دانلود مقاله Extremely ultra-high yield and wide size distribution of a large surface area zeolite prepared via hydrothermal condition: A brief BET review
سال انتشار: ۱۳۸۷
محل انتشار: دومین کنگره بین المللی علوم و فناوری نانو
تعداد صفحات: ۲
S Manafi – Materials Engineering Department, Islamic Azad University, Shahrood Branch, Shahrood, Iran
S Joughehdoust –
Zeolites are an increasingly important class of materials currently utilized in a wide variety of industrial applications, including catalysis, ion exchange, gas separation, membrane separation, nuclear waste disposal, chemical sensing, and pollution abatement. Zeolites are aluminosilicate molecular sieves with pores of molecular dimensions. Zeolites can be synthesized with a wide range of pore sizes and topologies and are used in applications such as catalysis and chemical separations .Zeolites constitute a framework based on an infinitely extending three-dimensional network of SiO4 and [AlO4]-1 tetrahedra linked through common oxygen atoms. The framework structure encloses cavities occupied by large ions and water molecules, both of which have considerable freedom of movement, permitting ion exchange and reversible dehydration. The isomorphic substitution of silicon by aluminum gives rise to a net negative charge compensated by cations. In general, the framework of a crystalline zeolite dictates the selectivity toward competing cations, and each zeolite has its own selectivity series .Surface area is an attribute that is used by catalyst manufacturers and users to monitor the activity and stability of catalysts. There are different methods used to measure surface area and each method can yield different results. Most methods are based on the isothermal adsorption of nitrogen. Either a single point or multipoint method is used to calculate the surface area. At Engelhard, the multipoint Brunauer, Emmett and Teller (BET) method is used to measure total surface area of fresh and equilibrium moving bed and fluid catalytic cracking (FCC) catalysts. It is also used as a quality control tool during catalyst manufacture . The BET method has limitations with respect to calculating the surface area of microporous materials, but is suitably used for comparative analysis of the surface area of a set of micro/mesoporous samples .