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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Intermetallic Nanocatalysts from Heterobimetallic Group 10–14 Pyridine-2-thiolate Precursors

Intermetallic compounds are atomically ordered inorganic materials containing two or more transition metals and main-group elements in unique crystal structures. Intermetallics based on group 10 and group 14 metals have shown enhanced activity, selectivity, and durability in comparison to simple metals and alloys in many catalytic reactions. While high-temperature solid-state methods to prepare intermetallic compounds exist, softer synthetic methods can provide key advantages, such as enabling the preparation of metastable phases or of smaller particles with increased surface areas for catalysis. In this work, we study a generalized family of heterobimetallic precursors to binary intermetallics, each containing a group 10 metal and a group 14 tetrel bonded together and supported by pincer-like pyridine-2-thiolate ligands. Upon thermal decomposition, these heterobimetallic complexes form 10–14 binary intermetallic nanocrystals. Experiments and density functional theory (DFT) computations help in better understanding the reactivity of these precursors toward the synthesis of specific intermetallic binary phases. Using Pd 2 Sn as an example, we demonstrate that nanoparticles made in this way can act as uniquely selective catalysts for the reduction of nitroarenes to azoxyarenes, which highlights the utility of the intermetallics made by our method. Employing heterobimetallic pincer complexes as precursors toward binary nanocrystals and other metal-rich intermetallics provides opportunities to explore the fundamental chemistry and applications of these materials.

10-14 intermetallics↗
DOE OSTI2021

Disordered TiO x –SiO x Nanocatalysts Using Bioinspired Synthetic Routes

Metal oxide nanomaterials have increasing significance and broad applications in catalysis, ranging from support materials to active catalysts. Here, we have demonstrated a facile synthetic strategy to create disordered, high-surface-area metal oxide nanomaterials using biomineralization-inspired methods. Using protamine as a protein template, a range of TiO x –SiO x nanomaterials were synthesized and implemented for catalytic CO 2 thermal reduction reactions. The modularity of synthetic options afforded via biomineralization enables increases in surface area, which are ideally suited for subsequent modification to regulate catalytic performance. All materials were thoroughly characterized using a suite of synchrotron scattering and spectroscopic methods. Through these techniques, we have demonstrated that protamine-induced biomineralization results in largely disordered materials with changes in the local atomic structure dependent on the applied synthetic conditions. Protamine removal with treatment under acidic conditions greatly increased material surface area while causing measurable changes in the structure as revealed by X-ray absorption spectroscopy. Upon subsequent hydrogenation, Ti- and Si-based defects were induced in the materials while the disordered nature of the material was still largely retained. Furthermore, we found that the incorporation of Si into TiO x was able to mitigate the known anatase to rutile phase change during the reaction while stabilizing the defect sites. The synthetic strategies described in this work are expected to be translatable to other metal oxide nanomaterial chemical structures, providing a means to control catalytic properties using benign synthetic strategies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Electrochemical Evolution of Fuel Cell Platinum Nanocatalysts on Carbon Nanotubes at the Atomic Scale

The evolution of Pt nanoparticles supported on carbon nanotubes is analyzed before and after electrochemical potential cycling, using identical location aberration-corrected transmission electron microscopy, for applications in proton exchange membrane fuel cells. The work is focused on the half-cell accelerated stress test protocol of potential cycles ranging between 1.0 and 1.5 V RHE to represent the start-up/shutdown settings of a fuel cell vehicle. The research work reveals that particle migration and coalescence are key mechanisms for a reduction in the Pt nanoparticle surface area at the early stages of potential cycling. Further, the mechanism for particle movement and coalescence is attributed to carbon corrosion, catalyzed either by Pt or by bulk corrosion of the carbon nanotubes. Carbon corrosion results in the appearance of carbon vacancies at the carbon nanotube/Pt nanoparticle interface during cycling, as well as the formation of edge and surface defects. During cycling, the concentration of the dissoluble Pt increases. As soon as a significant amount is reached, subnanometer/atomic clusters emerge on the carbon nanotube support, which can move and coalesce, or redeposit on the surface of larger particles through Ostwald ripening.

