Catalysis Letters, Vol.23, No.1-2, 25-35, 1994
Direct Differentiation of Surface and Bulk Compositions of Powder Catalysts - Application of Electron-Yield and Fluorescence-Yield NEXAFS to Lixni1-Xo
We have applied near-edge X-ray absorption fine structure (NEXAFS) to characterize the surface and bulk properties of LixNi1-xO catalysts. In our experimental set-up, NEXAFS spectra of powder materials could be obtained by measuring the intensity of either electron-yield or fluorescence-yield. While the electron-yield method is sensitive only to the top few atomic layers, the fluorescence-yield method can detect species up to a few thousands angstroms deep into the bulk structure. The ability to distinguish surface and bulk compositions is demonstrated in studies of a number of Li0.5Ni0.5O samples, of which the surface compositions vary as a function of preparation procedures. In addition, NEXAFS investigations following the reaction of LixNi1-xO with CH4 have also been carried out and the results indicate that the initial surface reaction intermediates are Li2CO3.