Search NASA⌕ Search

SEARCH · Search NASA

Results for “stability selection”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Recent Progress in Engineering Metal Halide Perovskites for Efficient Visible‐Light‐Driven Photocatalysis

Abstract Artificial photosynthesis has attracted increasing attention due to recent environmental and energy concerns. Metal halide perovskites (MHPs) demonstrating excellent optoelectronic properties have currently emerged as novel and efficient photocatalytic materials. Herein, the structural features of MHPs that are responsible for the photoinduced charge separation and charge migration properties are briefly introduced, and then important and necessary photophysical and photochemical aspects of MHPs related to photoredox catalysis are summarized. Subsequently, the applications of MHPs for solar energy harvesting and photocatalytic conversion, including H 2 evolution, CO 2 reduction, degradation of organic pollutants, and photoredox organic synthesis, are extensively demonstrated, with a focus on strategies for improving the performance (e.g., selectivity, activity, stability, recyclability, and environmental compatibility) of these MHP‐based photocatalytic systems. To conclude, existing challenges and prospects on the future development of MHP‐based materials towards photoredox catalysis applications are detailed.

Han, Chuang↗
DOE OSTI2017

Nitrogen-doped graphene catalysts: High energy wet ball milling synthesis and characterizations of functional groups and particle size variation with time and speed

Nitrogen-doped graphene (N-G) catalyst emerges as one of the promising non-platinum group metal (non-PGM) catalysts with the advantages of low cost, high oxygen reduction reaction (ORR) activity, stability, and selectivity to replace expensive PGM catalysts in electrochemical systems. This research investigated nanoscale high energy wet (NHEW) ball milling for the synthesis of N-G catalysts to make conventional problems such as sintering or localized overheating issues negligible. The successful synthesis of N-G catalysts with comparable catalytic performance to 10 wt% Pt/C by using this method has been published. This paper focuses on understanding the effect of grinding speed and grinding time on the particle size and chemical state of N-G catalysts through the physical and chemical characterization. The research result shows that (1) the final particle size, nitrogen doping percentage, and nitrogen bonding composition of synthesized N-G catalysts are predictable and controllable by adjusting the grinding time, the grinding speed, and other relative experimental parameters; (2) the final particle size of N-G catalysts could be estimated from the derived relation between the cracking energy density and the particle size of ground material in the NHEW ball milling process with specified experimental parameters; and (3) the chemical composition of N-G catalysts synthesized by NHEW ball milling is controllable by adjusting the grinding time and grinding speed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Investigation of Thermoplastic Polyurethanes Synthesized via Two Different Prepolymers

The man aim of this work was to investigate the effect of the molecular weight of polyols, mixture of prepolymers, and [NCO]/[OH] molar ratio used during the prepolymer chain extending step on the chemical structure, thermomechanical and mechanical properties, and thermal stability of thermoplastic poly(ether-urethane)s In this work thermoplastic poly(ether-urethane)s were synthesized by using polyols with a various molecular weight, 4,4′-diphenylmethane diisocyanate and bio-based glycol. Materials were obtained by a two-step method. The tests were carried out for polyurethanes obtained from a mixture of prepolymers and for reference samples. In the case of materials obtained with using mixture of prepolymers, the ratio of both prepolymers was determined on 50/50 weight percent. Soft segments of materials prepared with using mixture consist of two different polyols. The chemical structure was analyzed using FTIR spectroscopy. The Gaussian deconvolution technique was used to study the hydrogen bonding as well as to decompose carbonyl region of three peaks in various TPUs. The thermal degradation behavior was investigated by using thermogravimetric analysis at heating rates of 10 °C/min. It was confirmed that the mixture of prepolymers has an effect of the degree of phase separation, thermal stability and selected properties of synthesized thermoplastic poly(ether-urethane)s.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Single-atom materials boosting wearable orthogonal uric acid detection

Abstract Uric acid (UA) is a vital biomarker for the diagnosis and management of various health conditions, including cardiovascular diseases, gout, kidney disorders, metabolic syndrome, and wound healing. Despite significant advances in wearable sensor technology, challenges persist in developing wearable sensors that are capable of maintaining high sensitivity, selectivity, and stability. In this study, we present an epidermal sensing platform enhanced with single-atom materials (SAMs) designed for flexible and orthogonal electrochemical detection of UA. We designed and synthesized an SAM with Fe-N 5 active sites to boost the electrochemical sensing signals, integrating it with laser-engraved graphene (LEG) to fabricate a wearable SAM-based UA patch sensor. This design provides superior UA detection performance compared to sensors based on conventional nanomaterials. In addition, we enhanced the detection accuracy and range by using an orthogonal approach that combines direct oxidation through differential pulse voltammetry (DPV) along with parallel biocatalytic amperometric detection. The resulting SAM-based UA orthogonal sensor patch demonstrated exceptional performance in wearable applications through tests measuring sweat UA levels in subjects before and after consuming a purine-rich diet. Graphical Abstract

