Pt4 Cluster Research Articles

Dynamics of Oxidation of Reduced Forms of CO2 under Electrochemical and Open-Сircuit Conditions on Polycrystalline Pt in H2CO3

The problem of identifying correlations between catalytic and electrocatalytic processes is one of the fundamental problems of catalysis among “simple” organic substances, and the oxidation of CO and rCO2 is of great interest, since CO and CO2 are considered in pairs both during catalytic and electrocatalytic transformations. In the case of electrocatalysis, this analysis is important in the study of fuel cells. In this paper, we studied the correlation between the oxidation of reduced forms of CO2 (rCO2) under potentiodynamic-galvanoctatic electrochemical and open-circuit conditions of measurements on polycrystalline (pc)Pt in H2CO3. Periodic oscillations are revealed at the oxidation of Had and rCO2 on (pc)Pt. Quantum chemical calculations were carried out on the Pt13 cluster in order to identify the mechanisms of the rCO2 oxidation reaction. The correspondence in the energy parameters of the oxidation process of rCO2 under open-circuit conditions and electrochemical conditions is shown. The preliminary analysis of the system using density functional (DFT) calculations is carried out and the most stable systems that are based on Pt13 are found, namely rOH-Pt13-(CO)n, rOH-Pt13-(COH) and rOH-Pt13-(rCOOH). OH• species was chosen as the most likely candidate for the role of the oxidant for rCO2. Preliminary calculations for the expected reactions were carried out, and the optimal PES is revealed.

Influence of platinum cluster size on reactivity in the process of obtaining ethane from methane

The paper shows the influence of platinum cluster size on reactivity in the process of obtaining ethane from methane. The enthalpy of activation and geometric parameters of intermediates and transition state for the stage of methane activation on an Al6O9 substrate, As well as geometric parameters of clusters used in calculations of the mechanism of ethane formation from methane have been presented. The alumina was chosen as the substrate material since experimental data indicate that it stabilizes platinum nano clusters. Our calculations confirm this. Upon the adsorption of Pt4 and 3Pt6 clusters on the Al6O9 substrate, the energy of the system decreases by 242.5 and 421.7 kJ/mol, respectively, which is higher than the energies with which we will operate in the future, this is an indicator that the clusters formed on the Pt4Al6O9 and Pt6Al6O9 substrate are stable.

A Pt3 cluster anchored on a C2N monolayer as an efficient catalyst for electrochemical reduction of nitrobenzene to aniline: a computational study

A Pt3 cluster anchored on h-C2N exhibits ultra-high catalytic activity towards nitrobenzene reduction with a small limiting potential (−0.19 V).

Structure Matters – Direct In‐situ Observation of Cluster Nucleation at Atomic Scale in a Liquid Phase

AbstractThe formation of almost all solid crystalline materials starts with a nucleation reaction, where a handful of atoms come together to form the initial crystal seed, which then grows to a larger crystal. Thus, understanding and controlling nucleation is essential for the synthesis and manufacturing of most material systems, especially nanomaterials. Despite this, little is known from direct experimental observations about the initial steps of nucleation, the formation of sub‐nanometer sized clusters. Here, we directly study the atomic nucleation reactions of such sub‐nm clusters of Pt in‐situ in a liquid phase. We do this by inducing nucleation in suspended nanofilms and supported nanodroplets of an ionic liquid (1‐butyl‐3‐methyl imidazolium chloride, 5–50 nm thickness), which is observed at atomic resolution by scanning transmission electron microscopy. We can observe Pt atoms to nucleate into few‐atom clusters, which coalesce and grow into cluster agglomerates or nanoparticles, or redissolve. When comparing nucleation in nanofilms and carbon‐supported nanodroplets, nucleation is rarely observed in nanofilms, while easily observable at high nucleation rate in nanodroplets. This is due to the presence of the pre‐existing liquid‐solid interface, resulting in heterogeneous nucleation in the nanodroplets while there is only homogeneous nucleation in the nanofilms. Ultimately, our results show that the nucleation pathways of nanoparticles are not just determined by the local chemical environment, but are also influenced by size and structure of the initially formed clusters.

