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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Nanocolumnar Pt:Ni Alloy Thin Films by High Pressure Sputtering for Oxygen Reduction Reaction

Self-supported nanocolumnar Pt:Ni thin films (TFs) with varying Pt:Ni atomic ratios and Pt mass loadings were produced on a microporous layer (MPL)-like surface composed of carbon particles by high pressure sputtering and examined as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte membrane fuel cells. Cauliflower-like microstructures were observed from scanning electron microscopy imaging. Various Pt:Ni atomic ratios were obtained by simply changing the relative deposition power between Pt and Ni source and investigated by X-ray diffraction and quartz crystal microbalance analysis. Additionally, electrochemical characterization of the Pt:Ni-TF/MPL-like-layer/glassy-carbon samples was conducted through benchtop cyclic voltammetry and rotating disk electrode measurements. The electrochemically active surface area (ECSA) was found to be between 22–42 m 2 g -1 for different Pt:Ni atomic ratios. Lower Pt mass loadings exhibited a higher ECSA and the catalytic activity of all Pt:Ni ratios increased with the increase in Pt mass loading. The ORR activity of the Pt:Ni-TFs increased in the order of 3:1 < 1:1 < 1:3 with exhibiting a specific activity of 1781 μA cm -2 and mass activity of 0.66 A mg -1 for the Ni-rich film with 1:3 ratio. The catalytic performance of Pt:Ni-TFs were higher than traditional high surface area carbon supported Pt nanoparticles, elemental Pt nanorods, and Pt-Ni nanorods.

08 HYDROGEN↗
DOE OSTI2023

Cascade Reaction of Ethanol to Butadiene over Ag-Promoted, Silica- or Zeolite-Supported Ta, Y, Pr, or La Oxide Catalysts

Ethanol converts to 1,3-butadiene in the presence of suitable multifunctional catalysts. In this work, Lewis acid cations Ta, Y, Pr, and La were dispersed on amorphous silica or beta zeolite, and after physically mixing with silica-supported Ag nanoparticles, were tested in the cascade reaction of ethanol to butadiene at 573 K. The Lewis acid catalysts were characterized by X-ray fluorescence, N 2 physisorption, scanning transmission electron microscopy (STEM), X-ray diffraction, diffuse reflectance (DR) UV-Vis and X-ray photoelectron spectroscopy. High-resolution STEM images confirmed the small oxide cluster size on the silica support. Results from DR UV-Vis spectroscopy showed zeolite-supported Ta and Pr catalysts had a smaller metal oxide cluster size, relative to their SiO 2 counterparts. X-ray photoelectron spectroscopy confirmed the oxidation state of the cations supported on the zeolite remained the same as that of their SiO 2 -supported analogues. The selectivity of the C 4 coupling products toward butadiene relative to butanol correlated with acid strength of the Lewis acid cations, as evaluated by the 2-propanol decomposition reaction to propene and acetone, with Ta being the most selective. In conclusion, the rate of C-C coupling over the zeolite-supported cations was enhanced by an order of magnitude compared to those cations supported on amorphous SiO 2 .

C-C bond formation↗
DOE OSTI2025

Exploring Catalyst Compositions for Microwave-Assisted Methane Dehydroaromatization

The flaring of natural gas in U.S. shale regions remains a challenge for producers. One alternative to flaring is converting the wasted gas into valuable chemicals. Microwave-based processes offer a promising solution, potentially enabling the development of compact, modular systems for on-site production of chemicals, such as aromatics, from natural gas. This is due to the advantages of microwave heating, including efficient heating of compact volumes, accelerated reaction rates, and electrification of heating. However, developing effective catalysts for microwave-based processes is challenging, as conventional materials often require modification to be effectively heated by microwaves. This study provides an overview of a catalyst development project focused on a molybdenum-supported zeolite catalyst, optimized for the direct conversion of methane into aromatics under microwave irradiation. It details the synthesis, characterization, and the effects of promoters, as well as computational efforts undertaken to understand and enhance the catalyst's performance.

flare gas↗
DOE OSTI2021

Laser-Irradiated Holey Graphene-Supported Single-Atom Catalyst towards Hydrogen Evolution and Oxygen Reduction

