Effects of hydrothermal aging on NH3-SCR reaction over Cu/zeolites

Characterization of nanocrystalline zeolite Beta

Incorporation of Ti into the framework of aluminium-free zeolite Beta has been achieved in F- medium and has produced hydrophobic selective oxidation catalysts. The Ti−Beta(F) materials have been characterized by X ray diffraction, infrared, Raman, ultraviolet, XANES, EXAFS, 29Si MAS NMR, and 1H→29Si CP MAS NMR spectroscopies, adsorption microcalorimetry, and catalytic testing. At near neutral pH the incorporation of Ti into the framework appears to present an upper limit of ca. 2.3 Ti/uc, beyond which anatase is detected in the calcined materials. However, at higher pH (ca. 11) larger amounts of Ti can be incorporated without anatase formation. After calcination, Ti incorporation in the framework is characterized by an increase in the unit cell volume, the appearance of one Raman band and three infrared bands in the region near 960 cm-1 and the presence of a strong absorption band in the 205−220 nm ultraviolet spectrum. By 29Si MAS NMR, 1H→29Si CP MAS NMR, and infrared spectroscopies it is concluded that...

Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite

Crystalline microporous solids are an important class of inorganic materials with uses in different areas impacting our everyday lives, namely as catalysts, adsorbents, and ion exchangers. Advancements in synthesis have been invaluable in expanding the classical aluminosilicate zeolites to new unique framework types and compositions, motivating innovative developments. However, the inexhaustible post-synthetic options to tailor zeolite properties have been and will continue to be indispensable to realize emerging and to improve conventional applications. Starting from the routine drying and template removal processes that every zeolite must experience prior to use, a wide spectrum of treatments exists to alter individual or collective characteristics of these materials for optimal performance. This review documents the toolbox of post-synthetic strategies available to tune the properties of zeolitic materials for specific functions. The categorisation is based on the scale at which the alteration is aimed at, including the atomic structure (e.g. the introduction, dislodgment, or replacement of framework atoms), the micropore level (e.g. template removal and functionalisation by inorganic and organic species), and the crystal and particle levels (e.g. the introduction of auxiliary porosity). Through examples in the recent literature, it is shown that the combination of post-synthetic methods enables rational zeolite design, extending the characteristics of these materials way beyond those imposed by the synthesis conditions.

Tailored crystalline microporous materials by post-synthesis modification

This article covers the recent development in the remarkably growing field of synthesis, characterization and particularly catalytic investigation of zeolite‐based materials combining micro‐ and mesoporous features. New synthetic approaches for preparation of micro/mesoporous composites including recrystallization of originally amorphous matter, utilization of nanocrystalline zeolite seeds and formation of mesoporous zeolite single crystals are the first focus of this article. The advantages and disadvantages of composite materials in comparison with pure micro‐ and mesoporous molecular sieves will be discussed, as well. The relevance of individual experimental techniques for analysis of the composites, i.e., their structure, porosity, chemical composition, morphological features, and so on, are described in the second section of the article. The last Section is focused on the application of micro/mesoporous composites and mesoporous zeolites as catalysts in acid‐catalyzed reactions, oxidation reactions a...

Perspectives of Micro/Mesoporous Composites in Catalysis

Study of the state of aluminium in zeolite-β

Single step dealumination of zeolite beta precursors for the preparation of hydrophobic adsorbents

The mechanism of the thermal decomposition of tetraethylammonium (TEA) in zeolite {beta} has been investigated under air and argon atmosphere using a combined technique of thermogravimetric analysis and mass spectrometry. The nature of the volatile products and the characterization of the solid after each thermal phenomenon shows that all TEA species, occluded ion pairs and counteranions, decompose into triethylamine and ethylene in a single step, in the temperature range 200-350{degrees}C. The amine readsorbs on the acidic sites of the zeolite and, as the temperature is increased, decomposes into lighter amines by sequential Hofmann elimination reactions. Part of the ethylene also reacts with the acid sites yielding aliphatic and aromatic hyrocarbons. Complete desorption of the organic species form the structure requires a temperature higher than 500 {degrees}C. 14 refs., 5 figs., 8 tabs.

Mechanism of the thermal decomposition of tetraethylammonium in zeolite .beta.

Process for the synthesis of a silica-enriched crystalline aluminosilicate having the offretite structure from a nucleation gel A containing sources of silicon, aluminium, alkali metal ions, an organic structuring agent and water and a growth gel B containing sources of silicon, aluminium, alkali metal ions and water. The crystals formed are calcined, the ions are replaced by protons and the crystals are subjected to a hydrothermal treatment followed by a treatment with a strong mineral acid. The aluminosilicate formed has a good selectivity in acid catalysis reactions and is characterized by its good stability.

Process for the synthesis of a silica enriched crystalline aluminosilicate having the offretite structure, the aluminosilicate obtained and its use as a catalyst for the conversion of hydrocarbons

Calcination of as-synthesized or ammonium-exchanged forms of zeolite BETA induces an extensive loss of framework aluminium evidenced by27Al MAS NMR, XRD and FTIR spectroscopies. Treatment of the calcined solids in ammonium nitrate restores the tetrahedral Al sites. Material balances show that the latter process is quantitative.

Thierry Des Courieres

Papers

Study of the state of aluminium in zeolite-β

Single step dealumination of zeolite beta precursors for the preparation of hydrophobic adsorbents

Mechanism of the thermal decomposition of tetraethylammonium in zeolite .beta.

Process for the synthesis of a silica enriched crystalline aluminosilicate having the offretite structure, the aluminosilicate obtained and its use as a catalyst for the conversion of hydrocarbons

Stability of the tetrahedral aluminium sites in zeolite beta