催化学报

催化学报 ›› 2007, Vol. 28 ›› Issue (4): 371-376.

• 研究论文 • 上一篇    下一篇

Mo/HZSM-5催化剂上甲烷无氧芳构化反应—HZSM-5分子筛脱铝的影响

宋一兵1,2,孙长勇2,吴燕青1,申文杰2,林励吾2   

  1. 1 汕头大学化学系, 广东汕头 515063; 2 中国科学院大连化学物理研究所催化基础国家重点实验室, 辽宁大连 116023
  • 收稿日期:2007-04-25 出版日期:2007-04-25 发布日期:2011-03-28

Methane Dehydroaromatization over Mo/HZSM-5 Catalyst:Effect of Dealumination of HZSM-5 Zeolite

SONG Yibing1,2, SUN Changyong2, WU Yanqing1, SHEN Wenjie2*, LIN Liwu2*   

  1. 1 Department of Chemistry , Shantou University, Shantou 515063, Guangdong, China; 2 State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, The Chinese Academy of Sciences, Dalian 116023, Liaoning, China
  • Received:2007-04-25 Online:2007-04-25 Published:2011-03-28

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摘要： 采用两种不同的脱铝方法对HZSM-5分子筛进行了预处理,并利用MAS NMR和吸附吡啶的FT-IR对分子筛的结构和酸性质进行了表征,考察了分子筛的脱铝程度对Mo基催化剂上甲烷芳构化反应性能的影响. 结果表明, HZSM-5分子筛的酸性过强或B酸量不足,均会导致催化剂严重积炭,但积炭成因不同. 母体HZSM-5分子筛上的强B酸中心的存在可促使催化剂上反应中间物种深度脱氢,造成催化剂在反应过程中严重积炭. 经水热处理的HZSM-5分子筛,骨架铝脱出严重,造成B酸活性中心不足以及部分微孔阻塞,不利于C2中间物种芳构化,导致芳烃选择性显著降低. 经高温N2处理的HZSM-5分子筛,骨架铝脱出相对缓和,在消除母体分子筛上强B酸中心的同时,保留了较多的弱B酸中心,既可满足C2中间物种芳构化反应的需要,又可有效抑制催化剂积炭,导致甲烷芳构化反应性能显著改善.

关键词: 甲烷, 芳构化, 钼, HZSM-5分子筛, 负载型催化剂, 脱铝, 水热处理, 高温氮气处理

Abstract: Two dealumination methods were used to modify the framework composition of the HZSM-5 zeolite. The structure and acidity of dealuminated zeolite samples were investigated by MAS NMR and FT-IR. It was found that the catalytic performance of the Mo/HZSM-5 catalyst for methane dehydroaromatization was closely related to the acidity of the HZSM-5 zeolite. On the parent zeolite with n(Si)/n(Al)≈27, the presence of superfluous strong Brnsted acid sites caused severe coke deposition during the reaction. Hydrothermal treatment of the parent zeolite extracted tetrahedral Al from the framework and thus led to a significant reduction in the number of Brnsted acid sites. The formation of aromatics over this hydrothermally treated zeolite was suppressed owing to the deficiency of acid sites available for the aromatization of C2 intermediates. High-temperature N2 treatment induced mild dealumination of HZSM-5, destroyed the origin strong Brnsted acid sites, but retained sufficient weak acid sites. This treatment effectively restrained coke deposition and satisfied the requirement of the aromatization of C2 intermediates during the reaction. Therefore, a remarkable improvement in the catalyst durability and selectivity for aromatics was observed.

Key words: methane, aromatization, molybdenum, HZSM-5 zeolite, supported catalyst, dealumination, hydrothermal treatment, high temperature nitrogen treatment