Ding, Shichao↗
DOE OSTI2015

Ethane and propane dehydrogenation over PtIr/Mg(Al)O

Increased demand for light alkenes has motivated research on the catalytic dehydrogenation of the light alkanes and on understanding the role of catalyst composition on the activity, selectivity, and stability of Pt-based catalysts used for this purpose. This study examines the structure and performance of Pt-Ir catalysts for ethane and propane dehydrogenation, and compares them with the performance of Pt and Pt-Sn catalysts. Nanoparticles of Pt, PtSn, and PtIr were prepared in a colloidal suspension and then dispersed onto calcined hydrotalcite (Mg(Al)O). After characterization to confirm formation of a bimetallic alloy, it was observed that at high conversions, Pt 3 Ir/Mg(Al)O exhibited lower initial activity than Pt 3 Sn/Mg(Al)O but greater stability to coke deposition. Intrinsic rate measurements at low feed residence time revealed the following trend in activity: Pt 3 Sn > Pt 3 Ir > Pt. DFT calculations carried out on tetrahedral clusters (Pt 4 , Pt 3 Ir, Pt 3 Sn) reveals that this trend in activity can be replicated and Ir is capable of alkane activation, a trait unique to this bimetallic system.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dual-atom Ag 2 /graphene catalyst for efficient electroreduction of CO 2 to CO

Electrochemical reduction of CO 2 into value-added carbon compounds offers a promising strategy to mitigate global warming, but present challenges for chemistry due to the poor selectivity and stability of electrocatalysts. In this work, we report a dual-atom Ag 2 /graphene catalyst featuring well-defined AgN 3 -AgN 3 active site for CO 2 electrochemical reduction. This dual-atom catalyst can drive CO 2 reduction reaction at a potential as high as -0.25 V, and exhibit excellent CO Faradic efficiency up to 93.4 % with a current density of 11.87 mA cm -2 at -0.7 V and long-term stability, far surpassing the single-atom Ag 1 /graphene and the traditional silver nanoparticle catalysts. Finally, DFT calculations reveal that the dual-atom Ag site lowers the barrier for the formation of *COOH by stabilizing the *CO 2 through the concomitant interactions with the C and an O atom of CO 2 , resulting in excellent catalytic performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Gold nanocatalysts supported on heterostructured PbSO4-MCF mesoporous materials for CO oxidation

Metal oxides are commonly used as the supports of gold nanoparticles for catalytic CO oxidation, whereas metal salts are rarely considered suitable supports. In the present work, we developed a new kind of gold nanocatalyst supported on heterostructured PbSO4-MCF mesoporous materials that was prepared by an in situ growth method using dodecylbenzenesulfonate (SOBS) as a sulfonate precursor. It was found that an Au/PbSO4-MCF (SDBS) catalyst preheated at 300 degrees C showed high CO conversion below 100 degrees C. In addition, the stability of selected catalysts was studied as a function of time on stream. Because of the alteration of surface properties, these Au nanocatalysts were highly sinter-resistant. Published by Elsevier B.V.

Li, Lin↗
DOE OSTI2012

Synthesis of butenes through 2-butanol dehydration over mesoporous materials produced from ferrierite

Mesoporous materials synthesized from commercial ferrierite (MMZ-FER) were applied to butanol dehydration. The MMZ-FER was produced by disassembling ferrierite into unit structures in the presence of an alkali solution, adding a surfactant as a templating material, followed by hydrothermal treatment. The effect of the alkali/(Si+Al) ratio in the disassembling step on the characteristics of the catalyst and butanol dehydration performance were investigated. The MMZ-FER materials, synthesized in a condition in which the NaOH/(Si + Al) mole ratio in the disassembling step was 0.67 and 1.0, demonstrated similar textural properties to those of MCM-41. Many weak acid sites developed on the MMZ-FER(0.67) and MMZ-FER(1.0) samples, which is attributed to the creation of ferrierite-induced acid sites. The MMZ-FER materials showed excellent catalytic activity, selectivity, and stability during the dehydration of 2-butanol.

