The Effect of SnO2 Surface Properties on CO2 Photoreduction to Higher Hydrocarbons

CO₂ photoreduction using SnO₂ under UV radiation lead to CO, C₂H₄, and C₂H₆, with higher selectivity for CH₄. The same reaction under visible light using Au-decorated SnO₂ produces CH₄ and a smaller amount of CO but in much lower yields. Although the SnO₂ band structure does not indicate a good semiconductor for CO₂ reduction, its surface characteristics are responsible for its catalytic activity, and it does not act as a simple support for other catalysts, as plasmonic metals.

Abstract

Several photocatalysts have been developed for applications in reduction reactions, including tin oxide-based semiconductors. Although its band structure is unfavorable for CO₂ reduction reactions, strategies to modify its surface properties directly impacted its activity and selectivity during these reactions. Here, we analyze the influence of heat treatment and decoration of SnO₂ with gold nanoparticles on the gas phase CO₂ photoreduction process. In both cases, a deleterious effect was observed during reactions under UV radiation (with a drop of 59.81 % and 51.45 % in CH₄ production for SnO₂_150 °C and SnO₂/Au_cop, respectively, compared to SnO₂_cop), which is directly related to the availability of surface hydroxyl groups that play a crucial role in CO₂ adsorption. Under visible radiation, the gold plasmonic resonance took place in the production of methane (0.33 μmol g⁻¹ for SnO₂/Au_cop and 0.29 μmol g⁻¹ for SnO₂/Au_150 °C), with small amounts of carbon monoxide (0.06 μmol g⁻¹ for SnO₂/Au_cop and 0.03 μmol g⁻¹ for SnO₂/Au_150 °C). These results demonstrate that, though the SnO₂ band structure does not indicate a good semiconductor for CO₂ reduction, its surface characteristics are responsible for its catalytic activity.

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