Effects of Light Rare Earth on Acidity and Catalytic Performance of HZSM-5 Zeolite for Catalytic Cracking of Butane to Light Olefins
来源期刊：JOURNAL OF RARE EARTHS2007年第3期
论文作者：Duan Aijun Zhao Zhen Zhang Li Wang Xiaoning Jiang Guiyuan Xu Chunming
Key words：light rare earth; HZSM-5 zeolite; catalytic cracking; butane; acidity;
Abstract: The effects of rare earth (RE) on the structure, acidity, and catalytic performance of HZSM-5 zeolite were investigated. A series of RE/HZSM-5 catalysts, containing 7.54% RE (RE=La, Ce, Pr, Nd, Sm, Eu or Gd), were prepared by the impregnation of the ZSM-5 type zeolites (Si/Al=64:1) with the corresponding RE nitrate aqueous solutions. The catalysts were characterized by means of FT-IR, UV-Vis, NH3-TPD, and IR spectroscopy of adsorbed pyridine. The catalytic performances of the RE/HZSM-5 for the catalytic cracking of mixed butane to light olefins were also measured with a fixed bed microreactor. The results revealed that the addition of light rare earth metal on the HZSM-5 catalyst greatly enhanced the selectivity to olefins, especially to propylene, thus increasing the total yield of olefins in the catalytic cracking of butane. Among the RE-modified HZSM-5 samples, Ce/HZSM-5 gave the highest yield of total olefins, and Nd/HZSM-5 gave the highest yield of propene at a reaction temperature of 600℃. The presence of rare earth metal on the HZSM-5 sample, not only modified the acidic properties of HZSM-5 including the amount of acid sites and acid type, that is, the ratio of L/B (Lewis acid/Bronsted acid), but also altered the basic properties of it, which in turn promoted the catalytic performance of HZSM-5 for the catalytic cracking of butane.
Duan Aijun1，Zhao Zhen1，Zhang Li1，Wang Xiaoning1，Jiang Guiyuan1，Xu Chunming1
(1.State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China)
Abstract:The effects of rare earth (RE) on the structure, acidity, and catalytic performance of HZSM-5 zeolite were investigated. A series of RE/HZSM-5 catalysts, containing 7.54% RE (RE=La, Ce, Pr, Nd, Sm, Eu or Gd), were prepared by the impregnation of the ZSM-5 type zeolites (Si/Al=64:1) with the corresponding RE nitrate aqueous solutions. The catalysts were characterized by means of FT-IR, UV-Vis, NH3-TPD, and IR spectroscopy of adsorbed pyridine. The catalytic performances of the RE/HZSM-5 for the catalytic cracking of mixed butane to light olefins were also measured with a fixed bed microreactor. The results revealed that the addition of light rare earth metal on the HZSM-5 catalyst greatly enhanced the selectivity to olefins, especially to propylene, thus increasing the total yield of olefins in the catalytic cracking of butane. Among the RE-modified HZSM-5 samples, Ce/HZSM-5 gave the highest yield of total olefins, and Nd/HZSM-5 gave the highest yield of propene at a reaction temperature of 600℃. The presence of rare earth metal on the HZSM-5 sample, not only modified the acidic properties of HZSM-5 including the amount of acid sites and acid type, that is, the ratio of L/B (Lewis acid/Bronsted acid), but also altered the basic properties of it, which in turn promoted the catalytic performance of HZSM-5 for the catalytic cracking of butane.
Key words:light rare earth; HZSM-5 zeolite; catalytic cracking; butane; acidity;
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