Mechanism study on CO2 reforming of methane over platinum cluster doped graphene: A DFT calculation

Dry (CO2) reforming of methane is an important reaction in environmental catalysis, which can both reduce the greenhouse gas content and utilize syngas production. Density functional theory (DFT) calculations were carried out to investigate the reaction mechanism of CO2 and CH4 on Pt4 cluster doped single-vacancy graphene (Pt4/SV) catalyst. The adsorption configurations are optimized in advance to determine the initial states and final states in reactions. Then, the detailed reaction pathways for CH4 decomposition, CO2 activation, and CH/C oxidation were systematically investigated. In the process of CH4 decomposition, the stage from CH to C+H appears to be the rate-determining step. And the prior reaction pathway of CO2 activation may be CO2*→CO* + O*. In the process of CH/C oxidation, CH* + O*→CHO* + *→CO* + H* and C* + O*→CO* + * appear to be easier to occur. Finally, thermodynamic and kinetic analysis for CH/C oxidation is carried out to consider the temperature effect and reaction rate. This work gives a deep investigation of the CO2 reforming of methane on Pt4/SV from the theoretical perspective. It helps to develop the reliable catalyst which has low carbon deposition and high activity.

Effects of composition on catalytic activities of molybdenum doped platinum nanoparticles.

The physical and chemical properties of bimetallic nanoparticles can be optimized by tuning the particle composition. In this study, we identified CO adsorption and dissociation energetics on five Pt-Mo nanoparticles at different concentrations, the lowest energy Pt7, Pt6Mo, Pt5Mo2, Pt4Mo3, and Mo7 clusters. We have shown that the CO adsorption and dissociation energies and preferred CO adsorption sites are largely dependent on the composition of the nanoparticles. As the Mo concentration increases, the strength of the C-O internal bond in the adsorption complex decreases, as indicated by a decrease in the C-O stretching frequency. Also, more Mo sites in the nanoparticle become available for CO adsorption, and the preferred CO adsorption site switches from Pt to Mo. For these reasons, dissociation of CO is energetically favorable on Pt4Mo3 and Mo7. On both compositions, we have shown that the dissociation paths begin with CO adsorbed on a Mo site in a multifold configuration, in particular in a tilted configuration. These findings provide insight on the effects of the composition on the chemical and catalytical properties of Pt-Mo nanoparticles, thereby guiding future experiments on the synthesis of nanoparticles, especially those that may be suitable for various desired applications containing CO.

A Ti-MOF Decorated With a Pt Nanoparticle Cocatalyst for Efficient Photocatalytic H2 Evolution: A Theoretical Study.

Pt nanoparticles (NPs) are often used as cocatalysts to enhance the photocatalytic hydrogen production catalyzed by the metal organic framework (MOF) materials. The catalytic efficiency of many Pt/MOF systems can be greatly improved when Pt NPs are used as cocatalysts. In this work, the Pt/20%-MIL-125-(SCH3)2 was chosen as the template material to understand the functional role of a Pt metal cocatalyst in the catalytic process. Experimentally, the catalytic activity of Pt/20%-MIL-125-(SCH3)2 is more than 100 times that of the system without the help of Pt NPs. Firstly, we proposed a searching algorithm, which is based on the combined Monte Carlo (MC) method and principal component analysis (PCA) algorithm, to find that the most probable adsorption site of the Pt13 nanocluster loaded on the (001) surface of 20%-MIL-125-(SCH3)2. Next, by using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, we revealed that the accumulation of some positive charges on the Pt13 cluster and proton adsorbed on the Pt13 cluster, which can promote the separation of photogenerated electrons and holes, thus improving the photocatalytic efficiency. This work not only provides a method to obtain the adsorption configuration of metal clusters on various MOFs but also provides a new insight into increasing photocatalytic efficiency for H2 production in Pt/MOF systems.

Reagent-Triggered Isomerization of Fluxional Cluster Catalyst via Dynamic Coupling.

Metallic cluster catalysts have many thermodynamically accessible isomers with diverse active sites and low reaction barriers, and lately a strong hypothesis emerged that the many catalyst states collectively drive the catalysis. However, it remained a hypothesis that catalyst isomerization is actually kinetically feasible under the current reaction conditions. Using high-temperature dynamics simulations and sampling, a range of orientations, and vibrational energy distributions, we probe how thermal effects and molecular events affect cluster catalyst dynamics. We show that even such a delicate affair as the dissociation or scattering of a methane molecule on the heavy and thus slow Pt13 cluster triggers substantial isomerization of the catalyst, far beyond thermal at 700 K. A kinetic coupling between the methane activity and cluster catalyst dynamics is observed. In return, the thermal dynamics of the cluster affects the methane reaction and scattering probabilities. Hence, molecular events at the surfaces of fluxional cluster catalysts should facilitate the population of an ensemble of catalyst states under the current reaction conditions, with implications for available active sites, reaction mechanisms, and apparent rates.

