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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. [ABSTRACT FROM AUTHOR]

Galliation of USY zeolites in alkaline media creates tetracoordinated Lewis-acid centres linked to the framework which display outstanding selectivity in the isomerisation of dihydroxyacetone to ethyl lactate and full reusability. This simple and affordable post-synthetic route enables to tune the amount of Lewis acidity in the zeolite and has great potential for application in related biomass conversions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mechanochemical treatment, a versatile tool for zeolite synthesis and modification. [•] Scalable, efficient, and mechanistically-distinct to solvent-intensive routes. [•] Structural transformations classified according to the energy required. [•] Catalytic properties enhanced by mechanochemical activation. [•] Rationalization will facilitate the scale up of future zeolite technologies. [ABSTRACT FROM AUTHOR]

Hierarchical clinoptilolite and Lzeolites are prepared using optimizedtandem dealumination–desilication treatments. The main challengein the postsynthetic modification of these zeolites is the high Alcontent, requiring a tailored dealumination prior to the desilicationstep. For natural clinoptilolite, sequential acid treatments usingaqueous HCl solutions were applied, while for L a controlled dealuminationusing ammonium hexafluorosilicate is required. Subsequent desilicationby NaOH treatment yields mesopore surfaces of up to 4-fold (clinoptilolite,64 m2g–1; L, 135 m2g–1) relative to the parent zeolite (clinoptilolite,15 m2g–1; L, 45 m2g–1). A thorough characterization sheds light on thecomposition, crystallinity, porosity, morphology, coordination, andacidity of the modified clinoptilolite and L zeolites. It is elaboratedthat, besides the degree of dealumination, the resulting Al distributionis a critical precondition for the following mesopore formation bydesilication. Adsorption experiments of Cu2+and methyleneblue from aqueous solutions and the catalytic evaluation in alkylationsand Knoevenagel condensation evidence the superiority of the hierarchicalzeolites, as compared to their purely microporous counterparts. Finally,the postsynthetic routes for clinoptilolite and L are generalizedwith other recently reported modification strategies, and presentedin a comprehensive overview. [ABSTRACT FROM AUTHOR]