Stability Of Pt Clusters Research Articles

A density functional theoretical study on the stability of Pt clusters in MOF-808.

Metal organic framework (MOF)-encapsulated metal clusters have shown superior catalytic activity due to geometric and electronic properties of metal clusters, which are largely determined by adsorption sites and sizes and morphologies of encapsulated metal clusters. In the present work, anchoring sites, the stability, and the agglomeration probability of Ptn (n = 1-23) clusters over an MOF-808 framework structure were studied using density functional theory calculations and ab initio molecular dynamics simulation. It has been found that Ptn (n = 1-7) clusters bind more strongly at the Zr6 metal node sites than at the interface and linker sites. Upon adsorption, significant amounts of electrons (+0.92 to +1.96 |e|) are transferred from Ptn clusters to the MOF framework. The agglomeration of single Pt1 atoms at the Zr6 metal node to form a Ptn cluster is unlikely, while the agglomeration at the interface or the linker is energetically feasible. Compared with the single Zr6 node, the bonding of Ptn clusters with two Zr6 metal nodes is weaker, with less electron (+0.12 to +0.89 |e|) transfer. Finally, our calculations show that CO adsorption at the single Pt atom is stabilized at the interface site, preventing its further agglomeration with Ptn clusters between the two Zr6 metal nodes.

The Structure of Sub‐nm Platinum Clusters at Elevated Temperatures

AbstractLittle is known about metallic clusters consisting merely of a dozen of atoms or even less, despite of their importance in catalysis and crystal nucleation. Scanning transmission electron microscopy (STEM) provides direct atomic structure information but has inherently suffered from limited time resolution. We employ fast dynamic STEM combined with a spatio‐temporal image denoising algorithm to explore the structure and stability of Pt clusters on carbon, which represents a highly relevant catalysis system. At room temperature, dynamic amorphous 2D structures are found, while above ≈300 °C, the clusters transform into a crystalline state. Our experimental and theoretical data reveal an unexpected strong trend of the crystalline clusters to exhibit the face‐centered cubic, bulk structure of Pt with cuboidal geometries being most prominent.

The Structure of Sub-nm Platinum Clusters at Elevated Temperatures.

Little is known about metallic clusters consisting merely of a dozen of atoms or even less, despite of their importance in catalysis and crystal nucleation. Scanning transmission electron microscopy (STEM) provides direct atomic structure information but has inherently suffered from limited time resolution. We employ fast dynamic STEM combined with a spatio-temporal image denoising algorithm to explore the structure and stability of Pt clusters on carbon, which represents a highly relevant catalysis system. At room temperature, dynamic amorphous 2D structures are found, while above ≈300 °C, the clusters transform into a crystalline state. Our experimental and theoretical data reveal an unexpected strong trend of the crystalline clusters to exhibit the face-centered cubic, bulk structure of Pt with cuboidal geometries being most prominent.

Thermal stability of Pt nanoclusters interacting to carbon sublattice

The catalytic activity of Pt clusters is dependent not only on the nanoparticle size and its composition, but also on its internal structure. To determine the real structure of the nanoparticles used in catalysis, the boundaries of the thermal structure stability of Pt clusters to 8.0 nm in diameter interacting with carbon substrates of two types: a fixed α-graphite plane and a mobile substrate with the diamond structure. The effect of a substrate on the processes melting of Pt nanoclusters is estimated. The role of the cooling rate in the formation of the internal structure of Pt clusters during crystallization is studied. The regularities obtained in the case of “free” Pt clusters and Pt clusters on a substrate are compared. It is concluded that platinum nanoparticles with diameter D ≤ 4.0 nm disposed on a carbon substrate conserve the initial fcc structure during cooling.

Size dependence of thermal stability of Pt clusters bound to Si substrate surface prepared by cluster impact deposition

Thermal behavior of Pt10 and Pt1 bound to a silicon substrate prepared by the impact of size-selected Pt cluster ions at 1 eV per Pt atom was investigated. Their height and diameter were obtained by statistical analysis of their images using scanning-tunneling microscopy. The Pt10 are stably bound to the Si surface as monatomic-layered Pt10Si x disks with insertion of Si atoms into the clusters at the moment of the impact, and they start to be decomposed between 623 and 673 K under vacuum conditions. The thermal stability of the Pt10Si x disks is comparable to that of a Pt thin film prepared on a Si substrate, but inferior to that of Pt30 disks on the Si substrate. Comparing with thermal behavior of Pt atoms and a PtSi thin film on the Si substrate, it has been concluded that more Si atoms start to diffuse into a Pt10Si x disk between 623 and 673 K, while they do not into a Pt30 disk having a close-packed arrangement of the Pt atoms as high as 673 K, owing to a higher barrier for the Si insertion into the close-packed cluster disk than into the Pt10Si x disk having a longer Pt-Pt internuclear distance.

On the Catalytic Activity of Pt Supported by Graphyne in the Oxidation of Ethanol.

The adsorption of Pt clusters on β- and γ-graphyne (β-GY, γ-GY), graphdiyne (GDY), and graphene (GP) was extensively investigated with density functional theory. Ethanol adsorption and its partial oxidation on the Pt supported by the GY and GP were then explored to address the influence of the supporting materials on the activity of Pt nanoclusters to ethanol oxidation. Among the examined adsorption sites such as the hollow, Csp-Csp, and Csp-Csp2 bonds, the hollow site consisting of multiple triple bonds is the most attractive one to adsorb Pt and Pt4 regardless of β-GY, γ-GY, and GDY. The binding of Pt4 to the GDY is slightly stronger than those of β-GY and γ-GY (binding energy: -3.64, -3.73, and -4.08eV). It is remarkable that the adsorption of Pt4 on GY is 2-3 times stronger than that on GP (-3.6-4.1 vs -1.3 eV), showing that the GY and GDY are better substracts than the GP for the stability of Pt clusters. Furthermore, the potential energy profiles for the oxidation of ethanol show that in spite of the higher energy barrier for the adsorbed ethanol on Pt4 supported by γ-GY than by GP (1.54 vs 1.19eV), the dehydrogenation product and of ethanol on Pt-graphyne is much stabler than that on Pt-graphene, suggesting that graphyne is thermodynamically more favorable than graphene as a subtract for the Pt catalyst.

Electrocatalytic Activity and Stability of Pt clusters on State-of-the-Art Supports: A Review

Instability of supported Pt clusters due to limited bonding with conventional carbon supports and carbon dissolution leads to significant cathode performance losses with time, impeding the development of commercial proton exchange membrane fuel cells. One approach that has recently been gaining momentum is the use of the electrocatalyst support to enhance both the stability and activity of Pt clusters for the oxygen reduction reaction. This review article focuses on four support types: advanced carbons, conductive ceramics, metallic underlayers for Pt monolayer catalysts, and the 3M crystalline organic whiskers. Advantages and disadvantages of each support are summarized and promising future directions for research in this area are discussed.

Stability and lattice contraction of small platinum particles

The structural stability of Pt clusters of cubooctahedral and icosahedral shapes has been analytically studied by taking an approximation based on the second moment of the density of states to calculate the cohesive energy. We show that the predictions of this model are in agreement with the phenomenological ideas of Ino's model and the known experimental results for the transition from cubooctahedral to icosahedral geometrical structure. The agreement between the calculated values for the contraction of the interatomic distance as a function of decreasing size, and very recent experimental results is excellent.