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Abiotic Methane Generation via CO2 Hydrogenation With Natural Chromitite Under Hydrothermal Conditions
Geochemistry, Geophysics, Geosystems ( IF 3.275 ) Pub Date : 2021-03-16 , DOI: 10.1029/2020gc009533
Hisahiro Ueda, Yohei Matsui, Yusuke Sawaki

In modern continental serpentinization systems and ultramafic rock‐hosted sub‐seafloor hydrothermal systems, it is believed that chromitite plays an important role in abiotic hydrocarbon generation. Previous experiments have suggested that chromite acts as a catalyst of CH4 generation, but the composition of chromite used in the previous experiment is unrealistic on Earth. On the other hand, other studies have suggested that natural chromite including Mg and Al cannot function as a catalyst for CH4 generation. Consequently, it still remains uncertain whether naturally occurring Cr‐rich minerals promote CH4 generation. We monitored the reaction between naturally occurring chromitite and CO2‐rich fluid at 300°C, 500 bars. We performed two experiments in different initial CO2/H2 ratios. In both experiments, CH4 was generated immediately after the beginning of experiments. When CO2 was more abundant than H2, the CH4 concentration in the fluid decreased below the detection limit value. On the other hand, when H2 was more abundant than CO2, the CH4 concentration in the fluid was maintained above 0.01 mmol/kg. This is the first report to demonstrate that naturally occurring Cr‐rich minerals act as a promotor of CH4 generation. Cr‐rich minerals such as Cr spinel are common accessory mineral in ultramafic rock. Therefore, on the early Earth, a certain level (on the order of 0.01 mmol/kg) of CH4 was likely produced through reactions between ultramafic rock and CO2‐bearing fluid. To produce more abundant CH4, more favorable conditions featuring greater quantities of Cr spinel and much higher H2 concentration (H2/CO2 ratio) must be necessary.

中文翻译:

在水热条件下通过天然亚铬铁矿的CO2加氢生成非生物甲烷

在现代大陆的蛇纹石化系统和超镁铁质的岩浆下海底热液系统中,铬铁矿在非生物碳氢化合物的产生中起着重要的作用。先前的实验表明,亚铬铁矿是生成CH 4的催化剂,但是先前的实验中使用的亚铬铁矿的组成在地球上是不现实的。另一方面,其他研究表明,包括Mg和Al的天然亚铬酸盐不能用作生成CH 4的催化剂。因此,仍然不确定自然产生的富含Cr的矿物是否能促进CH 4的生成。我们监测了天然铬铁矿和CO 2之间的反应300°C,500 bar时富含流体。我们以不同的初始CO 2 / H 2比进行了两个实验。在两个实验中,实验开始后立即生成CH 4。当CO 2比H 2丰富时,流体中的CH 4浓度降低到检测极限值以下。另一方面,当H 2比CO 2丰富时,流体中的CH 4浓度维持在0.01mmol / kg以上。这是第一份证明天然存在的富含Cr的矿物可促进CH 4的报告。一代。富铬矿物如铬尖晶石是超镁铁质岩石中常见的辅助矿物。因此,在地球早期,超镁铁质岩石与含CO 2的流体之间的反应可能会产生一定水平(约0.01 mmol / kg)的CH 4。为了产生更丰富的CH 4,必须有更有利的条件,即具有更多数量的Cr尖晶石和更高的H 2浓度(H 2 / CO 2比)。
更新日期:2021-04-08
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