Silica, indicator supports

Fig. 20. Spin density, and water diffusion images for a 2.2-inm-diameter, spherical silica catalyst support pellet. In-plane pixel resolution was 45 pm x 45 pm image slice thickness was 0.3 mm. (a) Spin-density map lighter shades indicate higher liquid content, (b) map (150 00 ms) lighter shades indicate longer values of Ti. (c) Diffusivity map ((0-1.5) x 10 m s ) lighter shades indicate higher values of water diffusivity within the pellet.

The alumina or silica-alumina supports used in bifunctional catalysts have been shown to be acidic in nature. The acidic properties are readily demonstrated by the affinity of these solids for adsorption of basic compounds such as ammonia, trimethylamine, re-butylamine, pyridine, and quinoline (01, R5). Furthermore, adsorption of certain acid-base indicators such as butter yellow gives a coloration similar to that observed in acid media (B3, B4). With regard to the origin of the acidity, Tamele (Tl) has suggested in the case of silica-alumina that aluminum atoms replace silicon atoms in the surface of the silica structure, giving rise to surface sites of the form... 

Figure 13 represents measurements at 363 K with silica as a support. The curve measured with suspended silica in a nickel(II) solution at 363 K remains appreciably below the curve measured with nickel nitrate alone and does not approach the curve measured without suspended silica. The course of the pH with suspended silica indicates formation of a bulk compound with the support, as schematically indicated in Fig. 8. Formation of nickel antigorite (a 1 1 clay mineral) or nickel hectorite (a 1 2 clay mineral) is evident from X-...

The parallel bundle analysis of Figure 2 furnishes the results presented in Figure 5. The key to this analysis is the recognition that whatever the distribution of pore sizes is for each category of porosity (intra-particle, inter-pellet and intra-pellet) the actual amounts of pore volumes are integrals of those distributions. These take values specified by the density of the solid materials (zeolite, plus silica/alumina support) and the pore volumes per gm indicated by the porosimeter results in Figure 2. Thus the final penetration for the powder is the sum of inter-particle and intra-particle and intra-particle porosity. By the same token, the final penetration for the pellet comprises the sum of the intra-particle volume added to the intra-pellet and inter-pellet volumes. 

The specific surface area of supported CoPc shows unrealistic values in the case of supported samples on alumina and alumina-rich supports. Consequently, the calculated degrees of CoPc dispersion are relatively high. On the other hand, the specific surface area of CoPc supported on silica and silica-rich support show much lower values with much lower degrees of dispersion. These parameters decrease markedly as the complex loading increases up to 10.4% w/w. It is of interest to notice that, the stoichiometry of adsorption of oxygen on samples of supported CoPc on alumina and alumina-rich supports is almost close to 1. However, in samples of CoPc supported on silica and silica-rich supports, the stoichiometry becomes >2. These findings indicate clearly that supported CoPc molecules interact with the different support surfaces under study along widely different ways. 

The silica-zirconia support itself is thermally quite stable, and the presence of zirconia has even been reported to help protect silica against sintering [591-593]. Characterization of the catalysts represented in Figure 130 by X-ray diffraction did not indicate crystallinity on the Cr/Zr-silica catalysts calcined at 500 and at 700 °C. Even after calcination at 900 °C, only some faint lines characteristic of ZrC>2 were detected. 

All samples were labelled using sample codes. An example of a sample code is S/SD-C-R. The first part denotes the support (S = SBA-15 and G = silica gel support). The second part indicates the type of drying treatment (SD = slow drying and FD = faster drying). The last part stands for additional heat treatments C = calcination and R = reduction. 

In the same work, the authors performed reactions in open vessel systems, either in the absence of solvent or on silica gel support in dry media . The cycloaddition of ethyl 1,3-cyclohexadiene carboxylate 81 to ethyl propiolate 82 was improved compared with the harsh classical conditions (benzene at 320 °C for 24 h) (Scheme 11.22). No specific microwave effects were observed in this reaction this was in accordance with results from ah initio calculations which indicated a synchronous mechanism with similar polarity (dipole moment) in both ground and transition states. 

These columns yielded 15,000-30,000 theoretical plate counts per meter, with separations of the order of 5-20 minutes. pBondagel is a silica-based support with a particle size of about 10 pm. PVA was successfully fractionated using water as a mobile phase with a pBondagel E-Linear column. Detection was with a differential refractive index (DRI) detector and an ultraviolet (UV) photometer at 254 nm (Figure 2). The authors attributed the increase in the UV absorption of the used PVA as a probable indication of polymer oxidation. 

To establish the interaetion of the impregnating solutions with the surface of silica supports, Terorde measured the amount of water required to completely remove different iron salts applied onto the surface of silicagel in a column chromatograph [41], It appeared that an elution volume of water of 5.0 ml was required to remove the iron ammonium citrate, and of 6.2 ml to remove the Mohr s salt. Iron(III) chloride called for an elution volume of 6.3 ml, and iron(III) nitrate for a volume of 7.7 ml. Apparently, the iron species in the initially impregnated solution of iron ammonim citrate does not interact strongly with the silica surface. The relatively small interaction of the iron(III) complex of citric acid with the surface of silica indicates that the presence of the citric acid affects the adsorbed layer of water molecules that remains within the partially dried impregnated support. A thicker, less mobile layer of water molecules, citric acid anions, and iron(III) ions remains than without citric acid, where a layer of about six fairly mobile water molecules is present. 

The efficient solvent-free microwave-assisted procedure for C-alkyl pyrroles synthesis using silica gel-supported reagent has been reported. Thus, a general procedure for the Michael addition of pyrroles with electron-deficient olefin has been developed. In the case of the moderately bulky electron-deficient olefins, a catalytic amount of BiCls has to be employed to promote the reaction. The experimental results indicated that BiCla exhibited a high catalytic activity and did not induce polymerization and polyalkylation under microwave (Equation 5) [26a]. 

Examination of Table 3.4 shows that the deposition of Bis(triphenylsilyl) chromate into porous silica/alumina support increased catalyst activity by at least a factor of 500. The FI/MI ratio of 86-137 indicates that the molecular weight distribution of polyethylene prepared with this catalyst is relatively very broad compared to the Phillips catalyst, which may provide significant product advantages in certain applications over a similar grade of polyethylene prepared with the Phillips catalyst. 

Figure 8.40 The k ySk) extended X-ray absorption fine structure (EXAFS) signal, Fourier transformed and then retransformed after application of the filter window indicated, in (a) osmium metal and (b) a 1% osmium catalyst supported on silica. (Reproduced, with permission, Ifom Winnick, FI. and Doniach, S. (Eds), Synchrotron Radiation Research, p. 413, Plenum, New York, 1980)...

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