Three-Dimensional Hollow Square Array SAPO-34 with Optimal Acidity Distribution Showing Excellent Methanol-to-Olefins Performance

Abstract

SAPO-34 is an excellent catalyst for methanol-to-olefins (MTO) reaction. Simultaneously alleviating the diffusion limitations and optimizing the acidity of SAPO-34 is extremely challenging. Herein, a three-dimensional hollow square array SAPO-34 (SAPO-34-HSA) with a sinusoidal-like distribution of silicon was synthesized in a simple way. The role of triethylamine (TEA) switches between the etchant and structure-directing agent according to the reaction temperature. In the heating stage, the seed with high silicon content was etched by TEA; during the crystallization process, TEA guides the epitaxial growth of raw materials on the seed crystal, forming a hollow core−shell structure; after crystallization, the shell was partly leached to form a hollow square array structure. The sinusoidal-like distribution of silicon is conducive to promoting olefin cycling in the hydrocarbon pool mechanism and significantly improving the selectivity of ethylene. So the SAPO-34-HSA catalyst exhibits 70%−400% longer catalytic lifetime in MTO reaction compared with the seed under different reaction conditions.