Ordered mesoporous oxide materials

Ordered mesoporous materials of compositions other than silica or silica-alumina are also accessible. Employing the micelle templating route, several oxidic mesostructures have been made. Unfortunately, the pores of many such materials collapse upon template removal by calcination. The oxides in the pore walls are often not very well condensed or suffer from reciystallization of the oxides. In some cases, even changes of the oxidation state of the metals may play a role. Stabilization of the pore walls in post-synthesis results in a material that is rather stable toward calcination. By post-synthetic treatment with phosphoric acid, stable alumina, titania, and zirconia mesophases were obtained (see [27] and references therein). The phosphoric acid results in further condensation of the pore walls and the materials can be calcined with preservation of the pore system. Not only mesoporous oxidic materials but also phosphates, sulfides, and selenides can be obtained by surfactant templating. These materials have pore systems similar to OMS materials. 

The key effect of oxide supports on the catalytic activities of metal particles is exerted through the interface between oxides and metal particles. The key objective of this study is to develop synthesis methodologies for tailoring this interface. Here, an SSG approach was introduced to modify the surface of mesoporous silica materials with ultrathin films of titanium oxide so that the uniform deposition of gold precursors on ordered mesoporous silica materials by DP could be achieved without the constraint of the low lEP of silica. The surface sol-gel process was originally developed by Kunitake and coworkers.This novel technology enables molecular-scale control of film thickness over a large 2-D substrate area and can be viewed as a solution-based... 

In comparison to zeolites, ordered mesoporous materials overcome the pore-size constraint of zeolites and allow easier diffusion of bulky substrates. Unrestricted diffusion of reactants and products for mesoporous materials was observed even after the incorporation of large catalytically active sites in the mesopore system. Ordered mesoporous oxides have been used as supports for metals and metal oxides, and as a host material for anchoring stereo- and enantio-selective species. In reactions that require milder acidity and also involve bulky reactants and products, such as mild hydrocracking reactions, mesoporous materials exhibit great potential.[40,296]... 

Research in ordered mesoporous oxides has increased dramatically in intensity over the last years. Developments not foreseen at the time when MCM-41 and FSM-16 were discovered have taken place, and in some cases applications of these materials are on the horizon. This paper will cover the discoveries which have expanded the scope of research in this field and try to give an outlook where new developments could take place. 

When one searches for the key words (MCM-41 or FSM-16 or SBA-15 or ordered mesoporous oxides or ordered mesoporous materials) in the Web of Science,... 

The first ordered mesoporous materials reported were silicas or 2duminumsilicates. The majority of all published investigations is still based on such compositions. In addition, many different elements, recently listed in a comprehensive review [10], have been introduced into the framework of ordered mesoporous oxides, just as in zeolitic frameworks. Such compositions could... 

Iron modified zeolites and ordered mesoporous oxides have been studied as catalysts for the sulfur dioxide oxidation in sulfur rich gases. Both zeolitic materials and mesoporous oxides show very good activity in this reaction. Other than solid state or incipient wetness loaded MCM-41 materials, the zeolites do not show an initial loss of activity. However, they loose activity upon prolonged exposure to reaction conditions around 700°C. The zeolitic samples were analyzed via X-ray absorption spectroscopy, and the deactivation could be related to removal of iron from framework sites to result in the formation of hematite-like species. If the iron can be stabilized in the framework, these materials could be an interesting alternative to other iron based catalysts for the commercial application in sulfur rich gases. 

Mesoporous carbon materials were prepared using ordered silica templates. The Pt catalysts supported on mesoporous carbons were prepared by an impregnation method for use in the methanol electro-oxidation. The Pt/MC catalysts retained highly dispersed Pt particles on the supports. In the methanol electro-oxidation, the Pt/MC catalysts exhibited better catalytic performance than the Pt/Vulcan catalyst. The enhanced catalytic performance of Pt/MC catalysts resulted from large active metal surface areas. The catalytic performance was in the following order Pt/CMK-1 > Pt/CMK-3 > Pt/Vulcan. It was also revealed that CMK-1 with 3-dimensional pore structure was more favorable for metal dispersion than CMK-3 with 2-dimensional pore arrangement. It is eoncluded that the metal dispersion was a critical factor determining the catalytic performance in the methanol electro-oxidation. 

Invented less than a decade ago,1 EISA has rapidly developed into a universal technique for fabrication of organized porous and patterned nanocomposite materials, ranging from metal oxides and chalcogenides to carbons, polymers, and metals.2,3 In addition to generating ordered mesoporous films, this technique may also be used to incorporate functional molecules and... 

Although the mesoporous materials, such as Ti-MCM-41, have lower intrinsic epoxidation selectivity than TS-1 and Ti-beta, they must nevertheless be used as catalysts for reactions of large molecules typical in the fine chemicals industry. It is, therefore, interesting to elucidate how these ordered mesoporous materials compare with the earlier generation of amorphous titania-silica catalysts. Guidotti et al (189) recently compared Ti-MCM-41 with a series of amorphous titania-silica catalysts for the epoxidation of six terpene molecules of interest in the perfumery industry (Scheme 6). Anhydrous TBHP was used as the oxidant because the catalytic materials are unstable in water. The physical characteristics of these catalysts are compared in Table XII. 

Ordered mesoporous materials, such as described here, have been successfully tested as catalysts or catalyst supports for many different reactions [27], However, since this class of materials is rather new, the real potential of these materials in catalysis is of course not fully investigated. As for OMS materials, the production of such materials is rather cost intensive, e.g., compared to conventional oxide materials. Therefore, the benefit of a regular mesopore system has to be substantial to justify the use of elaborated but expensive catalyst materials for industrial applications. Nevertheless, many of the materials described above proved to perform very well in many different catalytic reactions and they may of course find applications in this field. 

Abstract This review highlights how molecular Zintl compounds can be used to create new materials with a variety of novel opto-electronic and gas absorption properties. The generality of the synthetic approach described in this chapter on coupling various group-IV Zintl clusters provides an important tool for the design of new kinds of periodically ordered mesoporous semiconductors with tunable chemical and physical properties. We illustrate the potential of Zintl compounds to produce highly porous non-oxidic semiconductors, and we also cover the recent advances in the development of mesoporous elemental-based, metal-chalcogenide, and binary intermetallic alloy materials. The principles behind this approach and some perspectives for application of the derived materials are discussed. 

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