Facile ionothermal synthesis of SAPO-LTA zeotypes with high structural stability and their catalytic performance in MTO reaction

Abstract

Silicoaluminophosphate zeotype with LTA structure (SAPO-LTA) was prepared using ionothermal approach in commercial 1-ethyl-3-methyl imidazolium ([emim]+) ionic liquid. 1H→13C CP/MAS NMR, TGA and CHN elementary analysis results demonstrated that ionic liquid acted as single organic template occluded in pairs in each α cage of the structure. SAPO-LTA exhibited high structural stability after detemplation with excellent BET surface area and microporous volume. Silica content in the products increased with that in the initial reactants with a maximum of SiO2 wt% lower than 5%. 29Si MAS NMR and NH3-TPD results further proved the incorporation of Si in the framework with improved acidity as compared with its aluminophosphate (AlPO) counterpart. SAPO-LTA was active in MTO reaction, showing higher butene and C5+ product selectivity than that of SAPO-34 with CHA structure, and higher propene to ethylene and lower C1 to C4 alkane selectivity in comparison with that of high-silica LTA zeolite (LTA-HSZ). The deactivation of SAPO-LTA catalyst was due to the occlusion of bulky polyaromatic coke in the LTA structure, and could be perfectly recovered during three cycles of regeneration by high-temperature calcination.