Binding alumina

In a second example, a cell—gelatin mixture is cross-linked with glutaraldehyde (43). When soluble enzyme is used for binding, the enzyme is first released from the cell, then recovered and concentrated. Examples of this type of immobilization include binding enzyme to a DEAE-ceUulose—titanium dioxide—polystyrene carrier (44) or absorbing enzyme onto alumina followed by cross-linking with glutaraldehyde (45,46). 

A selective poison is one that binds to the catalyst surface in such a way that it blocks the catalytic sites for one kind of reaction but not those for another. Selective poisons are used to control the selectivity of a catalyst. For example, nickel catalysts supported on alumina are used for selective removal of acetjiene impurities in olefin streams (58). The catalyst is treated with a continuous feed stream containing sulfur to poison it to an exacdy controlled degree that does not affect the activity for conversion of acetylene to ethylene but does poison the activity for ethylene hydrogenation to ethane. Thus the acetylene is removed and the valuable olefin is not converted. 

Alcoa Alumina Handbook R. B. Bind and co-workers. Transport Thenomena,)oEn NrA. y Sons, Inc., New York, 1965. 

PVA was used as a temporary binder owing to its water solubility, excellent binding strength and clean burning characteristics. To prepare the PVA solution, 4 g of PVA were added to 100ml distillated water. The mixture was heated and stirred vigorously until all the PVA was dissolved in the water. This took about half an hour. Peptisation was done by addition of 5 ml 1M HN03 to the solution. Finally, the solution was refluxed for 4 hours. The PVA solution was used in the preparation of the zirconia-alumina sol-gel solution. The preparation of the PVA solution can be summarised as follows ... 

In this reaction, an acidic site on the catalyst is shown as an aluminum atom bound to three oxygen atoms, and this is a site where an alcohol molecule can bind. If the acidic sites on the alumina are shielded by reacting it with a base, the oxide is no longer an effective acid catalyst. In other words, the acidity is removed by attaching molecules such as Nff3 to the acidic sites. 

Routinely used X-ray sources are Mg Ka (1253.6 eV) and A1 Ka (1486.3 eV). In XPS one measures the intensity of photoelectrons N(E) as a function of their kinetic energy. The XPS spectrum, however, is usually a plot of N(E) versus Ek, or, more often, versus the binding energy Eb. Figure 3.3 shows the XPS spectrum of an alumina-supported rhodium catalyst, prepared by impregnating the support with... 

Figure 9.3 Rh 3d5/2 binding energy versus particle size for half spherical rhodium particles on an alumina support (data from Huizinga el al. [14], and from Kip et al. [15], see also Fig. 6.18).

It is also evident that polishing (with alumina) the surface cut parallel to the basal planes can improve the response. In fact, the mechanical action breaks the covalent C/C bonds, which then reform binding oxygen from the air (O/C 0.11). 

Liquid chromatographic clean up [441,443,450] has been used either in normal phase flow using alumina, silica, or florisil [22,189,403,481,484] or with reverse-phase (RP) columns [409,452,480]. In most cases these techniques are well established and are used in an off-line mode, primarily to remove the bulk of co-extracted materials prior to a more refined clean-up prior to the final determination. These columns may be prepared in the laboratory [22,403 -405] or commercial solid phase extraction (SPE) cartridges can be used [409,452, 463,470,485,486]. In both cases, the normal phase cartridges and column materials are disposable since many of the polar co-extractants bind firmly to the substrate surface and are difficult to remove. This has been overcome to some... 

Table 2.1 shows the top site chemisorption energy for the adsorption of CO onto the Pt/Oj-a-alumina system as a function of metal layers, relative to Pt (111). For the monolayer of metal on the surface there is an enhancement of the CO top site binding energy relative to Pt (111). On the other hand, the second layer of Pt/Ox shows a dramatic decrease in the top site chemisorption energy. For three layers of Pt on this surface, the chemisorption energy oscillates above the Pt (111) energy, eventually returning to the Pt (111) value for n > A. 

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