Phosphorus modification of FER zeolite with H3PO2 for enhancement of hydrothermal stability

Phosphorus modification has been extensively demonstrated as the most effective approach to enhance the hydrothermal stability of ZSM-5 (MFI) zeolites on both industrial and research scales with phosphoric acid (H 3 PO 4 ) and phosphates as precursors. However, the incorporation of H 3 PO 4 into FER zeolites exerts a detrimental impact on their crystallinities, acidity, microporous structure, and hydrothermal stability. This phenomenon arises from two key factors: Firstly, the larger precursor size of H 3 PO 4 hinders its migration into the narrow channels of FER zeolite during the impregnation process; Secondly, the abundant Si-OH groups on the FER zeolites’ external surface can trap H 3 PO 4 to prevent it from penetrating channels of FER zeolites. It was verified that hypophosphorous acid (H 3 PO 2 ), owing to its smaller precursor size and slight tendency to be trapped by external isolated Si-OH groups, tended to migrate into the channels and subsequently disperse homogeneously, thereby enhancing the accessibility to tetrahedrally coordinated framework aluminium (TFAl). Moreover, 29 Si, 27 Al, and 31 P MAS NMR results proved the fact that the FER zeolite modified with H 3 PO 2 effectively facilitated the formation of more Si-OH-Al-O-P active sites during hydrothermal aging, which subsequently improved the conversion and light olefins yield in the catalytic cracking of 1-octene.