1-butene↗
DOE OSTI2026

Rational design of heterogeneous single-site catalysts via surface organometallic chemistry

Single-site heterogeneous catalysts offer an attractive route to unite the molecular precision of homogeneous catalysis with the durability and practical advantages of solids. Surface organometallic chemistry (SOMC) provides a particularly powerful strategy for this purpose by grafting molecular precursors onto tailored surfaces and converting support functionalities into ligand environments for isolated metal centers. As a result, SOMC brings the language and logic of coordination chemistry to heterogeneous catalysis, where the support becomes an integral part of the active site coordination sphere. This Review surveys recent progress in the rational design of SOMC-derived single-site catalysts, with emphasis on synthetic routes, post synthetic transformations, and the deliberate tuning of catalytic behavior through metal-support interactions. Discussions are made on how support identity, hydroxyl topology, acidity, and redox activity shape the geometry, electronic structure, and oxidation state of supported metal sites, as well as how these factors determine activity, selectivity, and stability. We also examine a central limitation of these systems: despite their molecularly informed design, supported single sites often exist as structurally distributed ensembles rather than uniform species, particularly on amorphous supports. This site heterogeneity, along with catalyst dynamics under operating conditions, remains a major barrier to definitive structure-activity relationships. Therefore, emerging approaches that combine advanced characterization, first-principles modeling, ensemble kinetics, and machine learning to resolve active-site structure and guide catalyst development are highlighted. Together, these advances position SOMC as a versatile coordination chemistry framework for the predictive design of heterogeneous catalysts with well-defined molecularly tailored active sites.

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

Heterogeneous hydroformylation of alkenes by Rh-based catalysts

Heterogeneously catalyzed hydroformylation reactions avert the problems of separation in homogeneous reactions, reduce the discharge of phosphorus-containing wastes, and prevent the loss of precious metals. This review summarizes the developments of catalysts for heterogeneous hydroformylation in the last decade and proposes potential modification methods for future improvements. The hydroformylation properties of different reactants are compared in order to emphasize the fact that various olefins face unique challenges. The hydroformylation of ethylene requires the enhancement of catalytic activity and chemoselectivity, whereas that of propylene needs improvements in both chemoselectivity and regioselectivity. The hydroformylation of longer-chain olefins and styrene seeks further improvement in regioselectivity. The catalytic properties of activity, selectivity, and stability can be tuned through electronic effects (bimetallic effects, phosphine ligands, and single-atom catalysts), steric hindrance (encapsulation structures, diphosphine ligands, and local functional groups), and reaction condition optimization (temperature, pressure, and solvents). Furthermore, the understanding of these effects is critical in future catalyst design for heterogeneous hydroformylation reactions.

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

Transition metal carbides and nitrides as catalysts for thermochemical reactions

Transition metal carbides and nitrides (TMCs and TMNs) have attracted much attention due to their unique physical and chemical properties brought by the incorporation of interstitial carbon and nitrogen into the crystal lattice of the parent metals. Recent advances in utilizing TMCs and TMNs have revealed their intriguing catalytic properties in many industrially important reactions, including heteroatom removal, CO 2 activation, alcohol reforming, and water–gas shift reactions. The promising activity, selectivity, and stability of TMCs and TMNs, either as catalysts or as supports for other metals, are often attributed to their strong interactions with the adsorbates, tunable surface properties, as well as the synergy with supported metals. This review summarizes the synthesis and characterization of TMC and TMN model surfaces and powder catalysts, and uses several case studies to demonstrate their unique catalytic properties in these important reactions. Finally, a discussion is also provided regarding the challenges and opportunities associated with the utilization of TMCs and TMNs in thermocatalysis.

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

Statistical analysis of HAADF-STEM images to determine the surface coverage and distribution of immobilized molecular complexes

The surface immobilization of molecular catalysts is attractive because it combines the benefits of homogeneous and heterogeneous catalysis. However, determining the surface coverage and distribution of a molecular catalyst on a solid support is often challenging, inhibiting our ability to design improved catalytic systems. Here, in this work, we demonstrate that the combination of scanning transmission electron microscopy (STEM) and image analysis of the individual positions of heavy atoms in transition metal complexes via a convolutional neural network (CNN) allows statistically robust determination of the surface coverage and distribution of immobilized molecular catalysts. These observations provide information about how changes in the functionalization conditions, attachment group, and structure of the molecular catalyst affect the surface coverage and distribution, providing insight into the chemical mechanism of surface immobilization. The method could be generally valuable for correlating the surface coverage and distribution to the activity, selectivity, and stability of a catalytic system.

