Activation of CO and CO2 on homonuclear boron bonds of fullerene-like BN cages: first principles study

Using density functional theory we investigate the electronic and atomic structure of fullerene-like boron nitride cage structures. The pentagonal ring leads to the formation of homonuclear bonds. The homonuclear bonds are also found in other BN structures having pentagon line defect. The calculated thermodynamics and vibrational spectra indicated that, among various stable configurations of BN-60 cages, the higher number of homonuclear N-N bonds and lower B:N ratio can result in the more stable structure. The homonuclear bonds bestow the system with salient catalytic properties that can be tuned by modifying the B atom bonding environment. We show that homonuclear B-B (B2) bonds can anchor both oxygen and CO molecules making the cage to be potential candidates as catalyst for CO oxidation via Langmuir-Hinshelwood (LH) mechanism. Moreover, the B-B-B (B3) bonds are reactive enough to capture, activate and hydrogenate CO2 molecules to formic acid. The observed trend in reactivity, viz B3 > B2 > B1 is explained in terms of the position of the boron defect state relative to the Fermi level.close0

Ab Initio Study of Thin Oxide-Metal Over layers as an Inverse Catalytic System for Dioxygen Reduction and Enhanced CO Tolerance

Using first-principles density functional theory calculations, we used a thin oxide overlayer, such as MgO, on a metal surface as an inverse catalyst for dioxygen reduction. Surface distortions in the oxide layer, combined with the tunneling of electron from the underneath metal, activated the adsorbed O2 in the form of a superoxo or peroxo. On the other hand, the thin MgO overlayer readily prevents the ??-back-bonding between CO and the metal surface, thereby efficiently mitigating the affinity of the metal surface for CO. The operating potential and overpotential for the oxygen reduction reaction (ORR) process have been estimated for various combinations of thin insulators and metals. The strongest binding intermediate in the overall reaction pathway influenced the overpotential. We show that for a Ag(100)-supported MgO surface, the ORR commences with a low overpotential, which is comparable to that of the Pt(111) surface. This suggests that an optimally chosen insulator-metal overlayer structure can yield a sharply tuned free energy profile for ORR.close

Ab Initio Study of Thin Oxide-Metal Over layers as an Inverse Catalytic System for Dioxygen Reduction and Enhanced CO Tolerance

Using first-principles density functional theory calculations, we used a thin oxide overlayer, such as MgO, on a metal surface as an inverse catalyst for dioxygen reduction. Surface distortions in the oxide layer, combined with the tunneling of electron from the underneath metal, activated the adsorbed O2 in the form of a superoxo or peroxo. On the other hand, the thin MgO overlayer readily prevents the π-back-bonding between CO and the metal surface, thereby efficiently mitigating the affinity of the metal surface for CO. The operating potential and overpotential for the oxygen reduction reaction (ORR) process have been estimated for various combinations of thin insulators and metals. The strongest binding intermediate in the overall reaction pathway influenced the overpotential. We show that for a Ag(100)-supported MgO surface, the ORR commences with a low overpotential, which is comparable to that of the Pt(111) surface. This suggests that an optimally chosen insulator−metal overlayer structure can yield a sharply tuned free energy profile for ORR.116191sciescopu

Magnetic, elastic and optical properties of zinc peroxide (ZnO2): First principles study

Using first principles method we elaborately discuss the magnetic, elastic and optical properties of pure, Zn and O vacant ZnO2. It is found that the electronic structure and band gap of ZnO2 is not sensitive to the active on-site Coulomb interaction term U-d, but found to be depending on the term U-p. The role of orbitals subject to the correlation is thus completely opposite for the case of ZnO2 in respect of ZnO. Interestingly, the Zn vacancy converts ZnO2 as "d(0) magnet''. Indeed, our analysis show that, Zn vacancy transmuted O-2(2) state into O-2(delta+2) state, indicating the partially filled pi* states are the governing reason for the d(0) magnetism. Both HSE06 and PBE0 functional confirm the same. The similar phenomena has been observed for other peroxide materials XO2 (X = Mg, Ca, Sr, Ba) studied here. Our results suggest that this class of materials can be studied further to exploit its potential in spintronic devices. Further the elastic properties have been estimated for pure ZnO2 at different pressures and for Zn and O vacant ZnO2 to know the stability of the system. Zn vacancy in ZnO2 also tunes optical properties, indicating its potential application in other areas.close

CO Oxidation Prefers the Eley–Rideal or Langmuir–Hinshelwood Pathway: Monolayer vs Thin Film of SiC

Using the first-principles approach, we investigated the electronic and chemical properties of wurtzite silicon carbide (2H-SiC) monolayer and thin film structures and substantiated their catalytic activity toward CO oxidation. 2H-SiC monolayer, being planar, is quite stable and has moderate binding with O₂, while CO interacts physically; thus, the Eley–Rideal (ER) mechanism prevails over the Langmuir–Hinshelwood (LH) mechanism with an easily cleared activation barrier. Contrarily, 2H-SiC thin film, which exhibits a nonplanar structure, allows moderate binding of both CO and O₂ on its surface, thus favoring the LH mechanism over the ER one. Comprehending these results leads to a better understanding of the reaction mechanisms involving structural contrast. Weak overlapping between the 2p_<i>z</i>(C) and 3p_<i>z</i>(Si) orbitals of the SiC monolayer system has been found to be the primary reason to revert the active site toward sp³ hybridization, during interaction with the molecules. In addition, the influences of graphite and Ag(111) substrates on the CO oxidation mechanism were also studied, and it is observed that the ER mechanism is preserved on SiC/G system, while CO oxidation on the SiC/Ag(111) system follows the LH mechanism. The calculated Sabatier activities of the SiC catalysts show that the catalysts are very efficient in catalyzing CO oxidation