Violations of Löwenstein's rule in zeolites

Abstract

Zeolites, microporous aluminosilicates, are amongst the most widely used catalysts in the petrochemical industry. Zeolite catalytic functionality is influenced by the location of tetrahedral alumina and associated counter-cations in the aluminosilicate framework, yet little is definitively known about the factors that govern the framework aluminium arrangement. It is generally accepted that all zeolites obey Löwenstein's rule of “aluminium avoidance”, and that –Al–O–Al– bond formation is forbidden. Here, we describe an unprecedented screening of aluminium distribution in catalytically active zeolite SSZ-13 (CHA) in both its protonated and sodium-containing forms, H-SSZ-13 and Na-SSZ-13, using density functional theory (DFT). We predict violations of Löwenstein's rule in high and low silica H-SSZ-13 and other protonated frameworks considered in this investigation: H-LTA, H-RHO, H-ABW and H-MOR. The synthetic realisation of these zeolites could spur the development of new catalytic routes and materials, and the optimisation of existing zeolite catalysts.