Mesoporous solids chemistry

Zeotype and Mesoporous Solids Chemistry Design, Synthesis and Catalytic Properties... 

Chapter 1 is a general overview of zeolite, zeotype and mesoporous solids chemistry, including their design, synthesis and general catalytic properties. Chapter 2 deals with the problems and pitfalls that may occur in the applications of zeolites and other microporous and mesoporous solids to fine chemical synthesis. The remaining chapters deal with specific applications of these catalysts to fine chemical synthesis. 

Yiu, H.H.P. and Wright P.A. (2005) Enzymes supported on ordered mesoporous solids a special case of an inorganic-organic hybrid. Journal of Materials Chemistry, 15, 3690-3700. 

We have presented the first method for directly imaging the position of functional tethers grafted onto the surface of a mesoporous material and, at the same time, validated a simple method by which one may direct the location of grafted functionality within mesoporous solids. This has been made possible by a strong partnership between supramolecular organometallic and solid state chemistry. The results presented now provide a foundation for the future examination of mesopore confinement effects on catalysis. 

The methods of soft chemistry include sol-gel, electrochemical, hydrothermal, intercalation and ion-exchange processes. Many of these methods are employed routinely for the synthesis of ceramic materials. - There have been recent reviews of the electrochemical methods, intercalation reactions, and the sol-gel technique. The sol-gel method has been particularly effective with wide-ranging applications in ceramics, catalysts, porous solids and composites and has given rise to fine precursor chemistry. Hydrothennal synthesis has been employed for the synthesis of oxidic materials under mild conditions and most of the porous solids and open-framework structures using organic templates are prepared hydro-thermally. The advent of supramolecular chemistry has started to make an impact on synthesis, mesoporous solids being well known examples. ... 

The chemistry and surface properties of porous and non-porous silica were extensively reviewed [8,9]. We have organized this review in several sections starting with a very brief account of mesoporous solids synthesis and their main structural characteristics (see the section on Mesoporous SUica ). This section also comments on the preparation of chemically modified solids and their properties as well as how the mesoporous structure can be controlled. We also present some theoretical results obtained through computer simulations. Those smdies model the sohd structure of sdica that will be employed in other simulations. Section 111 is devoted to the... 

It is possible to oxidise and reduce atoms in the framework and also those within the pores of microporous (and mesoporous) solids of appropriate chemical compositions. Although pure aluminosilicate, silicate and aluminophosphate frameworks cannot be oxidised or reduced, transition metal and some lanthanide cations within the framework can exist in different oxidation states. Also, although typical alkali, alkali metal and most lanthanide cations in extraframework positions possess no redox chemistry, transition metal cations such as nickel, copper and platinum do. In the case of the transition metals, this enables them to become important catalysts. The included sulfide species in ultramarine-related pigments described above are also prepared through the reduction of sulfate species. 

Mesoporous solids provide well-ordered scalfolds for chemistry based largely on surface functionalisation. This is readily achieved at the internal surfaces because of the large numbers of silanol hydroxyls that are present there, and which can be used to attach ligands via established synthetic procedures. 

Many studies have aimed to prepare mesoporous solids with active titanium, either by direct synthesis or by post-synthetic modifications. Although some of the advantages of crystalline framework solids are lost, the larger pore size increases markedly the size limit of molecules that can be converted by this catalytic chemistry, and active and selective catalysts have been prepared. In addition, such solids can be used with organic peroxides (such as tert-butylhy-droperoxide) that do not produce water as an inhibiting by-product. 

There is, therefore, much work to do on the chemical engineering side. But the task is still more important for the chemistry of catalytic materials and deposition techniques. A personal feeling is that the activity of the catalytic substance should essentially be due to its external surface or that it should possess no porosity or only very wide pores. Nanoclusters (e.g., of monodispersed TiOj on mesoporous silica. Reference 11), micelles (e.g.. Reference 12), nanometer crystallites of zeolites (see, for example. Reference 13), and mesoporous solids could be candidates. An ample choice is possible in a period where nanomaterials are the object of intense research (see, for example. Reference 14). 

FIGURE 14.8.2 Phase transition in mesoporous solids (a-d) lamellar-hexagonal (e-f) hexagonal-cubic. The circular objects around the surfactant assemblies are the metal-oxo species (From Ref. 19b, J. Mater. Chem. 8 (1998) 1631. 1998 Royal Society of Chemistry). 

Bronstein, L. (2003) Nanoparticles made in mesoporous solids, in Colloid Chemistry I (ed. M. Antonietti), Springer, Berlin,... 

High porosity carbons ranging from typically microporous solids of narrow pore size distribution to materials with over 30% of mesopore contribution were produced by the treatment of various polymeric-type (coal) and carbonaceous (mesophase, semi-cokes, commercial active carbon) precursors with an excess of KOH. The effects related to parent material nature, KOH/precursor ratio and reaction temperature and time on the porosity characteristics and surface chemistry is described. The results are discussed in terms of suitability of produced carbons as an electrode material in electric double-layer capacitors. 

Zeolites such as HZSM-5 were considered as superacids on the basis of the initial product distribution in accord with C-H and C-C bond protolysis when isoalkanes were reacted at 500°C (the Haag and Dessau mechanism).135 The reactivity was assigned to superacidic sites in the zeolite framework.136 The superacid character of other solid acids was claimed on the basis of Hammett indicator color change137,138 or on the basis of UV spectrophotometric measurements.139,140 In 2000, a special issue of Microporous and Mesoporous Materials141 was devoted to the superacid-type hydrocarbon chemistry taking place on solid acids as suggested by the late Werner Haag. 

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