The electrochemical carbon monoxide reduction reaction (CORR) holds significant potential for sustainable fuel and chemical production, offering an effective means to reduce carbon emissions and maintain environmental sustainability. Graphene, a single layer of carbon atoms arranged in a unique two-dimensional structure, possesses properties that make it suitable for various applications. Nitrogen-doped graphene (NDG) based metal single-atom catalysts (SACs) have emerged as one of the most effective methods for converting CO into C₁ products such as CH₄ and CH₃OH. In this study, defective graphene was doped with four nitrogen atoms, which stabilized the catalyst through complexation with metal species by binding with the nitrogen atoms. First-principles calculations were employed to investigate the catalytic performance of selected transition metals (TM₁ = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) as SACs anchored on the NDG surface for hydrogen evolution reaction (HER) and CORR processes. Theoretical analysis indicated that NDG is highly favorable for binding transition metal single adatoms with excellent stability, facilitating rapid electron transfer during catalysis and yielding outstanding catalytic performance. Among the SACs, Among the SACs, Cr supported by N₄-G catalyst selectively produces CH₄ with Cr-N₄-G exhibiting the lowest overpotential of 0.47 eV. This study demonstrates that the N₄-G support is a promising candidate for use as a single-atom catalyst for selective CO reduction and other electrochemical processes.

Single-atom catalysts (SACs) have provoked significant curiosity in heterogeneous catalysis due to the benefits of maximum metal atoms usage, robust metal-support interaction, single-metal-atom active sites, and high catalytic efficiency. In this study, the electronic structures and catalytic mechanism of ethyne hydrogenation of SACs with the group-9 metal atoms M₁ (M₁= Co, Rh, Ir) anchored on PTA (phosphotungstic acid) cluster have been explored by using first-principles quantum calculations. It is found that the catalytic activity of ethyne (C₂H₂) hydrogenation is determined by two critical parameters: the adsorption energies of the adsorbate (H₂, C₂H₂) and the activation energy barrier of ethyne hydrogenation. We have shown that the reaction pathway of ethyne hydrogenation reaction on the experimentally characterized Rh₁/PTA at room temperature consists of three steps: C₂H₂ and H₂ coadsorption on Rh₁/PTA, H₂ attacking C₂H₂ to form C₂H₄, then C₂H₄ desorbing or further reacting with H₂ to produce C₂H₆ and completing the catalytic cycle. The Rh₁/PTA possesses fair catalytic activity with a C₂H₄ desorption energy of 1.46 eV and a 2.59 eV barrier for ethylene hydrogenation. Moreover, micro-kinetics analysis is also carried out to understand the mechanism and catalytic performance further. The work reveals that the PTA-supported SACs can be a promising catalyst for alkyne hydrogenation.