NiCr2O4, ZnCr2O4, CuCr2O4, CuAl2O4, and CuFe2O4 were prepared and characterized by XRD, DRS, and IR and by measurements of surface area, acidity, and electrical conductivity. XRD analysis indicates, that chromites, aluminate, and ferrite have normal, partially inversed, and inversed spinel structure, respectively. Electrical conductivity measurements show the existence of pair localized ions which are positive in chromites and negative both in aluminate and ferrite. The catalytic activity of chromites and aluminate are comparable and higher than that of ferrite in the conversion of ethylbenzene under all experimental conditions. However selectivity to styrene formation follows in the following order: ferrite > chromites > aluminate. The ratio of B/T (benzene/toluene) is more than unity over aluminate and less than unity over chromites and ferrite. Evolution of CO2 remains constant while that of C2H4 increased with increase in temperature keeping its formation always higher over aluminate. Measurements of acidity and basicity by TGA show the presence of basic sites on chromites, acidic sites on aluminate, and both sites on ferrite which influence the conversion of ethylbenzene to various products. The XRD pattern of spent catalysts indicate the appearance of metallic copper phase over CuCr2O4, CuFe2O4, and CuAl2O4. In the case of NiCr2O4 and ZnCr2O4 no significant difference is observed.
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Jebarathinam et al. (1994) studied this question.