Abstract
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 gcat−1 was obtained after 45-min (85 μmol EtOH gcat−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.
Highlights
The global economy has been moving towards an ever-growing consumption of fossil fuels, together with the emission of anthropogenic greenhouse gases, which has led to an energy crisis and global warming
SrTiO3 :RuO2 :nickel oxide (NiO) photocatalyst, several characterization techniques were used, namely: (i) UV-Vis diffuse reflectance spectroscopy (DRS), which was applied for SrTiO3 and SrTiO3 :Ru2 intermediate samples (Figure 2); (ii) X-ray diffraction (XRD) and Raman spectroscopy (Figure 3); (iii) energy-dispersive X-ray spectroscopy (EDS) mapping and transition electron microscopy (TEM) (Figure 4); and (iv) X-ray photoelectron spectroscopy (XPS) (Figure 5)
Based on the XRD pattern (Figure 3), it can be observed that the SrTiO3 :RuO2 :NiO
Summary
The global economy has been moving towards an ever-growing consumption of fossil fuels, together with the emission of anthropogenic greenhouse gases, which has led to an energy crisis and global warming. The development of promising strategies aiming at the carbon dioxide (CO2 ) chemical conversion into renewable hydrocarbon fuels is urgent. Many of the studies have predominantly focused on synthesizing chemical intermediates, such as syngas (CO + H2 ), alkenes, and aromatic compounds [1,2,3,4]. The transport and storage of syngas and alkenes raise potential safety risks, due to the high toxicity range and flammability of these gases, respectively [5,6]. A lack of feasible approaches to produce valuable and safer oxygenate molecules directly from CO2 and other high environmental concern gases, such as shale gas, appears to exist
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