Ionothermal synthesis and characterization of AlPO4 and AlGaPO4 molecular sieves with LTA topology

Abstract

Abstract Aluminophosphate molecular sieves are recognized as very promising materials for catalysis, adsorption, and separation. This study presented an attempt to synthesize LTA-type AlPO4 and AlGaPO4 molecular sieves by an ionothermal method. The influences of the relevant synthesis parameters and various template removal methods were discussed. The optimum growth temperature, doses of ILs, and crystallization time were suggested. The two-step calcination method was recommended since the intact crystalline structure and microporosity of LTA-type AlPO4 were retained after template removal. Perfect cubic AlPO4-LTA molecular sieves were successfully prepared with an excellent micropore volume of 0.33 ml/g and water uptake of 0.38 g/g at P/P0 = 0.20. Moreover, an LTA-type AlGaPO4 molecular sieve was also successfully synthesized by an ionothermal method with partial Ga doping. Evident changes in morphology were found and could be ascribed to various crystal plane orientations. Ga-doped crystals subjected to template removal and water soaking showed worse thermal and hydrothermal stability. The microporosity and water sorption capacity of AlGaPO4-LTA also decreased greatly due to its sharply reduced stability and collapsed structure. After Ga doping, however, the materials became more hydrophilic, with slightly higher water uptake at low relative pressure. The materials also showed greater acidity strength at both Bronsted and Lewis acid sites.