CO2 hydrogenation to formic acid over platinum cluster doped defective graphene: A DFT study

The hydrogenation of CO2 to formic acid is an important reaction in environmental catalysis, which can both alleviate the greenhouse effect and produce useful chemicals. Platinum element catalysts need to be investigated to realize large-scale development due to the expensive and scarce features. In this work, CO2 hydrogenation to formic acid over Pt4 cluster doped single-vacancy graphene was investigated using density functional theory. Catalyst configuration was optimized to perform corresponding gas adsorption and reduction reaction. Four reaction pathways were explored according to the reaction mechanism of Langmuir-Hinshelwood (L-H), Eley-Rideal (E-R) and termolecular Eley-Rideal (TER). Kinetic analysis was used to evaluate the reaction rate of different processes under the given temperature range, and the potential effect of CO molecule was also considered to better understand the feasibility. Results showed that Pt4/SV was a stable and high activity catalyst. The minimum activation energy among different pathways was 0.56 eV and TER could be the dominant reaction mechanism of CO2 hydrogenation. This work not only provides a promising catalyst but also gives a more deep understanding of CO2 reduction technology and the future applicability of platinum metal catalysts.

Structures, stabilities and electronic properties of Pt-Rh clusters based on DFT and Sutton-Chen potential

Using the density functional theory (DFT) at meta-generalized gradient approximation (meta-GGA) exchange-correlation TPSSTPSS functional with LANL2DZ pseudopotential, the variations of the geometric structures, stabilities and electronic properties with the changes of n and m of PtnRhm (n + m ≤ 6) clusters are systematically investigated. Clusters with higher nuclearity favor three dimensional structure while clusters with low nuclearity (n + m < 4) and Pt6 cluster favor planar two dimensional configuration. The results for various properties including average binding energies per atom, the second-order difference of energies, HOMO-LUMO gap, vertical ionization potentials, vertical electron affinities, and chemical hardness are evaluated as a function of size of the system. It is found that Pt3Rh2 and Pt5Rh clusters possess stronger stability. Furthermore, Sutton-Chen potential is applied to study the stable structures of 38- and 55-atom Pt-Rh clusters by using adaptive immune optimization algorithm. Structural characteristic and relative stability are discussed.

Sn-modification of Pt7/alumina model catalysts: Suppression of carbon deposition and enhanced thermal stability.

An atomic layer deposition process is used to modify size-selected Pt7/alumina model catalysts by Sn addition, both before and after Pt7 cluster deposition. Surface science methods are used to probe the effects of Sn-modification on the electronic properties, reactivity, and morphology of the clusters. Sn addition, either before or after cluster deposition, is found to strongly affect the binding properties of a model alkene, ethylene, changing the number and type of binding sites, and suppressing decomposition leading to carbon deposition and poisoning of the catalyst. Density functional theory on a model system, Pt4Sn3/alumina, shows that the Sn and Pt atoms are mixed, forming alloy clusters with substantial electron transfer from Sn to Pt. The presence of Sn also makes all the thermally accessible structures closed shell, such that ethylene binds only by π-bonding to a single Pt atom. The Sn-modified catalysts are quite stable in repeated ethylene temperature programmed reaction experiments, suggesting that the presence of Sn also reduces the tendency of the sub-nano-clusters to undergo thermal sintering.

The growth pattern of Ptn (n = 1–6) clusters on pentagonal B2C monolayer support: A computational study

Using dispersion-corrected density functional theory (DFT-D), we systematically investigated the growth pattern of small platinum (Pt) clusters on pentagonal B2C (penta-B2C). Firstly we calculated the bonding energy of the single Pt atoms on (2 × 2), (3 × 3) and (4 × 4) penta-B2C supercells, and chose (3 × 3) penta-B2C for the subsequent simulations. Secondly we confirmed that the single Pt atom on penta-B2C is stable. And then we stepwise investigated the growth pattern of Pt clusters. The result indicates that the Pt1, Pt2 and Pt4 clusters on penta-B2C are stable, and the single Pt atom on penta-B2C is the most stable structure. Based on the analysis of the electronic structure and the frontier molecular orbitals, the Pt1, Pt2 and Pt4 clusters on penta-B2C have the potential to be used as the efficient catalysts.

