Different Zeolite Phases Obtained with the Same Organic Structure Directing Agent in the Presence and Absence of Aluminum: The Directing Role of Aluminum in the Synthesis of Zeolites

Abstract

Zeolites are a large family of crystalline microporous materials with, mainly, silicate and aluminosilicate composition. Each topology can only be synthesized in a specific range of aluminum content, Al/(Si + Al), within the interval [0-0.5], and this interval cannot, in general, be predicted for each structure. Aluminum and organic structure directing agents (OSDAs), among others, act together in obtaining the zeolite phase under each specific synthesis condition. The present study is an attempt to rationalize the role of aluminum as a structure directing agent in the synthesis of zeolites using computational chemistry and based on the criteria of energetic stability using both force field and periodic DFT methods. A proper selection of cases in which, using the same OSDA, different zeolite phases are obtained in the presence and absence of aluminum helps to rationalize how aluminum contributes to the relative stability of the different competing zeolite phases considered.