Abstract
Dehydrogenation of diethylbenzene was examined over Fe-based mixed oxide catalysts, including a commercial Fe2O3-Cr2O3-K2CO3 catalyst. The catalytic activity of Fe2O3-Cr2O3-K2CO3 increased gradually during the first several hours of reaction (Fig. 1). After the reaction the structure of the catalyst, revealed by X-ray diffraction (Fig. 2), included a compound KFeO2 as well as Fe3O4. The formation of KFeO2 was observed also by heat treatment in either air or in an H2-H2O stream. However, it decomposed to Fe2O3 and K2CO3 when it was exposed to CO2. Because the catalyst is exposed to CO2 during the reaction, the amount of KFeO2 is controlled by its equilibrium of formation and decomposition. The effect of H2-H2O pretreatment, as shown in Table 2, was found to accerelate the evolution of CO2 greater than that of He-H2O pretreatment (Fig. 4).
The catalytic activity of Fe2O3-A2CO3 (A=alkali metal) was examined. The results are shown in Table 3. The activity of Fe-K system was observed to be singularly high, and the reason for this seemed to be the tendency for the formation of mixed oxide KFeO2. In order to facilitate the mixing of Fe and alkali metals, oxalate complexes of Fe, A[Fe(C2O4)(H2O)2], were examined as catalyst precursors supported on alumina. Higher activities compared with that of Fe2O3-Cr2O3-K2CO3 were found with the Fe-K catalysts thus prepared (Table 4). In addition, comparable activities were observed also with other than K catalysts, and the highest activity was obtained with the Cs-Fe/alumina catalyst.
Dehydrogenation of ethylbenzene was also attempted over the same series of catalysts derived from oxalate complexes (Table 5). The activities and selectivities for dehydrogenation of ethylbenzene and diethylbenzene did not change in the same order of the series listed nor were optimum catalyst compositions always the same for the two reactions.
