Synthesis of Zeolites in the Presence of Diquaternary Alkylammonium Ions as Structure-Directing Agents

Abstract

Résumé -Synthèse de zéolithes en présence de cations alkyldiammonium quaternaires comme agents structurants -Cet article présente les résultats de synthèses réalisées pour la plupart en milieu purement silicique, en présence de cations (CH 3 ) 3 N + (CH 2 ) n N + (CH 3 ) 3 (n = 5, 6, 9 ou 10) en milieu fluoré, mais également en présence de cations (CH 3

Introduction to the Zeolite Structure-Directing Phenomenon by Organic Species: General Aspects

“…Degradation and rearrangement of organic cations to finally produce a smaller cation may be more frequent than thought. Other examples include: i) The degradation of certain diquats resulting in the crystallization of TMA-containing phases (AST, RUT and MTN [66] or Omega [67]); crystallization of TMA-containing AST when using the large N,N,N-trimethylbenzylammonium as SDA [68]; iii) cocrystallization of ITW together with MTW when using 1-benzyl-2,3dimethylimidazolium, obviously too large to fit into ITW cages, by degradation and rearrangement to produce 1,2,3-trimethylimidazolium [69]; iv) crystallization of CHA phases directed by 1,2-dimethylimidazolium formed by degradation of 1alkyl-3-methylimidazolium cations during the ionothermal synthesis of aluminophosphates [70]; v) crystallization of TMA-containing MTN from Hofmann degradation and rearrangement of (1R,2S)-dimethylephedrinium [71]; and vi) the use of unstable deep-eutectic mixtures as both solvent and SDA-delivering agent [72].…”

Synthesis of BEC-type germanosilicates with asymmetric diquaternary ammonium salts

“…The products synthesized with the OSDAs having the shortest carbon chain length ([C5]) produced some clathrasil-type structures like AST and UOZ. However, usual synthesis of silicogermanate or ger-manateAST includes tetramethylammonium, quinuclidine or DABCO as templates [26,43] which are much smaller in size than TM[C5](C 4 N) or TM[C5](C 5 N). It can be supposed that under such hydrothermal conditions, the corresponding molecules are decomposed, allowing the formation of the AST phase.…”

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

“…That is why increasing the silica content has been a challenge over the past decades. The synthesis of pure- and high-silica zeolites has been very fruitful thanks to organocations, especially diquaternary ammonium salts. − Among them, diquaternary alkylammonium ions with an N-heterocycle have directed the crystallization of many zeolites in hydroxide or fluoride medium. − Indeed, the addition of fluoride ions in the synthesis gel increases the solubility of the inorganic species, and it is especially suited for pure-silica syntheses which can be prepared with a better yield of crystallization in a more neutral media with fewer connectivity defects. − This fluoride route enabled the formation of open frameworks which are favored in concentrated media. The fluoride anions have a structure directing effect that helps the crystallization of new topologies because of their stabilization role of d4r units. − However, the substantial toxicity of hydrofluoric acid is a challenge for large scale syntheses of these zeolites.…”

“…[8][9][10] Among them, diquaternary alkylammonium ions having a N-heterocycle have directed the crystallization of many zeolites in hydroxide or fluoride medium. [11][12][13][14][15] Indeed, the addition of fluoride ions in the synthesis gel increases the solubility of the inorganic species, it is especially suited for pure-silica syntheses which can be prepared with a better yield of crystallization in a more neutral media with less connectivity defects. [16][17][18] This fluoride route enabled the formation of open frameworks which are favored in concentrated media.…”