Enhanced methanol-to-olefins (MTO) performance over SAPO-34 molecular sieves synthesized using novel sources of silicon and aluminium

New molecular sieve catalysts for methanol-to-olefin conversion were synthesized from amorphous aluminium silicate. Compared to catalysts synthesized by a conventional procedure from silica sol, the catalysts using amorphous aluminium silicate had longer catalytic lifetimes and higher selectivity for light olefins. As the core technology of methanol-to-olefins (MTO), the development of a high-efficiency and low-cost molecular sieve catalyst has always been the most important challenge. Herein, SAPO-34 molecular sieves were synthesized by using three different compositions of amorphous aluminium silicate as both Si and Al source under the same conditions. The structure and composition of synthesized SAPO-34s were investigated using X-ray diffraction and X-ray fluorescence, while the morphology and physical properties were characterized using scanning electron microscopy, N-2 adsorption-desorption and ammonia temperature-programmed desorption measurements. Compared to the silica sol as the Si source, the SAPO-34s prepared with amorphous aluminium silicate show the higher solid yields and crystallinity, larger surface area and lower numbers of acid sites. Besides the effect of Si, the effect of the Al source on the textural structure and catalytic performance of SAPO-34s in MTO reactions was investigated in detail. The results confirmed that the SAPO-34s prepared using amorphous aluminium silicate have low Si content and hierarchical structure, which results in a longer catalytic lifetime and higher selectivity for light olefins. The sample S2 exhibited the longest lifetime of 214 min and the highest selectivity for light olefins of 85.37%. This also provides a potential for the approach to obtain a high-efficiency catalyst with enhanced catalytic performance and low cost.