Turning Carbon Dioxide and Ethane into Ethanol by Solar-Driven Heterogeneous Photocatalysis over RuO2- and NiO-co-Doped SrTiO3

The current work focused on the sunlight-driven thermo-photocatalytic reduction of carbon dioxide (CO₂), the primary greenhouse gas, by ethane (C₂H₆), the second most abundant element in shale gas, aiming at the generation of ethanol (EtOH), a renewable fuel. To promote this process, a hybrid catalyst was prepared and properly characterized, comprising of strontium titanate (SrTiO₃) co-doped with ruthenium oxide (RuO₂) and nickel oxide (NiO). The photocatalytic activity towards EtOH production was assessed in batch-mode and at gas-phase, under the influence of different conditions: (i) dopant loading; (ii) temperature; (iii) optical radiation wavelength; (vi) consecutive uses; and (v) electron scavenger addition. From the results here obtained, it was found that: (i) the functionalization of the SrTiO₃ with RuO₂ and NiO allows the visible light harvest and narrows the band gap energy (ca. 14–20%); (ii) the selectivity towards EtOH depends on the presence of Ni and irradiation; (iii) the catalyst photoresponse is mainly due to the visible photons; (iv) the photocatalyst loses > 50% efficiency right after the 2nd use; (v) the reaction mechanism is based on the photogenerated electron-hole pair charge separation; and (vi) a maximum yield of 64 μmol EtOH g_cat⁻¹ was obtained after 45-min (85 μmol EtOH g_cat⁻¹ h⁻¹) of simulated solar irradiation (1000 W m⁻²) at 200 °C, using 0.4 g L⁻¹ of SrTiO₃:RuO₂:NiO (0.8 wt.% Ru) with [CO₂]:[C₂H₆] and [Ru]:[Ni] molar ratios of 1:3 and 1:1, respectively. Notwithstanding, despite its exploratory nature, this study offers an alternative route to solar fuels’ synthesis from the underutilized C₂H₆ and CO₂.