Computational and experimental approach to the role of structure-directing agents in the synthesis of zeolites:: The case of cyclohexyl alkyl pyrrolidinium salts in the synthesis of β, EU-1, ZSM-11, and ZSM-12 zeolites

The role of structure-directing agents (SDA) in the synthesis of zeolites is investigated, and the structures obtained in the synthesis are rationalized in terms of the energetic stabilization between the SDA and the microporous zeolite structure. An explanation is provided for the synthesis outcome in terms of a balance between kinetic and thermodynamic factors throughout the nucleation and crystallization stages. The stability of beta, EU-1, ZSM-11, and ZSM-12 zeolites is calculated over a wide range of Si/Al ratios when cyclohexyl alkyl pyrrolidinium salts are used as the SDA. The role of the SDA allows us to explain the final stability and the Si/Al range in which each structure can be synthesized. The stabilization of intermediate species during the nucleation is proposed to orient the final result of the synthesis. A simple kinetic model is proposed to explain the synthesis process.