Synthesis, characterization and hydroisomerization catalytic performance of nanosize SAPO-11 molecular sieves

A new static hydrothermal method was developed for synthesizing nanosize SAPO-11 molecular sieve.The new method involves aging pretreatment step followed by crystallization process of a precursor gel. The effect of the aging pretreatment on morphology and size of SAPO-11 molecular sieves was investigated. The results of XRD and SEM showed that the aging pretreatment changed the size and morphology of the SAPO-11 dramatically, and the size could be controlled by varying the time for aging. Nanocrystals of SAPO-11 molecular sieves were synthesized by aging the precursor gel at 150 °C for 135 min and then crystallizing the gel at 190 °C for 24 h. Compared with the SAPO-11 samples that exhibit the pseudo-spherical aggregates ranging from 3 to 15 μm synthesized by conventional method, the SAPO-11 samples synthesized by the new method not only possessed much smaller cubic single crystals of about 400–500 nm, but were more uniform in size. Moreover, the SAPO-11 samples synthesized by the new method had larger specific surface area and larger external specific surface area. The results of n−hexadecane hydroisomerization showed that the Pt/SAPO-11 prepared with the new method exhibited higher catalytic activity and better hydroisomerization selectivity than the Pt/SAPO-11 synthesized by conventional hydrothermal method.