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DOE OSTI2025

Effects of co-adsorbed water on different bond cleavages involved in acetic acid decomposition on Pt (111)

Acetic acid decomposition on Pt (111) in the presence of co-adsorbed water is a good model system for oxygenate decomposition on Pt (111) in aqueous phase, with application in hydrogen production and biomass conversion. Here, in this study, we present a density functional theory (DFT) theory calculation of how co-adsorbed water affects different bond cleavages of acetic acid decomposition on Pt (111). The presence of co-adsorbed water generally enhances O$-$H bond cleavage while inhibiting OC$-$O and OC$-$OH bond cleavage. The influence of co-adsorbed water on C$-$H bond cleavage varies the most and depends on the nature of the transition state and how co-adsorbed water stabilizes the initial and final state. Although these trends are useful as general guidance, they are not sufficient to predict the effect on a complex reaction network such as acetic acid decomposition on Pt (111) which has several parallel reaction paths with similar energies. In the absence of co-adsorbed water, the two lowest energy pathways are decarboxylation (DCX) and decarbonylation (DCN) pathways through a common CH 2 COO intermediate, in which the DCX pathway (C$-$H bond cleavage of CH 2 COO) is more favorable than DCN pathway (OC$-$O bond cleavage of CH 2 COO). In the presence of co-adsorbed water, the energy difference between Csingle bondH bond cleavage and OC$-$O bond cleavage of CH 2 COO increases, suggesting an increase in the favorability of acetic acid decarboxylation (formation of carbon dioxide) over acetic acid decarbonylation (formation of carbon monoxide) on Pt (111).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

“Intelligent” Pt Catalysts Studied on High-Surface-Area CaTiO 3 Films

CaTiO 3 -supported Pt is sometimes referred to as an “Intelligent” catalyst because Pt can reversibly leave or enter the perovskite lattice following high-temperature reduction or oxidation; however, slow egress-ingress kinetics associated with large perovskite crystallites make these systems impractical. In this study, thin films (~1 nm) of CaTiO 3 were deposited onto MgAl 2 O 4 and then examined as catalyst supports for Pt and Pd. While Pd/CaTiO 3 /MgAl 2 O 4 showed adsorption and CO-oxidation properties that were essentially the same as Pd/MgAl 2 O 4 , the Pt/CaTiO 3 /MgAl 2 O 4 catalyst exhibited evidence for strong support interactions. Pt/CaTiO 3 /MgAl 2 O 4 showed high activity for CO oxidation following reduction at 1073 K, even though CO adsorption was suppressed; but the catalysts were dramatically less active after oxidation at 1073 K and reduction at 773 K. Both Pt/CaTiO 3 /MgAl 2 O 4 and a catalyst formed by ex-solution of CaTi 0.95 Pt 0.05 O 3 exhibited very low rates for toluene hydrogenation in comparison to Pt/MgAl 2 O 4 . Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive Spectroscopy (EDS) showed that the CaTiO 3 films uniformly covered the MgAl 2 O 4 surface after both reduction and oxidation at 1073 K. Pt particles on reduced Pt/CaTiO 3 /MgAl 2 O 4 exhibited an unusual rhombohedral shape and may be flat, a further indication of strong interactions between the metal and the support. Low Energy Ion Scattering (LEIS) indicated that high-temperature reduction caused a restructuring of the CaTiO 3 . Lastly, the implications of these results for understanding catalysts formed by ex-solution of metals from a perovskite lattice are discussed.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Zeolite-Encapsulated Pt Nanoparticles for Tandem Catalysis

Encapsulation of metal nanoparticles in a zeolite matrix is a promising route to integrate multiple sequential reactions into a one-pot and one-step tandem catalytic reaction. We report a cationic polymer-assisted synthetic strategy to encapsulate Pt nanoparticles (NPs) into MFI zeolites. Degrees of encapsulation of Pt NPs in the synthesized catalysts exceeding 90% were demonstrated via kinetic studies of model reactions involving substrates with different molecular dimensions. HZSM-5 zeolite-encapsulated Pt NPs are able to selectively mediate the tandem Aldol condensation and hydrogenation of furfural and acetone to form hydrogenated C8 products with a combined yield of 87%. In contrast, hydrogenation and decarbonylation of furfural dominate on Pt NPs supported on HZSM-5 at otherwise identical conditions. The high selectivity towards the tandem reaction on the encapsulated catalyst is attributed to the distribution of metal and acid sites, which limits the access of furfural to Pt sites and promotes the acid-catalyzed Aldol condensation. This is the first demonstration that the product distribution in a tandem reaction is manipulated by tailoring the architecture of catalytic materials via encapsulation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

