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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Recent advances in single-atom catalysts and single-atom alloys: opportunities for exploring the uncharted phase space in-between

Single-atom catalysts (SACs) have gained significant world-wide attention for exhibiting distinct reactivity and selectivity for important reactions, while utilizing precious metals at the ultimate limit of efficiency. SACs involving reducible oxide supports are good catalysts for oxidation reactions, and metal-acid site pairs enable Csingle bondC bond formation, but SACs can deactivate by sintering under reducing conditions. On the other hand, single-atom alloys (SAAs) are robust towards sintering and exhibit exceptional catalytic performance for a wide range of reactions under reducing conditions but can deactivate under oxidizing environments. Therefore, there is tremendous opportunity to explore and exploit catalytic reactivity between the SAC and SAA extremes. Furthermore, this paper focuses on recent advances in both fields and highlights prospects for future research.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2003

CVD Growth of Carbon Nanotubes: Structure, Catalyst, and Growth

Carbon nanotubes (CNTs) exhibit extraordinary mechanical and unique electronic properties and hence have been receiving much attention in recent years for their potential in nanoelectronics, field emission devices, scanning probes, high strength composites and many more applications. Catalytic decomposition of hydrocarbon feedstock with the aid of supported transition metal catalysts - also known as chemical vapor deposition (CVD) - has become popular to produce single-walled and multi-walled nanotubes (SWNTs, MWNTs) and multiwalled nanofibers (MWNFs). The ability to grow CNTs on patterned substrates and in vertically aligned arrays, and the simplicity of the process, has made CVD growth of CNTs an attractive approach.

Delzeit, Lance↗
DOE OSTI2021

Electron donation of non-oxide supports boosts O 2 activation on nano-platinum catalysts

Activation of O 2 is a critical step in heterogeneous catalytic oxidation. Here, the concept of increased electron donors induced by nitrogen vacancy is adopted to propose an efficient strategy to develop highly active and stable catalysts for molecular O 2 activation. Carbon nitride with nitrogen vacancies is prepared to serve as a support as well as electron sink to construct a synergistic catalyst with Pt nanoparticles. Extensive characterizations combined with the first-principles calculations reveal that nitrogen vacancies with excess electrons could effectively stabilize metallic Pt nanoparticles by strong p-d coupling. The Pt atoms and the dangling carbon atoms surround the vacancy can synergistically donate electrons to the antibonding orbital of the adsorbed O 2 . This synergistic catalyst shows great enhancement of catalytic performance and durability in toluene oxidation. The introduction of electron-rich non-oxide substrate is an innovative strategy to develop active Pt-based oxidation catalysts, which could be conceivably extended to a variety of metal-based catalysts for catalytic oxidation.

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

Tuning the reactivity of carbon surfaces with oxygen-containing functional groups

Oxygen-containing carbons are promising supports and metal-free catalysts for many reactions. However, distinguishing the role of various oxygen functional groups and quantifying and tuning each functionality is still difficult. Here we investigate the role of Brønsted acidic oxygen-containing functional groups by synthesizing a diverse library of materials. By combining acid-catalyzed elimination probe chemistry, comprehensive surface characterizations, 15N isotopically labeled acetonitrile adsorption coupled with magic-angle spinning nuclear magnetic resonance, machine learning, and density-functional theory calculations, we demonstrate that phenolic is the main acid site in gas-phase chemistries and unexpectedly carboxylic groups are much less acidic than phenolic groups in the graphitized mesoporous carbon due to electron density delocalization induced by the aromatic rings of graphitic carbon. The methodology can identify acidic sites in oxygenated carbon materials in solid acid catalyst-driven chemistry.

