Aluminum Redistribution during the Preparation of Hierarchical Zeolites by Desilication.
A literature survey reveals a prominent reduction in the concentration of Brønsted 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.
Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, Vladimir-Prelog-Weg 1, 8093 Zurich (Switzerland).
Sharon
S
Mitchell
Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, Vladimir-Prelog-Weg 1, 8093 Zurich (Switzerland).
Maria
M
Milina
Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, Vladimir-Prelog-Weg 1, 8093 Zurich (Switzerland).
René
R
Verel
Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, Vladimir-Prelog-Weg 1, 8093 Zurich (Switzerland).
Manuel
M
Hernández-Rodríguez
Department of Materials Science, Laboratory of Crystallography, Vladimir-Prelog-Weg 5, 8093 Zurich (Switzerland).
Ana B
AB
Pinar
Department of Materials Science, Laboratory of Crystallography, Vladimir-Prelog-Weg 5, 8093 Zurich (Switzerland).
Lynne B
LB
McCusker
Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, Vladimir-Prelog-Weg 1, 8093 Zurich (Switzerland). jpr@chem.ethz.ch.
Javier
J
Pérez-Ramírez
acidity; aluminum; mesoporous materials; synthesis design; zeolites