(349x) The Effect of Non-Crystalline Al Species on Catalytic Performance of H-ZSM5 Zeolite

The purpose of this work was to investigate the role of non-crystalline Al species in H-ZSM5 zeolite on monomolecular cracking reaction of propane based on density functional theory (DFT) calculations. The non-crystalline Al species can be extra framework Al (EFAl) that is located in the proximity with Bronsted acid sites (BAS) after steaming treatment. Here, the structure and stability of different paired sites BAS/non-framework Al species were investigated and compared. Based on the thermodynamic analysis, the synergy of BAS and EFAl in the form of Al(OH)2 was the most stable among various EFAl species. We find that the deprotonation energy does not change much in the BAS-EFAl complex. We thus investigate the role of local stabilization of both reaction intermediates as well as transition states through hydrogen bonding and van der Waals interactions to clarify the cause of the rate enhancements observed in experiments. This work shows by tuning the BAS-EFAl paired structure the cracking reaction can be enhanced.