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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Sr2PtAu by Materials Project

Sr2PtAu crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are two inequivalent Sr sites. In the first Sr site, Sr is bonded in a 7-coordinate geometry to three equivalent Pt and four equivalent Au atoms. There are one shorter (3.27 Å) and two longer (3.28 Å) Sr–Pt bond lengths. All Sr–Au bond lengths are 3.25 Å. In the second Sr site, Sr is bonded in a 7-coordinate geometry to four equivalent Pt and three equivalent Au atoms. All Sr–Pt bond lengths are 3.25 Å. All Sr–Au bond lengths are 3.28 Å. Pt is bonded in a 9-coordinate geometry to seven Sr and two equivalent Au atoms. Both Pt–Au bond lengths are 2.87 Å. Au is bonded in a 9-coordinate geometry to seven Sr and two equivalent Pt atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb3Ga9Pt2 by Materials Project

Tb3Pt2Ga9 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are two inequivalent Tb sites. In the first Tb site, Tb is bonded to twelve Ga atoms to form TbGa12 cuboctahedra that share edges with two equivalent GaTb4Ga4Pt4 cuboctahedra and faces with two equivalent TbGa12 cuboctahedra. There are eight shorter (3.17 Å) and four longer (3.22 Å) Tb–Ga bond lengths. In the second Tb site, Tb is bonded in a 10-coordinate geometry to two equivalent Pt and twelve Ga atoms. Both Tb–Pt bond lengths are 3.07 Å. There are a spread of Tb–Ga bond distances ranging from 3.08–3.41 Å. Pt is bonded in a 10-coordinate geometry to two equivalent Tb and eight Ga atoms. There are a spread of Pt–Ga bond distances ranging from 2.59–2.83 Å. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded to four equivalent Tb, four equivalent Pt, and four equivalent Ga atoms to form GaTb4Ga4Pt4 cuboctahedra that share edges with two equivalent TbGa12 cuboctahedra and faces with two equivalent GaTb4Ga4Pt4 cuboctahedra. All Ga–Ga bond lengths are 2.73 Å. In the second Ga site, Ga is bonded in a 1-coordinate geometry to four Tb, one Pt, and four Ga atoms. There are a spread of Ga–Ga bond distances ranging from 2.53–2.70 Å. In the third Ga site, Ga is bonded in a 10-coordinate geometry to four Tb, two equivalent Pt, and four Ga atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La2NiPt by Materials Project

La2PtNi crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are two inequivalent La sites. In the first La site, La is bonded in a 7-coordinate geometry to four equivalent Pt and three equivalent Ni atoms. All La–Pt bond lengths are 3.05 Å. There are one shorter (3.07 Å) and two longer (3.16 Å) La–Ni bond lengths. In the second La site, La is bonded in a 7-coordinate geometry to three equivalent Pt and four equivalent Ni atoms. There are two shorter (3.11 Å) and one longer (3.14 Å) La–Pt bond lengths. All La–Ni bond lengths are 3.03 Å. Pt is bonded in a 9-coordinate geometry to seven La and two equivalent Ni atoms. Both Pt–Ni bond lengths are 2.90 Å. Ni is bonded in a 9-coordinate geometry to seven La and two equivalent Pt atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoPt3 by Materials Project

Pt3Mo1 crystallizes in the orthorhombic Pmm2 space group. The structure is three-dimensional. Mo6+ is bonded in a distorted q6 geometry to ten Pt2- atoms. There are a spread of Mo–Pt bond distances ranging from 2.74–2.83 Å. There are three inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded to four equivalent Mo6+ and eight Pt2- atoms to form a mixture of edge, corner, and face-sharing PtMo4Pt8 cuboctahedra. There are a spread of Pt–Pt bond distances ranging from 2.76–2.86 Å. In the second Pt2- site, Pt2- is bonded to four equivalent Mo6+ and eight Pt2- atoms to form a mixture of edge, corner, and face-sharing PtMo4Pt8 cuboctahedra. There are two shorter (2.79 Å) and four longer (2.83 Å) Pt–Pt bond lengths. In the third Pt2- site, Pt2- is bonded to two equivalent Mo6+ and ten Pt2- atoms to form a mixture of edge, corner, and face-sharing PtMo2Pt10 cuboctahedra. Both Pt–Pt bond lengths are 2.79 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoPt by Materials Project

