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.