Role of Back-Donation Deciphering CO₂ Adsorption Modes on 3d-Transition Metals

The development of effective and sustainable catalysts for the long-term use of CO₂ is highly dependent on understanding how CO₂ is adsorbed and activated on catalysts, mainly based on transition metals. Since catalysis is inherently a localized phenomenon and CO₂ tends to adsorb at the metal centers due to differences in electronegativity, detailed information on the mechanisms of CO₂ capture can be obtained by studying simplified molecular models, such as transition-metal dimers. Using such dimer models, this article addresses the importance of d-orbitals that facilitate the adsorption and activation of a CO₂ molecule. In addition, the influence of back-bonding is observed, where electrons from the filled 2π orbitals of CO₂ are donated to the vacant orbitals of metal atoms, in different adsorption configurations of CO₂ molecule. The findings elucidate a clear connection between back-bonding and CO₂ adsorption mechanism, highlighting particular configurations that facilitate optimal activation. Through evaluation of the correlation among d-orbitals, back-bonding, and CO₂ activation within transition-metal dimers, a viable approach is presented to design efficient catalysts to capture carbon dioxide.