A DFT study of ethanol interaction with the bimetallic clusters of PtSn and its implications on reactivity.

The comprehension of the factors affecting the adsorption of ethanol over metals and metal alloys is a crucial step for the rational development of new catalysts for hydrogen production through ethanol reforming. In this work, we analyze the effect of combining Pt and Sn on a metal cluster on the complexation energy and reactivity for OH dehydrogenation of ethanol. Metal clusters of Pt10, Sn10 and Pt5Sn5 had their putative minimum located with the help of the artificial bee colony algorithm. Whereas the isolated Pt cluster shows a high degree of polarization (ESP surface), the Sn cluster shows a quite uniform electron density surface. The PtSn cluster is strongly polarized, with Pt atoms withdrawing electron density of Sn atoms. Complexation occurs with the oxygen atom of ethanol directed towards the point of highest electron potential in the ESP surface. Pt presents the highest complexation energy, -20.90 kcal/mol, against only -7.83 kcal/mol (at the B97-3c level). For the PtSn cluster, the value is intermediate, namely -12.39 kcal/mol. The more malleable electron density of Pt and its electron affinity are responsible for its highest complexation energy. These characteristics are partially transferred to the PtSn cluster. QTAIM results show that, for the PtSn cluster, the O-H bond in ethanol is somewhat weaker than for pure Pt and Sn. As a consequence, the energy barrier for the O-H dehydrogenation has its lowest value for the PtSn cluster, which shows that the alloying of two metals can lead to quite quite unexpected results opening the perspective for a more rational fine tuning of catalysts properties.

Au16 Cd16 (SC6 H11 )20 : A Glance at Structure-Property Relationship.

Doping Cd atom(s) into gold clusters is very promising in both theoretical study and practical applications. However, it has long been a challenge to synthesize heavily Cd-doped AuCd bimetallic clusters and thereby reveal their structure-property correlations. Herein a novel AuCd bimetallic cluster: Au16 Cd16 (SC6 H11 )20 (SC6 H11 denotes deprotonated cyclohexanethiol) with a Cd to Au atomic ratio of 1:1 is reported. The precise structure of the cluster determined by single crystal X-ray diffraction demonstrates that it has a unique hexatetrahedron Au14 core and a distinctive shell. Intriguingly, due to the special protecting motifs, the cluster exhibits high stability in various conditions studied, indicating that the geometric structure is crucial in determining the stability of the cluster. Most importantly, the photothermal property of the cluster has been investigated in comparison with those of M13 -kernel (M denotes metal atoms) clusters, and the results imply that the compactness and the Cd atom doping of the core play important roles in dictating the photothermal effect of the cluster. The authors believe that this work will provide some ideas for the rational design of clusters with high stability and excellent photothermal property.

Thermally generated Au-Ag nanostructures with tunable localized surface plasmon resonance as SERS activity substrates.

Various Au-Ag bimetallic alloy nanostructures were obtained as sensitive surface-enhanced Raman scattering (SERS) substrates by changing the thermal annealing sequence. The atomic force microscopy (AFM) and scanning electron microscopy (SEM) results confirm that Au/Ag bimetallic clusters and Ag-Au core-shell like structures can be designed by thermal annealing. The absorption spectra showed that the localized surface plasmon resonance (LSPR) frequency of the annealed Au/Ag bimetallic alloy structure could effectively shift from the near ultraviolet to the visible region. At the same time, the Au/Ag bimetallic alloy films modified by thermal annealing have shown satisfactory performance as SERS substrates. Raman enhancement mechanism of Au-Ag bimetallic alloy films is verified by finite-difference time-domain (FDTD) simulation results.

Stability, Energetic, and Reactivity Properties of NiPd Alloy Clusters Deposited on Graphene with Defects: A Density Functional Theory Study.

Graphene with defects is a vital support material since it improves the catalytic activity and stability of nanoparticles. Here, a density functional theory study was conducted to investigate the stability, energy, and reactivity properties of NinPdn (n = 1-3) clusters supported on graphene with different defects (i.e., graphene with monovacancy and pyridinic N-doped graphene with one, two, and three N atoms). On the interaction between the clusters and graphene with defects, the charge was transferred from the clusters to the modified graphene, and it was observed that the binding energy between them was substantially higher than that previously reported for Pd-based clusters supported on pristine graphene. The vertical ionization potential calculated for the clusters supported on modified graphene decreased compared with that calculated for free clusters. In contrast, vertical electron affinity values for the clusters supported on graphene with defects increased compared with those calculated for free clusters. In addition, the chemical hardness calculated for the clusters supported on modified graphene was decreased compared with free clusters, suggesting that the former may exhibit higher reactivity than the latter. Therefore, it could be inferred that graphene with defects is a good support material because it enhances the stability and reactivity of the Pd-based alloy clusters supported on PNG.

Estudio teórico de la oxidación de CO con O2 usando catalizadores de Au-Pd y Au-Pt / Theoretical study of the CO Oxidation with O2 using Au-Pd and Au-Pt catalysts / Estudo teórico da oxidação de CO com O2 usando catalisadores de Au-Pd e Au-Pt

Resumen 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 PÍ9, seguido por AuPt s . 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 AuPt s y Pt 9 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 AuPt s podría ser un catalizador promisorio en la oxidación de CO.

