Effect of crystallization time on properties and catalytic performance of nanostructured SAPO-34 molecular sieve synthesized at high temperatures for conversion of methanol to light olefins

SAPO-34 molecular sieves were synthesized via high temperature hydrothermal method. The effects of crystallization time and temperature on physicochemical properties and catalytic performance were studied toward methanol to light olefins. The samples were characterized by XRD, FESEM, PSD, EDX, BET and FTIR techniques. The XRD patterns confirmed the influence of crystallization time and temperature on the crystallinity, phase purity and crystallite size. Also, all synthesized catalysts have nanosized crystallites, obtained by Scherrer formula. The relative crystallinity was enhanced by the increasing of crystallization time and then decreased which can be correlated well with recrystallization at high temperature and long crystallization time. By synthesis at high temperature, more nuclei were produced that leads to lower particle size compared to low temperature synthesis procedure. In addition, it was concluded that the impact of crystallization temperature on particle size is much more than that of crystallization time. It was found that the hydrothermal synthesis conditions greatly affected on the morphology, particle size, purity and textural properties. The synthesized catalyst at 300 T and 3 h has the best performance in terms of the lifetime and olefins selectivity. This catalyst showed 90% selectivity toward light olefins and 94% methanol conversion for more than 600 min. The catalysts synthesized via high temperature hydrothermal method have higher lifetime than the one produced by the conventional method, indicated more effectiveness of this method. (C) 2014 Elsevier B.V. All rights reserved.