PtMo crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are three inequivalent Mo2+ sites. In the first Mo2+ site, Mo2+ is bonded in a 8-coordinate geometry to eight Pt2- atoms. There are a spread of Mo–Pt bond distances ranging from 2.78–2.84 Å. In the second Mo2+ site, Mo2+ is bonded to eight Pt2- atoms to form distorted MoPt8 hexagonal bipyramids that share corners with eight PtMo8Pt4 cuboctahedra, corners with eight equivalent MoPt8 hexagonal bipyramids, corners with four equivalent MoPt6 octahedra, edges with twelve PtMo8Pt4 cuboctahedra, edges with four equivalent MoPt6 octahedra, faces with two equivalent PtMo6Pt6 cuboctahedra, and faces with four equivalent MoPt6 octahedra. The corner-sharing octahedral tilt angles are 59°. There are a spread of Mo–Pt bond distances ranging from 2.79–2.84 Å. In the third Mo2+ site, Mo2+ is bonded to six Pt2- atoms to form distorted MoPt6 octahedra that share corners with twelve PtMo8Pt4 cuboctahedra, corners with two equivalent MoPt8 hexagonal bipyramids, corners with seven equivalent MoPt6 octahedra, edges with five PtMo8Pt4 cuboctahedra, edges with two equivalent MoPt8 hexagonal bipyramids, edges with two equivalent MoPt6 octahedra, faces with two equivalent PtMo6Pt6 cuboctahedra, faces with two equivalent MoPt8 hexagonal bipyramids, and a faceface with one MoPt6 octahedra. The corner-sharing octahedra tilt angles range from 3–123°. There are a spread of Mo–Pt bond distances ranging from 2.75–2.84 Å. There are three inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded to eight Mo2+ and four equivalent Pt2- atoms to form PtMo8Pt4 cuboctahedra that share corners with six equivalent PtMo8Pt4 cuboctahedra, corners with four equivalent MoPt8 hexagonal bipyramids, corners with four equivalent MoPt6 octahedra, edges with eight equivalent PtMo6Pt6 cuboctahedra, edges with two equivalent MoPt8 hexagonal bipyramids, edges with two equivalent MoPt6 octahedra, and faces with twelve PtMo8Pt4 cuboctahedra. The corner-sharing octahedral tilt angles are 32°. All Pt–Pt bond lengths are 2.78 Å. In the second Pt2- site, Pt2- is bonded to six Mo2+ and six Pt2- atoms to form PtMo6Pt6 cuboctahedra that share corners with fourteen PtMo6Pt6 cuboctahedra, corners with two equivalent MoPt8 hexagonal bipyramids, corners with six equivalent MoPt6 octahedra, edges with eight PtMo8Pt4 cuboctahedra, edges with three equivalent MoPt8 hexagonal bipyramids, edges with four equivalent MoPt6 octahedra, faces with eight PtMo8Pt4 cuboctahedra, a faceface with one MoPt8 hexagonal bipyramid, and faces with two equivalent MoPt6 octahedra. The corner-sharing octahedra tilt angles range from 58–91°. There are a spread of Pt–Pt bond distances ranging from 2.81–2.86 Å. In the third Pt2- site, Pt2- is bonded to eight Mo2+ and four equivalent Pt2- atoms to form PtMo8Pt4 cuboctahedra that share corners with fourteen PtMo6Pt6 cuboctahedra, corners with eight equivalent MoPt6 octahedra, edges with four equivalent PtMo6Pt6 cuboctahedra, edges with four equivalent MoPt8 hexagonal bipyramids, and faces with twelve PtMo8Pt4 cuboctahedra. The corner-sharing octahedra tilt angles range from 61–119°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf2Pt3 by Materials Project

