Ordered Mesoporous Support

Most examples discussed so far made use of amorphous inorganic supports or sol-gel processed hybrid polymers. Highly disperse materials have recently become accessible via standard processes and, as a result, materials with various controlled particle size, pore diameter are now available. Micelle-templated synthesis of inorganic materials leads to mesoporous materials such as MCM-41, MCM-48, MSU, and these have been extensively used as solid supports for catalysis [52]. Modifications of the polarity of the material can increase the reactivity of the embedded centre, or can decrease its susceptibility to deactivation. In rare cases, enhanced stereo- or even 

Mesoporous supports have been studied in ligand-free rhodium-catalysed hydroformylation aiming at the stabilisation of specific catalytic species to induce 

TABLE 3.6. Comparison of the activity and selectivity in the hydroformylation of linear alkenes using homogeneous [HRh(CO)(PPh3)3] and [HRh(CO)(PPh3)3] encapsulated in MCM-48 a 

Catalyst Substrate Substrate concentr.b selectivity aldehyde (%) Aver. TOFc l b ratio 1-Octene conv. (%) 

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Figure 2.14. Schematic drawing of functionalized monolayers on ordered mesoporous supports. One end group of the monolayers is covalently bonded to the silica surface and the other end group can be used to bind heavy metals or other functional molecules. Reproduced with permission from [99],...

The use of ordered mesoporous supports has been investigated in parallel as an alternative strategy to obtain the high dispersion of chromium oxidic species for the ODH with CO2. Bi et al. investigated the catalytic behavior for the CO2-ODH of ethane using transition metal-doped M-MCM-41 (M = Ni, Co, Cr) mesoporous materials, prepared by the direct hydrothermal method. Cr-containing catalysts... 

It should be mentioned that the structure of carbon supports could have significant influence on the electro-catalytic properties of the nanocomposite catalysts. Recently, Pt/Ru nanoclusters prepared by the alkaline EG method were impregnated into a synthesized carbon support with highly ordered mesoporous. Although the Pt/ Ru nanoclusters can be well dispersed in the pores of this carbon substrate, the long and narrow channels in this material seem not suitable for the application in... 

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. 

Nanostructured silica and ordered mesoporous silicas have been envisaged as small enzyme immobilization supports [196]. The encapsulation approach is required either to further immobilize enzymes adsorbed in the channels by reducing the pore opening by further silylation or by encapsulating the enzyme directly [197]. 

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. 

Park, I.-S. Choi, S. Y. Ha, J., High-performance titanium dioxide photocataiyst on ordered mesoporous carbon support. Chem.Phys. Lett. 2008,456 198-201. 

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... 

Recently, isolated dioxoMo entities were docked onto the surfaces of ordered mesoporous materials such as MCM-41 and MCM-48. Mo grafting was performed by impregnation of the calcined and dehydrated silica with Mo02X(THF)2 (with X = Br or Cl) in dry dichloromethane. The resulting supported Mo complexes catalyzed the epoxidation of cyclooctene... 

Catalysts and catalytic supports are often formulated from aluminas owing to their low cost, and their thermal, chemical and mechanical stability [27], To this end, nonionic surfactant templating with polyethylene oxide surfactants was used to synthesize mesoporous alumina [28], Partially ordered mesoporous materials with wormhole channels were obtained - this seems to be a characteristic of templating with nonionic surfactants. Cationic surfactants have recently been found to template mesoporous aluminum oxide with pore sizes that could be fine-tuned by varying the molar ratio of the reactants [29]. The material obtained was thermally stable to 900 °C and exhibited a narrow pore size distribution. 

Recently, there has been an increasing interest in the synthesis of ordered mesoporous carbons, since such materials are very promising as adsorbents, catalyst supports, and electrochemical double-layer capacitors. Ordered mesoporous silicas have been shown as suitable templates to prepare periodic mesoporous carbons with various pore shapes and connectivity. The synthesis procedure involves impregnation of the mesoporous silica with an appropriate carbon precursor, carbonization of carbon source, and subsequent removal of silica using an aqueous solution of HF or NaOH. ... 

Figure 10.14 shows two examples of supported nanopartides from heterogeneous catalysis. A 20wt% loading of 4nm NiO particles has been deposited inside the mesopores of SBA-15, an ordered mesoporous silica. Reduction results in highly... 

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