Pd13 Clusters Research Articles

Energetic and Kinetic Competition on the Stability of Pd13 Clusters: Ab Initio Molecular Dynamics Simulations.

Material stability is the focus on both experiments and calculations, which includes the energetic stability at the static state and the thermodynamic stability at the kinetic state. To show whether energetics or kinetics dominates on material stability, this study focuses on the Pd13 clusters, because of their observable magnetic moment in experiment. Energetically, the CALYPSO searching method and first-principles calculations find that Pd13(C2) is the ground state at 0 K while the static frequency calculations demonstrate that the icosahedron Pd13(Ih) becomes more favorable on free energy as temperature increases. However, their magnetic moments (8 μB) are not in agreement with the experimental value (<5.2 μB). Kinetically, ab initio molecular dynamics simulations reveal that Pd13(C3v) (6 μB) has supreme isomerization temperature and the other 11 low-lying isomers transform to Pd13(C3v) directly or indirectly, demonstrating that Pd13(C3v) has the maximum probability to be observed in experiment. The magnetic moment difference between experiment (<5.2 μB) and this calculation (6 μB) may be due to the spin multiplicities. Our result suggests that the magnetic moment disparity between theory and experiment (in Pd13 clusters) originates from the kinetic stability.

The effect of water vapour and sulfur on the methane combustion reaction on Pd13 clusters: Insights from a first principles study

Catalytic methane combustion represents a highly efficient and environmentally-friendly approach, which can significantly reduce methane emissions in coal mines. However, the presence of water vapor and sulfides in coal mine methane exhaust gas can lead to catalyst poisoning deactivation. This article employs density functional theory calculations based on the GGA-PBE method to investigate the effects of water vapor and sulfur on methane combustion on Pd13 clusters. According to thermodynamic parameters, we have determined the optimal reaction pathway for CH4 decomposition as CH4* → CH3* → CH2* → CH* → CHO*, while the optimal reaction pathway for CO2 formation is CH* → CHO* →CO* → CO2*. Additionally, water vapor generates additional OH* radicals, which lower the adsorption energy of CH4 on Pd13 clusters and alter the reaction pathway for methane oxidation, inhibiting the catalytic oxidation of CH4. Sulfides occupy the active sites on the catalyst surface, leading to a decrease in the activity of methane oxidation. These findings deepen our understanding of the mechanisms by which palladium-based catalysts catalyze methane combustion. Based on these findings, we have also proposed strategies for water and sulfur resistance of the catalyst, providing guidance for the future development of water-resistant and sulfur-resistant CH4 catalytic combustion catalysts.

First principle study of NH3 adsorption on Pd13 clusters supported by transition metal dichalcogenide XY2 (X=Mo, W; Y = S, Se, Te)

The adsorption of NH3 on Pd13 clusters supported by two-dimensional, transition metal dichalcogenide XY2 (X = Mo, W; Y = S, Se, Te) has been studied using first principle, density functional theory with D3 correction. For NH3 adsorption on MoY2 (Y = S, Se, Te)-supported Pd13 clusters, the chemisorption energy is in the order of Pd13/MoS2 > Pd13/MoSe2 > Pd13/MoTe2, and the chemisorption energy is in the order of Pd13/WS2 > Pd13/WSe2 > Pd13/WTe2 on WY2 (Y = S, Se, Te)-supported Pd13 clusters. The order of adsorption strength correlates well with charge transfer and the integrated crystal orbital Hamiltonian population. Compared to pristine Pd (111) surfaces, the adsorption energies on the XY2-supported Pd13 cluster are significantly increased by 63–92%; compared to the experimental value on Pd foil, the adsorption energies on the XY2-supported Pd13 cluster are also significantly increased by 55–81%. Our results contribute to the understanding of the mechanism of NH3 adsorption enhancement on transition metal dichalcogenide-supported Pd clusters and to the design of high-performance Pd catalytic clusters for NH3 adsorption.

Comparative computational study of CO2 hydrogenation and dissociation on metal-doped Pd clusters

Density functional theory calculations are executed to research CO2 adsorption and initial conversion on Pd12M (M = Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd) bimetallic clusters, with a focus on finding optimal ancillary metal to Pd element. The stability analysis of the structures demonstrates that the transition metals with higher surface energy (compared to Pd element) doped Pd13 clusters possess better structural stability. For CO2 adsorption, the structural parameters of CO2* have remarkable linear relation with the amount of charges transfer. For CO2 initial conversion, it can be concluded that the Pd12Cu cluster is the best candidate with a lower activation barrier (0.69 eV) for the initial hydrogenation of CO2. According to the electronic structure analysis, the elevated HOMO caused by the doping of Cu atom is the main reason for the enhanced catalytic activity. In addition, the PdCu bimetallic clusters with larger size are constructed and their activity and selectivity towards CO2 initial conversion are also studied. Compared with Pd32Cu6 and Pd42Cu13 bimetallic clusters, Pd12Cu has more advantages in activity and selectivity. Therefore, Pd12Cu is the best choice, that is, it inhibits the generation of by-product and improves the catalytic activity, which makes it become an excellent bimetallic candidate for CO2 initial hydrogenation.

