Ne Ni,Ying Ouyang,Jianqiang Liu,Enhui Xing,Yibin Luo,Xingtian Shu
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.
In this work, a "bottom-up" strategy was proposed to one-step, in-situ synthesize P@ZSM-5 zeolites in a sodium-free system by elaborately self-designed tetrapropylphosphonium hydroxide as a new member of MFI-type zeolite organic templates inventory, and the interaction of phosphorus species with framework aluminum was investigated in detail. Multiple advanced characterizations confirm that the tetrahedrally-coordinated bidentate P IV -O 2 -Al IV structures are precisely customized and uniformly scattered in the zeolite channels. After experiencing harsh hydrothermal treatment (100 %H 2 O, 800 °C, 17 h), this new structure endows excellent hydrothermal stability of zeolite (crystallinity retention beyond 95 %) and reinforces its Brønsted acidity. Furthermore, methanol-to-propylene tests show that directly synthetic P@ZSM-5 zeolite performs extraordinarily long lifetime (180 h, WHSV = 1 h −1 ), enviable propylene selectivity (60.4 %) and propylene/ethylene ratio ( ca. 4.3) compared to the counterparts, which is benefited from encouragingly olefinic cycle pathway. These findings afford value-filled opportunities in novel catalyst production mode and understandings for phosphorus-zeolite chemistry . Synopsis -A "bottom-up" strategy was demonstrated to one-step, in-situ synthesize P@ZSM-5 zeolite in a sodium-free system by elaborately self-designed tetrapropylphosphonium hydroxide. The resultant P@ZSM-5 catalyst with hyperuniformly-stable bidentate P IV -O 2 -Al IV structures exhibited extraordinarily long lifetime (180 h) and enviable propylene selectivity (60.4 %).
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