首页 | 本学科首页   官方微博 | 高级检索  
     检索      


The role of Fischer-Tropsch catalysis in the origin of methane-rich Titan
Authors:Yasuhito Sekine  Seiji Sugita  Takashi Yamamoto  Toshihiko Kadono
Institution:a Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
b Department of Complexity Science and Engineering, Graduate School of Frontier Science, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 227-8562, Japan
c Department of Chemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
d Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan
Abstract:Fischer-Tropsch catalysis, which converts CO and H2 into CH4 on the surface of iron catalyst, has been proposed to produce the CH4 on Titan during its formation process in a circum-planetary subnebula. However, Fischer-Tropsch reaction rate under the conditions of subnebula have not been measured quantitatively yet. In this study, we conduct laboratory experiments to determine CH4 formation rate and also conduct theoretical calculation of clathrate formation to clarify the significance of Fischer-Tropsch catalysis in a subnebula. Our experimental result indicates that the range of conditions where Fischer-Tropsch catalysis proceeds efficiently is narrow (T∼500-600 K) in a subnebula because the catalysts are poisoned at temperatures above 600 K under the condition of subnebula (i.e., H2/CO = 1000). This suggests that an entire subnebula may not become rich in CH4 but rather that only limited region of a subnebula may enriched in CH4 (i.e., CH4-rich band formation). Our experimental result also suggests that both CO and CO2 are converted into CH4 within time significantly shorter than the lifetime of the solar nebula at the optimal temperatures around 550 K. The calculation result of clathration shows that CO2-rich satellitesimals are formed in the catalytically inactive outer region of subnebula. In the catalytically active inner region, CH4-rich satellitesimals are formed. The resulting CH4-rich satellitesimals formed in this region play an important role in the origin of CH4 on Titan. When our experimental data are applied to a high-pressure model for subnebula evolution, it would predict that there should be CO2 underneath the Iapetus subsurface and no thick CO2 ice layer on Titan's icy crust. Such surface and subsurface composition, which may be observed by Cassini-Huygens mission, would provide crucial information on the origin of icy satellites.
Keywords:Fischer-Tropsch catalysis  Titan  Cassini-Huygens mission  Circum-planetary subnebula  Methane
本文献已被 ScienceDirect 等数据库收录!
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号