Acidic medium synthesis of zeolites – an avenue to control the structure-directing power of organic templates

Guangying Fu (1) , Eddy Dib (2) , Qiaolin Lang (1) , Haonuan Zhao (2, 1) , Songxia Wang (1) , Ruiqin Ding (1) , Xiaobo Yang (1) , Valentin Valtchev (1, 2)

1 Qingdao Institute of Bioenergy and Bioprocess Technology [Qingdao, China]
2 LCS - Laboratoire catalyse et spectrochimie

This paper deals with the extension of the synthesis field of microporous zeolite-type materials and types of organic structure-directing agents (OSDA) that can be used to promote their crystallization. The highly hydrophilic hexamethylenetetramine (urotropine), with its C/N ratio = 1.5, which is unusual to act as a structure-directing agent in the crystallization of open-framework silica polymorphs, is used to exemplify the novelty of the employed approach. Namely, the protonation of urotropine in an acidic fluorine-containing medium transforms it into a very efficient OSDA that yields dodecasil 3C (MTN-type). This novel synthesis also allows gaining insights into OSDA-framework interactions in the MTN-type structure. The comprehensive 29Si and 19F MAS NMR indicate a small number of point defects of the framework T sites and the multiple bonding of F− ions to Si in a disordered manner. Based on this finding, a unit cell model has been generated using Monte Carlo simulation and validated with Rietveld refinement using experimental powder X-ray diffraction data. In the model, protonated urotropine cations are located in the center of the big hexakaidecahedral [51264] cages at full occupancy with random orientations. The charge balance is provided by the disordered F− ions.

Domaines: Matériaux

Guangying Fu, Eddy Dib, Qiaolin Lang, Haonuan Zhao, Songxia Wang, et al.. Acidic medium synthesis of zeolites – an avenue to control the structure-directing power of organic templates. Dalton Transactions, 2022, 51 (30), pp.11499-11506. ⟨10.1039/D2DT01554D⟩. ⟨hal-03779241⟩