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Issue 21, 2014
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Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

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Abstract

In order to elucidate phosphorus–zeolite H-ZSM-5 interactions, a variety of phosphorus-modified zeolite H-ZSM-5 materials were studied in a multi-spectroscopic manner. By deploying single pulse 27Al, 31P MAS NMR, 2D heteronuclear 27Al–31P correlation (HETCOR), 27Al MQ MAS NMR spectroscopy, TPD of pyridine monitored by FT-IR spectroscopy, and Scanning Transmission X-ray Microscopy (STXM) the interplay and influence of acidity, thermal treatment and phosphorus on the structure and acidity of H-ZSM-5 were established. It was found that while acid treatment did not affect the zeolite structure, thermal treatment leads to the breaking of Si–OH–Al bonds, a decrease in the strong acid site number and the formation of terminal Al–OH groups. No extra-framework aluminium species was observed. Phosphorus precursors interact with the zeolitic framework through hydrogen bonds and physical coordination, as phosphorus species can be simply washed out with hot water. After phosphatation and thermal treatment two effects occur simultaneously, namely (i) phosphorus species transform into water insoluble condensed poly-phosphoric acid and (ii) phosphoric acid binds irreversibly to the terminal Al–OH groups of partially dislodged four-coordinated framework aluminium, forming local silico-aluminophosphate interfaces. These interfaces are potentially the promoters of hydrothermal stability in phosphated zeolite H-ZSM-5.

Graphical abstract: Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

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Publication details

The article was received on 13 Nov 2013, accepted on 16 Dec 2013 and first published on 18 Dec 2013


Article type: Paper
DOI: 10.1039/C3CP54791D
Citation: Phys. Chem. Chem. Phys., 2014,16, 9892-9903
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    Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

    H. E. van der Bij and B. M. Weckhuysen, Phys. Chem. Chem. Phys., 2014, 16, 9892
    DOI: 10.1039/C3CP54791D

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