Defect sites in highly siliceous HZSM-5 zeolites: A study performed by alumination and IR spectroscopy

Journal Article · Thu Jan 24 00:00:00 EST 1991 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100155a071· OSTI ID:5854852

Yamagishi, Kouji; Namba, Seitaro; Yashima, Tatsuaki ^[1]

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1. Tokyo Institute of Technology (Japan)

The concentration of oxygen atoms on defect sites in a highly siliceous HZSM-5 type zeolite was estimated by the {sup 18}O-exchange reaction between C{sup 18}O{sub 2} and the zeolite. The concentration of oxygen atoms on defect sites could be controlled by means of changes of the gel composition and of the use of various silica sources in the hydrothermal synthesis. The relationship between the concentration of oxygen atoms on defect sites in a highly siliceous HZSM-5 and the concentration of aluminum introduced into the framework of the HZSM-5 by an alumination was examined. The concentration of the framework aluminum was the same as one-fourth that of the oxygen atoms on defect sites. These results suggest that the defect sites into which aluminum atoms are introduced tetrahedrally can be identified with hydroxyl nests that consist of four silanol groups. The existence of hydroxyl nests could be confirmed by IR spectroscopy. From the {sup 18}O-exchange reaction and IR measurements, the authors conclude that the sharp band at 3,740 cm{sup {minus}1} can be attributed to both isolated SiOH groups on the external surface and intracrystalline isolated SiOH groups and that the broad band at 3,505 cm{sup {minus}1} can be attributed to the SiOH groups in hydroxyl nests.

• OSTI ID: 5854852
• Journal Information: Journal of Physical Chemistry; (USA), Vol. 95:2; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
SILICATES
CRYSTAL DEFECTS
ZEOLITES
EXPERIMENTAL DATA
HYDROTHERMAL SYNTHESIS
INFRARED SPECTRA
MEASURING METHODS
CRYSTAL STRUCTURE
DATA
INFORMATION
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MATERIALS
MINERALS
NUMERICAL DATA
OXYGEN COMPOUNDS
SILICON COMPOUNDS
SPECTRA
SYNTHESIS
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies