Relationship between acidity and catalytic reactivity of faujasite zeolite: A periodic DFT study

The fundamental aspects of Bronsted acidity and catalytic reactivity of faujasite-type zeolites were investigated by periodic DFT calculations. The adsorption energies of ammonia and pyridine on the Bronsted acid site (BAS) were used to determine the acidity. It is demonstrated that the acid strength of zeolite materials increases with rising Si/AI ratio (low-silica faujasite), and then levels off at high Si/Al ratio (high-silica faujasite). The presence of multinuclear extra framework AI (EFAI) in the sodalite cages substantially enhances the Bronsted acidity. The catalytic reactivity of faujasite toward protolytic propane cracking correlates well with the characterized acidity by base adsorption. However, for HID exchange reaction of benzene the presence of EFAI species can induce deviations between the measured acidity and the reactivity of faujasite catalysts, indicating that acidity and reactivity are not always directly correlated. (C) 2016 Elsevier Inc. All rights reserved.