Enhancement of catalytic properties and lifetime of nanostructured SAPO-34 by La isomorphous substitution and alteration of Si/Al ratio used in methanol conversion to light olefins

Abstract

Successful synthesis of nanostructured LaAPSO-34 catalysts with different Si/Al ratios of 0.1, 0.2, 0.3 and 0.4 were used in methanol conversion to light olefins. The catalysts were prepared via a hydrothermal method and characterized by XRD, FESEM, PSD, EDX, TEM, BET, NH₃-TPD and FTIR techniques. The XRD results showed that the applied La ions preserve and complete the crystallite framework of SAPO-34 resulting in higher crystallinity. It was found that the crystallinity of SAPO-34 increased upon Si incorporation up to a Si/Al ratio of 0.3 followed by a decrease in intensity with further increases in silicon content. The FESEM micrographs for all the samples depict cubic shaped typical crystals of CHA type zeotype structure. The Si incorporation value was decreased by increasing the Si content in the initial gel. A stability test was conducted maintaining constant operational conditions to distinguish the effect of time on stream. Consequently, coke formation was delayed. The outstanding catalytic lifetime of the La modified catalyst with optimum Si content was reported to be 5500 min sustaining light olefin selectivity at higher values at a diminished reaction temperature of 350 °C.