DEHYDRO-OLIGOMERIZATION OF METHANE TO ETHYLENE AND AROMATICS OVER MOLYBDENUM/HZSM-5 CATALYST
DEHYDRO-OLIGOMERIZATION OF METHANE TO ETHYLENE AND AROMATICS OVER MOLYBDENUM/HZSM-5 CATALYST
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DOI：
10.1006/jcat.1995.1279
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发表时间：
1995-11-01
影响因子：
7.3
通讯作者：
ZHANG, T
中科院分区：
文献类型：
--
作者：
CHEN, LY;LIN, LW;ZHANG, T
采用XRD、IR、UV漫反射光谱、TPR、NH_3吸附和脱附等方法研究了不同Mo负载量的Mo/HZSM-5催化剂的结构。催化剂的BET比表面积和酸性均随钼负载量的增加而降低。钼的单层分散的阈值为约5g钼/100 g HZSM-5沸石。研究了Mo/HZSM-5催化剂在非氧化条件下的甲烷转化率。结果表明，钼负载量为2- 3wt%的催化剂对甲烷脱氢齐聚制芳烃具有最佳的活性。用锂或磷改性2%Mo/HZSM-5催化剂导致催化剂酸性以及催化剂活性的降低。锂的加入以苯的产率为代价改变了乙烯的选择性。它还表明，钼氧化物物种被部分还原甲烷在反应过程中。氧化钼的可去除晶格氧将吸附的CHx物种氧化成CO，这导致甲烷催化齐聚成芳烃的副反应。催化剂酸性降低和积炭堵塞HZSM-5分子筛孔道可能是催化剂失活的主要原因。甲烷齐聚反应被认为是由位于沸石孔道中的钼物种与HZSM-5沸石的Bronsted酸中心共同催化的。这两种中心之间的协同效应在催化反应中起着重要的作用。在甲烷的脱氢低聚反应中，乙烯被确定为主要产物，而苯是最终产物。(C)出版社：Academic Press
The structures of Mo/HZSM-5 catalysts with various molybdenum loadings were studied by means of XRD, IR, UV diffuse reflectance spectroscopy, TPR, and ammonia adsorption and desorption measurements. Both the BET surface areas and the acidities of catalysts decrease with an increase in molybdenum loading in the catalyst. The threshold of a monolayer dispersion of molybdenum is about 5 g of molybdenum per 100 g of HZSM-5 zeolite. Methane conversion under nonoxidizing conditions over Mo/HZSM-5 catalyst was tested. It was found that the catalyst with a molybdenum loading of 2-3 wt% exhibits optimum activity for the dehydro-oligomerization of methane to aromatics. Modifications of the 2% Mo/HZSM-5 catalyst with lithium or phosphorus cause a decrease in the acidity of the catalyst as well as in the catalyst activity. Addition of lithium shifts the selectivity toward ethylene at the expense of the yield of benzene. It is also demonstrated that the molybdenum oxide species are partially reduced by methane during the reaction. The removable lattice oxygen of molybdenum oxide oxidized adsorbed CHx species to CO, which results in a side reaction to the catalytic oligomerization of methane to aromatics. The diminution of acidity of the catalyst and the blockage of the channels of HZSM-5 zeolite due to deposited carbon may be the main reasons for the deactivation of the catalyst. The methane oligomerization reaction is proposed to be catalyzed by molybdenum species located in the zeolite channels together with the Bronsted acid sites of HZSM-5 zeolite. A synergistic effect between these two kinds of centers plays an important role in the catalysis of the title reaction. Ethylene is identified to be a primary product while benzene is a final product in the dehydro-oligomerization reaction of methane. (C) 1995 Academic Press, Inc.