25 ENERGY STORAGE↗
DOE OSTI2025

Redistribution of Ru in Fe 2 O 3 –Ru Nanocatalysts through an Oxidative Pretreatment Improves Reverse Water–Gas Shift Activity

We have synthesized Fe–Ru nanoparticles via a solvothermal method to create catalysts for the reverse water–gas shift reaction and demonstrated the impact of reductive and oxidative pretreatments on both catalytic performance and structure. Catalytic testing showed improved activity after exposure to O 2 at 600 °C. In contrast, the activity became lower if then exposed to H 2 at 600 °C. Environmental scanning transmission electron microscopy and scanning electron microscopy showed that exposure to O 2 at 600 °C changes the morphology and completely oxidizes Fe into Fe 2 O 3 . Exposure to H 2 at elevated temperature caused Ru coalescence at the surface of the nanoparticle, forming clusters which decreased the optimization of Ru. Reoxidation of the particles exposed to H 2 , however, caused a redistribution of Ru that appears beneficial in maximizing Ru exposure and synergy with Fe oxide, with no major changes in the morphology and oxide structure. Furthermore, our diagnostics demonstrate the complex and reversible rearrangements possible in these multicomponent particles and the benefits of oxidative pretreatment to enhance or regenerate Fe–Ru catalysts in other important catalytic reactions such as Fischer–Tropsch synthesis.

Fe−Ru nanoparticles↗
DOE OSTI2024

Enhancing Low-Temperature Syngas Production via Surface Tailoring of Supported Intermetallic Nanocatalysts

An active and coke-resistant silica-encapsulated intermetallic Ni 3 Zn nanoparticle catalyst was developed for low-temperature (450 °C) dry reforming of methane (DRM). The catalyst exhibited a remarkable 4-fold increase in activity (4.5 s –1 ) with over 99% CO selectivity and 3 orders of magnitude less carbonaceous species and demonstrated remarkable stability (70 h) compared to that of a monometallic Ni catalyst. Here, the key is the combined effect of surface ensemble structure and electronic interaction modulation through the surface composition tailoring achieved by off-stoichiometric Ni and Zn loading in controlling surface chemistry for achieving different activities and H 2 /CO ratios. Characterized by ion spectroscopy, X-ray photoelectron spectroscopy, and the neutron pair distribution function, it was revealed that paired Ni δ – –Zn δ+ active sites are crucial for DRM. Transient infrared spectroscopy and isotopic analysis uncovered the synergistic effect of Ni δ – –Zn δ+ sites in activating C–H bonds and dissociating CO 2 to prevent coke formation under low-temperature conditions.

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

Exploring Atomic-Scale Interactions at the Interface of Reducible Oxide and Ruthenium Nanocatalyst for Ammonia Decomposition

Restructuring atomic-scale interfaces between noble metal nanoparticles and metal oxides provides a promising approach to enhancing catalytic properties. In this study, Ru nanoparticles were supported on CeO 2 , ZrO 2 , and HfO 2 via pyrolysis of MOFs under oxygen-suppressed high-temperature conditions. Despite its nearly ideal particle size (∼2.3 nm), the Ru–CeO 2 /C catalyst exhibited the lowest ammonia decomposition activity. X-ray absorption spectroscopy and DFT calculations revealed that electron transfer from Ru to CeO 2 formed positively charged Ru and partially reduced Ce 4+ , weakening the catalytic performance. In contrast, oxygen-deficient ZrO 2 and HfO 2 support donated electrons to Ru, preserving its metallic state. These findings demonstrate that the reducibility of oxide supports governs the direction and magnitude of interfacial charge transfer, directly tuning catalytic behavior. This study provides insights into the design of oxide-supported Ru catalysts for ammonia decomposition.

