Acta Phys. -Chim. Sin. ›› 1989, Vol. 5 ›› Issue (02): 196-201.doi: 10.3866/PKU.WHXB19890213

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ACTIVE PHASE AND ROLE OF POTASSIUM IN POTASSIUM-PROMOTED IRON OXIDE CATALYST FOR DEHYDROGENATION OF ETHYLBENZENE

Zhu Yixiang; Lin Rencun; He Danyun; Yan Jian   

  1. Department of Chemistry; Xiamen University; Xiamen
  • Received:1987-09-28 Revised:1988-05-24 Published:1989-04-15
  • Contact: Zhu Yixiang

Abstract:

Fe_2O_3-K_2O binary catalysts prepared by high temperature calcination of the relevant mixtures and by KOH solution impregnation showed different catalytic behaviour in the reaction of dehydrogenation of ethylbenzene. The latter had longer stability period of the highest activity and shorter induction period. An impregnated multi-component catalyst, which was particularly prepared in our laboratory and had similar chemical composition to a well-known commercial catalyst(G-64I),showed that both the conversion of ethylbenzene and the selectivity to styrene were similar to G-64I although the impregnation amount of KOH corresponded to the fact that this impregnated catalyst had about 54 monolayers of K_2O on its surface. These facts indicated that the potassium promotor operated specifically on the surface of the iron oxide and that Fe_3O_4 was not the active phase of the catalyst as some authors had suggested. It was proved by using SEM, EDAX and XPS that, the Fe/K atom ratio on the surface of this impregnated catalyst increased obviously while the surface morphlogical structure changed simultaneously after this catlyst was operated for about 24 hrs. These suggested that a strong interaction between potassium promotor and iron oxide had occured on the surface and that the product resulting from the interaction should be the active phase of the catalyst. The XRD study at different temperatures showed that thte potassium promotor would reacted rapidly with iron oxide, thus forming K_2Fe_2O_4 in the temperature range 580—660℃, which was the usual operation temperature in the commercial production of ethylbenzene dehydrogenation to styrene. So, this paper suggested that the K_2Fe_2O_4 might be the active phase of the catalyst. Our experimental results could be satisfactorily explained according to this suggestion.