Preparation of floral mesoporous SAPO-34 with the aid of fluoride ion

A novel floral mesoporous SAPO-34 was synthesized via conventional hydrothermal method in the presence of NaF with F/Si = 0.02–0.2. X-ray diffraction (XRD) analysis shows that the crystallinity of SAPO-34 increases with the increasing F/Si ratio and reaches to the best at F/Si = 0.1. Further increasing of F/Si ratio leads to the decrease of the crystallinity and the ultimate phase transformation to SAPO-5. Scanning electron microscopy (SEM) analysis shows that the addition of NaF leads to the formation of floral SAPO-34 while the addition of other salts including NH4F, NH4Cl and NaCl leads to the formation of traditional cubic SAPO-34. N2 sorption isotherm and NH3 temperature programmed desorption (NH3-TPD) analyses indicate that floral SAPO-34 has the largest pore volume but lowest strong acidity compared with other samples with traditional cubic morphology. When applied to methanol to olefin (MTO) reactions, floral SAPO-34 shows the comparable yields of propylene and butylenes to other samples but lowest overall olefin yield, which is attributed to the synergistic effect of the largest pore volume and lowest strong acidity.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► A floral mesoporous SAPO-34 is fabricated with the aid of NaF for MTO. ► The formation of floral structure is due to the eroding effect of fluoride ions. ► Floral SAPO-34 shows the highest selectivities for propylene and butylene in MTO.