Catalysts↗
DOE OSTI2020

Revealing Sintering Kinetics of MoS 2 -Supported Metal Nanocatalysts in Atmospheric Gas Environments via Operando Transmission Electron Microscopy

The decoration of two-dimensional (2D) substrates with nanoparticles (NPs) serve as heterostructures for various catalysis applications. Deep understanding of catalyst degradation mechanisms during service conditions is crucial to improve the catalyst durability. In this work, we studied the sintering behavior of Pt and bimetallic Au-core Pt-shell (Au@Pt core–shell) NPs on MoS 2 supports at high temperatures under vacuum, nitrogen (N 2 ), hydrogen (H 2 ), and air environments by in situ gas-cell transmission electron microscopy (TEM). The key observations are summarized as effect of environment: while particle migration and coalescence (PMC) was the main mechanism that led to Pt and Au@Pt NPs degradation under vacuum, N 2 , and H 2 environments, the degradation of MoS 2 substrate was prominent under exposure to air at high temperatures. Pt NPs were less stable in H 2 environment when compared with the Pt NPs under vacuum or N 2 , due to Pt–H interactions that weakened the adhesion of Pt on MoS 2 . Effect of NP composition: under H 2 , the stability of Au@Pt NPs was higher in comparison to Pt NPs. This is because H 2 promotes the alloying of Pt–Au, thus reducing the number of Pt at the surface (reducing H 2 interactions) and increasing Pt atoms in contact with MoS 2 . Effect of NP size: The alloying effect promoted by H 2 was more pronounced in small size Au@Pt NPs resulting in their higher sintering resistance in comparison to large size Au@Pt NPs and similar size Pt NPs. The present work provides key insights into the parameters affecting the catalyst degradation mechanisms on 2D supports.

2D materials↗
DOE OSTI2025

Optimization of La 2 NiO 4+δ Electrolysis Cell Oxygen Electrode through Surfactant-Enabled LaCoO 3±δ Nanocatalyst Deposition

Lanthanum nickelate (LNO) has shown promise as a Cr-resistant air electrode material for SOECs but has suboptimal surface oxygen exchange properties. Nanocoating of the LNO surface with lanthanum cobaltite (LCO) was chosen to improve cell performance as a surface oxygen conductor. The work focused on the implementation of a two-step nano-LCO film deposition utilizing catechol molecules in a porous LNO electrode. The subgoals of the work were to maintain nanosized LCO particles/ grains to increase active surface area and to control the regularity/ homogeneity of the coating across the microstructure. To achieve these goals, a novel surfactant-enhanced liquid infiltration method was utilized, where nucleation sites were spread across the electrode structure to control the location and size of LCO particles. Various catechol surfactant compositions were evaluated for their ability to control the kinetics of nanoparticle deposition and the homogeneity of the coating. Chelated LCO was characterized by X-ray diffraction (XRD), which found a substantial improvement in LCO formation with surfactant addition and determined polymerized norepinephrine to be the best-performing surfactant, with 88.4% pure LCO formed at low temperature. X-ray photoelectron spectroscopy (XPS) confirmed LCO nanostructures formed by the two-step infiltration process, showing no impurities and a stable perovskite structure. Deposition kinetics were analyzed using atomic force microscopy (AFM), correlating infiltration times and solution molarity to nanoparticle size and distribution, the results of which were confirmed in symmetrical cell samples by scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) testing demonstrated substantial improvements in polarization resistance, where the nanocoating reduced the resistance by ∼55% to 0.152 Ω·cm 2 at 700 °C and 0.039 Ω·cm 2 at 800 °C. Electrical conductivity relaxation (ECR) at this temperature confirmed an improved surface oxygen exchange coefficient of the LCO + LNO heterostructure predicted by the Bode data from EIS, alongside a reduction in activation energy by about 30%.

Deposition↗
DOE OSTI2022

Intra-crystalline mesoporous zeolite encapsulation-derived thermally robust metal nanocatalyst in deep oxidation of light alkanes

Zeolite-confined metal nanoparticles (NPs) have attracted much attention owing to their superior sintering resistance and broad applications for thermal and environmental catalytic reactions. However, the pore size of the conventional zeolites is usually below 2 nm, and reactants are easily blocked to access the active sites. Herein, a facile in situ mesoporogen-free strategy is developed to design and synthesize palladium (Pd) NPs enveloped in a single-crystalline zeolite (silicalite-1, S-1) with intra-mesopores (termed Pd@IM-S-1). Pd@IM-S-1 exhibited remarkable light alkanes deep oxidation performances, and it should be attributed to the confinement and guarding effect of the zeolite shell and the improvement in mass-transfer efficiency and active metal sites accessibility. The Pd–PdO interfaces as a new active site can provide active oxygen species to the first C–H cleavage of light alkanes. This work exemplifies a promising strategy to design other high-performance intra-crystalline mesoporous zeolite-confined metal/metal oxide catalysts for high-temperature industrial thermal catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Synthesis of monodisperse high entropy alloy nanocatalysts from core@shell nanoparticles