N 2 O Formation Mechanism and Suppression Strategy on Pt Catalysts for NO x Removal from Hydrogen-Internal Combustion Engines

Pt-based catalysts exhibit excellent low-temperature activity in the selective catalytic reduction of NO x with H 2 (H 2 -SCR), but their tendency to form N 2 O poses a significant challenge for practical use. This issue is further complicated by unclear formation mechanisms, hindering the development of more efficient catalysts. This study explored the N 2 O generation mechanisms on Pt catalysts supported by MgO, Al 2 O 3 , SiO 2 , and TiO 2 , aiming to achieve a deep understanding that could advance the Pt catalysts with high NO x conversion and minimized N 2 O emissions. Through systematic kinetics and characterization analyses, the direct influence of the support acidity and reactant dynamics (O 2 and NO) on N 2 O formation was clearly revealed. Notably, the Pt catalysts with strong NO adsorption capacity showed reduced N 2 O generation, highlighting the critical role of NO adsorption sites in the H 2 -SCR process. By incorporation of NO adsorption sites (i.e., MgO, BaO, CeO 2 ) onto Pt/SiO 2 , both the H 2 -SCR efficiency and N 2 selectivity (reduced N 2 O selectivity) were significantly enhanced, effectively reducing the N 2 O emissions through optimized surface NO adsorption. These findings provide a design framework for more selective Pt-based catalysts, advancing H 2 -SCR systems for effective NO x abatement from hydrogen-internal combustion engines, which is a promising carbon-free transportation technology.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Enhancement in Ethanol Electrooxidation by SnO(x) Nanoislands Grown on Pt(111): Effect of Oxide-Metal Interface Sites

An integrated surface science and electrochemistry approach has been used to prepare and characterize SnO{sub x}/Pt(111) model catalysts and evaluate their electrochemical activity for the ethanol oxidation reaction (EOR). Nanoislands of SnO{sub x} are deposited onto the Pt(111) by reactive layer assisted deposition in which Sn metal is vapor deposited onto a Pt(111) surface precovered by NO{sub 2}. X-ray photoelectron spectroscopy (XPS) shows that the SnO{sub x} islands are highly reduced with Sn{sup 2+} being the dominant chemical species. After exposing the SnO{sub x}/Pt(111) surface to H{sub 2}O or an electrolyte solution, XPS provides evidence for a significant amount of H{sub 2}O/OH adsorbed on the reduced SnO{sub x} surfaces. Electrochemical testing reveals that the catalytic performance of Pt(111) toward ethanol electrooxidation is significantly enhanced with SnO{sub x} islands added onto the surface. The enhanced EOR activity is tentatively attributed to the efficient removal of CO{sub ads}-like poisoning species at Pt sites by oxygen-containing species that are readily formed on the SnO{sub x} nanoislands. Moreover, the strong dependence of the EOR activity on SnO{sub x} coverage provides experimental evidence for the importance of SnO{sub x}-Pt interface sites in the EOR.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2017

Alumina-supported sub-nanometer Pt 10 clusters: Amorphization and role of the support material in a highly active CO oxidation catalyst

Catalytic CO oxidation is unveiled on size-selected Pt 10 clusters deposited on two very different ultrathin (≈0.5–0.7 nm thick) alumina films: (i) a highly ordered alumina obtained under ultra-high vacuum (UHV) by oxidation of the NiAl(110) surface and (ii) amorphous alumina obtained by atomic layer deposition (ALD) on a silicon chip that is a close model of real-world supports. Notably, when exposed to realistic reaction conditions, the Pt 10 /UHV-alumina system undergoes a morphological transition in both the clusters and the substrate, and becomes closely akin to Pt 10 /ALD-alumina, thus reconciling UHV-type surface-science and real-world experiments. The Pt 10 clusters, thoroughly characterized via combined experimental techniques and theoretical analysis, exhibit among the highest CO oxidation activity per Pt atom reported for CO oxidation catalysts, due to the interplay of ultra-small size and support effects. Lastly, a coherent interdisciplinary picture then emerges for this catalytic system.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Stabilizing atomic Pt with trapped interstitial F in alloyed PtCo nanosheets for high-performance zinc-air batteries

Recently, considerable attention has been paid to the stabilization of atomic platinum (Pt) catalysts on desirable supports in order to reduce Pt consumption, improve the catalyst stability, and thereafter enhance the catalyst performance in renewable energy devices such as fuel cells and zinc-air batteries (ZABs). Herein, we rationally designed a novel strategy to stabilize atomic Pt catalysts in alloyed platinum cobalt (PtCo) nanosheets with trapped interstitial fluorine (SA-PtCoF) for ZABs. The trapped interstitial F atoms in the PtCoF matrix induce lattice distortion resulting in weakening of the Pt–Co bond, which is the driving force to form atomic Pt. As a result, the onset potentials of SA-PtCoF are 0.95 V and 1.50 V for the oxygen reduction and evolution reactions (ORR and OER), respectively, superior to commercial Pt/C@RuO 2 . When used in ZABs, the designed SA-PtCoF can afford a peak power density of 125 mW cm -2 with a specific capacity of 808 mA h g Zn -1 and excellent cyclability over 240 h, surpassing the state-of-the-art catalysts.