Hf2Pt3 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Hf is bonded in a 9-coordinate geometry to nine Pt atoms. There are a spread of Hf–Pt bond distances ranging from 2.76–2.96 Å. There are two inequivalent Pt sites. In the first Pt site, Pt is bonded in a distorted body-centered cubic geometry to eight equivalent Hf atoms. In the second Pt site, Pt is bonded in a 10-coordinate geometry to five equivalent Hf atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiPt by Materials Project

PtNi crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded to six equivalent Pt2- and six Ni2+ atoms to form a mixture of distorted face, edge, and corner-sharing PtNi6Pt6 cuboctahedra. All Pt–Pt bond lengths are 2.72 Å. All Pt–Ni bond lengths are 2.63 Å. In the second Pt2- site, Pt2- is bonded to ten equivalent Pt2- and six Ni2+ atoms to form distorted PtNi6Pt10 cuboctahedra that share corners with twelve PtNi6Pt6 cuboctahedra, edges with sixteen PtNi6Pt6 cuboctahedra, and faces with sixteen equivalent PtNi6Pt10 cuboctahedra. There are a spread of Pt–Pt bond distances ranging from 2.72–5.44 Å. All Pt–Ni bond lengths are 2.63 Å. There are three inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded in a hexagonal planar geometry to six equivalent Pt2- atoms. In the second Ni2+ site, Ni2+ is bonded in a hexagonal planar geometry to six Pt2- atoms. All Ni–Pt bond lengths are 2.63 Å. In the third Ni2+ site, Ni2+ is bonded in a hexagonal planar geometry to six Pt2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MgPt5 by Materials Project

MgPt5 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. Mg2+ is bonded to twelve Pt+0.40- atoms to form a mixture of edge and face-sharing MgPt12 cuboctahedra. All Mg–Pt bond lengths are 2.82 Å. There are two inequivalent Pt+0.40- sites. In the first Pt+0.40- site, Pt+0.40- is bonded in a distorted water-like geometry to two equivalent Mg2+ atoms. In the second Pt+0.40- site, Pt+0.40- is bonded in a distorted trigonal planar geometry to three equivalent Mg2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U2SnPt2 by Materials Project

U2Pt2Sn crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. there are two inequivalent U sites. In the first U site, U is bonded in a 6-coordinate geometry to six equivalent Pt and four equivalent Sn atoms. There are two shorter (2.86 Å) and four longer (2.97 Å) U–Pt bond lengths. All U–Sn bond lengths are 3.37 Å. In the second U site, U is bonded in a 6-coordinate geometry to six equivalent Pt and four equivalent Sn atoms. There are two shorter (2.84 Å) and four longer (3.03 Å) U–Pt bond lengths. All U–Sn bond lengths are 3.46 Å. Pt is bonded in a 6-coordinate geometry to six U and two equivalent Sn atoms. Both Pt–Sn bond lengths are 3.04 Å. Sn is bonded to eight U and four equivalent Pt atoms to form a mixture of distorted face and corner-sharing SnU8Pt4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y3Ga9Pt2 by Materials Project

