SAPO-34 crystals with nanosheet morphology synthesized by pyrophosphoric acid as new phosphorus source

Abstract

The nanosheet SAPO-34 zeolite crystals with a diameter of 300 nm and a thickness of 50 nm using a new phosphorus source (pyrophosphoric acid, H4P2O7) were synthesized. The roles of the pyrophosphate (P2O74−) species in the crystallization of SAPO-34 were elucidated. The results suggested that one P atom from the P2O74− species participated in the formation of the CHA framework structure while the other P atom served as a crystallization control agent, facilitating preferential crystal growth in [100] crystal plane. The SAPO-34 nanosheets have silica-rich shell and phosphorus-rich core leading to superior catalytic performance in methanol-to-olefin reaction (MTO). The catalytic lifetime of the SAPO-34 nanosheets was significantly improved due to the larger amount of medium-strong surface acidity and short diffusion pathway in comparison to the conventional SAPO-34 catalyst synthesized in the presence of the classical phosphorus source (H3PO4).