25 ENERGY STORAGE↗

DOE OSTI2017

PT -symmetry in kagome photonic lattices

Photonic lattices composed of balanced gain and loss waveguides have attracted considerable attention due of their potential applications in optical beam engineering and image processing. These photonic lattices belong to a larger class of intriguing active metamaterials that exhibit the parity-time ( PT ) symmetry. Kagome lattice is a two-dimensional network of corner-sharing triangles and is often associated with geometrical frustration. In particular, the frustrated coupling between waveguide modes in a kagome array leads to a dispersionless flat band consisting of spatially localized modes. Recently, a PT -symmetric photonics lattice based on the kagome structure has been proposed by placing PT -symmetric dimers at the kagome lattice points. Each dimer corresponds to a pair of strongly coupled waveguides. With balanced arrangement of gain and loss on individual dimers, the system exhibits a PT -symmetric phase for finite gain/loss parameter up to a critical value. Here we discuss the linear and nonlinear optical beam propagations in this novel PT -symmetric kagome system. The linear beam evolution in this complex kagome waveguide array exhibits a novel oscillatory rotation of optical power along the propagation distance. Long-lived local chiral structures originating from the nearly flat bands of the kagome structure are observed when the lattice is subject to a narrow beam excitation. We further show that inclusion of Kerr-type nonlinearity leads to novel optical solitons.

42 ENGINEERING↗

DOE OSTI2020

Materials Data on Pt by Materials Project

Pt is Copper structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Pt is bonded to twelve equivalent Pt atoms to form a mixture of edge, face, and corner-sharing PtPt12 cuboctahedra. All Pt–Pt bond lengths are 2.81 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Durable High-Power Membrane Electrode Assemblies with Low Pt Loading

Recent progress in developing and implementing Pt-alloy cathode catalysts and thin (10-15 micron) low resistance membranes has enabled high performance state of art (SOA) membrane electrode assembly (MEA) with low Pt loading. However, these high performing MEAs do not meet durability requirements, especially at peak power, because of complex degradation mechanisms that are sensitive to the materials, MEA design, and fuel cell operating strategy. Specifically, power degradation of the cathode occurs via Pt and Co dissolution as well as deterioration of O 2 transport properties. Additionally, thin membranes are subject to failure due to manufacturing defects in the adjacent gas diffusion media and electrodes and the formation of membrane-attacking radical species caused by high gas crossover. In this project led by General Motors LLC (GM), the objective was to enhance the durability of SOA MEA through optimization of operating conditions, instead of new materials development. Along with our project partners, we have mapped the impact of operating conditions on the durability of SOA MEA. Output of the project include a low Pt loading SOA MEA that exceeds Department of Energy (DOE) 2020 target of >1 W/cm 2 at rated power and pathway to achieve >5000 h of durability. Durability studies in the project provide a detailed understanding of failure modes and operating condition sensitivity on cathode and membrane failure, critical for defining operating conditions and hybridization strategies that can guide system controls to maximize low-Pt MEA life. The project also generated and validated degradation models that will provide future research direction, critical for guiding future cycles of automotive MEA development.

08 HYDROGEN↗

DOE OSTI2019

“Intelligent” Pt Catalysts Based on Thin LaCoO3 Films Prepared by Atomic Layer Deposition

LaCoO3 films were deposited onto MgAl2O4 powders by atomic layer deposition (ALD) and then used as catalyst supports for Pt. X-ray diffraction (XRD) showed that the 0.5 nm films exhibited a perovskite structure after redox cycling at 1073 K, and scanning transmission electron microscopy and elemental mapping via energy-dispersive X-ray spectroscopy (STEM/EDS) data demonstrated that the films covered the substrate uniformly. Catalysts prepared with 3 wt % Pt showed that the Pt remained well dispersed on the perovskite film, even after repeated oxidations and reductions at 1073 K. Despite the high Pt dispersion, CO adsorption at room temperature was negligible. Compared with conventional Pt on MgAl2O4, the reduced forms of the LaCoO3-containing catalyst were highly active for the CO oxidation and water gas shift (WGS) reactions, while the oxidized catalysts showed much lower activities. Surprisingly, the reduced catalysts were much less active than the oxidized catalysts for toluene hydrogen. Catalysts prepared from thin films of Co3O4 or La2O3 exhibited properties more similar to Pt/MgAl2O4. Possible reasons for how LaCoO3 affects properties are discussed.

