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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Examining Metal Identity and Proximity Effects on Acetylene Hydrogenation with Azolate-Based MOFs

Liquid organic hydrogen carriers (LOHCs) are an attractive fuel source due to their compatibility with existing transportation methods and ease of use. However, they suffer from sluggish (de)hydrogenation kinetics. One promising platform for developing next-generation catalysts is metal–organic frameworks (MOFs), which can enable systematic interrogation into the influence of metal identity and spatial arrangement. In this study, the effect of the coordination environment was investigated using Ni- and Co-based azolate MOFs: MFU-4l-OH (M x Zn 5–x (OH) 4 (BTDD) 3 ; x = 4 for M = Co and x = 3 for M = Ni, H 2 BTDD = bis(1H-1,2,3-triazolo[4,5-b][4′,5′-i])dibenzo[1,4]dioxin), composed of single-site nodes, and M(OH) 2 BBTA (M = Ni, Co; H 2 BBTA = 1H,5H-benzo(1,2-d:4,5-d’)bistriazole), composed of extended chain-type nodes. The catalysts were characterized by isotherms, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS) analysis. Acetylene hydrogenation activity under steady state conditions (150 °C, 1:1 C 2 H 2 :H 2 ) revealed higher turnover frequencies (TOFs) up 1.17 × 10 –2 mol C 2 H 2 mol −1 Ni min −1 and 1.98 × 10 –3 mol C 2 H 2 mol −1 Co min −1 for Ni-MFU-4l-OH and Co-MFU-4l-OH, respectively, compared to their BBTA analogues. However, the Co-based MOFs, particularly Co 2 (OH) 2 -BBTA, exhibited greater selectivity (up to 19%) for the fully hydrogenated ethane product. Isosteric heat of adsorption (Q st ) measurements for ethylene and ethane revealed that the BBTA framework had stronger binding to the products than MFU-4l. Furthermore, these findings demonstrate that metal identity and coordination environment may modulate acetylene hydrogenation performance, leading to design principles for tuning LOHC hydrogenation catalysts.

catalysts↗
DOE OSTI2018

Creation And Ordering Of Oxygen Vacancies At WO3-d And Perovskite Interfaces

Changes in structure and composition resulting from oxygen deficiency can strongly impact the physical and chemical properties of transition metal oxides. However, it is extremely difficult to accurately characterize the oxygen deficiency levels and pinpoint how these materials properties change in response. In this paper, the effects of substrate strain and oxidizing power on the creation and distribution of oxygen defects in WO3 thin films are investigated in detail. An 18O2 isotope labeled time-of-flight secondary ion mass spectrometry (ToF-SIMS) study reveals that WO3-films grown on STO display a significantly larger oxygen vacancy gradient along the growth direction. This result is corroborated by scanning transmission electron microscopy (STEM) images which reveal a large number of defects present close to the interface to accommodate interfacial strain, leading to ordering of oxygen vacancies and formation of semi-aligned Magnéli phases. The strain is gradually released and tetragonal phase with much better crystallinity is observed at the film/vacuum interface. The changes in structure resulting from oxygen defect creation are shown to have a direct impact on the electronic and optical properties of the films.

Zhang, Kelvin H.↗
DOE OSTI2020

Understanding Time Dependence on Zinc Metal-Organic Framework Growth Using In Situ Liquid Secondary Ion Mass Spectrometry

The abundance of novel metal-organic framework (MOF) materials continues to increase as more applications are discovered for these highly porous, well-ordered crystalline adsorbents. The simplicity of its constituents allows for the design of new MOFs with virtue of functionality and pore topology towards target adsorbates. However, the fundamental understanding of how these frameworks age during nucleation and growth is mostly limited to speculation from simulation studies. In this effort, we utilize the microfluidic interface of liquid and vacuum in a unique SALVI device to analyze the formation and aging of the benchmark MOF-74 framework using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Principal component analysis (PCA) of the SIMS mass spectra together with ex situ microscopy and porosimetry, provide new insights into the growth and aging process.

