Ionothermal syntheses of transition-metal-substituted aluminophosphate molecular sieves in the presence of tetraalkylammonium hydroxides

Transition-metal-substituted aluminophosphate (MeAPO) molecular sieves with SOD and AEI framework types have been synthesized ionothermally in the ionic liquid 1-ethyl-3-methylimidazolium bromide with adding four tetraalkylammonium hydroxides, including tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide. Detailed synthetic investigation shows that the nature and concentration of the tetraalkylammonium hydroxide, the Me/Al ratio in the reaction mixture and the metal sources greatly influence the phase selectivity of the reaction. The products have been characterized by PXRD, SEM, ICP, CHN, UV-Vis spectroscopy, C-13, Al-27 and P-31 MAS NMR, and TG. The results reveal that the tetraalkylammonium cations compete with the ionic liquid cations to act as the structure directing agent. The templating ability of the tetraallcylammonium cations and the ionic liquid cations is closely related to their charge densities. (c) 2015 Elsevier Inc. All rights reserved.