Single-atom catalysts (SAC) can boost the intrinsic catalytic activity of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). However, the challenge remains due to the complex synthesis process and insufficient stability. A sustainable approach is applied to synthesizing SACs through laser irradiation and gaining mesoporous graphene oxide (MGO). The surface dangling bonds of nitrogen-doped MGO (NMGO) extract metal atoms species from Co or Fe metal foams and convert them to SAC via an appropriate synthesis approach. Notably, the Co-NMGO electrocatalyst requires low potentials of 146 mV to convey a current density of 10 mA cm -2 towards HER. Similarly, the Fe-NMGO electrocatalyst offers an onset of 0.79 V towards ORR in acidic solution. The individual metal atoms are confirmed via aberration-corrected scanning transmission electron microscopy, and X-ray absorption near-edge structure and extended X-ray absorption fine structure. Density functional theory calculations by applying the grand canonical potential kinetics model revealed that Co-NMGO shows the optimum free reaction energy of -0.17 eV at -0.1 V for HER, and Fe-NMGO has less limiting potential than that of Co-NMGO for ORR case. Furthermore, this work opens a new approach towards the synthesis of SAC and its mechanistic understandings.

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

Ligation of Single-Site Ruthenium within Perovskite Oxides for Efficient Conversion of Thermodynamically Stable Molecules

Ru cation ligation in SrTiO 3 perovskite and their migration to the surface through exsolution are investigated for the dry reforming of methane (DRM), a chemistry that requires activation of two thermodynamically stable molecules, CH 4 and CO 2 . Compared to a supported 1 wt % Ru/SrTiO 3 benchmark, doped and exsolved Ru-SrTiO 3 demonstrate ≥3× higher CH 4 turnover rates (873 K), with isolated, ligated Ru exhibiting higher reactivity. Reactor studies assert that CH 4 and CO 2 activation are both kinetically relevant for CH 4 turnover rates on exsolved Ru-SrTiO 3 , unlike for supported Ru systems, where H-abstraction from CH 4 is the sole kinetically relevant step. As such, exsolved and doped Ru architectures are responsive toward co-reactant activation strategies, with their consequent reaction networks showing marked departures from those established for supported Ru catalysts. In situ spectroscopy and kinetic analyses propose distinct sensitivity toward CO 2 on Ru-SrTiO 3 systems, where higher CH4 turnover rates result from O-assisted C─H bond activation pathways. These pathways occur on paired Ru-oxygen vacancy sites that are inherent to the perovskite structure and are not readily accessible on supported Ru catalysts. Here, CO 2 is activated on oxygen vacancies directly adjacent to Ru active sites, which facilitates CH 4 C─H bond activation through a surface methoxy intermediate. The high reactivity of Ru-SrTiO 3 systems enables stable CH 4 turnover rates at milder reaction temperatures (673 K), conditions under which the supported counterpart, Ru/SrTiO 3 , is inactive. Overall, this work demonstrates that ligation of catalytically active cations in perovskite oxides facilitates site engineering toward atom-efficient activation of thermodynamically stable feedstocks.

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

Revealing the Configuration and Conformation of Surface Organometallic Catalysts with DNP-Enhanced NMR

Although single-site, supported organometallic catalysts were designed with homogeneity in mind, little is strictly known about their atomic-level structure and uniformity. This is in large part due to the inability of conventional characterization tools to provide structural information with adequate resolution and range for this purpose. In this work, we show that dynamic nuclear polarization (DNP)-enhanced solid-state nuclear magnetic resonance (NMR) enables the measurement of distances between the surface and individual carbons, making it possible to orient complexes and molecules on surfaces. We use this approach to determine the orientation and configuration of naturally 13 C-abundant acetate and supported organoiridium(III) pincer complex, both supported on γ-Al 2 O 3 . By combining solid-state NMR and extended X-ray absorption fine structure spectroscopy (EXAFS) experiments with periodic density functional theory (DFT) calculations, we are able to determine the three-dimensional arrangement of ligands around the metal center and thereby identify the structure of the supported complex at a resolution reminiscent of that associated with single-crystal diffractometry.

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

Elucidating the Roles of Amorphous Alumina Overcoat in Palladium-Catalyzed Selective Hydrogenation

Amorphous alumina overcoats generated by atomic layer deposition (ALD) have been shown to improve the selectivity and durability of supported metal catalysts in many reactions. Several mechanisms have been proposed to explain the enhanced catalytic performance, but the accessibilities of reactants through the amorphous overcoats remain elusive, which is crucial for understanding reaction mechanisms. Here, we show that an AlO x ALD overcoat is able to improve the alkene product selectivity of a supported Pd catalyst in acetylene (C 2 H 2 ) hydrogenation. We further demonstrate that the AlO x ALD overcoat blocks the access of C 2 H 2 (kinetic diameter of 0.33 nm), O 2 (0.35 nm), and CO (0.38 nm) but allows H 2 (0.29 nm) to access Pd surfaces. A H–D exchange experiment suggests that H 2 might dissociate heterolytically at the Pd–AlO x interface. These findings are in favor of a hydrogen spillover mechanism.

