Spontaneous oxygen isotope exchange between carbon dioxide and natural clays: Refined rate constants referenced to TiO2 (anatase/rutile)

The photocatalytic reduction of CO2 to CH4 is a chemical process that to some extent occurs on the surface of rocky planets. The effect of an acidic proton on the rate of the photocatalytic reduction of CO2 on mineral surfaces was explored through the addition of HCl to our reaction system. HCl serves a dual role: it is a H-donor (reactant) and creates a band gap in the case of siderite and kaolinite (modifies the chemical environment of the reaction). Of the tested minerals, Al2O3, ilmenite (FeTiO3), and one sample of soil containing fossilized remains of diatoms from the Soos Nature Reserve (Czech Republic) have shown significant activity in the methanogenesis process. Kaolinite, natural rutile, MgO, basalt, acidic and ferrous synthetic clays, the Nakhla meteorite, and two diatomaceous earth samples from the Soos Nature Reserve showed weak photocatalytic properties; the reaction was slower than that on, e.g., Al2O3. The newly recognized photocatalytic activity of some of these natural minerals and the effect of the acidic proton should be included in the atmospheric models of both our planet and exoplanets alike, as it may play a role in the estimation of methane production from CO2 in the presence of minerals on the planetary surface upon UV radiation.

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Formation of Methane and (Per)Chlorates on Mars

Civiš

Knížek

Rimmer

et al. 2018

ACS Earth Space Chem.

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Methane, perchlorates, chlorates, and methyl chlorides have all been detected on Mars. The origin of these species has never been adequately explained. In this paper, we irradiated mixtures of CO2, HCl, and a mineral catalystanatase, rutile, montmorillonite, and the Nakhla meteoritewith soft UV radiation for up to 3500 h and observed the formation of perchlorates, chlorates, methyl chlorides, and methane in a single experiment. Additionally, the methanogenesis for anatase was observed at −196 °C. Further, we propose that while methane is decomposed relatively quickly and therefore attains a steady-state concentration (0.41 ± 0.16 ppbv), the chlorinated compounds are much more stable and therefore would have accumulated throughout the Martian history. We estimate that this mechanism would be sufficient in the course of Martian history to accumulate perchlorate in the soil in 0.5 wt % in 5–50 cm depth, which is in accordance with the observed perchlorate content on Mars. This predicted perchlorate gradient may be observed with the Insight rover. Further, if microbes are present on Mars, they will likely inhabit depths below the perchlorate (i.e., 5–50 cm). This chemistry likely still continues on Mars to a certain extent, and any future exploration by rovers or planetary models should account for this process during their analyses.

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Spontaneous oxygen isotope exchange between carbon dioxide and natural clays: Refined rate constants referenced to TiO2 (anatase/rutile)

Cited by 3 publications

References 34 publications

Comparative SIFT-MS, GC–MS and FTIR analysis of methane fuel produced in biogas stations and in artificial photosynthesis over acidic anatase TiO2 and montmorillonite

Comparative SIFT-MS, GC–MS and FTIR analysis of methane fuel produced in biogas stations and in artificial photosynthesis over acidic anatase TiO2 and montmorillonite

Acidic Hydrogen Enhanced Photocatalytic Reduction of CO₂ on Planetary Surfaces

Formation of Methane and (Per)Chlorates on Mars

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Spontaneous oxygen isotope exchange between carbon dioxide and natural clays: Refined rate constants referenced to TiO2 (anatase/rutile)

Cited by 3 publications

References 34 publications

Comparative SIFT-MS, GC–MS and FTIR analysis of methane fuel produced in biogas stations and in artificial photosynthesis over acidic anatase TiO2 and montmorillonite

Comparative SIFT-MS, GC–MS and FTIR analysis of methane fuel produced in biogas stations and in artificial photosynthesis over acidic anatase TiO2 and montmorillonite

Acidic Hydrogen Enhanced Photocatalytic Reduction of CO2 on Planetary Surfaces

Formation of Methane and (Per)Chlorates on Mars

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Product

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Acidic Hydrogen Enhanced Photocatalytic Reduction of CO₂ on Planetary Surfaces