Design of Active Sites in Zeolite Catalysts using Modern Semiempirical Methods: The Case of Mordenite

Publication date: Available online 30 August 2019Source: Computational and Theoretical ChemistryAuthor(s): Alexander V. Vorontsov, Héctor Valdés, Panagiotis G. SmirniotisAbstractZeolites are widely used for numerous processes for production of a vast number of chemicals, fuels and commercial goods. Preparation of zeolite catalysts that have improved selectivity for the desired products, operate at lower temperature and possess increased stability is therefore of great interest. The key to such improved zeolite catalysts is in the design of active sites and facilitation of mass transfer via optimization of the porous structure. At the same time, undesirable sites that inhibit desirable properties of the active sites need to be removed or blocked. The strength and structure of either the Brønsted or Lewis acid sites, directly determines their catalytic activity and selectivity for each reaction. In the present study, the structure and acidity of active sites in zeolites are investigated for the example of mordenite using modern semiempirical methods pm7 and scc-dftb (dftb2). Models AlHSi95O192 and Al2H2Si94O192 are used for Brønsted acid sites and Al2Si94O191 for Lewis acid sites. In agreement with previous studies, the stability of T1, T2, T3 and T4 sites is similar. Many different configurations of pair-wise located Al atoms were studied. In the present work it was found that some of the pair-wise located Al atoms possess Brønsted acid sites with strength much higher tha...

Source: Computational and Theoretical Chemistry - August 30, 2019 Category: Chemistry Source Type: research