Modeling extra framework aluminum (EFAL) formation in the zeolite ZSM-5 using parametric quantum and DFT methods

Quantum-chemical calculations were performed using the DFT method and a qualitative parametric quantum method (PQM) named CATIVIC, in order to model the whole EFAL formation process. Two clusters (AlSi3O12H9 and AlSi63O152H49) were employed to model zeolite ZSM-5. Formation of intermediate Al species was reported with four to zero bond coordinations to the zeolite framework. The EFAL formation process was analyzed by the evaluation of bond distances, diatomic bond energies changes (ΔDBE) and Wiberg's indexes (WI) of Al–O bonds. Penta- and hexacoordinated intermediates were produced and free Al(OH)3 and Al(OH)3(H2O)2 EFAL species were formed from the small and big clusters, respectively. Comparisons with the DFT method permit establishing that CATIVIC or a well-parameterized PQM method can be used to understand zeolite changes under hydrothermal treatment.

Final species formed in modelling the ZSM5 zeolite dealumination process. Dark balls go with O atoms, small white balls are H atoms, and gray balls correspond to Si atoms.Figure optionsDownload as PowerPoint slide