All-Silica SSZ-74 Synthesized in Fluoride or Fluoride-Free Media: Investigation on Organic Structure-Directing Agent’s Locations Inside Pores

• Published in: Crystal growth & design Vol. 21; no. 7; pp. 4013 - 4022
• Main Authors: Isaac, Carole, Deroche, Irena, Paillaud, Jean-Louis, Daou, T. Jean, Ryzhikov, Andrey, Michelin, Laure, Rigolet, Séverinne, Josien, Ludovic, Nouali, Habiba
• Format: Journal Article
• Language: English
• Published: American Chemical Society 07.07.2021
• Subjects: Chemical Sciences; Material chemistry
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.1c00322

Pure silica SSZ-74 zeolite (-SVR type) was synthesized in fluoride or fluoride-free media using the hydroxide salts of the symmetric 1,6-bis­(N-methylpyrrolidinium)­hexane and asymmetric 1-methyl-1-[6-(trimethyl-azaniumyl)-hexyl]­pyrrolidinium diquaternary structures as organic structure directing agents (OSDA). A structural study using the Rietveld method revealed unexpected orientation of the OSDAs inside the micropores of the zeolite. Unlike the original structural elucidation, which proposed the OSDA’s location inside the channel parallel to c-axis in a distorted conformation, in both samples, the OSDAs are here located elsewhere, inside the undulated connecting channels along the [110] direction and in a more favorable linear conformation. This surprising result was confirmed from an energy point of view using a computational method together with solid-state NMR experiments. Moreover, the impact of a thermal treatment on this particular structure containing ordered vacancies was studied by high-temperature powder X-ray diffraction under different atmospheres.