Hydrogen adsorbed silica

Figure 3. Maximum hydrogen adsorbed at 30-mm. hydrogen pressure as function of palladium concentration on silica gel surface...

At the same time, specific properties (primarily the Si/Al ratio) of a zeolite should be taken into account when discussing the mechanism of its dehy-droxylation. It is quite possible that the mechanism typical of H forms of faujasites would be completely improper for high-silica-containing zeolites. Thus, in their studies of dehydroxylated forms of ZSM-5 zeolite by means of IR spectroscopy of molecular hydrogen adsorbed at low temperatures, Kazansky et al. (72, 76) have demonstrated that the Uytterhoeven-Cristner-Hall scheme seems valid in this case. 

Fig. 5. Effect of hydrogen adsorbed at room temperature on a 26% nickel-silica coprecipitate showing diminishing influence of hydrogen on smallest particles of nickel (i.e., those observed at low temperatures only).

Krylova and Dolin [319,320] investigated the radiolysis of water adsorbed on silica gel induced by y-radiation ( Co). The radiolysis products, H2 and CO2, formed as a result of the energy transfer from the solid adsorbent silica gel to the molecules of the adsorbed water. The oxidation component of radiolysis is spent on the oxidation of trace amounts of organic compounds present on the sample surface carbon dioxide results. Radiolysis was investigated in relation to the conditions of the prehminary treatment of Si02, the amount of adsorbed water, and the intensity of the radiation. The formation of hydrogen from the surface OH groups of sihca gel was also possible. A likely mechanism of radiolysis was described. 

Walaszek, B., Yeping, X., Adamczyk, A. et al. 2009. H-solid-state-NMR study of hydrogen adsorbed on catalytically active ruthenium coated mesoporous silica materials. Solid State Nucl. Magn. Reson. 35 164-171. 

Kagel (29) found that whereas pyridine is hydrogen bonded to a silica gel surface 2-chloropyridine is not, the spectrum of 2-chloropyridine adsorbed on silica gel being identical with that of the liquid, and concluded that steric hindrance probably prevents hydrogen bond formation in this case. 

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