Y3Pt2Ga9 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are two inequivalent Y sites. In the first Y site, Y is bonded to twelve Ga atoms to form distorted YGa12 cuboctahedra that share edges with two equivalent GaY4Ga4Pt4 cuboctahedra and faces with two equivalent YGa12 cuboctahedra. There are eight shorter (3.17 Å) and four longer (3.24 Å) Y–Ga bond lengths. In the second Y site, Y is bonded in a 10-coordinate geometry to two equivalent Pt and twelve Ga atoms. Both Y–Pt bond lengths are 3.09 Å. There are a spread of Y–Ga bond distances ranging from 3.09–3.45 Å. Pt is bonded in a 10-coordinate geometry to two equivalent Y and eight Ga atoms. There are a spread of Pt–Ga bond distances ranging from 2.60–2.85 Å. There are three inequivalent Ga sites. In the first Ga site, Ga is bonded to four equivalent Y, four equivalent Pt, and four equivalent Ga atoms to form GaY4Ga4Pt4 cuboctahedra that share edges with two equivalent YGa12 cuboctahedra and faces with two equivalent GaY4Ga4Pt4 cuboctahedra. All Ga–Ga bond lengths are 2.74 Å. In the second Ga site, Ga is bonded in a 1-coordinate geometry to four Y, one Pt, and four Ga atoms. There are a spread of Ga–Ga bond distances ranging from 2.54–2.71 Å. In the third Ga site, Ga is bonded in a 10-coordinate geometry to four Y, two equivalent Pt, and four Ga atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on La4CdPt by Materials Project

La4PtCd crystallizes in the cubic F-43m space group. The structure is three-dimensional. there are three inequivalent La sites. In the first La site, La is bonded in a 3-coordinate geometry to three equivalent Pt and three equivalent Cd atoms. All La–Pt bond lengths are 2.99 Å. All La–Cd bond lengths are 3.64 Å. In the second La site, La is bonded in a distorted bent 150 degrees geometry to two equivalent Pt and two equivalent Cd atoms. Both La–Pt bond lengths are 2.98 Å. Both La–Cd bond lengths are 3.69 Å. In the third La site, La is bonded in a 4-coordinate geometry to two equivalent Pt and two equivalent Cd atoms. Both La–Pt bond lengths are 3.69 Å. Both La–Cd bond lengths are 3.45 Å. Pt is bonded in a 6-coordinate geometry to nine La atoms. Cd is bonded to nine La and three equivalent Cd atoms to form a mixture of distorted corner and face-sharing CdLa9Cd3 cuboctahedra. All Cd–Cd bond lengths are 3.32 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Dy7(TePt)2 by Materials Project

Dy7(PtTe)2 crystallizes in the orthorhombic Imm2 space group. The structure is three-dimensional. there are four inequivalent Dy sites. In the first Dy site, Dy is bonded in a 5-coordinate geometry to two equivalent Pt and three Te atoms. Both Dy–Pt bond lengths are 2.88 Å. There are one shorter (3.13 Å) and two longer (3.21 Å) Dy–Te bond lengths. In the second Dy site, Dy is bonded in a 4-coordinate geometry to three equivalent Pt and one Te atom. There are two shorter (2.87 Å) and one longer (3.18 Å) Dy–Pt bond lengths. The Dy–Te bond length is 3.19 Å. In the third Dy site, Dy is bonded in a 4-coordinate geometry to two equivalent Pt and two equivalent Te atoms. Both Dy–Pt bond lengths are 2.91 Å. Both Dy–Te bond lengths are 3.17 Å. In the fourth Dy site, Dy is bonded in a 3-coordinate geometry to three Te atoms. There are two shorter (3.21 Å) and one longer (3.26 Å) Dy–Te bond lengths. Pt is bonded in a 7-coordinate geometry to seven Dy atoms. There are two inequivalent Te sites. In the first Te site, Te is bonded in a 8-coordinate geometry to eight Dy atoms. In the second Te site, Te is bonded in a 7-coordinate geometry to seven Dy atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Eu5Pt2 by Materials Project

Eu5Pt2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are three inequivalent Eu sites. In the first Eu site, Eu is bonded in a 2-coordinate geometry to three equivalent Pt atoms. There are a spread of Eu–Pt bond distances ranging from 2.99–3.60 Å. In the second Eu site, Eu is bonded to four equivalent Pt atoms to form distorted edge-sharing EuPt4 tetrahedra. There are two shorter (3.09 Å) and two longer (3.10 Å) Eu–Pt bond lengths. In the third Eu site, Eu is bonded in a 3-coordinate geometry to three equivalent Pt atoms. There are a spread of Eu–Pt bond distances ranging from 3.05–3.25 Å. Pt is bonded in a 8-coordinate geometry to eight Eu atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PtAu by Materials Project

