Ethylbenzene dehydrogenation over Mg₃Fe_0.5−xCo_xAl_0.5 catalysts derived from hydrotalcites: Comparison with Mg₃Fe_0.5−yNi_yAl_0.5 catalysts

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• 作者：Luqman A. Atanda^a ; Rabindran J. Balasamy^a ; Alam Khurshid^a ; Ali A.S. Al-Ali^a ; Kunimasa Sagata^b ; Makiko Asamoto^b ; Hidenori Yahiro^b ; Kiyoshi Nomura^c ; Tsuneji Sano^d ; Katsuomi Takehira^a ; ^{takehira@hiroshima-u.ac.jp} ; Sulaiman S. Al-Khattaf^a ; ^{skhattaf@kfupm.edu.sa}
• 关键词：Ethylbenzene dehydrogenation ; Styrene ; Mg₃Fe_0.25Co_0.25Al_0.5 catalyst ; Fe³⁺&#x2013 ; Co²⁺ active species ; Hydrotalcite
• 刊名：Applied Catalysis A: General
• 出版年：2011
• 出版时间：15 April 2011
• 年：2011
• 卷：396
• 期：1-2
• 页码：107-115
• 全文大小：522 K

文摘

A series of Mg₃Fe_0.5−xCo_xAl_0.5 (x = 0–0.5) catalysts were prepared from hydrotalcite precursors and their activities in the dehydrogenation of ethylbenzene were compared with those of a series of Mg₃Fe_0.5−yNi_yAl_0.5 (y = 0–0.5) catalysts also derived from hydrotalcite. The hydrotalcites prepared by co-precipitation were calcined at 550 °C to the mixed oxides with a high surface area of ; they were composed of Mg(Fe,Me,Al)O periclase and Mg(Me)(Fe,Al)₂O₄ spinel (Me = Co or Ni). Bimetallic Fe³⁺–Co²⁺ system showed a synergy, i.e., an increase in the activity, whereas Fe³⁺–Ni²⁺ bimetallic system showed no synergy. The high styrene yield was obtained on Mg₃Fe_0.1Co_0.4Al_0.5; however, a large substitution of Fe³⁺ with Co²⁺ caused a decrease in styrene selectivity along with coking on the catalysts, due to an isolation of CoO_x on the catalyst surface. The highest yield as well as the highest selectivity for styrene production was obtained at x = 0.25 at time on stream of 30 min. The coprecipitation at pH = 10.0 and the composition of Mg₃Fe_0.25Co_0.25Al_0.5 were the best for preparing the active catalyst. This is partly due to the formation of a good hydrotalcite structure. On this catalyst, the active Fe³⁺ species was reduced at a low temperature by the Fe³⁺–Co²⁺ bimetal formation, leading to a high activity. Simultaneously, the amount of reducible Fe³⁺ was the smallest, resulting in a high stability of the active Fe³⁺ species. It is likely that the dehydrogenation was catalyzed by the reduction–oxidation between Fe³⁺ and Fe²⁺ and that Co²⁺ assisted the reduction–oxidation by forming Fe³⁺–Co²⁺ (1/1) bimetallic active species.