Issue 21, 2014

Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolites

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

Supplementary files

Article information

Article type
Paper
Submitted
13 nov. 2013
Accepted
16 déc. 2013
First published
18 déc. 2013

Phys. Chem. Chem. Phys., 2014,16, 9892-9903

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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