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

Introduction to (Photo)electrocatalysis For Renewable Energy

Humanity is facing a significant and growing energy demand, necessitating a new energy paradigm built on clean and abundant renewable energy.1 Within this context, electrocatalysis and (photo)electrocatalysis hold great promise for enabling renewable energies such as solar and wind power to overcome the transient nature of their energy output.2-6 Developing catalysts that operate efficiently and selectively, and that are also robust, has been the focus of much research. This special issue brings together the latest advances in the fundamental and applied science addressing the synthesis, characterization, mechanisms, and performance of (photo)electrocatalysts for energy storage and conversion of small molecules into useful specialty and commodity chemicals and fuels. The electrocatalysts and (photo)electrocatalysts highlighted in this issue include metalloenzymes, homogeneous and supported molecular catalysts, and diverse heterogeneous nanoparticulate and thin film systems. The reports span across basic and applied studies and encompass both experimental and theoretical investigations.

Dey, Abhishek↗
DOE OSTI2022

Carbon supports for oxygen reduction catalysts

The invention provides a method of making a electrocatalyst from waste tires. The method comprises the steps of providing rubber pieces; optionally contacting the rubber pieces with a sulfonation bath to produce sulfonated rubber; pyrolyzing the rubber to produce tire-derived carbon composite comprising carbon black, wherein the pyrolyzing comprises heating to at least 200° C.-2400° C.; activating the tire-derived carbon composite by contacting the tire-derived carbon composite with an alkali anion compound to provide activated tire-derived carbon supports; and loading the activated carbon-based supports with platinum cubes. In another embodiment, the tire-derived carbon composite is activated by annealing in a carbon dioxide atmosphere.

Naskar, Amit K.↗
DOE OSTI2020

Pt-Ligand single-atom catalysts: tuning activity by oxide support defect density

The support–metal interaction is an important element of heterogeneous catalyst design and is particularly critical for the rapidly growing field of single-atom catalysts (SACs). In this work, we investigate the impact of varying the defect density of the titania support on metal–organic Pt SACs for hydrosilylation reactions. Pt SACs are decorated on the powder titania support, employing a metal–ligand interaction with a dipyridyl-tetrazine ligand (DPTZ). The single-atom nature of Pt is verified by X-ray absorption spectroscopy (XAS) on both pristine and defective titania surfaces. These Pt species have a +2 oxidation state and are stabilized by bonding with DPTZ, surface oxygen, and residual chloride from the metal precursor. The catalytic activity is evaluated for the alkene hydrosilylation reaction and it is discovered that the activity of Pt-ligand is positively correlated with the defect density of the titania support. The turn-over number (TON) is calculated to be 12 530 for Pt SACs on a defective surface, which is significantly higher than Pt SACs on a pristine titania surface (830) for the same reaction period (10 min) under the same conditions (70 °C). We ascribe the high activity of Pt SACs on defective titania surfaces to two aspects: the coordination of Pt with more chloride than on pristine titania surfaces, which shortens the induction period of the reaction, and the preferential dispersion of Pt–DPTZ units on defective regions of titania surfaces, allowing facile contact between Pt sites and reactants. The supported Pt–DPTZ SACs show high stability through multiple cycles of batch reactions. This work demonstrates an efficient approach to improve the activity and stability of SACs by optimizing the metal–support interaction, which can also be applied to other oxide surfaces to further develop next-generation heterogeneous single-atom catalysts.

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

Advances in solid-state NMR for the studies of mesoporous solids: fast magic spinning and dynamic nuclear polarization

Here, this review provides an up-to-date account of the development of two solid-state (SS)NMR methods for enhancing resolution and sensitivity, fast magic angle spinning (MAS) and dynamic nuclear polarization (DNP), and the resulting progress in surface science. We demonstrate the high resolution and efficiency that can be achieved by using two-dimensional homo- and heteronuclear correlation experiments with small rotors capable of MAS at rates exceeding 100 kHz. DNP has offered significant enhancements in signal sensitivity and allowed access to nuclei and experiments that are beyond the limits of conventional SSNMR. The continuing progress in fast MAS and DNP methodologies in recent years generated an unprecedented shift in SSNMR’s capabilities in the studies of surface and interface regions of solids, especially mesoporous supports and catalysts. We give numerous examples of recent applications and discuss the prospects for further improvements of both methods.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Ionic Liquid Sheath Stabilizes Atomically Dispersed Reduced Graphene Aerogel‐Supported Iridium Complexes during Ethylene Hydrogenation Catalysis

