Theoretical catalytic performance of single-atom catalysts M₁/PW₁₂O₄₀ for alkyne hydrogenation materials

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.