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Results for “Heterogeneous catalysis”

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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Controlling Exsolution Dynamics in High‐Entropy Oxides for Highly Active and Selective Acetylene Semi‐Hydrogenation

Exsolution-derived catalysts feature robust metal–support interactions that enhance catalytic performance; yet achieving precise control over exsolution dynamics in multicomponent oxides remains challenging. In this study, we demonstrate that exsolution behavior in high-entropy oxides (HEOs) can be rationally tuned through coupled lattice- and valence-engineering to create a highly active and selective catalyst for acetylene semi-hydrogenation. Incorporation of Li + into a rock salt-structured HEO (LiNiMgCuZnCoO x and LiHEO) induces local lattice distortion, generates oxygen vacancies, and partially oxidizes Co sites from Co 2+ to Co 3+ , collectively modulating local charge redistribution. This strategy enables facilitated Cu nanoparticle exsolution and alters the exsolution sequence from Cu 0 > Ni 0 > Co 0 in pristine HEO to Cu 0 > Co 0 > Ni 0 in the LiHEO. The resulting catalyst via controlled exsolution exhibits superior activity and ethylene selectivity, outperforming state-of-the-art transition metal systems. This work establishes entropy-enabled lattice and valence engineering as a facile route to programmable exsolution for enhanced catalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Direct Comparison of the Activity and Selectivity of Rh 1 Cu and Ni 1 Cu Single-Atom Alloy Sites for Ethanol Decomposition

Ethanol is an important source of clean hydrogen, acetaldehyde, acetic acid, acetate esters, and light hydrocarbons. Controlling the divergent reaction pathways to these products requires understanding how different active sites influence the elementary steps involved. Herein, we present a combined surface science, theory, and nanoparticle catalysis study demonstrating how two single-atom dopants (Rh and Ni) in a Cu host can distinctively alter the selectivity of alcohol conversion. Specifically, our model studies reveal that ethanol reacts on Ni 1 Cu single-atom alloys to selectively produce acetaldehyde, whereas methane and CO are also formed on Rh 1 Cu single-atom alloys. Interestingly, these different reactivities are in contrast to the behavior of the pure metals as Ni(111) and Rh(111) surfaces favor methane/CO and surface carbon/CO, respectively. DFT calculations of reaction pathways and simulated product desorption based on microkinetic analyses explain these reactivity differences, demonstrating that C–C cleavage leading to methane formation has a lower barrier on Rh single-atom sites. To test the catalytic relevance of these fundamental results we synthesized and characterized supported Ni 1 Cu and Rh 1 Cu single-atom alloy nanoparticles with dopant:Cu ratios of 1:200. Flow reactor results revealed that both Ni and Rh increased ethanol conversion over Cu and that Ni 1 Cu catalysts were >99.9% selective to acetaldehyde, while Rh 1 Cu also produced 0.6%–2.6% of equimolar methane and CO between 433 and 493 K, demonstrating that C–C bond cleavage is enabled by isolated Rh sites. Furthermore, these catalytic results bridge the pressure and materials gaps, and together, this study provides insights into how different isolated dopant sites promote different catalytic pathways.

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

Unusual Electrochemical Activity of Thin SiO 2 Layers Leads to Instability of Molecular Attachment in Hybrid Photoelectrodes

Hybrid photoelectrodes, comprised of a light-absorbing semiconductor and a surface-integrated molecular catalyst, are attractive for applications in artificial photosynthesis, since they combine the advantages of broadband semiconductor light absorption with the selectivity of molecular catalysis. A widely used class of hybrid photoelectrodes is based on Si substrates passivated by a thin (<3 nm) layer of silicon oxide, which is commonly prepared by controlled chemical or thermal oxidation, resulting in chemical oxide (ChO) or thermal oxide (ThO) layers, respectively. However, the electrochemical stability of these oxide layers, and the chemical stability of the semiconductor-molecule assembly in hybrid photoelectrodes, are not well understood, with evidence that covalently-bound molecules detach from the oxide surface upon application of cathodic bias. We have examined the intrinsic electrochemical reactivity of silicon oxide layers and how it affects the attachment of molecular monolayers. We determined that the surface of Si|ThO is primarily terminated with hydrophobic siloxane moieties, whereas that of Si|ChO contains a higher concentration of hydrophilic silanol groups. Initial high current densities for Si|ChO under applied bias up to -2 V vs. Ag/AgCl, decrease during repeated cyclic voltammetry scans, due to the consumption of surface-bound water. This is manifested by a reversible wave around -0.5 V in CH 3 CN solution, and a similar pH-dependent wave in water, revealing the pK a of the silanol groups to be ~4. Here, our combined observations support the electrochemically-induced dehydration of the SiO 2 surface, which converts silanol groups to siloxanes and proceeds through an H-atom intermediate that is most likely stabilized by pentavalent Si. We propose that similar reactivity is responsible for the electrochemical loss of alkylsiloxane-attached molecules under cathodic bias, which has important implications for the choice of catalyst attachment strategy in hybrid photoelectrodes.