Sabale, Sandip R.↗
DOE OSTI2018

Versatile Ligand-Exchange Method for the Synthesis of Water-Soluble Monodisperse AuAg Nanoclusters for Cancer Therapy

A general-applicable two-phase ligand exchange method is developed to prepare a series of monodisperse water-soluble AuAg nanoclusters. This method relies on the ligand exchange of the water-soluble ligands (e.g., tiopronin, captopril, N-acetyl-l-cysteine, 4-mercaptobenzoic acid, glutathione, and mercaptosuccinic acid) with phenylacetylene and triphenylphosphine co-protected AuAg precursors. Both polyacrylamide gel electrophoresis (PAGE) and transmission electron microscopy (TEM) indicate the monodispersity and ultrasmall size of the prepared water-soluble metal nanoclusters. In addition, the structure has also been characterized by UV–vis absorption spectroscopy, extended X-ray absorption fine structure (EXAFS), electrospray ionization time-of-flight mass spectra (ESI-TOF-MS), etc. The preliminary application of the as-prepared AuAg nanoclusters protected with tiopronin has been explored via the postmodification of the carboxyl groups of thiols with doxorubicin (DOX).

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Enhanced Hydrogenation of Carbon Dioxide to Methanol by a Ruthenium Complex with a Charged Outer-Coordination Sphere

In this paper, we report the hydrogenation of CO₂ to MeOH by a new Ru(triphos) catalyst containing a cationic tetraalkylammonium moiety in the outer coordination sphere. This new catalyst affords superior TON and TOF values for MeOH in comparison to previously reported isostructural catalysts. Kinetic data from operando NMR spectroscopy studies indicate the improvement in MeOH production arises from a 12-fold enhancement in the rate for hydrogenation of the transient formaldehyde intermediate. These results provide insight into the catalyst characteristics that promote methanol formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Valorization of Ethanol: Ruthenium-Catalyzed Guerbet and Sequential Functionalization Processes

We report a ruthenium-catalyzed tandem Guerbet–alkylation strategy for the valorization of ethanol. The products of ethanol upgrading (higher-order alcohols) undergo subsequent C–C bond forming reactions with four carbon pronucleophiles and one ylide. Studies into catalyst design led to the development of ClRu(5-Mebpi)(PPh 3 ) 2 (bpi = 1,3-bis(2'-pyridylimino)isoindolate) as a highly efficient catalyst for producing biofuels and value-added chemicals from ethanol via Guerbet and tandem Guerbet reactions. Furthermore, this catalyst affords 65% higher-order alcohols in short reaction times (2 h), providing the highest TON (155,890) and TOF (12,690 h –1 ) for a homogeneous catalyst reported to date.

09 BIOMASS FUELS↗
DOE OSTI2022

Optimizing Catalysis by Combining Molecular Scaling Relationships: Iron Porphyrin-Catalyzed Electrochemical Oxygen Reduction as a Case Study

Here, the present work demonstrates the generality of molecular scaling relationships toward achieving faster catalysis at lower overpotentials. In iron porphyrin-catalyzed oxygen reduction, independent tuning of the catalyst E 1/2 and buffer pK a resulted in improvement of both the maximum turnover frequency (TOF max ) and the effective overpotential (η eff ). Interestingly, the most optimal system is achieved with the most reducing catalyst and a weak buffered acid—a perhaps counterintuitive conclusion. More generally, this study illustrates a path to optimization of catalytic systems through their differing responses to changes in the intrinsic features of the system.

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

Contrasting Capability of Single Atom Palladium for Thermocatalytic versus Electrocatalytic Nitrate Reduction Reaction

The occurrence of high concentrations of nitrate in various water resources is a significant environmental and human health threat, demanding effective removal technologies. Single atom alloys (SAAs) have emerged as a promising bimetallic material architecture in various thermocatalytic and electrocatalytic schemes including nitrate reduction reaction (NRR). This study suggests that there exists a stark contrast between thermocatalytic (T-NRR) and electrocatalytic (E-NRR) pathways that resulted in dramatic differences in SAA performances. Among Pd/Cu nanoalloys with varying Pd–Cu ratios from 1:100 to 100:1, Pd/Cu (1:100) SAA exhibited the greatest activity (TOF Pd = 2 min –1 ) and highest N 2 selectivity (94%) for E-NRR, while the same SAA performed poorly for T-NRR as compared to other nanoalloy counterparts. DFT calculations demonstrate that the improved performance and N 2 selectivity of Pd/Cu (1:100) in E-NRR compared to T-NRR originate from the higher stability of NO 3 * in electrocatalysis and a lower N 2 formation barrier than NH due to localized pH effects and the ability to extract protons from water. Here, this study establishes the performance and mechanistic differences of SAA and nanoalloys for T-NRR versus E-NRR.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Machine Learning Accelerated First-Principles Study of the Hydrodeoxygenation of Propanoic Acid

