Abstract
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 Hdonor (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.