Enhancing CO2 hydrogenation via nitrogen-doped carbon nanospheres and in situ ruthenium nanoparticle synthesis†
Abstract
As the excessive presence of CO2 continues to infiltrate the Earth's atmosphere, a crucial mitigation strategy is not merely capturing CO2 but converting it into more useful fuels and chemicals, such as CO and CH4, through CO2 hydrogenation. This process is easily accelerated using a catalyst. A Ru/CNS nano-catalyst was studied, in which 1 wt% of ruthenium metal nanoparticles were dispersed over nitrogen-doped carbon nanospheres (CNSs) derived from resorcinol (Res) or 3-aminophenol (APF) and synthesized with or without a direct in situ mixing method. The generated C–N surface of the Ru/CNS-APF (in situ) catalyst not only possessed smaller, embedded, and well-dispersed Ru nanoparticles (2.38 nm), but also had a strong synergistic effect with the Ru species. The characterization and reaction test results indeed evidenced that this catalyst possessed the strongest activity (∼60% CO2 conversion and ∼85% CO selectivity at 600 °C and 3H2 : 1CO2 molar feed ratio). A 10 h stability test effectively demonstrated that the catalyst maintained its active and stable performance, with no major structural changes post-reaction. A density functional theory (DFT) model comprising a Ru nanostructure adsorbed on a C–N layer (graphene with substituted pyridinic-N) demonstrated easier CO2 capture on C–N before subsequent diffusion onto Ru. A strong electronic and material synergy between Ru and C–N was verified, and the preferred reaction intermediate was trans-COOH. The analysis proved both that a nitrogen-doped carbon nanosphere (CNS) support synthesized via in situ Ru incorporation enhances CO2 hydrogenation efficiency and that such Ru/C–N-based catalysts are highly capable towards addressing the global climate challenge.