Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities Christophe Copeŕet,*,† Aleix Comas-Vives,† Matthew P. Conley,† Deven P. Estes,† Alexey Fedorov,† Victor Mougel,† Haruki Nagae,†,‡ Francisco Nuñ́ez-Zarur,† and Pavel A. Zhizhko†,§ †Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir Prelog Weg 1−5, CH-8093 Zürich, Switzerland ‡Department of Chemistry, Graduate School of Engineering Science, Osaka University, CREST, Toyonaka, Osaka 560-8531, Japan A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov str. 28, 119991 Moscow, Russia

Surface Organometallic and Coordination Chemistry toward Single-Site Heterogeneous Catalysts: Strategies, Methods, Structures, and Activities

Ion-specific effects influencing the dissolution of tricalcium silicate

Mesoporous ZSM-22 zeolite (TON structure) is prepared by controlled silicon extraction in aqueous NaOH under different conditions of concentration, temperature, and time. The first challenge is to synthesize a pure ZSM-22 sample, since ZSM-5 and cristobalite impurities are hard to avoid. For this purpose, hydrothermal syntheses in autoclaves of 30–1000 cm3 using tumbling or magnetic mixing were conducted. The parent (calcined) and alkaline-treated samples are characterised by XRD, AAS, N2 and Ar adsorption, TEM, 27Al MAS NMR, and FTIR. The introduction of mesoporosity in ZSM-22 crystals is not straightforward due to their peculiar characteristics: the rod-like morphology of their small crystallites, the one-dimensionality of the ellipsoidal micropore system, and an uneven Al distribution. Compared to other zeolite frameworks such as MFI, the generation of up to 95 m2 g−1 of (both inter- and intracrystalline) mesopore surface area by NaOH treatment leads to a sizeable drop of the micropore volume (down to 0.006 cm3 g−1), attributed to blocking by re-deposited Al species. A subsequent mild acid treatment in aqueous HCl restores ca. 90% of the original micropore volume and increases the mesopore surface area to 114 m2 g−1. However, due to the particular Al distribution in the parent ZSM-22 crystals, only 37% of the original Bronsted acidity is recovered. A new descriptor ‘desilication efficiency’ is introduced to relate the mesopore area generated to the mass of zeolite dissolved. In the case of ZSM-22 nanorods and ferrierite platelets, the desilication efficiency is relatively low compared to ZSM-5, most likely due to the crystal morphology of the former two zeolites. The auxiliary mesoporosity developed in ZSM-22 brings new prospects to catalytic applications of the zeolite due to the extensive creation of pore mouths in the hierarchical sample.

Mesoporous ZSM-22 zeolite obtained by desilication: peculiarities associated with crystal morphology and aluminium distribution

In this paper, we report the synthesis of hexagonally ordered aluminum-containing mesoporous silica, Al-MCM-41, from natural attapulgite (Al-substituted Si(8)O(20)Mg(5)(OH)(2)(H(2)O)(4) x 4 H(2)O) without addition of silica or aluminum reagents A pretreatment process involving sequential mechanical grinding and acid leaching is critical to the successful use of attapulgite as a source of both Si and Al in the surfactant-templated hydrothermal synthesis of Al-MCM-41 The resulting mesophase had a surface area of 1030 m(2)/g and an average pore diameter of 37 nm with narrow pore size distribution The influence of changes in processing parameters, such as grinding time, hydrothermal conditions, and calcination temperature, on the textural characteristics of the Al-MCM-41 products is studied Investigations of the mechanism of structural evolution indicate that grinding of attapulgite results in amorphization and partial structural breakdown, transformation of the fibrous mineral bundles into rod-shaped particles, and partial displacement of octahedrally coordinated Al(3+) ions into the Si-O tetrahedral framework Subsequent acid etching dissolves the Mg-rich octahedral sheets to produce samples with variable texture due to modifications in the residual aluminum-containing silicate sheets and associated silica fragments Solid-state magic-angle spinining NMR spectroscopy indicates that Al(3+) ions are located in both octahedral and tetrahedral sites in the as-synthesized Al-MCM-41 samples, but that the calcined products consist primarily of Al(3+) ions substituted in the tetrahedrally coordinated silica matrix of the ordered channel wall structure

From natural attapulgite to mesoporous materials: methodology, characterization and structural evolution.

Despite the widespread use of amorphous aluminosilicates (ASA) in various industrial catalysts, the nature of the interface between silica and alumina and the atomic structure of the catalytically active sites are still subject to debate. Here, by the use of dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS) and density functional theory (DFT) calculations, we show that on silica and alumina surfaces, molecular aluminum and silicon precursors are, respectively, preferentially grafted on sites that enable the formation of Al(IV) and Si(IV) interfacial sites. We also link the genesis of Bronsted acidity to the surface coverage of aluminum and silicon on silica and alumina, respectively.

/pdf/atomic-description-of-the-interface-between-silica-and-58k736y8w2.pdf

Atomic Description of the Interface between Silica and Alumina in Aluminosilicates through Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy and First-Principles Calculations

Pentacoordinated Aluminum in Noncalcined Amorphous Aluminosilicates, Prepared in Alkaline and Acid Mediums

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Pentacoordinated Aluminum in Noncalcined Amorphous Aluminosilicates, Prepared in Alkaline and Acid Mediums