A comparative study of CO preferential oxidation over Pt and Pt0.5Co0.5 nanoparticles: Kinetic study and quantum-chemical calculations

CO preferential (PROX) and total (TOX) oxidation were studied over Pt and Pt0.5Co0.5 nanopowders. Pt0.5Co0.5 exhibited much higher CO PROX performance than Pt, being highly active and selective at 0–80 °C. Low-temperature activity in CO oxidation was shown to be the key feature of bimetallic Pt-Co catalysts in comparison with monometallic Pt. Density functional theory calculations of the oxidation of CO on Pt13 and Pt12Co clusters revealed that a better catalytic activity of bimetallic cluster is due to an electronic effect: the calculated atomic charges on platinum atoms change when cobalt is introduced into its composition.

TiN and TiC as stable and promising supports for oxygen reduction reaction: Theoretical and experimental study

Instability of catalyst supports is a primary reason for energy loss in proton exchange membrane fuel cells. In this study, Pt/TiN and Pt/TiC catalysts were synthesized by a solvothermal process. Density functional theory calculations revealed smaller distortion energies of Pt13 cluster and larger interaction between the Pt-TiN and Pt-TiC systems. The partial density of state calculations demonstrated that the Pt-d and C-p states and Ti-d and N-p states are energetically favorable and allow Pt-C-Ti and Pt-N-Ti to strongly bind to the TiC or TiN supports. As a result, Pt/TiN and Pt/TiC showed excellent durability as electrocatalysts.

Effect of Tunneling-Assisted Intersystem Crossing on the Magnetic Behavior of the Pt13 Cluster

We show the existence of a dynamic spin equilibrium introduced by intersystem crossing (ISC) between several spin multiplicity states in the Pt13 cluster. Employing weak-coupling transition probabilities, nonadiabatic transition state theory, and density functional theory, we obtain rate constants for each spin transition and, from these results, we find the equilibrium populations as a function of temperature for each state. At very low temperatures, neither ground-state calculations nor Maxwell–Boltzmann distributions are able to reproduce the experimental magnetic moment of Pt13. The origin of such differences, as transition probabilities show, is attributed to tunneling and zero-point energy-assisted ISC, producing mixed spin vibronic states, and to the large orbital contribution to the magnetic moment confirmed by simulated X-ray magnetic circular dichroism. At low temperatures, these physical processes provide the transition mechanism, whereas as temperature increases, quantum effects are less important, and thermal hopping becomes the predominant path. These results reproduce the experimental magnetic moment found in Pt13 and may explain the origin of anomalous magnetic properties on small metallic clusters.

The composition effect for the thermal properties of PdnAg(42-n)Pt13 ternary nanoalloys: a molecular dynamics study

ABSTRACTIn this study, the classical molecular dynamics simulations in canonical ensemble conditions (NVT) were used to investigate the dynamical properties of trimetallic Pd–Pt–Ag nanoalloy clusters with the interatomic interactions modelled by the Gupta many-body potential. The optimisations for best homotops were performed using the basin-hopping algorithm for 55 atom icosahedral PdnAg(42-n)Pt13 trimetallic clusters. We performed optimisations to search the best chemical ordering of icosahedron structure not allowing any geometric changes. The icosahedron structures which are the best homotops have a core-shell segregation. The obtained icosahedral structures with best homotops were taken as the initial configurations for MD simulations. The temperature ranges were explored which the surface sites of the clusters stay thermally stable. We estimated the melting temperatures of PdnAg(42-n)Pt13 trimetallic clusters using caloric curves and Lindemann parameters. No simple correlation between alloy composition and melting temperatures was determined. The Pd35Ag7Pt13 composition has the highest melting temperature, however, the Pd21Ag21Pt13 is the most stable composition according to the relative stability investigation. The simulation results showed that the melting of all PdnAg(42-n)Pt13 clusters takes place as a whole without any surface premelting.