The complex reaction network of catalytic biomass conversions often involves hundreds of surface intermediates and thousands of reaction steps, greatly hindering the rational design of metal catalysts for these conversions. Here, we present a framework of machine learning (ML)-accelerated first-principles studies for the hydrodeoxygenation (HDO) of propanoic acid over transition metal surfaces. The microkinetic model (MKM) is initially parametrized by ML-predicted energies and iteratively improved by identifying the rate-determining species and steps (RDS), computing their energies by density functional theory (DFT), and reparameterizing the MKM until all the RDS are computed by DFT. The Gaussian process (GP) model performs significantly better than the linear ridge regression model for predicting both the adsorption free energies and transition state free energies. Parameterized with energies from the GP model, only 5–20% of the full reaction network has to be computed by DFT for the MKM to possess DFT-level accuracy for the TOF and dominant reaction pathway. While the linear ridge regression model performs worse than the GP model, its performance is greatly improved when only transition states are predicted by the regression model and adsorption energies are computed by DFT. Overall, we find that a high accuracy in adsorption free energies is more important for a reliable MKM than a high accuracy in TS free energies. Lastly, based on the GP model with GOH and GCHCHCO as catalyst descriptors, we build two-dimensional volcano plots in activity and selectivity that can help design promising alloy catalysts for HDO reactions of organic acids.

adsorption↗
DOE OSTI2024

Impact of Sn Lewis Acid Sites on the Dehydration of Cyclohexanol

The impact of Sn on the concentration and strength of acid sites in Al containing zeolites with MFI topology and their catalytic activity for the dehydration of cyclohexanol in the aqueous phase has been investigated. The materials maintain constant Al concentrations and consequently Bro̷nsted acid site (BAS) concentrations, while exhibiting an increasing concentration of Sn Lewis acid sites (LAS). The presence of water alters LAS (Sn) , leading to weak BAS (Sn) that increases the concentration of water in the zeolite micropore, while leaving the rate of dehydration of cyclohexanol unchanged. The TOF increases with the concentration of BAS (Al) in close contact with framework LAS (Sn) , referred to as BAS (Pair) . The increase in the Arrhenius pre-exponential factor, without affecting the activation barrier (E a ), leads to the hypothesis that the proximity of both sites allows for a later transition state induced by the polarization of the C–O bond, leading in turn to a higher transition entropy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Active Palladium Structures on Ceria Obtained by Tuning Pd–Pd Distance for Efficient Methane Combustion

Efficiently removing/converting methane via methane combustion imposes challenges on catalyst design: how to design local structures of a catalytic site so that it has both high intrinsic activity and atomic efficiency? By manipulating the atomic distance of isolated Pd atoms, herein we show that the intrinsic activity of Pd catalysts can be significantly improved for methane combustion via a stable Pd 2 structure on a ceria nanorod support. Guided by theory and confirmed by experiment, we find that the turnover frequency (TOF) of the Pd 2 structure with the Pd–Pd distance of 2.99 Å is higher than that of the Pd 2 structure with the Pd–Pd distance of 2.75 Å; at least 26 times that of ceria supported Pd single atoms and 4 times that of ceria supported PdO nanoparticles. The high intrinsic activity of the 2.99 Å Pd–Pd structure is attributed to the conductive local redox environment from the two O atoms bridging the two Pd 2+ ions, which facilitates both methane adsorption and activation as well as the production of water and carbon dioxide during the methane oxidation process. In conclusion, this work highlights the sensitivity of catalytic behavior on the local structure of active sites and the fine-tuning of the metal–metal distance enabled by a support local environment for guiding the design of efficient catalysts for reactions that highly rely on Pt-group metals.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Single-Atom Manganese-Based Catalysts for the Oxidative Dehydrogenation of Propane

Combinatorial screening of 150 supported metal oxide (manganese and additives) catalysts was carried out via a high-throughput synthesis platform and parallel reactors for the oxidative dehydrogenation (ODH) of propane to propylene. Specifically, an organomanganese (0.05-2.5 Mn atoms/nm 2 ) complex was grafted on metal oxide supports (Al 2 O 3 , SiO 2 , TiO 2 , and ZrO 2 ) premodified with either Lewis acid (Al, Ti, Zn, and Zr) or redox-active (Cu, Cr, Ga Ni, V) additives at various surface coverages (25, 50, and 75%). Catalysts were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and UV-vis spectroscopy. Catalysts 0.05 Mn/V(50%)/Al 2 O 3 and 0.05 Mn/Ni(50%)/ZrO 2 showed the highest combined propane conversion and propylene selectivities (31/41% and 15/85%), with excellent stability at 500 degrees C for 25 h. The presence of Ni in Mn/Ni/ZrO 2 resulted in a 6-fold increase in turnover frequency (TOF) over the Mn/ZrO 2 . HRTEM identified single Mn atoms after 500 degrees C heat treatment. For the Mn/Ni/ZrO 2 system, Mn was incorporated into the support lattice due to the similar ionic radius of Mn 2+ and Zr 4+ , which was also enhanced by the presence of Ni. For the Mn/V/Al 2 O 3 system, highly active MnO was prevalent as observed by Raman. Both V and Mn contributed to an increase in mutual dispersion, but both species remained on the surface. Finally, it is proposed that the highly dispersed atom and interactions between Mn with either Ni or V are responsible for the ODH performance and stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Behavior of the Ru-bda water oxidation catalyst covalently anchored on glassy carbon electrodes

