Theoretical study of CO adsorption and oxidation on the gold–palladium bimetal clusters

Pd2 and CoPd dimers/N-doped graphene sensors with enhanced sensitivity for CO detection: A first-principles study

CONTEXT

The detection and monitoring of CO gas are essential to avoid human health problems. Therefore, the CO adsorption on Pd2 and PdCo dimers deposited on pyridinic Nx-doped graphene (PNxG; x = 1 - 3) was investigated employing the auxiliary density functional theory. In the most stable arrangements for the Pd2 dimer supported on PNxG, a Pd atom is in the PNxG vacancy, and the other Pd atom is placed on C atoms. For the PdCo dimer deposited on PNxG, the most stable interaction is like Pd2 dimer supported on PNxG, but with the Co atom centered over the vacancy site. Concerning the stability of the Pd2 and PdCo dimers supported on PNxG, the interaction energies (Eint) of the PdCo dimer deposited on PNxG are higher than those obtained with the Pd2 dimer. Also, the Eint of Pd2 and PdCo dimers deposited on PNxG are higher than those supported on pristine graphene. The CO adsorption energies on Pd2/PNxG and PdCo/PNxG composites are higher than those reported in the literature for pristine graphene, showing that the Pd2/PNxG and PdCo/PNxG composites have a good sensitivity toward the CO molecule.

METHODS

All electronic structure calculations were performed using the auxiliary density functional theory implemented in the deMon2k program. For exchange and correlation functional, the revised PBE was used. The Pd atoms were treated with an 18-electron QECP|SD basis set, while the remaining atoms were subjected to a DZVP-GGA basis set. The GEN-A2* auxiliary-function-set was used for all computations.

Estudio teórico de la oxidación de CO con O2 usando catalizadores de Au-Pd y Au-Pt

En el presente estudio se realizaron cálculos con base en la Teoría del Funcional de la Densidad Electrónica (DFT) con la aproximación B3PW91/LANL2DZ para optimizar los sistemas monometálicos y bimetálicos Au9, Au8Pd, Au8Pt, AuPd8, AuPt8, Pd9 y Pt9. Los materiales fueron teóricamente evaluados como catalizadores para la oxidación de monóxido de carbono (CO) y se determinó el sistema más favorable para la adsorción de esta molécula. La sustitución de átomos de Pt y Pd por átomos de Au en los nonámeros generó un cambio en la estructura tridimensional del sistema. El análisis de reactividad global mostró que el clúster más reactivo es 𝑃𝑡9, seguido por 𝐴𝑢𝑃𝑡8. Los índices de Fukui identificaron los sitios más susceptibles para un ataque nucleofílico de ambos clústeres. La adsorción de CO generó una cascada de oxidación que liberó ~4,5 eV, indicando que la reacción es altamente exotérmica y exergónica. Los clústeres 𝐴𝑢𝑃𝑡8 y 𝑃𝑡9 mostraron los valores más bajos de energía de activación de la etapa determinante del mecanismo. En general, la sustitución de un átomo de platino (o paladio) por un átomo de oro no afecta la reactividad de los nonámeros y, por tanto, se infiere que el clúster 𝐴𝑢𝑃𝑡8 podría ser un catalizador promisorio en la oxidación de CO.

Density Functional Study of Trimetallic AuxPdyPtz (x + y + z = 7) Clusters and Their Interactions with the O2 Molecule

Density functional theory calculations were performed to investigate the structural and energetic properties of trimetallic Au_xPd_yPt_z clusters with x + y + z = 7. The possible stable geometrical configurations with their electronic states are determined. We analyze the chemical order, binding energies, vertical ionization potential, electron affinity, and HOMO-LUMO gaps as a function of the whole concentration range. The affinity of Au_xPd_yPt_z clusters toward one O₂ molecule is also evaluated in terms of the changes in geometry, adsorption energy, and charge transfer.

