Supports monoliths

The conventional selective reduction of NOx for car passengers still competes but the efficient SCR with ammonia on V205/Ti02 for stationary sources is not available for mobile sources due to the toxicity of vanadium and its lower intrinsic activity than that of noble metals, which may imply higher amount of active phase for compensation. As illustrated in Figure 10.9, such a solution does not seem relevant because a subsequent increase in vanadium enhances the formation of undesirable nitrous oxide at low temperature. Presently, various attempts for the replacement of vanadium did not succeed regarding the complete conversion of NO into N2 at low temperature. Suarez et al. [87] who investigated the reduction of NO with NH3 on CuO-supported monolithic catalysts... 

The synthesis of self-supporting monolithic cylindrical rods ( lcmxlOcm) again with compositions and morphologies similar to resins has been reported [51]. These can also be prepared with a texture that allows each rod to be cleaved into discs. ( lcmx0.2cm, mass 250-500mg) (Fig. 1.10). The latter can be handled by a robot arm and soHd phase synthesis on one disc allows up to 0.5 mmole of a single compound to be produced. Similar disc and alternative shaped macroscopic supports have now been reported [52-54]. 

The selection of the carrier is relatively simple. It may be imposed by the type of reaction to be promoted. For instance, if the latter requires a bifunctional catalyst (metal + acid functions), acidic supports such as silica-aluminas, zeolites, or chlorinated aluminas, will be used. On the other hand, if the reaction occurs only on the metal, a more inert support such as silica will be used. In certain cases, other requirements (shock resistance, thermal conductivity, crush resistance, and flow characteristics) may dominate and structural supports (monoliths) have to be used. For the purpose of obtaining small metal particles, the use of zeolites has turned out to be an effective means to control their size. However, the problem of accessibility and acidity appearing on reduction may mask the evidence of the effect of metal particle size on the catalytic properties. 

Figure 11.4 TEM image of ruthenium on a carbon-supported monolithic catalyst.

The use of monolithic columns in LC has advanced rapidly since their first introduction in the 1990s [18-21]. In contrast to capillary columns packed with particulate stationary phases, monolithic columns consist of a single continuous support. Monolithic stationary phases can be subdivided in two classes, i.e., polymer-and silica-based materials. 

Apart from this, highly porous and self-supporting monolithic foams, which are found to have many important applications, including novel bioseparation [67], can be obtained from the previously mentioned materials after applying the supercritical CO2 extraction. 

The above-described bis(norbom-2-ene)-functionalized, chiral biphenyl ligand has also been immobilized on monolithic supports. Monoliths were designed in a way that they could be cut into pieces and, after encasement, could be used for HTS (Scheme 30). 

For monolithic disk synthesis, solutions of NBE, DMN-H6, and tris(norborn-5-ene-2-ylmethylenoxy)methylsilane, respectively, in 2-propanol and toluene (25 25 41 9, all wt.%) were subject to ROMP using the first-generation Gmbbs initiator RUCI2 (PCy3)2(CHPh) and triphenylphosphine (PPhs) as modulator. To come up with disks with sufficient mechanical strength, poly (amide) membranes were soaked with the polymerization mixture (Scheme 33). This way, membrane-supported monolithic disks up to 2 mm in thickness were realized. These disks were successfully used for the preconcentration of iodine and selected organic solutes from dilute aqueous samples by SPE. Quantitative measurement of the extracted solutes was achieved by diffuse-reflectance spectroscopy (DRS) directly on the surface of the disk. 

---