HAADF-STEM↗
DOE OSTI2019

Colloidal nanocrystals for heterogeneous catalysis

Catalytic materials are an essential component of the chemical industry. They find applications in everything from fine chemical manufacturing to greenhouse gas mitigation. They are indispensable for developing a sustainable future. Their development has been continuous, from early trial and error efforts to the first fundamental insights gained through surface science, to modern in-situ characterization and computational predictions. The accumulation of knowledge on the working principles of catalytic surfaces allowed designing and producing better systems with improved performance. Even though tremendous progress has been made thanks to surface science techniques, these studies are usually performed under ultra-high vacuum and are therefore limited in their applicability to more relevant industrial conditions. The control over size, shape and composition in colloidal nanocrystals makes them formidable precursors for model heterogeneous catalysts. These model systems enable linking the insights from surface science studies via in-situ and operando studies to realistic catalytic reaction conditions. In this review, colloidal nanocrystals are presented as powerful building blocks for catalytic materials in the quest for fundamental understanding. A review of the principal methods to produce colloidal nanocrystals with a high level of control is reported, complemented by procedures for how to prepare active catalysts from these particles. Examples and guidelines for the catalytic applications of these materials revolve around the three guiding objectives in catalysis science: activity, selectivity and stability. This work will be limited to examples of this colloidal approach in the areas of thermal, electro- and photocatalysis. In conclusion, the exposed approaches can be used and extended to many other areas of catalysis science, thus providing a new avenue to explore fundamentals and applications of catalytic materials.

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

Shape-persistent phthalocyanine cages

Phthalocyanine (Pc), an electro-redox active moiety, has many attractive properties stemming from its large aromatic system and ability to act as a catalyst in electrochemical reactions, such as the CO 2 reduction reaction (CO 2 RR). However, due to the synthetic challenge related to geometric requirements and poor solubility (strong aggregation), discrete shape-persistent cages consisting of site-isolated, readily accessible Pc moieties have not been available. Here, we report the synthesis of Zn- and Ni-metallated Pc-based molecular cages via one-step dynamic spiroborate linkage formation in high yields. The ZnPc cage structure is unambiguously elucidated at the atomic level by single-crystal X-ray diffraction. Moreover, owing to the site-isolated redox-active metal centers, readily accessible intrinsic cavity, and shape-persistent backbone, the Ni-metallated Pc (NiPc) cage exhibits high catalytic efficiency, selectivity, and stability, superior to the non-caged control molecules in electrocatalytic CO 2 RR.

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

Memory Effect on the Synthesis of Perovskite-Type Li-Ion Conductor Li x La 2/3– x /3 TiO 3 (LLTO)

The structural chemistry of the solid ion-conducting Li x La 2/3–x/3 TiO 3 (LLTO) is rich with various polymorphs related to atomic segregation. Here, we explored the LLTO reaction pathway from various structurally related precursors (La 2 LiO 3 H, Li 2 TiO 3 , and Li 4 Ti 5 O 12 ), focusing on the effects of LLTO-like structural motifs in precursors using a combination of experimental and computational techniques. Density functional theory (DFT) calculations revealed that the failure of syntheses to produce LLTO below 1300 °C is due to the presence of multiple competing low-energy phases that result in competitive byproduct formation. In all syntheses where T = 1300 °C, LLTO was the sole product; however, varying phase fractions of I4/mcm and P4/nbm polymorphs and double-perovskite P4/mmm can be obtained depending on the synthesis route. This is an unusual result as at 1300 °C, LLTO should only be the ideal cubic Pm-3m perovskite structure, yet there appears to be a memory effect from the different precursors resulting in the unique phase selectivity and stabilization.

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

Bifunctional Electrocatalysts with High-Entropy Alloys: Bridging Hydrogen Evolution and Oxygen Reduction

High-entropy alloys (HEAs) have emerged as a promising class of bifunctional electrocatalysts capable of simultaneously driving the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) with high activity and durability. Their near-equiatomic multicomponent compositions give rise to unique physicochemical characteristics, including lattice distortion, sluggish diffusion, high-entropy stabilization, and pronounced electronic heterogeneity, that collectively generate diverse and synergistic active sites inaccessible in conventional alloys. This review summarizes recent progress in HEA-based bifunctional electrocatalysis, with a focus on the fundamental mechanisms governing HER and ORR activity, stability, and selectivity. We discuss advances in synthesis strategies, ranging from confined growth and step-alloying to scalable continuous-flow methods, that enable precise control over composition, size, and surface structure. Complementary computational and data-driven approaches, including density functional theory, machine-learning-assisted screening, and descriptor development, are highlighted as essential tools for navigating the vast HEA design space and establishing structure−property relationships. Particular attention is paid to adsorption-energy distributions, multisite cooperativity, and environmental effects under realistic electrochemical conditions. Finally, we outline current challenges and future opportunities for integrating mechanistic understanding with AI-guided, closed-loop design frameworks to accelerate the discovery of next-generation HEA bifunctional electrocatalysts for sustainable energy conversion.

Alloys↗