Performance of three different cations based on imidazolium ring as structure directing agents in the synthesis of aluminophosphates and silicoaluminophosphates microporous materials

Abstract

Abstract In this work three different cations based on imidazolium rings, 2-ethyl-1,3,4-trimethylimidazolium (2E134TMI), 1,2,3-triethyl-4-methylimidazolium (123TE4MI) and 1,2,3-triethylimidazolium (123TEI), were employed as structure directing agents (SDA) for the synthesis of aluminophosphate and silicoaluminophosphate microporous materials. The cations allowed the crystallization of three different structures (AFI, CHA and AEI). Nevertheless, even though these SDAs are similar as in size, shape and flexibility conformational, they presented different specificity for these phases. While CHA structure was synthesized with 2E134TMI and 123 TMI4MI cations, the AEI phase was obtained only with 123TEI. The resulting materials were characterized by different chemical and physical-chemical techniques. A complementary computational study shows that the ability of 123TE4MI cation to crystallize CHA framework does not only depend on a good fitting of the cation itself within this framework cavity, but also on an adequate packing between cations within adjacent cavities. On the other hand, the best host-guest chemistry for 123TEI SDA occurs when occluded within the AEI framework cavities, explaining the experimental observations.