An investigation of the roles of surface aluminum and acid sites in the zeolite MCM-22
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AbstractAmmonia 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 delta(ISO) approximate to 0 in the (27)Al NMR spectrum; this is a superposition of two NMR signals from the different Al species on the water-re constructed zeolite surface. A sharp resonance assigned to framework Al reversibly transforms on ammonia adsorption to delta(ISO) (27)Al approximate to 55 from tetrahedral Al(F), while the broad peak is assigned to nonframework aluminium 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.
All Author(s) ListMa D, Han XW, Xie SJ, Bao XH, Hu HB, Au-Yeung SCF
Journal nameChemistry - A European Journal
Volume Number8
Issue Number1
Pages162 - 170
LanguagesEnglish-United Kingdom
Keywordsaluminum; Lewis acids; NMR spectroscopy; zeolites
Web of Science Subject CategoriesChemistry; Chemistry, Multidisciplinary; CHEMISTRY, MULTIDISCIPLINARY

Last updated on 2021-15-01 at 23:13