Unraveling the Role of the d-Electron Reservoir of ZrNi₃/Al₂O₃ for C–O Breaking during CO Methanation: Zr-Induced Active Sites Make the Difference

Abstract

According to density functional theory results, ZrNi 3 / Al 2 O 3 exhibits a higher activity of CO methanation with a decreased E a of the C−O bond breaking compared to Zr 2 Ni 11 and Zr 2 Ni 11 /Al 2 O 3 . This phenomenon is attributed to the presence of active, lowcoordinated sites of the Zr-promoter and the large electronic perturbations in contact with the Al 2 O 3 support. The calculations demonstrate that the Zr-promoting effect on C−O breaking is due to the synergy between Zr, Ni, and Al 2 O 3 , leading to a shift of ε d of ZrNi 3 / Al 2 O 3 . This promoting effect is able to reduce the electrical band gap of the CO dissociation by creating a new energy state between the d-state of ZrNi 3 /Al 2 O 3 and the p-state of CO. Even more, this promoting effect tunes C 2p and O 2p to higher energy, sufficient to produce the more 2π*antibonding states, and thus, enough to weaken further the C−O bond resulting in a more reactive CO. More importantly, ZrNi 3 / Al 2 O 3 activates CO efficiently, prevents the production of CH 3 OH, and via the direct C−O breaking pathway generates CH 4 .