14 SOLAR ENERGY↗
DOE OSTI2019

Knittable and Washable Multifunctional MXene-Coated Cellulose Yarns

Textile-based electronics enable the next generation of wearable devices, which have the potential to transform the architecture of consumer electronics. Highly conductive yarns that can be manufactured using industrial-scale processing and be washed like everyday yarns are needed to fulfill the promise and rapid growth of the smart textile industry. By coating cellulose yarns with Ti 3 C 2 T x MXene, highly conductive and electroactive yarns are produced, which can be knitted into textiles using an industrial knitting machine. It is shown that yarns with MXene loading of ≈77 wt% (≈2.2 mg cm -1 ) have conductivity of up to 440 S cm -1 . After washing for 45 cycles at temperatures ranging from 30 to 80 °C, MXene-coated cotton yarns exhibit a minimal increase in resistance while maintaining constant MXene loading. The MXene-coated cotton yarn electrode offers a specific capacitance of 759.5 mF cm -1 at 2 mV s -1 . Additionally, a fully knitted textile-based capacitive pressure sensor is also prepared, which offers high sensitivity (gauge factor of ≈6.02), wide sensing range of up to ≈20% compression, and excellent cycling stability (2000 cycles at ≈14% compression strain). This work provides new and practical insights toward the development of platform technology that can integrate MXene in cellulose-based yarns for textile-based devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

From Highly Purified Boron Nitride to Boron Nitride-Based Heterostructures: An Inorganic Precursor-Based Strategy

The current approaches used to fabricate hexagonal boron nitrides (h-BN) from boron trioxide and urea always results in contamination of the h-BN product with carbon/oxygen. Thus, discovering a facile way of mass producing high-purity h-BN remains a challenge. A simple yet highly efficient thermal treatment approach to large-scale fabrication of nanoporous h-BN with high yield, high purity, and high crystallinity is described using NaNH 2 and NaBH 4 as the oxygen- and carbon-free precursors. The unique properties of inorganic metal salts, i.e., high melting point and strong electrostatic interaction with carbon substrates, render this strategy suitable for the production of homogeneous h-BN/mesoporous carbon and h-BN/carbon nanotube heterostructures of high crystallinity, high h-BN dispersity, and with a strong interfacial effect. Therefore, these unique features make them promising candidates for supercapacitor applications, resulting a significantly enhanced specific capacitance. This study provides new insight into the fabrication of high-purity h-BN and h-BN-based heterostructures thus expanding their application in the field of energy storage and transformation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Monolayer Support Control and Precise Colloidal Nanocrystals Demonstrate Metal-Support Interactions in Heterogeneous Catalysts

We report that electronic and geometric interactions between active and support phases are critical in determining the activity of heterogeneous catalysts, but metal-support interactions are challenging to study. Here, it is demonstrated how the combination of the monolayer-controlled formation using atomic layer deposition (ALD) and colloidal nanocrystal synthesis methods leads to catalysts with sub-nanometer precision of active and support phases, thus allowing for the study of the metal-support inter-actions in detail. The use of this approach in developing a fundamental understanding of support effects in Pd-catalyzed methane combustion is demonstrated. Uniform Pd nanocrystals are deposited onto Al2O 3 /SiO 2 spherical supports prepared with control over morphology and Al 2 O 3 layer thicknesses ranging from sub-monolayer to a ≈4 nm thick uniform coating. Dramatic changes in catalytic activity depending on the coverage and structure of Al 2 O 3 situated at the Pd/Al 2 O 3 interface are observed, with even a single monolayer of alumina contributing an order of magnitude increase in reaction rate. By building the Pd/Al 2 O 3 interface up layer-by-layer and using uniform Pd nanocrystals, this work demonstrates the importance of controlled and tunable materials in determining metal-support interactions and catalyst activity.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Rigid Supramolecular Aramid Nanotubes as Catalyst Supports