Understanding the carbon-monoxide oxidation mechanism on ultrathin palladium nanowires: a density functional theory study

The CO oxidation mechanism catalyzed by ultrathin helical palladium nanowires (PdNW) was investigated by density functional theory (DFT) calculation. The helical PdNW structure was constructed on the basis of the simulated annealing basin-hopping (SABH) method with the tight-binding potential and the penalty method in our previous studies (J. Mater. Chem., 2012, 22, 20319). The low-lying adsorption configurations as well as the adsorption energies for O2 and CO molecules on different PdNW adsorption sites were obtained by DFT calculation. The most stable adsorption configurations for the Langmuir-Hinshelwood (LH) mechanism processes were considered for investigating the CO oxidation mechanism. The nudged elastic band (NEB) method was adopted to obtain the transition state configuration and the minimum energy pathways (MEPs).

Multisource Synergistic Electrocatalytic Oxidation Effect of Strongly Coupled PdM (M = Sn, Pb)/N-doped Graphene Nanocomposite on Small Organic Molecules

A series of palladium-based catalysts of metal alloying (Sn, Pb) and/or (N-doped) graphene support with regular enhanced electrocatalytic activity were investigated. The peak current density (118.05 mA cm(-2)) of PdSn/NG is higher than the sum current density (45.63 + 47.59 mA cm(-2)) of Pd/NG and PdSn/G. It reveals a synergistic electrocatalytic oxidation effect in PdSn/N-doped graphene Nanocomposite. Extend experiments show this multisource synergetic catalytic effect of metal alloying and N-doped graphene support in one catalyst on small organic molecule (methanol, ethanol and Ethylene glycol) oxidation is universal in PdM(M = Sn, Pb)/NG catalysts. Further, The high dispersion of small nanoparticles, the altered electron structure and Pd(0)/Pd(II) ratio of Pd in catalysts induced by strong coupled the metal alloying and N-doped graphene are responsible for the multisource synergistic catalytic effect in PdM(M = Sn, Pb) /NG catalysts. Finally, the catalytic durability and stability are also greatly improved.

Catalytic mechanisms of Au₁₁ and Au₁₁-nPt n (n=1-2) clusters: a DFT investigation on the oxidation of CO by O₂

The oxidation of CO catalyzed by clusters of Au11, Au10Pt and Au9Pt2 was investigated using the M06 functional suite of the density functional theory. Au and Pt atoms were described with the double-ζ valence basis set Los Alamos National Laboratory 2-double-z (LanL2DZ), whereas the standard 6-311++G(d,p) basis set was employed for the C and O atoms. Our theoretical model showed that (1) after coordination to Au and Au-Pt cluster, O2 and CO are apparently activated, and Mulliken charges show that the gold atoms in the active sites of Au11 are negatively charged; (2) Au-Pt clusters with 11 atoms can effectively catalyze the oxidation of CO by O2; (3) Au11 exhibits good catalytic performance for the oxidation of CO; (4) oxidation of CO occurs preferably on the Au-Pt active sites in Pt-doped clusters, and the single-center mechanisms are more favorable energetically than the two-center mechanisms; (5) after adsorption, an O2 molecule oxidates two CO molecules via stepwise mechanisms; and (6) the catalytic processes are highly exothermic.

Catalytic activity of anionic Au–Ag dimer for nitric oxide oxidation: a DFT study

The oxidation of NO is effectively catalyzed by Au–Ag⁻ dimer with Au site is the preferable one.

CO oxidation catalysed by Pd-based bimetallic nanoalloys

Density functional theory based global geometry optimization has been used to demonstrate the crucial influence of the geometry of the catalytic cluster on the energy barriers for the CO oxidation reaction over Pd-based bimetallic nanoalloys.

The effect of the size of surface Pd island ensembles on electron transfer of adsorbed perchlorate ions on Au(111)

A progressive increase in the size of Pd ensembles on a mica-supported Au(111) single crystal surface can facilitate electron transfer of perchlorate ions at lower anodic potential in CV curves than pure Au(111) due to a strong ligand effect and Pd-Au neighbouring pairs at edge sites render a higher degree of electron transfer.