A theoretical study of the Pd10Sb3 single-atom alloy cluster for CO oxidations

Inspired by the experimental synthesis of Pd-based single-atom alloy (SAA) catalysts which display high performance for reactions in the chemical industry. In this work, we have designed a Pd10Sb3 SAA alloy cluster as an efficient catalyst for CO oxidation. It is stable at 400 K for 3 ps under the ab-initio molecular dynamic simulation. Compared with Pd13, the Sb atom transfers electrons to the neighbour Pd atom, which induces its 4d states near the fermi level reduced much more. As a result, Pd10Sb3 show much weaker adsorptions of CO and O2. In addition, CO and O2 prefer to be adsorbed on the Pd site rather than on the Sb site. Thus, we have considered the full path for CO oxidation on the pure Pd site on Pd13 and Pd10Sb3 clusters. Compared with Pd13, on Pd10Sb3 the barrier of the rate-limiting step, that is the peroxide-like OO-CO intermediate formation, decreases by 0.54 eV which indicates Pd10Sb3 can be a potential catalyst for CO oxidation.

On the structural, energetic, and magnetic properties of M@Pd (M = Co, Ni, and Cu) core–shell nanoclusters and their comparison with pure Pd nanoclusters

Electronic structure computations of pure Pd and Pd-based core–shell clusters were studied employing auxiliary density functional theory (ADFT). For this investigation icosahedral clusters with 13 and 55 atoms and octahedral clusters with 19 and 44 atoms were employed to analyze the change in the properties of the Pd and M@Pd core–shell clusters. All properties calculated for the M@Pd clusters are directly compared with the ones of pure palladium clusters. Spin multiplicities, spin magnetic moments, spin densities, binding energies per atom, segregation energies, and average bond lengths were calculated to understand their changes when varying the size, composition and shape of the M@Pd (M = Co, Ni, and Cu) core–shell clusters. The M1@Pd12 and M1@Pd18 (M = Co and Cu) clusters exhibit changes in the spin multiplicity and spin magnetic moment with respect to the Pd13 and Pd19 clusters, respectively, whereas the Ni1@Pd12 and Ni1@Pd18 clusters maintain the same properties as their pure Pd counterparts. The spin multiplicities and spin magnetic moments of the M6@Pd38 and M13@Pd42 (M = Co, Ni, and Cu) clusters greatly differ from their pure Pd counterparts. This study reveals that the Pd-Pd bond lengths are shorter in the M@Pd core–shell clusters compared to the ones of pure Pd clusters. This work demonstrates that the binding energy per atom of the M@Pd core–shell clusters is greater than the binding energy per atom of the pure Pd clusters. The calculated segregation energies indicate that 3d atoms prefer to be in the center of core–shell systems.

Uncovering the structural, electronic and vibrational properties of atomically precise PdmCun clusters and their interaction with CO2 molecule.

In this work, we address the structural stability, electronic properties and effect of metal-metal interaction on Raman spectra of icosahedral (Ih) PdmCun (m+n=13) clusters using first principles calculations based on dispersion-corrected density functional theory (DFT-D2). Initially, we investigated the relative stability of Ih PdmCun clusters over monometallic Ih Pd13 and Cu13 clusters by calculating the average binding energy per atom, mixing energy, second order energy difference and average bond length. The Ih Pd5Cu8 is the most stable bimetallic cluster with the 2.88eV, -0.218eV and 0.678eV average binding energy per atom, mixing energy and second order energy difference, respectively. The main goals of the present study are to figure out the chemical enhancement, modulation in electronic properties and Pd-Cu bond length in Ih PdmCun clusters after systematic doping of Cu-atom. Further, to examine the doping effect of Cu atom in Pd cluster, we have also analysed the Raman spectra of Ih PdmCun clusters. In case of Ih Cu13 cluster, the contraction of Cu-Cu bond length as compared to its bulk form resulted in a significant blue-shift of characteristic Raman peak (212cm-1) of Ih Pd13 cluster. Finally, the interaction mechanism of the CO2 gas molecule over Pd-Cu alloy clusters have also been studied to understand the effect of composition on reactivity of CO2 gas molecule.