Solution‐phase heterogeneous catalysts benefit from nanoscale dimensions, which maximize specific surface area and enhance catalytic activity. However, the ease of recovering such nanocatalysts depends on the design of the support materials, which are often particle‐like. Rigid 1D nanomaterials are proposed as supports that can enhance separability while offering high volumetric specific surface area for greater catalyst loading and activity. Here, aramid amphiphiles (AAs) are designed to spontaneously self‐assemble in water into high‐aspect‐ratio supramolecular nanotubes with tunable surface chemistry. These AA nanotubes exhibit high persistence lengths (P = 750 ± 340 µm) and mechanical stiffnesses (3 N/m). Incorporating surface thiol groups enables immobilization of catalytic gold nanoparticles. The resulting AA nanotube‐gold nanoparticle complexes exhibit high catalytic activity, efficient recoverability via simple microfiltration, and sustained reusability over ten reaction cycles. This study demonstrates the utility of molecular self‐assembled 1D nanomaterials as versatile scaffolds for the reuse and recovery of nanoscale catalysts.

1D nanomaterials↗
DOE OSTI2019

Tuning the Electrochemical Performance of Titanium Carbide MXene by Controllable In Situ Anodic Oxidation

MXenes are a class of two-dimensional (2D) transition metal carbides, nitrides and carbonitrides that have shown promise for high-rate pseudocapacitive energy storage. However, the effects that irreversible oxidation have on the surface chemistry and electrochemical properties of MXenes are still not understood. In this work, we report on a controlled anodic oxidation method which improves the rate performance of titanium carbide MXene (Ti 3 C 2 T x , T x refers to -F, =O, -Cl and -OH) electrodes in acidic electrolytes. The capacitance retention at 2000 mV s -1 (with respect to the lowest scan rate of 5 mV s -1 ) increases gradually from 38% to 66% by tuning the degree of anodic oxidation. At the same time, a loss in the redox behavior of Ti 3 C 2 T x is evident at high anodic potentials after oxidation. Several analysis methods are employed to reveal changes in the structure and surface chemistry while simultaneously introducing defects, without compromising electrochemically active sites, are key factors for improving the rate performance of Ti 3 C 2 T x . This study demonstrates improvement of the electrochemical performance of MXene electrodes by performing a controlled anodic oxidation.

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

Predicting a Sharp Decline in Selectivity for Catalytic Esterification of Alcohols from van der Waals Interactions

Controlling the selectivity of catalytic reactions is a critical aspect of improving energy efficiency in the chemical industry; thus, predictive models are of key importance. Herein the performance of a heterogeneous, nanoporous Au catalyst is predicted for the complex catalytic self-coupling of the series of C 2 –C 4 alkyl alcohols, based solely on the known kinetics of the elementary steps of the catalytic cycle for methanol coupling, using scaling methods augmented by density functional theory. Notably, a sharp decrease in selectivity for ester formation with increasing molecular weight to favor the aldehyde due to van der Waals interactions of reaction intermediates with the surface was predicted and subsequently verified quantitatively by experiment. Further, the agreement between theory and experiment clearly demonstrates the efficacy of this approach for building a predictive model of catalytic behavior for a homologous set of reactants using a small set of experimental information.

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

Gel-Derived Amorphous Bismuth–Nickel Alloy Promotes Electrocatalytic Nitrogen Fixation via Optimizing Nitrogen Adsorption and Activation

To achieve the electrochemical nitrogen reduction reaction (NRR) for efficient and sustainable NH 3 production, catalysts should exhibit high selectivity and activity with optimal adsorption energy. Herein we developed a three-dimensional (3D) amorphous BiNi alloy toward a significantly enhanced NRR compared with its crystalline and metal counterparts. Ni alloying enables the chemisorption of nitrogen and the lower fre-energy change for the *NNH formation, and the 3D alloy electrocatalyst exhibits high catalytic activity for NH 3 production with a yield rate of 17.5 μg h -1 mg cat -1 and Faradaic efficiency of 13.8 %. The enhanced electron transfer and increased electrochemical surface area were revealed in the interconnected porous scaffold, affording it sufficiently efficient and stable activity for potential practical applications. Furthermore, this work offers new insights into optimizing the adsorption energy of reactants and intermediates combined with tuning the crystallinity of NRR electrocatalysts.