Zhou, Jiahua↗
DOE OSTI2021

Synthesis of Highly Active Pd@Cu–Pt/C Methanol Oxidation Electrocatalysts via Continuous, Co-Electroless Deposition

Controlled deposition of metals is essential for the creation of bimetallic catalysts having predictable composition and character. Continuous co-electroless deposition (co-ED) permits the creation of bimetallic catalysts with predictive control over composition. This method was applied to create a suite of Cu–Pt mixed-metal shell catalysts for use in methanol electrooxidation in direct methanol fuel cell applications (DMFCs). Enhanced performance of Cu–Pt compositions over Pt alone was predicted by existing computational studies in the literature. Experimental evidence from this study supports the bifunctional catalyst explanation for enhanced activity and confirms the optimum Cu:Pt ratio as Cu 3 Pt for this methanol electrooxidation. This ability to control the composition of a bimetallic shell can be extended to other systems where the ratio of two metals is critical for catalytic performance.

preparation↗
DOE OSTI2022

Intuitive study on the effect of support morphology over Cs-Ru/CeO 2 catalyst for microwave-initiated ammonia synthesis

Microwave-initiated ammonia synthesis is a potential candidate to the current Haber-Bosch process that can operate from stranded renewable energy source. Our previous studies indicated Cs-Ru/CeO 2 is a promising catalyst for microwave-assisted ammonia synthesis and the morphology of CeO 2 significantly affects the catalytic performance. In this paper, CeO 2 support with distinct morphologies nanorod, nanoparticle, and microstructure, is studied comprehensively at ambient pressure and low temperature under microwave irradiation. Moreover, CeO 2 nanorods of various sizes were synthesized at different timing (24, 36, and 48 h). Nanorods synthesized at 36 h exhibited superior activity associated to high dispersion and small Ru particle size.

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

Controlling Selective C–O and C–H Bond Scission of Methanol by Supporting Pt on TiN and Mo 2 N Model Surfaces and Powder Catalysts

Transition metal nitrides (TMNs) have been explored as effective supports for Pt due to their Pt-like electronic properties. However, there is a lack of fundamental understanding regarding the behavior of Pt on different TMNs (Pt/TMN). Herein two TMNs, Mo 2 N and TiN, were modified with Pt and compared using methanol decomposition as a probe reaction via both ultrahigh vacuum (UHV) studies on thin films and ambient-pressure batch reactor studies of powder catalysts. Temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) measurements were conducted under UHV conditions with Mo 2 N and TiN thin films. Mo 2 N was shown to favor C–H bond scission to form CO with a 56.2% selectivity, while TiN favored C–O bond scission to form CH 4 with a 74.5% selectivity. The addition of 0.9 monolayers (MLs) of Pt increased C–H bond scission selectivity to 89.7% and 49.2% for Mo 2 N and TiN respectively. Density functional theory (DFT) calculations on model surfaces revealed that the binding energy of O (BE *O ) was significantly reduced on Pt/TMNs, from −4.02 eV on Mo 2 N to −1.31 eV on Pt/Mo 2 N and −4.74 eV on TiN to −1.37 eV on Pt/TiN. As a result, C–O bond scission pathways were suppressed, leading to the preferential C–H bond scission that was observed experimentally. The C–O and C–H bond scission trends observed on thin films were then extended to powder catalysts, which demonstrated similar trends toward methanol decomposition. In conclusion, results from the current study establish that by combining UHV studies and DFT calculations over model surfaces, one can effectively predict the catalytic behavior of realistic TMN powder catalysts.

08 HYDROGEN↗
DOE OSTI2021

Highly dispersed Pt atoms and clusters on hydroxylated indium tin oxide: a view from first-principles calculations

Supported single-atom and small cluster catalysts have become highly popular in heterogeneous catalysis. These catalysts can maximize the metal atom utilization while still showing superior catalytic performance. One of the main challenges in producing these small cluster catalysts is their low binding strength with the support, which causes these small clusters to sinter into larger nanoparticles. We have used first-principles simulations to study small Pt n ( n : 1,2,3) clusters on indium oxide, tin doped indium oxide, and hydroxylated tin doped indium oxide. We report that the Pt n cluster is stabilized in the presence of tin and that this is especially the case for Pt single atoms on the hydroxylated indium tin oxide support, which are anchored to the support via the hydroxyl group. On this support, the Pt single atoms become more stable than Pt 2 and Pt 3 clusters, hence decreasing sintering. These findings provide a promising way to design single-atom catalysts on electrically conducting supports for electrocatalytic applications and to better understand how functional groups on supports can increase the adhesion of cluster catalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Selective and Stable In-Promoted Fe Catalyst for Syngas Conversion to Light Olefins

