Formaldehyde is abundant in the universe and one of the fundamental molecules for life. Hydrothermal vents produce a substantial amount of hydrogen molecules by serpentinization and promote reductive reactions of single carbon compounds. The abundance of formaldehyde is expected to be low due to the high Gibbs free energy in hydrothermal vents. We consider two competing formation pathways of formaldehyde: (1) the reduction of CO by H2 and (2) the reduction of HCOOH by H2 to form a methanediol, followed by the dehydration of the methanediol. We performed a number of quantum chemical simulations to examine the formation of formaldehyde in the gas phase as well as in aqueous solution. The energy barrier is significantly reduced by the catalytic effect of water molecules in aqueous solution and becomes lowest when a water cluster consisted of 5 water molecules catalyzes the reduction. The energy barrier to form a methanediol by the reduction of HCOOH is lower by 17.5 kcal/mol than that to form a formaldehyde by the reduction of CO. Considering the low energy barrier to dehydrate methanediol, the primary pathway to form formaldehyde in hydrothermal vents is concluded to be the reduction of HCOOH by H2, followed by the dehydration of methanediol.

中文翻译：

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热液喷口中甲醛的主要形成途径。

甲醛在宇宙中是丰富的，是生命的基本分子之一。热液喷口通过蛇形化作用产生大量氢分子，并促进单个碳化合物的还原反应。由于热液喷口中的吉布斯自由能高，因此甲醛的含量预计较低。我们考虑了甲醛的两个竞争形成途径：（1）H2还原CO和（2）H2还原HCOOH形成甲烷二醇，然后进行甲烷脱水。我们进行了许多量子化学模拟，以研究气相和水溶液中甲醛的形成。能量垒通过水溶液中水分子的催化作用而显着降低，并且当由5个水分子组成的水簇催化该还原时，能量垒变得最低。通过还原HCOOH形成甲烷二醇的能垒比通过减少CO形成甲醛的能垒低17.5 kcal / mol。考虑到脱水甲烷二醇的低能垒，在水热喷口中形成甲醛的主要途径是结论是H2OH还原HCOOH，然后进行甲烷二醇脱水。