Controllable Fabrication of Hollow Structure within SAPO-34 Molecular Sieves via a Novel Synthesis Route Using Industrial Waste Catalyst

Abstract

Features of hollow structure within molecular sieves inevitably influence the catalytic performance, while the precise control of hollow structure parameters via a facile method remains challenging. Herein, a novel and facile approach is proposed to regulate the shape and size of the hollow structure within SAPO-34 using industrial waste methanol-to-olefins (MTO) catalyst as raw materials. The hole-like or butterfly-like hollow structure of various sizes was fabricated by pretreating the raw materials with phosphoric acid. The hole-like hollow structure results from the dissolution of the encapsulated nanocrystalline fragments provided by the waste catalyst. However, the phosphoric acid pretreatment decomposes these microcrystalline structures. It causes the synthesis system to be closer to the conventional one, where a butterfly-like hollow structure always forms. In addition, the size of the hollow structure is tuned by varying the extent of decomposition of the microcrystalline structure, which is realized by different leaching times with phosphoric acid. The obtained SAPO-34 with an optimized hollow structure exhibits a lifetime of 560 min in the MTO reaction. It also exhibits the light olefin selectivity as high as 89.4%. Therefore, this study provides a novel strategy to regulate the features of hollow SAPO-34 and lays the foundation for MTO catalyst design characterized by long lifetime.