物理化学学报 >> 2001, Vol. 17 >> Issue (11): 966-971.doi: 10.3866/PKU.WHXB20011102

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MgO/HZSM-5中MgO分散状态和催化性能的关系

王珏;赵璧英;谢有畅   

  1. 北京大学物理化学研究所,北京　100871
  • 收稿日期:2001-04-11 修回日期:2001-06-25 发布日期:2001-11-15
  • 通讯作者: 赵璧英 E-mail:zby@pku.edu.cn

Correlations between the Dispersion State of MgO and Catalytic Behavior of

Wang Jue;Zhao Bi-Ying;Xie You-Chang   

  1. Institute of Physical Chemistry,Peking University,Beijing　100871
  • Received:2001-04-11 Revised:2001-06-25 Published:2001-11-15
  • Contact: Zhao Bi-Ying E-mail:zby@pku.edu.cn

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摘要： 以硝酸镁、醋酸镁为前身物,通过浸渍法制备了不同系列MgO/ HZSM-5催化剂,用XRD、XPS方法研究了MgO在HZSM-5上的分散状态,用NH3-TPD方法考察了催化剂的酸性,用常压连续流动微型反应装置考察MgO/ HZSM-5在甲苯甲醇烷基化反应中的催化性能.发现前身物不同,MgO在HZSM-5上的分散状态也不同,催化剂的活性和选择性与MgO分散状态密切相关.MgO负载量相同时,在以硝酸镁为前身物制备的催化剂中,MgO在HZSM-5内外表面均有分散,催化剂的对位选择性较高,而活性较低；在以醋酸镁为前身物制备的催化剂中,MgO较多分布在HZSM-5外表面,催化剂的活性较高,但选择性较低.使用醋酸镁为前身物,通过二次浸渍和高温水汽处理,适当改变MgO在分子筛表面的分布并使孔道窄化,可在活性降低较少的情况下显著提高催化剂对二甲苯选择性.

关键词: 择形催化, 表面修饰, 甲苯甲基化, HZSM-5, MgO

Abstract: Two series of MgO/HZSM-5 catalysts were prepared by impregnating HZSM-5 with solution of Mg(NO3)2 and Mg(CH3COO)2.The structures of the samples were characterized by XRD and XPS,and the acidity was determined by NH3-TPD.The catalytic behavior of MgO/HZSM-5 in the reaction of toluene methylation was investigated on a continuous flow micro-apparatus under atmospheric pressure.It was found that the dispersion of MgO was related to the precursor of MgO and had an important effect on the behavior of MgO/HZSM-5 catalyst.MgO disperses both on the internal surface and on the external surface of HZSM-5 in the catalysts prepared with Mg(NO3)2 as the precursor of MgO,therefore the para-selectivity of the catalyst is higher and the activity is lower.However MgO mainly deposits on the external surface of HZSM-5 in the catalysts prepared with Mg(CH3COO)2,and the activity of catalysts is higher and the para-selectivity is lower.By secondary impregnation and hydrothermal treatment MgO/HZSM-5 catalyst with relatively high activity and high para-selectivity was obtained.

Key words: Shape-selectivity, Surface modification, Toluene methylation, HZSM-5, MgO