Abstract In the current study were development calculations based on Density Functional Theory (DFT) with the B3PW91/LANL2DZ approach for optimizing both monometallic and bimetallic systems: Au9, AusPd, Au8Pt, AuPds, AuPts, Pd9 y Pt9. Such materials were theoretically tested as catalyst for the oxidation of carbon monoxide (CO) and the most favorable system for its further adsorption was determined. The substitution of Pt and Pd by Au atoms in the nonamers generated a change in the tridimensional structure of the system. The global reactivity analysis showed that the most reactive cluster is Pt9 followed by AuPts. On the other hand, the Fukui indexes identified the most susceptible sites for a nucleophilic attack of both clusters. The CO adsorption generated an oxidation cascade which liberated ∼ 4.5 eV, indicating that the reaction is highly exothermic and exergonic. Both AuPt8 and Pt9 showed the lowest values of activation energy in the determining step of the mechanism. In general, the substitution of a Pt (Pd) atom by an Au atom does not affect the reactivity of the nonamers and then it is inferred that the AuPds cluster could be a promissory catalyst in the CO oxidation.

Resumo No presente estudo, cálculos baseados na Teoria do Funcional da Densidade Eletrônica (DFT) com a abordagem B3PW91/LANL2DZ foram realizados para otimizar sistemas monometálicos e bimetálicos Au9, Au8Pd, Au8Pt, AuPd8, AuPt8, Pd9 y Pt9. Tais materiais foram teoricamente avaliados como catalisadores para a oxidação do monóxido de carbono (CO) e foi determinado o sistema mais favorável para a adsorção desta molécula. A substituição dos átomos de Pt e Pd por átomos de Au nós não-nomes gerou uma mudança na estrutura tridimensional do sistema. A análise de reatividade global mostrou que o cluster mais reativo é Pt9, seguido por AuPt8. Os índices de Fukui identificaram os sítios mais suscetíveis ao ataque nucleofílico de ambos os clusters. A adsorção de CO gerou uma cascata de oxidação que liberou ~4,5 eV, indicando que a reação é altamente exotérmica e exergônica. Os aglomerados AuPt 8 y Pt 9 apresentaram os menores valores de energia de ativação do estágio determinante do mecanismo. Em geral, a substituição de um átomo de platina (ou paládio) por um átomo de ouro não afeta a reatividade dos não-nomes e, portanto, infere-se que o aglomerado AuPt 8 pode ser um catalisador promissor na oxidação do CO.

The pathways of the CO2 hydrogenation by NiCu/ZnO from DFT molecular dynamics simulations.

Metal nanoparticles supported on semiconductor surfaces have been proposed as promising nanocatalyst candidates of CO2 conversion to energy carrier molecules such as formic acid or carbon monoxide, which can be used as a feedstock for fuels synthesis. This study is focused on the bimetallic Cu/Ni nanoparticles supported on the ZnO. The respective reaction mechanisms have been studied by means of the Molecular Dynamics with the DFT methodology. The results suggest that on CuNi/ZnO CO2 hydrogenation to formate pathway is more favorable than carboxyl route. These pathways are competitive with the CO2 reduction to CO.

Theoretical study of the structures of bimetallic Ag-Au and Cu-Au clusters up to 108 atoms.

The stable structures of Ag-Au and Cu-Au clusters with 1 : 1, 1 : 3 and 3 : 1 compositions with up to 108 atoms are obtained using a modified adaptive immune optimization algorithm with Gupta potential. The dominant motifs of Ag-Au and Cu-Au clusters are decahedron and icosahedron, respectively. However, in Ag-rich Ag-Au clusters, more icosahedra are found, and in Cu-rich Cu-Au clusters, there exist several decahedral motifs. Four Leary tetrahedral motifs are predicted. CucoreAushell configurations are predicted in Cu-Au clusters. In Ag-Au clusters, most Ag atoms are on the surface, but partial ones are located in the inner shell, while Au atoms are interconnected in the middle shell.

On the Possibility of Using the Jellium Model as a Guide To Design Bimetallic Superalkali Cations.

The potential application of the jellium model as guidance in the rational design of bimetallic superalkali cations is examined under gradient-corrected density functional theory for the first time. By using Li, Mg, and Al as atomic building blocks, a series of bimetallic cationic clusters with 2, 8, 20, and 40 valence electrons are obtained and investigated. As the corresponding neutral clusters tend to lose one valence electron to achieve closed-shell states in the jellium model, these studied cations exhibit much lower vertical electron affinities (EAvert , 3.42-4.95 eV) than the ionization energies (IEs) of alkali metal atoms, indicating their superalkali identities. The high stability of these cationic clusters is guaranteed by their considerable HOMO-LUMO gaps and binding energies per atom. Moreover, the feasibility of using the designed superalkalis as efficient reductants to activate CO2 and N2 molecules and as stable building blocks to assemble ionic superatom compounds is explored. Therefore, this study may provide an effective method for obtaining various metallic superatoms with extensive applications on the basis of the simple jellium rule.