Electrochemical reduction of the dizaonium complex, [Ru II (bda)(NO)(N–N 2 ) 2 ] 3+ , 2 3+ (N–N 2 2+ is 4-(pyridin-4-yl) benzenediazonium and bda 2– is [2,2'-bipyridine]-6,6'-dicarboxylate), in acetone produces the covalent grafting of this molecular complex onto glassy carbon (GC) electrodes. Multiple cycling voltammetric experiments on the GC electrode generates hybrid materials labeled as GC-4, with the corresponding Ru-aqua complex anchored on the graphite surface. GC-4 has been characterized at pH = 7.0 by electrochemical techniques and X-ray absorption spectroscopy (XAS) and has been shown to act as an active catalyst for the oxidation of water to dioxygen. This new hybrid material has a lower catalytic performance than its counterpart in homogeneous phase and progressively decomposes to form RuO 2 at the electrode surface. The resulting metal oxide attached at the GC electrode surface, GC-RuO 2 , is a very fast and rugged heterogeneous water oxidation catalyst with TOF i s of 300 s –1 and TONs >45000. The observed performance is comparable to the best electrocatalysts reported so far, at neutral pH.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Highly robust hydrogen generation by bio-inspired Ir complexes for dehydrogenation of formic acid in water: Experimental and theoretical mechanistic investigations at different pH

Hydrogen generation from formic acid (FA), one of the most promising hydrogen storage materials, has attracted much attention due to the demand for the development of renewable energy carriers. Catalytic dehydrogenation of FA in an efficient and green manner remains challenging. Here, we report a series of bio-inspired Ir complexes for highly robust and selective hydrogen production from FA in aqueous solutions without organic solvents or additives. One of these complexes bearing an imidazoline moiety (complex 6 ) achieved a turnover frequency (TOF) of 322,000 h⁻¹ at 100 °C, which is higher than ever reported. The novel catalysts are very stable and applicable in highly concentrated FA. For instance, complex 3 (1 μmol) affords an unprecedented turnover number (TON) of 2,050,000 at 60 °C. Deuterium kinetic isotope effect experiments and density functional theory (DFT) calculations employing a “speciation” approach demonstrated a change in the rate-determining step with increasing solution pH. This study provides not only more insight into the mechanism of dehydrogenation of FA but also offers a new principle for the design of effective homogeneous organometallic catalysts for H₂ generation from FA.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Effect of Chloride Anions on the Synthesis and Enhanced Catalytic Activity of Silver Nanocoral Electrodes for CO 2 Electroreduction

Metallic silver (Ag) is known as an efficient electrocatalyst for the conversion of carbon dioxide (CO 2 ) to carbon monoxide (CO) in aqueous or nonaqueous electrolytes. However, polycrystalline silver electrocatalysts require significant overpotentials in order to achieve high selectivity toward CO 2 reduction, as compared to the side reaction of hydrogen evolution. Here we report a high-surface-area Ag nanocoral catalyst, fabricated by an oxidation–reduction method in the presence of chloride anions in an aqueous medium, for the electro-reduction of CO 2 to CO with a current efficiency of 95% at the low overpotential of 0.37 V and the current density of 2 mA cm –2 . A lower limit of TOF of 0.4 s –1 and TON > 8.8 × 10 4 (over 72 h) was estimated for the Ag nanocoral catalyst at an overpotential of 0.49 V. The Ag nanocoral catalyst demonstrated a 32-fold enhancement in surface-area-normalized activity, at an overpotential of 0.49 V, as compared to Ag foil. We found that, in addition to the effect on nanomorphology, the adsorbed chloride anions play a critical role in the observed enhanced activity and selectivity of the Ag nanocoral electrocatalyst toward CO 2 reduction. Synchrotron X-ray photoelectron spectroscopy (XPS) studies along with a series of control experiments suggest that the chloride anions, remaining adsorbed on the catalyst surface under electrocatalytic conditions, can effectively inhibit the side reaction of hydrogen evolution and enhance the catalytic performance for CO 2 reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Dynamics of CrO 3 –Fe 2 O 3 Catalysts during the High-Temperature Water-Gas Shift Reaction: Molecular Structures and Reactivity