PtAu crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Pt2- sites. In the first Pt2- site, Pt2- is bonded to six equivalent Pt2- and six Au2+ atoms to form a mixture of face, edge, and corner-sharing PtPt6Au6 cuboctahedra. All Pt–Pt bond lengths are 2.87 Å. All Pt–Au bond lengths are 2.88 Å. In the second Pt2- site, Pt2- is bonded to ten equivalent Pt2- and six Au2+ atoms to form PtPt10Au6 cuboctahedra that share corners with twelve PtPt6Au6 cuboctahedra, edges with sixteen PtPt6Au6 cuboctahedra, and faces with sixteen equivalent PtPt10Au6 cuboctahedra. There are a spread of Pt–Pt bond distances ranging from 2.87–5.74 Å. All Pt–Au bond lengths are 2.88 Å. There are three inequivalent Au2+ sites. In the first Au2+ site, Au2+ is bonded in a 6-coordinate geometry to six equivalent Pt2- atoms. In the second Au2+ site, Au2+ is bonded in a 6-coordinate geometry to six Pt2- atoms. All Au–Pt bond lengths are 2.88 Å. In the third Au2+ site, Au2+ is bonded in a 6-coordinate geometry to six Pt2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Co-Design of Charge Transport Superhighways to Connect Catalytic Sites in Soft Photoelectrochemical Systems

Efficient photon-to-electron-to-molecule conversion requires multi-length scale control over charge transport pathways, where electronic charges are delivered to catalytic sites under high mass transport flux. A fundamental question is how can we co-design charge transport pathways to promote efficient charge transfer to/from catalytic sites in complex three-dimensional architectures? Soft conducting polymer systems offer exceptional promise to provide three-dimensional charge transport networks, where electrolyte (ion and solvent) can interdiffuse to promote long-lived charge carriers and the molecular nature allows for strategic synthetic design of catalytic sites. Herein we combine theoretical and experimental approaches to investigate the earliest stages of photoelectrochemical deposition of near-surface catalytic sites (Pt) on soft bulk heterojunction polymeric semiconductors composed of a prototype donor (PTB7-Th) and a prototype acceptor (N2200) as a model system towards better understanding molecular catalyst-polymer site interactions. We focus initially on photoelectrochemical deposition of low Pt loadings, nanoparticle sizes (formed by progressive nucleation) below 20 nm, for both density functional theory (DFT) modeling studies and for spectroscopic characterization using surface-sensitive X-ray and UV-photoemission (XPS/UPS). DFT modeling of “n-type” N2200 slabs reveal for the first time that sulfur atoms in the thiophene units serve as the lowest-energy adsorption sites for single Pt atoms, while larger Pt clusters engage more complexly with both thiophene and naphthalene diimide (NDI) core sites. Changes in chemical composition observed by X-ray photoelectron spectroscopy (XPS) support the DFT predictions, and the angle-resolved measurements reveal that Pt nucleation initiates at subsurface sites which appear to be localized active domains that promote charge transport/transfer and enable vertical growth toward the surface. These results suggest that light-activated Pt nanoparticle deposition decorates energetically distinct sites, where photoactivity is dictated by the local energetics of those sites, and the fact that they represent the termini of charge transport “super-highways” – a small percentage of the total volume of the donor/acceptor polymeric active layer which carries most of the photocurrent generated during both Pt deposition and photoelectrochemical HER. We posit that these initial studies provide a foundational strategy for design of catalytic sites in the near surface regions of complex polymeric materials and advancing soft semiconductor-based photoelectrochemical systems. Achieving a nanometer-scale understanding of catalyst deposition and the impact of local composition and energetics on that placement, should ultimately provide the design guidelines (co-design) for a broad array of catalysts at sites that optimize that efficiency and maximize platform durability.

