Intergrowth Silicoaluminophosphate Molecular Sieves Synthesized and Their Catalytic Performances for Methanol to Olefins Reaction

A series of SAPO-34/SAPO-18 molecular sieves with an intergrowth CHA/AEI crystal structure were synthesized under hydrothermal conditions in the presence of a single or a mixture of N,N-diisopropylethylamine (DIEA), triethylamine (TEA), and diethylamine (DEA) as template agents. The effects of different types, amounts, and combinations of templates on the structure, morphology, and surface acidity of SAPO-34/SAPO-18 molecular sieves were investigated by XRD, XRF, BET, SEM, and NH3-TPD. These results show that the intergrowth ratio of CHA and AEI structures in SAPO-34/SAPO-18 molecular sieves depends on the nature and composition of mixture template largely. For the methanol to olefins (MTO) reaction, the obtained SAPO-34/SAPO-18 with different intergrowth ratios of CHA and AEI structures exhibits different catalytic performances varying with the acid properties and structural differences. Sample S6 with hierarchical structure and suitable acidity exhibits higher selectivity to ethylene plus propylene and longer catalyst life.