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

Precise Identification and Characterization of Catalytically Active Sites on the Surface of γ-Alumina

γ-alumina is one of the oldest and most important commercial catalytic materials with high surface area and stability. These attributes enabled its use as the first commercial large-scale heterogeneous catalyst for ethanol dehydration. Despite progress in materials characterization the nature of the specific sites on the surface of γ-alumina that are responsible for its unique catalytic properties has remained obscure and controversial. By using combined infrared spectroscopy, electron microscopy and solid-state nuclear magnetic resonance measurements we identify the octahedral, amphoteric (O) 5 Al(VI)-OH sites on the (100) segments of massively restructured (110) facets on typical rhombus-platelet γ-alumina as well as the (100) segments of irrational surfaces (invariably always present in all γ-alumina samples) responsible for its unique catalytic activity. Such (O) 5 Al(VI)-OH sites are also present on the macroscopically defined (100) facets of γ-alumina with elongated/rod-like geometry. The mechanism by which these sites lose -OH groups upon thermal dehydroxylation resulting in coordinatively unsaturated penta-coordinate Al +3 O 5 sites is clarified. These coordinatively unsaturated penta-coordinate Al sites produce well-defined thermally stable Al-carbonyl complexes. Overall, our findings contribute to the understanding of the nature of coordinatively unsaturated Al sites on the surface of γ-alumina and their role as catalytically active sites.

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

Thermal Unequilibrium of PdSn Intermetallic Nanocatalysts: From In Situ Tailored Synthesis to Unexpected Hydrogenation Selectivity

Effective control on chemoselectivity in the catalytic hydrogenation of C=O over C=C bonds is uncommon with Pd-based catalysts because of the favored adsorption of C=C bonds on Pd surface. Here we report a unique orthorhombic PdSn intermetallic phase with unprecedented chemoselectivity toward C=O hydrogenation. We observed the formation and metastability of this PdSn phase in situ. During a natural cooling process, the PdSn nanoparticles readily revert to the favored Pd 3 Sn 2 phase. Instead, using a thermal quenching method, we prepared a pure-phase PdSn nanocatalyst. Furthermore, PdSn shows an >96% selectivity toward hydrogenating C=O bonds of various α,β-unsaturated aldehydes, highest in reported Pd-based catalysts. Further study suggests that efficient quenching prevents the reversion from PdSn- to Pd 3 Sn 2 -structured surface, the key to the desired catalytic performance. Density functional theory calculations and analysis of reaction kinetics provide an explanation for the observed high selectivity.

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

A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R 3 Si + Species

The silylium-like surface species [ i Pr 3 Si][(R F O) 3 Al-OSi≡)] activates (N^N)Pd(CH 3 )Cl (N^N=Ar-N=CMeMeC=N-Ar, Ar=2,6-bis(diphenylmethyl)-4-methylbenzene) by chloride ion abstraction to form [(N^N)Pd-CH 3 ][(R F O) 3 Al-OSi≡)] ( 1 ). A combination of FTIR, solid-state NMR spectroscopy, and reactions with CO or vinyl chloride establish that 1 shows similar reactivity patterns as (N^N)Pd(CH 3 )Cl activated with Na[B(Ar F ) 4 ]. Multinuclear 13 C{ 27 Al} RESPDOR and 1 H{ 19 F} S-REDOR experiments are consistent with a weakly coordinated ion-pair between (N^N)Pd-CH 3 + and [(R F O) 3 Al-OSi≡)]. 1 catalyzes the polymerization of ethylene with similar activities as [(N^N)Pd-CH 3 ] + in solution and incorporates up to 0.4% methyl acrylate in copolymerization reactions. 1 produces polymers with significantly higher molecular weight than the solution catalyst, and generates the highest molecular weight polymers currently reported in copolymerization reactions of ethylene and methylacrylate.

