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, ZrNi3/Al2O3 exhibits a higher activity of CO methanation with a decreased Ea of the C–O bond breaking compared to Zr2Ni11 and Zr2Ni11/Al2O3. This phenomenon is attributed to the presence of active, low-coordinated sites of the Zr-promoter and the large electronic perturbations in contact with the Al2O3 support. The calculations demonstrate that the Zr-promoting effect on C–O breaking is due to the synergy between Zr, Ni, and Al2O3, leading to a shift of εd of ZrNi3/Al2O3. 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 ZrNi3/Al2O3 and the p-state of CO. Even more, this promoting effect tunes C2p and O2p 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, ZrNi3/Al2O3 activates CO efficiently, prevents the production of CH3OH, and via the direct C–O breaking pathway generates CH4.