42 ENGINEERING↗

DOE OSTI2019

Systematic Control of the Orientation of Organic Phosphorescent Pt Complexes in Thin Films for Increased Optical Outcoupling

Abstract Orienting light‐emitting molecules relative to the substrate is an effective method to enhance the optical outcoupling of organic light‐emitting devices. Platinum(II) phosphorescent complexes enable facile control of the molecular alignment due to their planar structures. Here, the orientation of Pt(II) complexes during the growth of emissive layers is controlled by two different methods: modifying the molecular structure and using structural templating. Molecules whose structures are modified by adjusting the diketonate ligand of the Pt complex, dibenzo‐( f , h )quinoxaline Pt dipivaloylmethane, (dbx)Pt(dpm), show an ≈20% increased fraction of horizontally aligned transition dipole moments compared to (dbx)Pt(dpm) doped into a 4,4′‐bis( N ‐carbazolyl)‐1,1′‐biphenyl, CBP, host. Alternatively, a template composed of highly ordered 3,4,9,10‐perylenetetracarboxylic dianhydride monolayers is predeposited to drive the alignment of a subsequently deposited emissive layer comprising (2,3,7,8,12,13,17,18‐octaethyl)‐21H,23H‐porphyrinplatinum(II) doped into triindolotriazine. This results in a 60% increase in horizontally aligned transition dipole moments compared to the film deposited in the absence of the template. The findings provide a systematic route for controlling molecular alignment during layer growth, and ultimately to increase the optical outcoupling in organic light‐emitting diodes.

Kim, Jongchan↗

DOE OSTI2019

Sub‐3 nm Intermetallic Ordered Pt 3 In Clusters for Oxygen Reduction Reaction

Abstract Industrial applications of Pt‐based oxygen‐reduction‐reaction (ORR) catalysts are limited by high cost and low stability. Here, facile large‐scale synthesis of sub‐3‐nm ordered Pt 3 In clusters on commercial carbon black as ORR catalyst that alleviates both these shortcomings is reported. As‐prepared Pt 3 In/C exhibits a mass activity of 0.71 mA mg −1 and a specific area activity of 0.91 mA cm −2 at 0.9 V vs reversible hydrogen electrode, which are 4.1 and 2.7 times the corresponding values of commercial Pt/C catalysts. The as‐prepared ordered Pt 3 In/C catalyst is also remarkably stable with negligible activity and structural decay after 20 000 accelerated electrochemical durability cycles, due to its ordered structure. Density‐functional‐theory calculations demonstrate that ordered‐Pt 3 In is more energetically favorable for ORR than the commercial Pt/C catalysts because ∆ G O is closer to the peak of the volcano plot after ordered incorporation of indium atoms.

Chemistry↗

DOE OSTI2017

Bimetallic Ag‐Pt Sub‐nanometer Supported Clusters as Highly Efficient and Robust Oxidation Catalysts

Abstract A combined experimental and theoretical investigation of Ag‐Pt sub‐nanometer clusters as heterogeneous catalysts in the CO→CO 2 reaction (COox) is presented. Ag 9 Pt 2 and Ag 9 Pt 3 clusters are size‐selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first‐principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano‐aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O 2 , and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species.

Negreiros, Fabio R.↗

DOE OSTI2015

Aberration‐Corrected Transmission Electron Microscopy and In Situ XAFS Structural Characterization of Pt/γ‐Al 2 O 3 Nanoparticles

Abstract Aberration‐corrected (AC) STEM, AC TEM and in situ X‐ray absorption fine structure spectroscopy (XAFS) were used to characterize the Pt clusters present on a 0.35 wt % Pt on γ‐alumina support after reduction in hydrogen at 700 °C. STEM high‐angle annular dark field imaging shows that cluster formation takes place at temperatures up to approximately 350 °C, and this is followed by gradual growth in cluster size for heat treatments in hydrogen up to 700 °C. The STEM data show that after 700 °C reduction the Pt clusters are present in a narrow size distribution centered at 0.88 nm, and using a method involving a redistribution of the Pt atoms using a high electron dosage in the STEM, it is shown that the clusters are present in two‐dimensional morphology. This conclusion is verified using intensity line scans. The in situ extended X‐ray absorption fine structure data are in good agreement with these observations. High‐resolution AC–TEM, which uses a broad coherent electron beam, and can thus offer advantages relative to STEM for structure determination of fine clusters, supported by image simulations of through‐focus series, were used to analyze the structures of Pt particles. The structures determined by using AC–TEM are consistent with STEM and EXAFS data in having a flat two‐dimensional morphology. Comparison of AC–STEM and AC TEM data for the same 700 °C reduced sample suggests that parallel‐beam TEM mode of imaging may be advantageous because of the less pronounced beam‐induced structural rearrangements that occur when imaging with a fine STEM probe.

