Oxygen adsorption properties of 16 metal oxides were investigated by means of a temperature programmed desorption (TPD) technique. Although oxygen adsorption phenomena were largely different depending on metal oxides, it was possible to classify the oxides as follows: (A) V205, MoOa, Bi203, W03, and 203•2 03 which exhibit no oxygen desorption over the range 10-560 °C; (B) Cr203, Mn02, Fe203, Co304, NiO, and CuO which always give relatively large amounts of oxygen desorption; and (C) Ti02, ZnO, Sn02, A1203, and Si02for which evacuation at high temperature followed by oxygen adsorption at relatively low temperature is required for oxygen desorption to appear over the range 10-400 °C, except the last two oxides. It is noted that group A oxides have layer structures except for Bi2Oa, while group B consists of oxides with cations of d1-d9 electronic structures. Among the oxygen species adsorbed on group C oxides, the 02" ion was directly identified by means of ESR spectroscopy,• and was assigned to specific desorption peaks of respective TPD spectra. The amounts of desorbed oxygen (V^o) for group B and C oxides were only a few percent of the surface coverage, suggesting that the adsorption sites are some sorts of surface defects. There was a fairly good correlation between V560 and the heat of oxide formation per g mol of (-H°), and the amount of adsorbed oxygen tended to decrease with increasing -AH°. These results are discussed in relation to the catalytic properties of the oxides.

The chemisorption of oxygen on nickel oxide was investigated over a wide range of temperature (0-600 °C) by means of the temperature programmed desorption (TPD) technique. At least four different states of adsorbed oxygen were indicated by the appearance of four TPD peaks, with peak maxima located at 30-~40 (a), 320~360 (ß), 420~450 ( ), and 520~550 °C (6), respectively. Taking into account their adsorptive characteristics, the corresponding adsorbed species were tentatively assigned to 02 ( ), 02~(ß), and -( and ). Experimental facts that none of the ß, y, and oxygen retarded the chemisorption of the'others suggested that these chemisorptions took place on different surface sites, while the chemisorption site for a was estimated to be common to ß oxygen. The activation energies of adsorption for ß and y were 12.8 and 17.5 kcal/mol, respectively, and that of desorption for ß was 23 kcal/mol. Adsorbed oxygen in various forms amounted altogether to ca. 3 X 1013 molecules/(cm2 of NiO surface). The corresponding surface coverage was estimated to be ca. 4% with respect to surface nickel atoms, suggesting adsorptions on some sorts of surface defects. Discussions of these results are presented in relation to the oxidation power distribution of the surface excess oxygen, the oxygen isotopic exchange reaction, the binding energy of oxygen, etc.

ABSTRACT:Isotherms for absorption of iodine by various polymers have been measured at 25°C in aqueous media. Poly(3-vinyl-10-methylphenothiazine) (PVMP), poly(4-vinylpyridine), and poly(tetramethylene ether glycol) absorb 3.0 g, 2.3 g, and 1.8 g of iodine, respectively, per 1.0 g of the polymer when dipped in a 0.05 M aqueous solution of 12 containing KI at 25°C. 6-Nylon, poly(vinyl alcohol), poly(acrylonitrile), poly(acrylamide) absorb 1.7 g, 1.5 g, 1.2 g, and 0.82 g of iodine, respectively, per 1.0 g of the polymer when dipped in a 0.10 M aqueous solution of 12 under the same conditions. Except for 6-nylon, the dependence of the amount of absorbed iodine on [12] K obeys a Langmuir-type equation obtained assuming the equilibrium, 12 +polymer=='" 12.-polymer complex. The equilibrium constant K ranges from 13 M-1 (for poly(vinyl alcohol)) through 53 M-1 (for PVMP). Cyclic voltammograms obtained using a polymer electrode coated on a Pt wire show the occurrence of smooth oxidation and reduction of 1-and 12 , respectively, on the surface of the polymer electrode and inside of the polymer electrode.

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