Beta zeolite is an old zeolite discovered before Mobil began the "ZSM" naming sequence. As the name implies, it was the second in an earlier sequence. The structure of zeolite beta was only recently determined because the structure is very complex and interest was not high until the material became important for some dewaxing opertions. Zeolite beta consists of an intergrowth of two distinct structures termed Polymorphs A and B. The polymorphs grow as two-dimensional sheets and the sheets randomly alternate between the two. Both polymorphs have a three dimensional network of 12-ring pores. The intergrowth of the polymorphs does not significantlyaffect the pores in two of the dimensions, but in the direction of the faulting, the pore becomes tortuous, but not blocked. The two hypothetical polymorphs are depicted here.
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