Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 21, Issue 40, Pages 14156-14164Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201500992
Keywords
acidity; aluminum; mesoporous materials; synthesis design; zeolites
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A literature survey reveals a prominent reduction in the concentration of Bronsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends.
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