Mesoporous oxide

Abstract A review of the thermolytic molecular precursor (TMP) method for the generation of multi-component oxide materials is presented. Various adaptations of the TMP method that allow for the preparation of a wide range of materials are described. Further, the generation of isolated catalytic centers (via grafting techniques) and mesoporous materials (via use of organic templates) is simimarized. The implications for syntheses of new catalysts, catalyst supports, nanoparticles, mesoporous oxides, and other novel materials are discussed. 

The hydroamination of alkenes has been performed in the presence of heterogeneous acidic catalysts such as zeolites, amorphous aluminosilicates, phosphates, mesoporous oxides, pillared interlayered clays (PILCs), amorphous oxides, acid-treated sheet silicates or NafioN-H resins. They can be used either under batch conditions or in continuous operation at high temperature (above 200°C) under high pressure (above 100 bar). 

G.J. de A. Soler-Illia, C. Sanchez, B. Lebeau, J. Patari, Chemical strategies to design textured materials from microporous and mesoporous oxides to nanonetworks and hierarchical structures. Chem. Rev. 102 (2002) 4093. 

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. 

M. C. Rogers, B. Adisa, and D. A. Bruce, Synthesis and characterization of dendrimer-templated mesoporous oxidation catalysts, Catal Lett. 98,29-36 (2004). 

When 1,2-dichlorobenzene in hydrogen-saturated deionized water was exposed to a slurry of palladium catalyst (1%) at room temperature, benzene formed via the intermediate chlorobenzene. The reaction rate decreased in the order of MCM-41 (mesoporous oxide having a silicon aluminum ratio of 35) > alumina > Y (dealuminated zeolite having a silicon aluminum ratio of 15). It appeared the reaction rate was directly proportional to the surface area of the support catalyst used (Schiith and Reinhard, 1997). 

Ordered mesoporous oxides, obtained for example by block copolymer-... 

The concept presented in Fig. 6 could use also other type of ordered mesoporous membranes, based on silica for example. As discussed before, oxides such as Ti02 provide better multi-functionalities for the design of such a type of nanofactory catalysts. Worth to note is that in the cover picture of the recent US DoE report Catalysis for Energy a very similar concept was reported. This cover picture illustrates the concept, in part speculative, that to selectively convert biomass-derived molecules to fuels and chemicals, it is necessary to insert a tailored sequence of enzyme, metal complexes on metal nanoparticles in a channel of a mesoporous oxide. 

Synthetic aspects template theory for mesoporous oxides synthesis. 7... 

SYNTHETIC ASPECTS TEMPLATE THEORY FOR MESOPOROUS OXIDES SYNTHESIS... 

The procedure is similar to that used for the formation of micellar hexagonal phases which is applied in preparing mesoporous oxides. Here, the precursor is mixed with water, a surfactant and a catalyst (NaOH or HC1). The Si—C bond is generally preserved from cleavage, except in the case of basic conditions or with products having a sensitive Si—Cs/p bond. 

Soler-Illia G., Sanchez C., Lebeau B., Patarin J. (2002) Chemical Strategies To Desing Textured Materials from Microporous and Mesoporous Oxides to Nanonetworks and Hierarchical Structures, Chem. Rev., 102(11), 4093-4138. 

Soler-Illia GJdAA, Crepaldi EF, Grosso D, Sanchez C. Block copolymer-templated mesoporous oxides. Current Opinion in Colloid Interface Science. 2003 8(1) 109—126. 

Soler-Illia, G., Crepaldi, E. L., Grosso, D. and Sanchez, C. (2003). Block copolymer-templated mesoporous oxides. Curr. Opin. Colloid Interface Sci. 8(1), 109-126. 

The interface between organic and inorganic substructures has been manipulated in the preparation of hybrid materials which exhibit composite or even new properties, representative examples of which include zeolites [34-36], mesoporous oxides of the MCM-41 class [37] and metal phosphates with entrained organic cations [38-55] (Refs 39-55 are representative examples of the expanding family of oxovanadium-phosphate-organic cation materials). 

---