IR spectroscopic investigation of cation distribution in Zn-Co oxide catalysts with spinel type structure

The structure of Zn-Co spinel prepared by coprecipitation was studied by IR spectroscopy. The characteristic bands of extra OH- and H3O+ groups were shown to exist in IR spectra up to 700 degrees C. Comparing IR spectra of a poorly crystallized low temperature catalyst with that of a perfect Zn-Co spinel, we have associated the noticeable splittings and shifts of the F-1u bands with definite structural distortions. The presence of extra anions in the catalyst with a spinel-like structure in the temperature region 100-700 degrees C is the factor that stabilized the unusual cation distribution in this catalyst. The most plausible cation distribution in such a spinel is proposed as follows: Co3+ and Zn2+ are in octahedral positions, and Co2+ and Zn2+ are in tetrahedral ones. (C) 2000 Elsevier Science B.V. All rights reserved.