Abstract
In this work we report on the combined impact of active phase nature (M: Co or Cu) and ceria nanoparticles support morphology (nanorods (NR) or nanocubes (NC)) on the physicochemical characteristics and CO2 hydrogenation performance of M/CeO2 composites at atmospheric pressure. It was found that CO2 conversion followed the order: Co/CeO2 > Cu/CeO2 > CeO2, independently of the support morphology. Co/CeO2 catalysts demonstrated the highest CO2 conversion (92% at 450 °C), accompanied by 93% CH4 selectivity. On the other hand, Cu/CeO2 samples were very selective for CO production, exhibiting 52% CO2 conversion and 95% CO selectivity at 380 °C. The results obtained in a wide range of H2:CO2 ratios (1–9) and temperatures (200–500 °C) are reaching in both cases the corresponding thermodynamic equilibrium conversions, revealing the superiority of Co- and Cu-based samples in methanation and reverse water-gas shift (rWGS) reactions, respectively. Moreover, samples supported on ceria nanocubes exhibited higher specific activity (µmol CO2·m−2·s−1) compared to samples of rod-like shape, disclosing the significant role of support morphology, besides that of metal nature (Co or Cu). Results are interpreted on the basis of different textural and redox properties of as-prepared samples in conjunction to the different impact of metal entity (Co or Cu) on CO2 hydrogenation process.
Highlights
It is widely accepted amongst the scientific community that the increasing trend of CO2 emissions in the Earth’s atmosphere since the onset of industrialization is the key attributor for the planet temperature rise over the last two centuries [1]
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Summary
It is widely accepted amongst the scientific community that the increasing trend of CO2 emissions in the Earth’s atmosphere since the onset of industrialization is the key attributor for the planet temperature rise over the last two centuries [1]. Efforts of mitigation of the aforementioned environmental issue can be simplified into three general approaches: (i) complete and/or partial replacement of carbon-based fuels with renewable energy sources (RESs), (ii) carbon dioxide capture and storage (CCS) technology and (iii) chemical conversion/utilization of CO2 toward value-added chemicals and fuels [4]. The latter approach has attracted intense interest over the past decades, with hydrogenation of CO2 being one of the most thoroughly investigated methods, owing to the wide variety of possible products [5]. This route can provide an effective way to valorize CO2 emissions and efficiently store the surplus power from non-intermittent RESs (e.g., solar, wind) in the form of “green” hydrogen, providing either CO via the mildly endothermic reverse water-gas shift (rWGS) reaction (Equation (1)) or CH4 via the highly exothermic methanation reaction, often referred to as the “Sabatier reaction” (Equation (2)), discovered in 1902 by the French scientist Paul Sabatier [6].
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