14 SOLAR ENERGY↗
DOE OSTI2020

Platinum and Palladium Monolayer Electrocatalysts for Formic Acid Oxidation

The direct formic acid fuel cell holds great promise as a next generation portable power source. In this paper we report an experimental study on Pt and Pd monolayer (Pt* and Pd*) atop the close-packed facet of transition metal substrates (denoted Pt*/M or Pd*/M, where M = Pt, Pd, Ir, Au, Rh and Ru) model catalysts for formic acid oxidation (FAO) and demonstrate a promotional effect on Pt*/Au(111) and Pd*/Pt(111) surfaces. Contrary to findings on monometallic surfaces, in situ infrared reflection adsorption spectroscopy collected during formic acid oxidation at potentials anodic of 375 mV reveal that the poisoning reaction intermediate CO is not formed on the monolayer surfaces, suggesting a promotion of the direct mechanisms of FAO at the expense of the indirect mechanism through CO. Our density functional theory calculations on model surfaces with 1:1 stoichiometry for overlayer to support metal atoms for the thermochemistry of the elementary steps defined by adsorbed CO, OH, COOH, and HCOO on the (111) facet of Pt, PtML/Au, Pd, and PdML/Pt largely attribute the promotional effect observed for the monolayer catalysts to easier removal of CO brought about by easier activation of water, relative to the monometallic catalysts. This synergy between experiments and theory brings us closer to a fundamental understanding of FAO electrocatalysts under reaction conditions, paving the way to achieving more active electrocatalysts possibly with less Pt or Pd; a pre-requisite for the mass commercialization of this technology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Effect of CO on alcohol oxidation over commercial oxidation catalysts for control of emissions from lean-burn engines

For commercialization, alcohol-based net-zero carbon fuels in diesel-driven internal combustion engines must meet emissions standards set by the U.S. Environmental Protection Agency. Here, a series of aged commercial oxidation catalysts, Pt diesel oxidation catalyst (DOC), Pd+Pt DOC, and Pt oxidation catalyst (Pt OC), were studied using an automated flow reactor and in situ DRIFTS techniques to investigate the impact of CO on alcohol oxidation. Surface formate and acetate intermediates were formed due to partial oxidation of methanol and ethanol, respectively. Sequential introduction of alcohol and CO experiments using in situ DRIFTS on all three catalysts showed that CO inhibited low temperature methanol oxidation. Mutual inhibition effects between CO and ethanol were observed during co-oxidation. Acetate species shifted CO oxidation to higher temperatures on Pt DOC and Pt OC, whereas CO pre-exposure inhibited acetate formation. CO oxidation occurred at lower temperatures during ethanol and CO co-oxidation on Pd+Pt DOC.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2022

Differentiating supported platinum single atoms, clusters and nanoparticles by styrene hydrogenation

Supported metal catalysts often consist of metal sites ranging from nanoparticles to subnanometer clusters and single atoms. It remains a necessity to differentiate these sites to guide design of optimal catalysts. Here we report a simple method to assess the distribution of metal active sites in catalyst samples. The method takes the advantage of the structure sensitivity of styrene hydrogenation over titania supported platinum (Pt) catalysts with Pt aggregates varied from single atom to ~1.40 nm nanoparticles. The physicochemical properties were characterized by STEM, XPS, XANES, H2-TPR and CO-chemisorption measurements. The reactivity of Pt sites was quantified by styrene hydrogenation at ambient conditions. The nanometer-sized Pt clusters have significantly higher activity than Pt nanoparticles, sub-nanometer clusters or isolated single atoms. Additionally, the relationship between activity and structural/electronic properties of Pt sites influenced by particle sizes was discussed. Similar relationship was found in the carbon supported Pt catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