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

Steam-Assisted Selective CO 2 Hydrogenation to Ethanol over Ru–In Catalysts

Multicomponent catalysts can be designed to synergistically combine reaction intermediates at interfacial active sites, but restructuring makes systematic control and understanding of such dynamics challenging. In this work, we unveil how reducibility and mobility of indium oxide species in Ru-based catalysts crucially control the direct, selective conversion of CO 2 to ethanol. When uncontrolled, reduced indium oxide species occupy the Ru surface, leading to deactivation. With the addition of steam as a mild oxidant and using porous polymer layers to control In mobility, Ru–In 2 O 3 interface sites are stabilized, and ethanol can be produced with superior overall selectivity (70 %, rest CO). Our work highlights how engineering of bifunctional active ensembles enables cooperativity and synergy at tailored interfaces, which unlocks unprecedented performance in heterogeneous catalysts.

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

Rhodium Single–Atom Catalysts on Titania for Reverse Water Gas Shift Reaction Explored by First Principles Mechanistic Analysis and Compared to Nanoclusters

The thermocatalytic reduction of CO2 by H2 often proceeds via two competing reaction mechanisms—the reverse water gas shift reaction (rWGSR, CO2 + H2 ⇌ CO + H2O) and methanation (CO2 + 4H2 ⇌ CH4 + 2H2O). Atomically dispersed Rh1 catalysts on TiO2 show high selectivity toward the rWGSR compared with larger Rh nanoclusters, but the origin of this size-dependent selectivity has not been fully explained. Here we report density functional theory (DFT) calculations and microkinetic simulations that clarify the Rh1 active sites and rWGSR pathway on anatase TiO2(101), as well as the high rWGSR selectivity of Rh1 compared with supported Rhx (x = 2–8 atoms) nanoclusters. DFT-computed formation energies, vibrational frequency analysis, and microkinetic modeling suggest three plausible active sites: Rh1 on titania (Rh1/TiO2(101)), Rh1 with a nearby hydroxyl group (Rh1OH/TiO2(101)), and Rh1 near an oxygen vacancy at a three-fold coordinated site (Rh1 near O3cvac). Predicted turnover frequencies and apparent activation barriers for Rh1 indicate a faster reaction involving CO2 dissociation assisted by a support oxygen vacancy via Rh1 near O3cvac, as well as slower reactions involving Rh1OH/TiO2(101) or Rh1/TiO2(101) through a COOH intermediate. Furthermore, these Rh1 sites are selective toward CO rather than CH4 because of the weak adsorption of CO, large barrier for C-O bond dissociation, and the lack of nearby metal sites for H2 dissociation, in contrast to Rhx nanoclusters, including Rh2 dimers.

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

Challenges and Opportunities of Fe-based Core-Shell Catalysts for Fischer-Tropsch Synthesis

Here, Fe-based catalysts are an active, selective, and low-cost option for tuning Fischer-Tropsch synthesis (FTS) selectivity toward desirable light olefins. By encapsulating Fe within ZSM-5, the resultant core-shell catalysts have the potential to control the product distribution via secondary reactions that occur over the acid sites of the zeolite shell. In this paper, Fe is encapsulated within ZSM-5 via the seed-directed growth technique and characterized with a suite of analytical techniques including Mössbauer spectroscopy and X-ray absorption fine structure (XAFS). Characterization of the core-shell catalysts indicates that some of the Fe-based active phase is destabilized during seed-directed growth, demonstrating the challenges associated with encapsulating an Fe-based active phase within zeolites. However, comparing FTS performance of the core-shell catalyst with the Fe-based control synthesized via incipient wetness impregnation demonstrates improved selectivity toward the desired C 2 -C 4 olefins and C 5+ hydrocarbons.

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

Microkinetic Modeling of the Transient CO 2 Methanation with DFT–Based Uncertainties in a Berty Reactor

The transient operation of methanation reactors can become desirable when coupled with fluctuating renewable energies in Power-to-Gas scenarios, which requires suitable kinetic approaches that can describe the transient catalytic phenomena. A combined experimental and theoretical investigation of the transient CO 2 methanation is conducted using concentration forcing to derive a suitable microkinetic model. Methanation experiments are performed with a Ni/SiO 2 catalyst in a Berty-type reactor at industrially relevant conditions. The microkinetics are based on previous work and were automatically constructed for the Ni(111) facet using the Reaction Mechanism Generator. A feasible set of energetic parameters of the microkinetic models was identified in a theory-constrained optimization procedure within the DFT uncertainty space that can accurately reproduce the experimental results on a first-principles basis. The microkinetic model unravels that the formation of H 2 O* and CH 3 * control the activity and selectivity of Ni(111) under the investigated conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