Adsorption temperature rise

As noted above, an isothemi plots the muiiber of molecules adsorbed on the surface at some temperature in equilibrium with the gas at some pressure. Adsorption gives rise to a change in the free energy which, of... 

Figure 7 shows spectra recorded during a TPR experiment in which a mixture of NO, O2, and CH4 are passed over the catalyst. At room temperature several new bands are present. These are located at 2189, 1878, and 1747 cm-. The peak at 2189 cm- is most likely due to N02 [36, 37], since this band is observed upon adsorption of NO2 at room temperature (see Figure 8). The band at 1747 cm- is assigned to N2O4 [38], and the feature at 1878 cm- is probably due to N2O3 [30, 39]. Elevating the temperature removes all three of these bands. The NO2/NO3 bands are quite intense at room temperature relative to the mono- and dinitrosyl nitrosyl bands. As the temperature rises, the ratio of nitrosyl to NO2/NO3 band intensities increases in a manner similar to that seen in Figure 6. Above 350 °C, the intensities of the NO2 and NO3 bands are smaller than those observed in the absence of CH4, a pattern identical to that already noted in the comparison of Figures 2 and 3. When the temperature is raised to 450 °C, the only features remaining are weak bands located at 2264, 1934, and 1635 cm-1. The first two bands are attributed to A13+-NCO and C02+-NO, respectively, and the third is due to adsorbed H2O.

At -196 "C, oxygen is freely adsorbed by Ca-zeolite A, whereas nitrogen is essentially excluded. The two molecules are not very different in size O2 has a diameter of 346 pm whereas that of N2 is 364 pm. As the temperature rises, the adsorption of N2 increases to a maximum at around -i00 "C. The main reason is probably due to the thermal vibrations of the oxygen atoms in the window. Over a range of 80 to 300 K, a variation of vibrational amplitude of 10 to 20 pm could well be expected. Thus, a variation of 30 pm... 

Zeolites are suitable for heavy-duty purifications of gas streams. Moreover, like resins, they can be manufactured with pore stincUires of the desired diameter in order to be used for the selective adsorption of specific contaminants based on their molecular size. They are resistant to temperature rise, being stable at temperatures up to 800 °C in dry air and up to 500 °C in humid air. Therefore, they can be treated at high temperature with air to avoid the... 

Fewer nonsteady-state measurements have been carried out on iridium than on platinum and palladium. Figure 50 shows the results of a 02—CO coadsorption experiment on Ir(lll) (203). Initially 02 was adsorbed, followed by CO adsorption, after which the crystal was heated with a linear temperature rise. It is seen that the peak temperature for COz desorption is shifted to lower values with increasing CO coverage. This may be due to a second-order desorption effect (203) or a reduced activation energy for the reaction owing to interactions in the adlayer, as was found on Pd(lll) (176). 

The heat-of-adsorption hygrometer uses a column that selectively adsorbs moisture, and the temperature rise due to heat liberation is in proportion to the amount of moisture being adsorbed. 

There is a large group of workers who consider that the slow phenomena, and also the very large increase in adsorption shown in Fig. 47, when the temperature rises to a certain point, is due not to the slowness of activation energy of the actual adsorption process at low temperatures, but to slow diffusion (itself often an activated process) along the surface to areas inaccessible at low temperatures. Ward was the first to take this view l and more recently it has been adopted by Garner and his pupils,2 and by Bradley.3... 

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