A selective and stable alumina-supported In-promoted Fe catalyst (10 mol % In based on Fe) was discovered for converting syngas (2:1 H 2 /CO ratio) to olefins with high selectivity (45% with CO 2 included) and a remarkable stability (72 h run) at a CO conversion of 10% at 400 °C and 5 bar. The X-ray photoelectron spectroscopy results indicated that incorporating In into Fe catalysts changed the chemical bonding state of Fe and Fe/In composition near the surface layers, which affected the catalytic reactivity. Steady-state isotopic transient kinetic analysis showed that more stable CHx fragments are present on the catalyst surface when incorporating In into Fe, which can promote C–C coupling reaction toward olefins. Our study demonstrates that introducing In into Fe catalysts on Al 2 O 3 support can lower CO activation abilities. It has more impacts on lowering hydrogenation activity, which permits more C–C couplings and like of “ene” hydrogenation. Furthermore, weakening CO adsorption both in terms of sites and strength encouraged CO toward hydrocarbons rather than CO 2 .

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

In Situ Strong Metal–Support Interaction (SMSI) Affects Catalytic Alcohol Conversion

Strong metal–support interactions (SMSIs) and catalyst deactivation have been heavily researched for decades by the catalysis community. The promotion of SMSIs in supported metal oxides is commonly associated with H 2 treatment at high temperature (>500 °C), and catalyst deactivation is commonly attributed to sintering, leaching of the active metal, and overoxidation of the metal, as well as strong adsorption of reaction intermediates. Alcohols can reduce metal oxides, and thus here we have hypothesized that catalytic conversion of alcohols can promote SMSIs in situ . In this work we show, via IR spectroscopy of CO adsorption and electron energy loss spectroscopy (EELS), that during 2-propanol conversion over Pd/TiO 2 coverage of Pd sites occurs due to SMSIs at low reaction temperatures (as low as ~ 190 °C). The emergence of SMSIs during the reaction ( in situ ) explains the apparent catalyst deactivation when the reaction temperature is varied. A steady-state isotopic transient kinetic analysis (SSITKA) shows that the intrinsic reactivity of the catalytic sites does not change with temperature when SMSI is promoted in situ ; rather, the number of available active sites changes (when a TiO x layer migrates over Pd NPs). SMSI generated during the reaction fully reverses upon exposure to O 2 at room temperature for ~15 h, which may have made their identification elusive up to now.

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

Electrically Insulated Catalyst–Ionomer Anode Interfaces toward Durable Alkaline Membrane Electrolyzers

Anion-exchange-membrane water electrolysis (AEMWE) is an emerging technology for scalable hydrogen production. AEMWE has poor durability when operating without supporting electrolyte due to the oxidation of ionomers and membranes in contact with the anode oxygen evolution reaction (OER) catalyst. We report a new “passivated” anode architecture for AEMWE where the OER catalysts and ionomers are physically separated with a thin film amorphous oxide coating that is electrically insulating but conductive to hydroxide ions. We find that 2–3 nm of HfO x passivation layers show sufficient hydroxide ion transport to minimally limit the cell performance while suppressing ionomer degradation with both Ir (500 mA·cm –2 for 40 h) and CoO x (1.0 A·cm –2 for 100 h) model porous-transport-layer-supported catalysts in AEMWE. As a result, this interfacial engineering approach guides electrode design to improve the durability of AEMWE, particularly for systems operating with pure-water feed.