We report that high-entropy alloy (HEA) nanoparticles (NPs) hold great promise in electrocatalysis because of their nearly unlimited compositions, tailorable active sites, and high durability. However, the synthesis of these compositionally complex structures as monodisperse NPs remains a challenge by colloidal routes because the different rates of metal precursor reduction lead to phase separation. Here, we report the conversion of core@shell NPs into HEA NPs through annealing, with conservation of sample monodispersity. This potentially general route for high-quality HEA NPs was demonstrated by preparing PdCu@PtNiCo NPs via seed-mediated co-reduction, wherein Pt, Ni, and Co were co-deposited on PdCu seeds in solution. These multimetallic NPs were then converted to single-crystalline and single-phase PdCuPtNiCo NPs through annealing. On account of their small particle size, highly dispersed Pt/Pd content, and low elemental diffusivity, these HEA NPs were found to be a highly efficient and durable catalyst for the oxygen reduction reaction. They were also highly selective for the four-electron transfer pathway. We expect that this new synthetic strategy will facilitate the synthesis of new HEA NPs for catalysis and other applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Synthesis of Pt 3 Zn 1 and Pt 1 Zn 1 intermetallic nanocatalysts for dehydrogenation of ethane

Pt 3 Zn 1 and Pt 1 Zn 1 intermetallic nanoparticles supported on SiO 2 were synthesized by combining atomic layer deposition (ALD) of ZnO, incipient wetness impregnation (IWI) of Pt, and appropriate hydrogen reduction. Here, the formation of Pt 1 Zn 1 and Pt 3 Zn 1 intermetallic nanoparticles was observed by both X-ray diffraction (XRD) and synchrotron X-ray absorption spectroscopy (XAS). STEM images showed that the 2–3 nm Pt-based intermetallic nanoparticles were uniformly dispersed on a SiO 2 support. The relationships between Pt–Zn intermetallic phases and synthesis conditions were established. In situ XAS measurements at Pt L 3 and Zn K edges during hydrogen reduction provided a detailed image of surface species evolution. Owing to a combined electronic and geometric effect, Pt 1 Zn 1 exhibited much higher reactivity and stability than Pt 3 Zn 1 and Pt in both the direct dehydrogenation and oxidative dehydrogenation of ethane to ethylene reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Morphology and chemical behavior of model CsO x /Cu 2 O/Cu(111) nanocatalysts for methanol synthesis: Reaction with CO 2 and H 2

Cs is a promoter of Cu-based catalysts for the synthesis of alcohols from CO 2 hydrogenation. Scanning tunneling microscopy and ambient-pressure x-ray photoelectron spectroscopy were used to study the morphology and chemical properties of surfaces generated by the deposition of cesium on Cu 2 O/Cu(111) and Cu(111) substrates. CsO x nanostructures were formed after Cs metal was deposited on Cu 2 O/Cu(111) at 300 K. The formed CsO x protrude over the surface of copper oxide by 2–4 Å, with the dimension at the base of the nanostructures being in the range of 1–3 nm. Heating to elevated temperature induced significant changes in the size and dispersion of the CsO x nanostructures, and there was a clear reconstruction of the copper oxide substrate, which then exhibited long range order with a hexagonally packed structure. The as-deposited and annealed surfaces of CsO x /Cu 2 O/Cu(111) were more reactive toward CO 2 than plain Cu 2 O/Cu(111) or clean Cu(111). Yet, none of them were stable in the presence of H 2 , which fully reduced the copper oxide at 400–450 K. In CsO x /Cu(111), the CsO x nanoclusters were dispersed all over the metallic copper in no particular order. The CsO x species had an average width of 2 nm and ~1 Å height. The CsO x /Cu(111) systems exhibited the highest activity for the binding and dissociation of CO 2 , indicating that the CsO x -copper interface plays a key role in alcohol synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