Conversion of methanol to hydrocarbons over zeolite H-ZSM-5: On the origin of the olefinic species

被引:919
作者
Bjorgen, Morten
Svelle, Stian
Joensen, Finn
Nerlov, Jesper
Kolboe, Stein
Bonino, Francesca
Palumbo, Luisa
Bordiga, Silvia
Olsbye, Unni
机构
[1] Haldor Topsoe Res Labs, DK-2800 Lyngby, Denmark
[2] Univ Oslo, Dept Chem, Ctr Mat Sci & Nanotechnol, N-0315 Oslo, Norway
[3] Univ Turin, Ctr Riferimento INSTM, NIS Ctr Excellence, Dept Inorgan Phys & Mat Chem, I-10125 Turin, Italy
关键词
ZSM-5; MFI; MTO; MTH; MTG; methanol; zeolite; mechanism; hydrocarbon pool; coking; deactivation;
D O I
10.1016/j.jcat.2007.04.006
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
This study examined the reaction mechanism with respect to both catalyst deactivation and product formation in the conversion of methanol to hydrocarbons over zeolite H-ZSM-5. The reactivity of the organics residing in the zeolite voids during the reaction was assessed by transient C-12/C-13 methanol-switching experiments. In contrast to previously investigated catalysts (H-SAPO-34 and H-beta), hexamethylbenzene is virtually unreactive in H-ZSM-5 and is thus not a relevant reaction intermediate for alkene formation. However, the lower methylbenzenes are reaction intermediates in a hydrocarbon pool-type mechanistic cycle and are responsible for the formation of ethene and propene. An additional reaction cycle not applicable for ethene also must be taken into account. The C3+ alkenes are to formed through rapid alkene methylation and cracking steps to a considerable extent; thus, methanol is converted to hydrocarbons according to two catalytic cycles over H-ZSM-5. Moreover, in contrast to what occurs for large-pore zeolites/zeotypes, molecules larger than hexamethyl benzenes are not built up inside the H-ZSM-5 channels during deactivation. Thus, deactivation is explained by coke formation on the external surface of the zeolite crystallites only. This is a plausible rationale for the superior lifetime properties of H-ZSM-5 in the methanol-to-hydrocarbon reaction. (c) 2007 Elsevier Inc. All rights reserved.
引用
收藏
页码:195 / 207
页数:13
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