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

Enhanced Oxygen Activation Achieved by Robust Single Chromium Atom-Derived Catalysts in Aerobic Oxidative Desulfurization

Oxidative desulfurization (ODS) plays critical roles in the production of high-quality sulfur impurity-free fuels, especially procedures using molecular oxygen as the sole oxidant. However, the state-of-the-art systems still rely on noble metal nanocatalysts, with deactivation issues caused by coking and sintering still present. In this work, leveraging the merits of single-atom catalysts (SACs) with earth-abundant metal cores and robust nanoporous supports, a series of catalysts composed of homogeneously distributed single chromium atoms anchored on multiwalled carbon nanotubes were fabricated and deployed to catalyze the aerobic ODS transformation. Adopting aromatic sulfur compound (ASC)-containing alkanes as a model system with molecular oxygen as the oxidant, efficient oxygen-to-active O 2 •– transformation and subsequent ASCs-to-sulfone conversion have been achieved, with the former benefiting from the chromium-active sites and the latter arising from the robust, nanoporous, and π-conjugated architecture of the supports. The attractive catalytic performance and cycling stability of the chromium-based SACs make them promising candidates in practical sulfur species removal from liquid fuels, supplying an alternative guidance on the catalyst design toward cost-effective and energy-efficient ODS procedures.

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

Three-way catalyst with reduced palladium loading and method of making the three-way catalyst

A three-way catalyst for reduced palladium loading is provided. The catalyst includes an inert substrate and a palladium catalyst material coating the substrate. The palladium catalyst material includes a support material formed from one of 10% CeO 2 /Al 2 O 3 , 20% CeO 2 —Al 2 O 3 (20CeAlOy), 30% CeO 2 —Al 2 O 3 (30CeAlOy), Al 2 O 3 , and MOx-Al 2 O 3 , wherein M is one of copper, iron, manganese, titanium, zirconium, magnesium, strontium, and barium. The palladium catalyst material includes a layer of CeO 2 material disposed upon the support material, wherein the layer of CeO 2 material is dispersed on a surface of the support material. The palladium catalyst material includes an active component including a layer of praseodymium oxide particles dispersed across the surface of the layer of CeO 2 material and a layer of palladium particles disposed upon and dispersed across the surface of the layer of CeO 2 material at locations each corresponding to a respective location of each of the praseodymium particles.

Gu, Yuntao↗
DOE OSTI2024

Acetylene ligands stabilize atomically dispersed supported rhodium complexes under harsh conditions

Facile sintering of atomically dispersed supported noble metal catalysts at catalytically relevant temperatures, particularly under reducing conditions, poses a challenge for their practical applications. Some ligands, such as carbonyls, aid in improving the stability at the expense of severely suppressing the catalytic activity. In this work, we demonstrate that substitution of the carbonyl ligands with reactive acetylene ligands can maintain the atomic dispersion of the supported mononuclear rhodium complex under harsh reducing conditions (>573 K), as confirmed by in-situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. In contrast, the supported rhodium carbonyl complex aggregates into nanoclusters under identical conditions. Furthermore, our results indicate that the acetylene ligands provide this anti-sintering ability while retaining the hydrogenation activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Bioadaptive Ni single atoms unlock high rate microbial electrosynthesis of isopropanol from CO 2

Hybrid systems that integrate electrochemical CO 2 reduction with microbial upgrading offer a viable route to high value organic compounds from CO 2 at ambient conditions. However, electrocatalyst deactivation in microbial growth media remains a key barrier, limiting efficiency and increasing cost. Here we show that a bioadaptive single-atom nickel catalyst (Ni SAC), coupled with genetically engineered Clostridium ljungdahlii, enables robust electrosynthesis of isopropanol (IPA) from CO 2 via a CO-mediated pathway. Instead of relying on H 2 as an electron carrier, the system applies high-rate CO formation in complex growth media, maintaining a tunable CO Faradaic efficiency up to 92%, which is 9.4 to 52.7 times greater than conventional Ag catalysts. This performance supports stable IPA production at current density of 10.8 A/m 2 and production rate of 161.3 mg/L/day. In situ Raman and X-ray absorption spectroscopy, together with theoretical calculations, indicate that the Ni SAC can resist competing organic adsorption and retain its coordination structure during CO 2 reduction in bioelectrolytes, providing a mechanistic basis for the catalyst stability and integrated process performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