Pd-catalyzed decarbonylation of furfural: Elucidation of support effect on Pd size and catalytic activity using in-situ XAFS

Palladium (Pd) clusters on zirconia (ZrO2) and single Pd atoms on ceria (CeO2) exhibited high catalytic activity and selectivity for decarbonylation of furfural to furan without additives in the liquid phase. To study the active size of Pd and changes in chemical states or structures during the reaction, in-situ X-ray absorption fine structure (XAFS) measurements were conducted. The size of Pd clusters consisting of less than 10 Pd atoms was maintained on ZrO2 during the reaction. In contrast, single Pd atoms were aggregated during heating and only Pd clusters consisting of 13 atoms were present after the reaction. According to the in-situ XAFS results, the size of Pd particles did not gradually increase to Pd13 clusters. Instead, Pd13 clusters were partly formed from the beginning of the reaction, and the proportion of Pd13 clusters increased with time while keeping the size of Pd13 clusters. This result suggests that a single Pd atom is inactive, but Pd clusters are active for decarbonylation. Ab-initio calculation revealed that ZrO2 (1 1 1) surface had lower adsorption and migration energies than CeO2 (1 1 1), implying that Pd was easily diffused on the surface and stabilized as small Pd clusters.

NO adsorption and dissociation on palladium clusters: The importance of charged state and metal doping

The NO adsorption and dissociation on neutral, charged and Ni-doped Pd13 clusters were studied by using density functional calculations. Our results revealed that NO always prefers to adsorb on the hollow site rather than the top or bridge sites. However, the charge state and Ni doping remarkably influence NO adsorption energy, dissociation barrier and reaction energy. The reaction on Pd13− has the lowest energy barrier and largest reaction energy. The Hirshfeld charge analysis discloses that the origin of the catalytic activity difference is the charge transfer from clusters to NO in the metastable NO adsorption state.

H2 Reactions on Palladium Clusters

Adsorption of an H2 molecule on Pd(N) clusters (N = 2-4, 7, 13, 19, and 55) is investigated using density functional theory with the hybrid PBE0 functional. Low-energy Pd(N) isomers, taken from a large pool of candidate structures for all cluster sizes (except N = 55), are used in systematic searches for the most stable Pd(N)H2 (molecular) and Pd(N)2H (dissociative) adsorption complexes. Molecular adsorption of H2 is found to occur strictly at atop sites, with the strongest binding typically occurring at the site with the smallest coordination. Binding of dissociated H atoms occurs preferentially on 3-fold faces and on certain favorable edge sites, while binding at atop sites is unstable. Dissociative adsorption is energetically preferred to molecular adsorption for all cluster sizes. The dissociative adsorption energy decreases with cluster size, with pronounced variations due to cluster size effects for the smallest clusters. Adsorption reaction pathways are computed for cluster sizes up to N = 13. Molecular adsorption is found to be barrierless in all cases. Dissociative adsorption occurs without a barrier for the pathways studied for N = 7 and 13 and with a small barrier on the smaller clusters. Finally, lowest-energy pathways for the migration of a dissociated hydrogen atom between local minima on a cluster surface are computed for the Pd4, Pd7, and Pd13 clusters. Calculated migration barriers range from 0.05 to 0.25 eV.

Magnetostructural effects in ligand stabilized Pd13 clusters: a density functional theory study

We show computationally that ligation allows tuning of the magnetostructural properties of the Pd(13) cluster. The bare, phosphine and thiol capped clusters were investigated at the density functional level. The most stable conformers of the bare cluster are of high spin, septet and nonet and of distorted C(3v), C(s) and I(h) geometries. Ligation stabilizes the I(h) geometry and quenches the high spin states, down to a triplet for Pd(13)(PH(3))(12) and to a quintet for Pd(13)(SCH(3))(12).The influence of the two capping systems on the magnetostructural properties of the ligated clusters is analyzed in connection with their different bonding properties. The mixed ligand species Pd(13)(SCH(3))(6)(PH(3))(6) is also characterized. Due to the multiple energetically accessible spin states, unusual thermal behaviour of the average magnetic moment is predicted for these clusters.

Atomic structure of Pd n (4 ≤ n ≤ 15) nanoclusters

The results of molecular dynamics simulation of the process of atom-by-atom growth of palladium nanoparticles are presented. The structures obtained for the Pdn clusters agree well with the results of the first-principles calculations. The low-symmetry atomic configurations for the structure of the Pd4 and Pd13 clusters have been obtained using the semiempirical potentials of the interatomic interaction for the first time.

