Adsorption on zinc oxide

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... 

Heat of Adsorption—Some data on the heat of adsorption on zinc oxide by different gases and vapors are presented in Table 42. This... 

The effect of ultraviolet and visible radiation on carbon monoxide adsorption on zinc oxide has also been studied (118). Both photoadsorption and photodesorption have been found, depending on the temperature, and there is a quite different pattern of behavior if oxygen has been preadsorbed. Reaction to give oxidized complexes, presumably of the COa,., or... 

Nagoe, M. Morimoto, T. (1969). Differential heat of adsorption and entropy of water absorbed on zinc oxide surface. Journal of Physical Chemistry, 73, 3809-14. 

Moreover, quantitative relations of stationaiy concentrations of these particles with variation of the electric conductivity of a semiconductor sensor (based on zinc oxide) caused by their adsorption are also similar. 

The shift in the C=C frequency, vi, for adsorbed ethylene relative to that in the gas phase is 23 cm-1. This is much greater than the 2 cm-1 shift that is observed on liquefaction (42) but is less than that found for complexes of silver salts (44) (about 40 cm-1) or platinum complexes (48) (105 cm-1). Often there is a correlation of the enthalpy of formation of complexes of ethylene to this frequency shift (44, 45). If we use the curve showing this correlation for heat of adsorption of ethylene on various molecular sieves (45), we find that a shift of 23 cm-1 should correspond to a heat of adsorption of 13.8 kcal. This value is in excellent agreement with the value of 14 kcal obtained for isosteric heats at low coverage. Thus, this comparison reinforces the conclusion that ethylene adsorbed on zinc oxide is best characterized as an olefin w-bonded to the surface, i.e., a surface w-complex. 

Oxygen adsorption has also been studied on zinc oxide, an n-type oxide, by Wagner (63) and later by Bevan and Anderson (64). The conductivity decreases with increase in oxygen pressure, a result interpreted by Wagner by assuming the equilibrium... 

An interesting feature of this slow adsorption was pointed out by Taylor (6) in a discussion of early data obtained on zinc oxide between 132° and 184°C. (7). From the temperature coefficient of the slow adsorp-... 

A Suggested Mechanism for the Adsorption of Hydrogen on Zinc Oxide.. 290... 

A possible intermediate case discussed in Section IV,3 applies to the adsorption of hydrogen on zinc oxide. The extra surface levels are considered to be previously adsorbed oxygen. 

Fig. 4. Adsorption of oxygen on zinc oxide. Sample was cleaned at 600°C for 1 min. before lowering the temperature to To and admitting oxygen.

Morrison and Miller (33) have made some direct measurements on the adsorption of oxygen on zinc oxide powder (Fig. 4), which seem in accord with the conductivity measurements of Bevan and Anderson on sintered zinc oxide. The reversible region of chemisorption was shown to be above about 45O C, corresponding to the reversible region of conductivity versus oxygen pressure found by Bevan and Anderson to be above about 500°C. 

In this section, considerable space will be allotted to an examination of the conductivity effects in order to indicate how surface effects and adsorption may influence conductivity measurements, and to attempt to correlate the many anomalous electrical effects on zinc oxide with similar anomalous effects often observed in adsorption studies. 

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