation of guest compounds into host materials [21, 22, 23, 24]. * Hybrid composites, which comprise a matrix material (polymer, carbon, _etc._) in which one or more material phases are dispersed, including polymer/carbon nanotube composites, PVC/nano-SiO\({}_{2}\) composites, PVC-ZnO composite films, polypyrrole (PPy)/C composites, _etc._[25, 26, 27, 28]. * Hierarchical porous composites, which have pore systems of micropores, mesopores and macropores combined together [29, 30, 31]. Although it is doubtful that every component contributes to the catalytic performance, there must be some effective components that do. The mechanism for such good effects is the key point, and these effects may be one of those listed below:  
* Simple supporting effect [32, 33]. * Stabilizing the microstructure or active components [34, 35]. * Formation of new compounds which act as active components or stabilizers [36, 37]. * Having two or more functions [38, 39, 40, 41, 42]. * Dual-function effect in elementary reactions [43]. * Adjusting the performance of acid and base sites [44, 45, 46, 47]. * Controling of surface bonding state, coordination state and electronic state [48, 49, 50, 51]. * Controling of redox performances [52, 53, 54, 55]. * Influencing the speed of adsorption/desorption and diffusion of molecules [56, 57, 58, 59]. * Influencing the migration or transference of the active species such as O, H, _etc._[60, 61, 62, 63]. * Incorporating guest active compounds or centers into host materials, which provides heterogeneous catalysts [21; 22; 23; 24]. * Enhancing the mechanical, thermomechanical, electronic or other physical and chemical properties, especially for polymer matrix composite catalysts [25; 26; 27; 28]. Nowadays, processes like light olefin (C\({}_{2}^{-}\) to C\({}_{4}^{=}\)) production and the production of aromatics and their derivatives such as aromatic isomerization, disproportionation, and alkylation are of great importance in the petrochemical industry, and great advances have been made in the catalytic procedures including maximum propylene production, methanol to olefins (MTO), methanol to propylene (MTP), toluene selective disproportionation, heavy aromatics disproportionation, aromatics synthesis from LPG, and ethylbenzene and cumene manufacture and other small volume petrochemical manufacture. Besides the catalyst technology for petrochemical industry, chiral catalysts have become another new focus of development in the fine chemical industry.