The First Systematic Study on the Conditions Affecting the Ionothermal Synthesis of Silicoaluminophosphates

• Published in: ChemistrySelect (Weinheim) 2018-11, Vol.3 (44), p.12495-12503
• Main Authors: Azim, Muhammad Mohsin, Stark, Annegret
• Format: Article
• Language: English
• Subjects: Ionic liquids; ionothermal synthesis; microporous materials; silicoaluminophosphates; zeolite analogues
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.201802959

The first systematic study on the ionothermal synthesis of silicoaluminophosphates (SAPOs) was performed to study the influence of reaction time, Si/Al or F/Al ratios and changing ionic liquid (cation, anion and alkyl group). The resulting materials were characterised by XRD, liquid (1H) and solid state (29Si) NMR, TPDA, SEM images, Volhard titration, as well as thermogravimetric and nitrogen sorption analyses. 1‐Butyl‐3‐methylimidazolium bromide ([C4mim]Br) as both solvent and structure‐directing agent (SDA) produced the AFI framework. It was found that the resulting Si/Al ratio of SAPO‐AFI increases with an increase in initial Si/Al ratio but decreases with F/Al ratio in the reaction mixture. Different ionic liquids giving the same framework type have no effect on the silicon uptake. The formation of Si‐islands is favoured at extended reaction times or higher silicon content. The framework type of SAPOs can be changed from AEL to AFI by changing either the alkyl chain from ethyl to butyl, substituting the C2‐position of the cation with a methyl moiety, or altering the cation (imidazolium vs. pyridinium). The framework selectivity was altered from AFI to LTA by changing the anion (of [C4py]Br to Cl−), and to CHA by 1‐methylimidazole addition. The first successful ionothermal synthesis of the AFI, LTA and CHA framework types of SAPOs is presented, providing a more efficient method than the conventional hydrothermal synthesis. The first systematic study on the ionothermal synthesis of SAPOs is presented. The framework type of SAPOs is influenced by the ionic liquid's cation, anion, alkyl chain (length and position), the nature and the amount of fluoride precursor, and the addition of a co‐SDA. The ionothermal synthesis of the SAPO‐AFI, ‐AEL, ‐CHA and ‐LTA is presented which is more efficient compared to the conventional hydrothermal methods.