A study was made of adsorption of n -dotriacontane and n -butanol dissolved in n -heptane onto graphitized carbon black and various ground graphites having surface areas ranging from 5 to 700 m 2 g -1 . It was established that the adsorption of n -dotriacontane by the graphites is confined entirely to the basal planes of graphite crystals. This is attributed to a remarkable fit between the hydrogen atoms attached to one side of the zig-zag carbon chain in the normal paraffins and the centres of hexagons formed by the carbon atoms in the basal planes of the substrate. The longer the chain the more contacts it can form with the graphite surface and the more strongly it is adsorbed. More detailed studies of the adsorption of n -paraffins on ground graphites have shown that they form close-packed monolayers of horizontally disposed molecules on the basal planes. There is little further adsorption after the monolayers are complete. The heat of adsorption per molecule increases uniformly with the chain length reaching very high values for the normal paraffins having more than 30 carbon atoms. The formation of the close-packed layers has been used for the measurement of the proportion of basal plane surface in different types of graphites. n -Butyl alcohol also forms closely packed monolayers, but on the polar sites of graphites, which can be used for the estimation of their area. The basal plane and polar sites act independently in adsorption and their relative proportions characterize the adsorptive properties of graphites. Examination of graphite ground in n -heptane, which consists of plates of average area of several square micrometres and average thickness of 5 nm, shows that its surface consists predominantly of basal planes having a high adsorptive capacity for n -paraffins.
Changes in a Au/TiO(2) catalyst during the activation process from an as-prepared state, consisting of supported AuO(x)(OH)(4-2x)(-) species, were monitored with X-ray absorption spectroscopy and FTIR spectroscopy, complemented with XPS, microcalorimetry, and TEM characterization. When the catalyst was activated with H(2) pulses at 298 K, there was an induction period when little changes were detected. This was followed by a period of increasing rate of reduction of Au(3+) to Au(0), before the reduction rate decreased until the sample was fully reduced. A similar trend in the activation process was observed if CO pulses at 273 K or a steady flow of CO at about 240 K was used to activate the sample. With both activation procedures, the CO oxidation activity of the catalyst at 195 K increased with the degree of reduction up to 70% reduction, and decreased slightly beyond 80% reduction. The results were consistent with metallic Au being necessary for catalytic activity.
Measurements of the surface areas of hydrophilic and hydrophobic sites in a variety of carbonaceous and mineral solids, which were known to be at least partly hydrophobic, have been carried out by flow adsorption microcalorimetry. The surface areas of the hydrophilic and hydrophobic sites were shown to be related to the integral heats of displacement of 1-butanol from n-heptaneand water solutions, respectively. The concentrations of the solutions used for the determination of the heats of displacement were those for which the adsorbed 1-butanol formed closed packed monolayers at the solid/solution interface. For microporous solids the heata of adsorption of 1-butanol from both n-heptane and water solutions are enhanced and 80 is the constant relating the surface areas of solids to the heats of adsorption, resulting in the estimates of surface areas of polar and hydrophobic sites that are significantly higher than the surface areas measured by the BET gas adsorption method. It is considered, however, that the comparison of the heata of 1-butanol adsorption from n-heptane and water permita a more accurate evaluation of the relative hydrophobicity (or hydrophilicity) of the surface of the solids than the measurements of the heats of wetting or adsorptions of individual polar and nonpolar liquids or vapors.
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