Sequential H&lt;SUB&gt;2&lt;/SUB&gt; Chemisorption and H Desorption on Icosahedral Pt&lt;SUB&gt;13&lt;/SUB&gt; and Pd&lt;SUB&gt;13&lt;/SUB&gt; Clusters: A Density Functional Theory Study

We present a density functional theory (DFT) study on the sequential H-2 dissociative chemisorption and H desorption on icosahedral Pt-13 and Pd-13 clusters. The coverage dependence of the sequential adsorption and desorption energies are given along with the charge transfer from metals to H. At low H coverage, the dissociation takes place at an atop site before diffusion redistributes the atoms to well-separated edge sites. At higher coverage, the edge sites become filled and the cluster undergoes a structure-transition from icosahedral to an fcc-like structure (these transitions occur at 10 H atoms for Pt-13 and 24 H atoms for Pd-13). Upon further H loading, the dissociated H atoms may reside at the cluster surface or be pulled inside to interact with the core metal atom. Ab initio molecular dynamics simulation and bond-distance distribution analysis shows that H-saturation occurs at 44 H atoms for Pt-13 and 30 H atoms for Pd-13. The calculated H-2 dissociative chemisorption energy and H desorption energy at saturation is 0.90 eV and 2.02 eV for Pt-13, and 0.76 eV and 2.04 eV for Pd-13, respectively. These values are comparable with what was reported for smaller close-packed clusters, which suggests that the catalytic performance of these transition metal clusters may not vary significantly with particle size or shape but instead depends primarily on the available surface metal atoms which can be accessed by H atoms.

Hydrogen adsorption and desorption on the Pt and Pd subnano clusters — a review

In this review, we present our recent first principles studies on the sequential H2 dissociative chemisorption and H desorption on the Ptn and Pdn clusters (n=2–9, 13). Upon full saturation by H atoms, the calculated H2 dissociative chemisorption energy and H desorption energy on Pt13 and Pd13 clusters are similar to the corresponding values on smaller close-packed clusters. Indeed, the catalytic performances of these subnano clusters do not vary significantly with the particle sizes or shapes. Instead, they are dependent on the surface metal atoms which can be accessed by H atoms. In addition to the coverage dependency of the H2 dissociative chemisorption and H sequential desorption energies, the phase transition of both Pt13 and Pd13 from the icosahedral to fcc-like structures at certain H coverage was also investigated.

Lyapunov exponent as an indicator of phase transition in melting Pd13 clusters

In this study, the chaotic behaviour of Pd13 clusters is investigated in a wide total energy range. To identify interactions between atoms, the embedded atom potential is used in the computer simulation. Various analyses including power spectra, maximal Lyapunov exponents (λ) and rms bond-length fluctuations (δ) are carried out to identify the characteristics of the system. As a result of these analyses, it is observed that Lyapunov spectra can clearly indicate the co-existence region for Pd13 clusters and exponents have fixed values above a certain total energy value of the system. In addition, while the fast Fourier transforms give the existence of diffusive motion above the transitional region, the correlation dimension values exhibit a smooth character relevant to the total energies of the system.

Spontaneous dispersion of PdO and generation of metal Pd cluster in zeolites studied by means of in situ DXAFS

Spontaneous dispersion and clustering processes of Pd were measured by means of energy-dispersive XAFS. The spontaneous dispersion of bulky metal Pd into highly dispersed PdO was directly observed on the H-type zeolite in the atmosphere of O2. Various clustering processes of metal Pd was observed over different kind of zeolite supports. The selective formation of Pd6 and Pd13 clusters were found over H-ZSM-5, H-Mordenite and H-Y supports, respectively. It was concluded that the crystal structure and acid sites of zeolites had significant influences on the dynamic behavior and the genesis of Pd clusters.

Energy-Dispersive XAFS Studies on the Spontaneous Dispersion of PdO and the Formation of Stable Pd Clusters in Zeolites

Spontaneous dispersion and clustering processes of Pd were measured by means of the energy-dispersive EXAFS method. The spontaneous dispersion of bulky metal Pd into highly dispersed PdO was directly observed on the H-type zeolite in the atmosphere of O2. In contrast to H-type zeolites, simple oxidation of the agglomerated Pd was observed on Na-ZSM-5. The structural change of Pd was followed in the atmosphere of hydrogen. The clustering processes of metal Pd depended on the kind of zeolite, and these were categorized into three groups. The first group, i.e., Na-ZSM-5 and H-beta, showed monotonic agglomeration of metal Pd by increasing the reduction temperature. The second group consisted of H-ZSM-5 and H-mordenite where the formation of Pd6 clusters was found. On these zeolites, the generation of Pd6 clusters was reversibly observed upon the repetition of reduction and oxidation treatments. The third group consisted of H-Y and USY zeolites where the formation of Pd13 clusters was observed. From these findings, it was concluded that the crystal structure and acid sites of zeolites had profound influences on the dynamic behavior and the genesis of Pd clusters with various structures.