ABSTRACT

The objective of this work is to propose a more effective way to prepare an in-house CO₂ with known triple oxygen isotope compositions. The major experimental steps include: (1) the O₂ is combusted to CO₂ on a graphite rod at 750 °C with Pt-catalyst for 3–4 min; and (2) converted CO₂ is subsequently purified by two cryogenic traps. The results show high reproducibility of δ¹³C and δ¹⁸O values of the converted CO₂ within 0.010–0.020 ‰ and 0.006–0.010 ‰ (1σ, SD), and the identical δ¹⁸O value within error with that of the original O₂. Additionally, we have measured the triple oxygen isotope compositions of converted CO₂ using an O₂–CO₂ Pt-catalyzed oxygen-isotope equilibration method. The measured δ¹⁷O values of CO₂ show high reproducibility within 0.006 ‰ (1σ, SD), and are identical within error with the original O₂ as well. Notably, our experiments also found that the O₂ with heavier oxygen isotope ratios (δ¹⁸O > 40 ‰, VSMOW) might have a lesser conversion efficiency, and this effect, combined with the lighter isotope preferential fractionations during the reaction processes of O₂ to CO and CO to CO₂, may explain the observed lower ¹⁷O/¹⁶O and ¹⁸O/¹⁶O ratios of the converted CO₂ relative to the original O₂.

摘要

这项工作的目的是提出一种更有效的方法来制备具有已知三氧同位素组成的内部 CO ₂。主要实验步骤包括：（1）将O ₂燃烧成CO ₂上的石墨棒在750℃下用Pt催化剂3-4分钟; (2)转化后的CO ₂随后由两个低温捕集器净化。结果表明，转化后的 CO ₂的δ ¹³ C 和δ ¹⁸ O 值在 0.010–0.020 ‰ 和 0.006–0.010 ‰ (1 σ , SD)范围内具有很高的重现性，并且与原始值相同的δ ¹⁸ O 值在误差范围内氧₂. 此外，我们还使用 O ₂ –CO ₂ Pt 催化的氧同位素平衡方法测量了转化后的 CO ₂的三重氧同位素组成。测得的 CO ₂ δ ¹⁷ O 值在 0.006 ‰ (1 σ , SD)内具有很高的重现性，并且在误差范围内与原始 O ₂相同。值得注意的是，我们的实验还发现，具有较重氧同位素比 ( δ ¹⁸ O > 40 ‰, VSMOW)的 O ₂可能具有较低的转化效率，并且这种影响与 O ₂反应过程中较轻的同位素优先分馏相结合到 CO 和 CO 到 CO ₂，可以解释观察到的较低的¹⁷ O/ ¹⁶ O 和¹⁸ O/ ¹⁶ O 的转化 CO ₂相对于原始 O _{2 的}比率。