A series of supported CrO 3 /Fe 2 O 3 catalysts were investigated for the high-temperature water-gas shift (WGS) and reverse-WGS reactions and extensively characterized using in situ and operando IR, Raman, and XAS spectroscopy during the high-temperature WGS/RWGS reactions. The in situ spectroscopy examinations reveal that the initial oxidized catalysts contain surface dioxo (O=) 2 Cr 6+ O 2 species and a bulk Fe 2 O 3 phase containing some Cr 3+ substituted into the iron oxide bulk lattice. Operando spectroscopy studies during the high-temperature WGS/RWGS reactions show that the catalyst transforms during the reaction. The crystalline Fe 2 O 3 bulk phase becomes Fe 3 O 4 ,and surface dioxo (O=) 2 Cr 6+ O 2 species are reduced and mostly dissolve into the iron oxide bulk lattice. Consequently, the chromium–iron oxide catalyst surface is dominated by FeO x sites, but some minor reduced surface chromia sites are also retained. The Fe 3–-x Cr x O 4 solid solution stabilizes the iron oxide phase from reducing to metallic Fe0 and imparts an enhanced surface area to the catalyst. Isotopic exchange studies with C 16 O 2 /H 2 → C 18 O 2 /H 2 isotopic switch directly show that the RWGS reaction proceeds via the redox mechanism and only O* sites from the surface region of the chromium–iron oxide catalysts are involved in the RWGS reaction. The number of redox O* sites was quantitatively determined with the isotope exchange measurements under appropriate WGS conditions and demonstrated that previous methods have undercounted the number of sites by nearly 1 order of magnitude. The TOF values suggest that only the redox O* sites affiliated with iron oxide are catalytic active sites for WGS/RWGS, though a carbonate oxygen exchange mechanism was demonstrated to exist, and that chromia is only a textural promoter that increases the number of catalytic active sites without any chemical promotion effect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Propane Dehydrogenation over Alumina-Supported Iron/Phosphorus Catalysts: Structural Evolution of Iron Species Leading to High Activity and Propylene Selectivity

A series of alumina-supported Fe-based catalysts is prepared via a dry impregnation method in the presence of a phosphorus source (phosphate salt) and then used for the catalytic dehydrogenation of propane. Specifically, supported catalysts with Fe:P molar ratios of 1:1, 2:1, and 3:1 are prepared and their chemical composition, textural properties, and redox properties are characterized with an array of techniques. In the nonoxidative dehydrogenation (PDH) of propane at 600 °C and atmospheric pressure, the most active catalyst (Fe:P ratio of 3:1) exhibits 15% propane conversion and >80% C 3 H 6 selectivity. The calculated activity is 9.9 mmol/(h g Fe ) (mass basis) or 13 μmol/(h m 2 ) (surface area basis), with a corresponding TOF of 19 h –1 . During the initial stages of reaction under PDH conditions, the precatalyst is reduced and Fe(0) species are generated, eventually giving way to iron carbide species. During this induction period, significant carbon is incorporated into the catalyst and propylene selectivity is low. Only after the iron carbide phase appears do the reactivity and selectivity achieve steady-state conditions with high propylene selectivity and good activity. The addition of the phosphorus source in the precatalyst is found to be important in obtaining a catalyst with superior performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Water-Gas Shift Activity of Atomically Dispersed Cationic Platinum versus Metallic Platinum Clusters on Titania Supports

Atomically dispersed supported metal catalysts offer unique opportunities for designing highly selective catalysts and maximizing the utility of precious metals that have potential applications in a wide variety of industrial chemical reactions. While substantial advances in understanding the origin of the activity of such highly dispersed metal catalysts have been made for a few chemical reactions, the reaction mechanisms and the nature of the active site—small metal clusters versus single atoms—are still highly debated. Using a combination of density functional theory and microkinetic modeling, we confirm that a positively charged single Pt atom on TiO 2 (110) can exhibit a very high low-temperature activity for the water-gas shift reaction (TOF > 0.1 s –1 at 473 K). A comparison of these findings with our work on TiO 2 -supported Pt cluster models provides clear evidence that different active sites are responsible for the experimentally observed activity at low and high temperatures. Lastly, we explain why contradictory experimental conclusions have been reported.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