Zinc oxide hydrogen adsorption

Adsorption Processes. The processes based on adsorption of hydrogen sulfide onto a fixed bed of soHd material are among the oldest types of gas treating appHcations (4). Two common sorbent materials for low concentration gas streams are iron oxide and zinc oxide. 

On experimental level the question regarding the centers of adsorption was addressed in numerous papers. For instance, in [66] the experimental data were used to show that in case of adsorption of hydrogen atoms on the surface of zinc oxide the centers of chemisorption can be provided by regular oxygen ions of the lattice, i.e. the process of chemisorption of H-atoms can be shown as the following sequence of reactions ... 

The experiment was carried out in a reaction cell shown in Fig. 3.3 with inner walls covered by a zinc oxide film having thickness 10 pm [20]. The surface area of the measuring film on the quartz plate was about 1/445 of the total film area on the wall of the vessel. The results of direct experimental measurements obtained when the adsorbent temperature was -196 C and temperature of pyrolysis filament (emitter of H-atoms) 1000°C and 1100°C, are shown on Fig. 3.4. One can see a satisfactory linear dependence between parameters A r (the change in film conductivity) and APh2 (reduction of hydrogen pressure due to adsorption of H-atoms), i.e. relations... 

It is known [16] that at room temperature antimony evaporates as molecules. The molecules of antimony according to [17] do not affect conductivity of the sensor made of zinc oxide. Similar conclusion can be obtained from experiments with freshly reduced antimony films. It occurs that without initial adsorption of hydrogen atoms one fails to detect any signals from the sensor in contrast to experimental data (see Fig. 6.2). The resistivity of the sensor remains constant for any distance from the surface of the antimony film. Consequently, the signals of the sensor detected in experiment are not linked with effects of the antimony particles on the sensor. 

Over zinc oxide it is clear that only a limited number of sites are capable of type I hydrogen adsorption. This adsorption on a Zn—O pair site is rapid with a half-time of less than 1 min hence, it is fast enough so that H2-D2 equilibration (half-time 8 min) can readily occur via type I adsorption. If the active sites were clustered, one might expect the reaction of ethylene with H2-D2 mixtures to yield results similar to those obtained for the corresponding reaction with butyne-2 over palladium That is, despite the clean dideutero addition of deuterium to ethylene, the eth-... 

Butanol, reaction over reduced nickel oxide catalysts, 35 357-359 effect of ammonia, 35 343 effect of hydrogen, 35 345 effect of pyridine, 35 344 effect of sodium, 35 342, 351 effect of temperature, 35 339 over nickel-Kieselguhr, 35 348 over supported nickel catalysts, 35 350 Butanone, hydrogenation of, 25 103 Butene, 33 22, 104-128, 131, 135 adsorption on zinc oxide, 22 42-45 by butyl alcohol dehydration, 41 348 chemisorption, 27 285 dehydrogenation, 27 191 isomerization, 27 124, 31 122-123, 32 305-308, 311-313, 41 187, 188 isomerization of, 22 45, 46 isomers... 

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