| Abstract: | Zeolite materials are microporous aluminosilicates with various uses, including acting as important catalysts in many processes. One such process is the methanol to gasoline reaction, used widely in industry. This reaction is known to be associated with Brønsted acid sites in the zeolite, formed when Si is substituted by Al in the framework, with an associated H+ being bound nearby to maintain charge neutrality. However, it is not clear exactly what role the proton plays in this reaction. Because of the large unit cell (generally 50-300 atoms, depending on the particular zeolite) of such structures, most ab initio calculations of these materials have focused on studying small clusters representing just a portion of the framework. However, by choosing the chabazite zeolite structure, which has only 36 atoms in the primitive unit cell, we have been able to perform a full periodic ab initio calculation. This has used density functional theory with a generalized gradient approximation for the exchange-correlation energy, a plane-wave basis set, and norm-conserving optimized pseudopotentials. Using these methods we have examined the geometry and electronic structure of a zeolite acid site and considered one way in which a methanol molecule may bind to such a site. © 1997 John Wiley & Sons, Inc. |