Abstract An atomically dispersed reduced graphene aerogel (rGA)‐supported iridium catalyst having reactive ethylene ligands was synthesized at an iridium loading of 9.9 wt % and coated with an ionic liquid, 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]). Continuous‐scan X‐ray absorption spectra demonstrated that the iridium remained site‐isolated in flowing equimolar C 2 H 4 and H 2 during a temperature ramp to 100 °C. The data further showed the lack of detectable iridium aggregation when the feed was H 2 ‐rich or even pure H 2 at 100 °C. An Arrhenius plot determined for ethylene hydrogenation catalysis with the sample in flowing equimolar ethylene and hydrogen showed no variation in the apparent activation energy at temperatures up to 100 °C, confirming that the active sites remained intact at the higher temperatures. The results point to opportunities for overcoming the stability limitations of atomically dispersed supported noble metal catalysts by choice of electron‐donor supports and ionic liquid sheaths.

Kurtoğlu‐Öztulum, Samira F.↗
DOE OSTI2022

A Study of Support Effects for the Water-Gas-Shift Reaction over Cu

The water–gas-shift (WGS) reaction was studied on a series of supported Cu catalysts in which the MgAl 2 O 4 (MAO) support was modified by depositing ZnO, CeO 2 , Mn2O 3 and CoO using Atomic Layer Deposition (ALD). Addition of Cu by one ALD cycle gave rise to catalysts with nominally 1-wt% Cu. A 1.1-wt% Cu/MAO catalyst prepared by ALD exhibited twice the dispersion but ten times the WGS activity of a 1-wt% Cu/MAO catalyst prepared by impregnation, implying that the reaction is structure sensitive. However, Cu catalysts prepared with the ZnO, CeO 2 , and Mn 2 O 3 films showed negligible differences from that of the Cu/MAO catalyst, implying that these oxides did not promote the reaction. Cu catalysts prepared on the CoO film showed a slightly lower activity, possibly due to alloy formation. The implications of these results for the development of better WGS catalysts is discussed.

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

Metal–organic framework (MOF) materials as polymerization catalysts: a review and recent advances

Synthetic polymers are ubiquitous across both the industrial and consumer segments of the world economy. Catalysts enable rapid, efficient, selective, and even stereoselective, formation of desired polymers from any of a host of candidate monomers. While numerous molecular catalysts have been shown to be effective for these reactions, separation of the catalysts from reaction products is typically difficult – a potentially problematic complication that suggests instead the use of heterogeneous catalysts. Many of the most effective heterogeneous catalysts, however, comprise supported collections of reaction centres that are decidedly nonuniform in their composition, siting, and activity. Nonuniformity complicates atomic-scale evaluation of the basis for catalytic activity and thus impedes scientific hypothesis-driven understanding and development of superior catalysts. In view of the fundamental desirability of structural and chemical uniformity at the meso, nano, and even atomic scale, crystallographically well-defined, high-porosity metal–organic frameworks (MOFs) have attracted attention as model catalysts and/or catalyst-supports for a wide variety of chemical transformations. In the realm of synthetic polymers, catalyst-functionalized MOFs have been studied for reactions ranging from coordination-mediated polymerization of ethylene to visible-light initiated radical polymerizations. Nevertheless, many polymerization reactions remain to be explored – and, no doubt, will be explored, given the remarkable structural and compositional diversity of attainable MOFs. Noteworthy emerging studies include work directed toward more sophisticated catalytic schemes such as polymer templating using MOF pore architectures and tandem copolymerizations using MOF-supported reaction centres. Finally, it is appropriate to recognize that MOFs themselves are synthetic polymers – albeit, uncoventional ones.

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

Mechanistic study of heterogeneous propene metathesis on WO x /SiO 2 catalysts

Silica-supported tungsten oxides are widely used industrial catalysts for olefin metathesis due to their low cost and robustness, yet the mechanisms for heterogeneously catalyzed metathesis reactions remain comparatively less understood. In this work, density-functional theory (DFT) calculations were used to study the model reactions of propene metathesis. Our calculations confirm that the metathesis reactions catalyzed by WO x /SiO 2 largely follow the Chauvin cycle, with an overall energetic barrier of 142 kJ/mol. To understand how the initial alkylidene active sites are generated, three mechanisms were examined: The pseudo-Wittig mechanism was found to be most favorable and proceeds with a metallacycle intermediate, while the allylic and vinylic C-H activations are much more difficult and require the reduction of surface sites to W(+4). Relative to the adsorbed reactant state, the overall intrinsic barriers for three mechanisms were computed to be 193, 261, and 355 kJ/mol, respectively. In conclusion, the higher barriers for active-site formation than for the metathesis cycle are consistent with the difficult, high-temperature pretreatment required in experiments to activate WO x /SiO 2 catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