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An experimental study on Fischer‐Tropsch catalysis: Implications for impact phenomena and nebular chemistry
Author(s) -
SEKINE Yasuhito,
SUGITA Seiji,
SHIDO Takafumi,
YAMAMOTO Takashi,
IWASAWA Yasuhiro,
KADONO Toshihiko,
MATSUI Takafumi
Publication year - 2006
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2006.tb00987.x
Subject(s) - fischer–tropsch process , catalysis , nickel , disproportionation , chemistry , bar (unit) , atmospheric pressure , inorganic chemistry , organic chemistry , physics , meteorology , selectivity
— Fischer‐Tropsch catalysis, by which CO and H 2 are converted to CH 4 on the surface of transition metals, has been considered to be one of the most important chemical reactions in many planetary processes, such as the formation of the solar and circumplanetary nebulae, the expansion of vapor clouds induced by cometary impacts, and the atmospheric re‐entry of vapor condensate due to asteroidal impacts. However, few quantitative experimental studies have been conducted for the catalytic reaction under conditions relevant to these planetary processes. In this study, we conduct Fischer‐Tropsch catalytic experiments at low pressures (1.3 times 10 −4 bar ≤ P ≤ 5.3 times 10 −1 bar) over a wide range of H 2 /CO ratios (0.25–1000) using pure iron, pure nickel, and iron‐nickel alloys. We analyze what gas species are produced and measure the CH 4 formation rate. Our results indicate that the CH 4 formation rate for iron catalysts strongly depends on both pressure and the H 2 /CO ratio, and that nickel is a more efficient catalyst at lower pressures and lower H 2 /CO ratios. This difference in catalytic properties between iron and nickel may come from the reaction steps concerning disproportionation of CO, hydrogenation of surface carbon, and the poisoning of the catalyst. These results suggest that nickel is important in the atmospheric re‐entry of impact condensate, while iron is efficient in circumplanetary subnebulae. Our results also indicate that previous numerical models of iron catalysis based on experimental data at 1 bar considerably overestimate CH 4 formation efficiency at lower pressures, such as the solar nebula and the atmospheric re‐entry of impact condensate.