Sinkler, Wharton↗

DOE OSTI2020

Bidentate N‐based Ligands for Highly Reusable, Ligand‐coordinated, Supported Pt Hydrosilylation Catalysts

Abstract A significant challenge in designing supported metal‐ligand catalysts for solution‐phase reactions is the stabilization of the metal active sites against leaching into solution. Here, we examine alkene hydrosilylation reactions as model systems to improve the stability of highly dispersed Pt using a metal‐ligand coordination strategy on high surface area oxide supports. By evaluating a series of bidentate N‐based ligands, we demonstrate several design strategies to improve stability of the highly dispersed Pt 2+ centers against leaching, while maintaining a high level of catalytic activity, selectivity, and recyclability for alkene hydrosilylation batch reactions under mild conditions. These involve a bi‐functional approach to ligand design, which considers interaction to the support and a well‐defined coordination environment for the metal active site. Three strategies are reported: modifying ligands for stronger interaction with oxide surfaces, mixing ligands, and pre‐depositing an “anchoring ligand” to the support before loading the metal‐ligand catalyst. Each of these is successful in enhancing Pt recyclability. Particularly, two Pt‐phenanthroline catalysts exhibit excellent reusability for multiple batch reaction cycles, due to high stability of the active Pt species. Addressing the active site leaching problem significantly enhances the utility of ligand‐coordinated supported metal catalysts as highly stable and selective catalysts for solution‐phase reactions.

Chen, Linxiao↗

DOE OSTI2018

Electronic, Transport, and Magnetic Properties of La-Doped Ba{sub 1−x}Fe{sub 1.9}Pt{sub 0.1}As{sub 2} (x = 0, 0.4, 0.6, 0.8) Compounds

We briefly reported the structural variation and the nature of superconductivity properties correlating with magnetic and resistivity data of La-doped Ba{sub 1−x}Fe{sub 1.9}Pt{sub 0.1}As{sub 2} compounds. A solid-state reaction method was chosen to prepare bulk-type materials. The peak definition was studied to clarify the crystal structure of the samples, and it was observed that all samples were in ThCr{sub 2}Si{sub 2}-type structures, which is in harmony with similar compositions in the literature. Critical temperatures emphasizing superconductivity states have been clarified using magnetization measurements in the temperature range 5–170 K under magnetic field at 20 Oe, and the obtained results matched with resistivity measurements’ results for consistency of critical temperatures. We obtained a limit doping number for the Ba{sub 1−x}La{sub x}Fe{sub 1.9}Pt{sub 0.1}As{sub 2} samples synthesized by the solid-state reaction method. Increasing La and decreasing Ba amounts in the Ba{sub 1−x}La{sub x}Fe{sub 1.9}Pt{sub 0.1}As{sub 2} samples showed a fluctuation in T{sub c} values with inducing superconductivity. x = 0.6 was determined to have the highest T{sub c} value for the Ba{sub 0.4}La{sub 0.6}Fe{sub 1.9}Pt{sub 0.1}As{sub 2}sample, and a further increment in the amount of La revealed a deterioration in superconductivity. Replacing La with Ba should be the reason for lattice shrinkage, and slightly, the geometric factor was affected by replacing lower radius La with bigger radius Ba in the Ba{sub 0.4}La{sub 0.6}Fe{sub 1.9}Pt{sub 0.1}As{sub 2} compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Isolation of Au and Pt radionuclides from deuteron-irradiated platinum using TBP resin

A separation procedure was developed and implemented for the isolation of gold (Au) and platinum (Pt) radionuclides from deuteron irradiated Pt using tri-butyl phosphate (TBP) resin. Results of the procedure demonstrated a Pt recovery of 98 ± 2% and a Au recovery of 92±7%, in their respective fractions (n=4, ±1s). The decontamination factors were 2900 ± 500 for Au removal from the Pt fraction and 830±30 for Pt removal from the Au fraction (n=4, ±1s).

radiochemical separation, deuteron, Tributyl phosp↗