Modification on Interaction between P Species and Framework Al of ZSM-5 for Better Hydrothermal Stability with Hypophosphorous Precursors

It was the thermostability and acidity of P precursors that influenced the interaction between P species and framework Al to determine the hydrothermal stability of P modified ZSM-5. With H3PO2 and NH4H2PO2 as P precursors, the P–Al interactions of P modified ZSM-5 samples calcined under different temperatures were systematically investigated by X-ray fluorescence, X-ray photoelectron spectroscopy, 27Al, and 31P MAS NMR spectroscopy, and temperature-programmed desorption of NH3 (NH3-TPD). With H3PO2 as the precursor, lower calcination temperature favored less self-polymerization of P species; however, obvious loss of phosphorus was observed during hydrothermal treatment. Conversely, higher calcination temperature tended to result in excessive interaction between P and framework Al for dealumination. Therefore, moderate interactions between P and framework Al were obtained over H3PO2 modified ZSM-5 calcined at 350 °C, which contributed to weaken the self-polymerization of P species. Compared with H3PO2, neutral NH4H2PO2 generated a relatively weaker P-zeolite interaction, which was less affected by the calcination temperature.