Local silico-aluminophosphate interfaces within phosphated H-ZSM-5 zeolitesElectronic supplementary information (ESI) available. See DOI: 10.1039/c3cp54791d

• Main Authors: van der Bij, Hendrik E, Weckhuysen, Bert M
• Format: Journal Article
• Language: English
• Published: 06.05.2014
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c3cp54791d

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 27 Al, 31 P MAS NMR, 2D heteronuclear 27 Al- 31 P correlation (HETCOR), 27 Al 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. In zeolite H-ZSM-5, H 3 PO 4 binds irreversibly to the Al-OH groups of partially dislodged four-coordinated framework aluminium, forming local silico-aluminophosphate interfaces.