Electron Transfer in Mixed Phase of Anatase and Rutile

The ESR spectrum of the P-25 sample was well simulated by the superposition of two distinct Ti signals from the anatase and rutile phases with a 1 1 concentration ratio, see Fig. 6.22(c). The P-25 sample originally consists of a phase composition ratio of 4 1 for the anatase and rutile. The increased ratio of the rutile Ti + ions in comparison to the original phase composition indicates that in the mixed phase the 

The superoxide (O2 ) ion radical is one of the most important oxide radical intermediates in catalysis and has been extensively studied by means of ESR spectroscopy. Kanzig and Cohen [124] have reported the first ESR spectrum of 02 trapped in a single crystal of alkaU hahdes five decades ago. The reported g-value analysis has been well accepted and adapted by Lunsford [3], Kasai [4] and other scientists (for 

The previously reported gz values of 02 range from 2.03 to 2.02. Consistent with this, for the present 02 /Ti /oxide support system, the following g-values were derived from the ESR spectrum recorded at 4.2 K gx = 2.0027, gy = 2.0092 and gz = 2.0268. The small shift of gx and gy from ge and the order of gx gy are also supported by the theory [3c, 4d]. 

The labeling is a powerful method for identifying oxygen species and their structure in the adsorbed phase on oxides and other catalysts by ESR. An observation of (/ = 7/2) hyperfine structure can give an unambiguous assignment of the ESR spectrum, e.g. if it is due to a superoxide ion 02 , and not other oxide radicals such as 0 and 03 . Furthermore, it can provide important experimental evidence if the 02 consists of either equivalent or non-equivalent oxygen nuclei. 

Comparing the experimental ESR spectra with the simulated ones the following conclusions were suggested. (1) The principal values of the /i/tensor are almost axially symmetric with the perpendicular component A( A2 A3) being less than the linewidth of ca. 3 G. (2) Two different parallel components of hf splittings were observed for both ( O— 0) and — 0) radical ions with 

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