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An Investigation of the Roles of Surface Aluminum and Acid Sites in the Zeolite MCM‐22
Author(s) -
Ma Ding,
Han Xiuwen,
Xie Sujuan,
Bao Xinhe,
Hu Hongbing,
AuYeung Steve C. F.
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20020104)8:1<162::aid-chem162>3.0.co;2-4
Subject(s) - zeolite , aluminium , surface (topology) , materials science , chemistry , metallurgy , organic chemistry , mathematics , geometry , catalysis
Abstract Ammonia adsorption studies reveal that the observed Lewis acidity in the zeolite MCM‐22 is derived from at least two types of framework aluminum sites (Al F ), that is, octahedral Al F and three‐coordinate Al F . Comparative ammonia or trimethylphosphine (TMP) adsorption experiments with MCM‐22 confirm that octahedral Al species gives rise to the signal at δ iso ≈0 in the 27 Al NMR spectrum; this is a superposition of two NMR signals from the different Al species on the water‐reconstructed zeolite surface. A sharp resonance assigned to framework Al reversibly transforms on ammonia adsorption to δ iso 27 Al≈55 from tetrahedral Al F , while the broad peak is assigned to nonframework aluminum which results from hydrothermal treatment. This study also demonstrates the effectiveness of 27 Al magic angle spinning (MAS) and multiple quantum (MQ) MAS NMR spectroscopy as a technique for the study of zeolite reactions.