Hydrogen from powdered sample

On the first stage of hydrogenation reaction the C/H composition of fulleranes can be approximately determined by XRD from increase of unit cell parameter. The crystal structure of fulleranes powder remains to be fee like in pristine C60 but the cell parameter increases proportionally to the number of attached hydrogen atoms due to increase of van der Waals diameter of molecules. Using chemical analysis on carbon/hydrogen ratio performed on samples hydrogenated at various conditions we constructed the dependence which could be used for approximate evaluation of hydrogen content from known cell parameter determined from powder XRD, see Fig. 5.3... 

Powder XRD pattern recorded from this sample was indexed as a bcc structure with cell parameter, a = 11.99(2) A, corresponding to a cell volume per fullerene molecule of about 862 A3. That a-value is somewhat larger than reported previously for pure C60H36, a = 11.785 A (Halle et al. 1993) and a = 11.83 A (Meletov et al. 2001) which indicated presence of some higher hydrogenated hydrofullerenes. 

Sample CFD consisted of mostly agglomerated particles, because about 70-75% of the products could be collected from the reactor bottom. Quantity of C samples is almost negligible. Agglomeration could be suppressed by the addition of carbon powder to the sample. Although carbon could not reduce oxides without hydrogen, in the presence of carbon, hydrogen reduction was more effective and the ratio of nomeacted powder (sample RB) decreased from 70-75 to 40%. 

Figure 1 shows the results obtained under thermal decomposition of samples using the method of prolong exposure at constant temperature. As one can see, the pressure of hydrogen release from the samples at 150 and 250°C is higher after the mechanical activation as compared with non-treated powder of MgH2. This effect is much more pronounced for the samples with graphite. 

The value of 120 has been calculated from the amount of charge associated with the voltammet-ric reduction of hydrogen peroxide preadsorbed at the TiOj electrode (cf. Fig. 11), using the H2O2 adsorption isotherm determined by Boonstra and Mutsaers for an anatase powder sample. 

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