Preparation of Size- and Composition-Controlled PtnSnx/SiO2 (n = 4, 7, 24) Bimetallic Model Catalysts with Atomic Layer Deposition

Model catalysts prepared by mass-selected cluster deposition are useful in fundamental studies, but for bimetallic clusters, a precise selection of both size and composition can be difficult except for very small clusters. We discuss an alternative method for preparing bimetallic PtSn model catalysts, in which size-selected Pt4, Pt7, and Pt24 clusters, deposited on SiO2 and then hydrogenated, are used to seed selective addition of Sn by a self-limiting reaction with SnCl4. Catalysts are characterized using X-ray photoelectron spectroscopy, ion scattering spectroscopy, and CO temperature-programmed desorption, and structures are calculated by plane-wave density functional theory. It is found that Sn deposition saturates at a relatively low SnCl4 exposure, indicating that the reaction is self-limiting, and that nonselective Sn deposition on the SiO2 support is ∼40 times less efficient than Sn deposition on hydrogenated Pt cluster sites. The resulting PtnSnx stoichiometry is near 1:1 for Pt4 and Pt7, cluster...

The Role of Cu in Adsorption of O2 and CO Molecules on the Pt12Cu Cluster

Using density functional theory method, we have studied O2 and CO molecules adsorption on the Pt13 and Pt12Cu clusters, respectively. Analysis of the adsorption energies, O–O bond length, and natural bond orbital (NBO) charge indicates that the copper doping plays an important role in the enhanced reduction of O2 molecule in low temperature fuel cells (LTFCs). On the other hand, contrary to the adsorption of O2 molecule, the calculated adsorption energies, NBO charge and molecular orbitals show that the copper doping significantly weakens the adsorption of the CO molecule, indicating that the Cu-doped Pt catalyst is resistant to CO poisoning in the LTFCs. Our studies provide an important clue to understand the catalytic mechanism of platinum copper alloy catalysts in the LTFCs.

Properties of Isolated and TiO2(110) Supported Pt13 Clusters: A Theoretical Study

Metallic subnanoparticles deposited over supports such as TiO2 play an important role for the design of model catalysts for heterogeneous catalysis applications. In this work we study the structure and energetic of Pt13 clusters deposited on TiO2(110) surfaces, using an ab initio DFT + U modeling method. We first examine the structural and dynamical stability of the isolated Pt13 nanoclusters by considering as initial configurations symmetrical Ih and Oh structures and new layered isomers. We determine their equilibrium geometries, cohesive energies, magnetic moments, electronic and vibrational density of states. The analysis of the vibrational modes reveal that the Oh and Ih structures are dynamically unstable unlike the layered structures that have lower energies. We then examine the Pt13-titania system to characterize the cluster/substrate interaction for both the stoichiometric and reduced surfaces. We characterize different aspects of the metal-oxide interaction by determining their equilibrium geometries, adsorption energies, charge transfer effects and electronic density of states. We find that the Pt13 cluster suffers a strong restructuration when adsorbed on the surface, it deforms towards increasing the interaction of the platinum atoms with the surface, leading to a high value of the adsorption energy and getting oxidized. The Pt13-rutile system is semiconductor; for the stoichiometric system a localized state in the band gap is predicted. The calculated surface oxygen vacancy formation energy is prefered by the cluster deposition as a fact that favours the use of this system in the CO oxidation reactions from a surface oxygen, an important step in the water gas shift reaction.

Ammonia borane dehydrogenation tendencies using Pt4, Au4, and Pt2Au2 clusters as catalysts

Small metallic clusters -mediated gas phase catalysis studies give lights to understand simple and complex catalytic processes, and help in the discovery and explanation of non-traditional “molecular-scale” catalytic systems. In this framework and in the context of clean energy sources based on hydrogen, a comparative study about ammonia borane (AB = NH3BH3) dehydrogenation tendencies, using Pt4, Au4, and Pt2Au2 clusters as catalysts, is made. Molecular details on thermal, kinetic (mechanistic) and reactivity factors are revealed. Our results indicate that all the metal tetramers studied here tends to dehydrogenate the ammonia borane molecule, being the processes exothermic, exergonic and fast. Among the studied catalysts, Pt2Au2 shows the best results, because is capable of easily detach several hydrogen atoms, with high probability of taking them out simultaneously, both from B and N, which helps in avoiding the breakage of B–N bond of AB, what is known to produce the poisoning of the catalyst by ammonia generation.