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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Recent Progress in Electrochemical Nitrogen Reduction on Transition Metal Nitrides

Distributed electrochemical nitrogen reduction reaction (ENRR) powered by renewable energy for the on-site production of ammonia is an attractive alternative to the industrial Haber–Bosch process, which is responsible for roughly 2 % of global energy consumption. Here, in this Review, we summarize recent progress in the ENRR catalyzed by transition metal nitrides (TMNs). The unique electronic structures of TMNs make them promising ENRR catalysts for active and selective ammonia production, which have been predicted theoretically and demonstrated experimentally. Reaction pathways and deactivation mechanisms of the ENRR on different TMNs are surveyed, and current understanding of structure-activity relations is discussed. To develop highly active, selective, and stable TMN catalysts for industrial-scale ENRR, membrane electrode assembly configuration is recommended in catalyst evaluation. Furthermore, we highlight the importance of developing mechanistic understanding on ENRR with different operando spectroscopic techniques.

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

Hydrogenolysis of Poly(Ethylene–co–Vinyl Alcohol) and Related Polymer Blends over Ruthenium Heterogeneous Catalysts

The hydrogenolysis of polymers is emerging as a promising approach to deconstruct plastic waste into valuable chemicals. Yet, the complexity of plastic waste, including multilayer packaging, is a significant barrier to handling realistic waste streams. Herein, we reveal fundamental insights into a new chemical route for transforming a previously unaddressed fraction of plastic waste – poly(ethylene–co­­–vinyl alcohol) (EVOH) and related polymer blends – into alkane products. Additionally, we report that Ru/ZrO2 is active for the concurrent hydrogenolysis, hydrogenation, and hydrodeoxygenation of EVOH and its thermal degradation products into alkanes (C1–C35) and water. Detailed reaction data, product analysis, and catalyst characterization reveal that the in–situ thermal degradation of EVOH forms aromatic intermediates that are detrimental to catalytic activity. Increased hydrogen pressure promotes hydrogenation of these aromatics, preventing catalyst deactivation and improving alkane product yields. Calculated apparent rates of C–C scission reveal that the hydrogenolysis of EVOH is slower than low–density polyethylene. We apply these findings to achieve hydrogenolysis of EVOH/polyethylene blends and elucidate the sensitivity of hydrogenolysis catalysts to such blends. Overall, we demonstrate progress towards efficient catalytic processes for the hydroconversion of waste multilayer film plastic packaging into valuable products.

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

Active and Stable PtPd Diesel Oxidation Catalysts under Industry‐Defined Test Protocols

Nanoparticle-supported Pt and Pd catalysts are employed industrially to convert CO and hydrocarbon residue from incomplete diesel fuel combustion into more environmentally-benign products. However, these catalysts deactivate over time due to sintering, especially for Pt nanoparticles which readily generate volatile species under high operating temperatures. Here, we turned the detrimental vapor-mediated sintering of Pt into an advantage by using a physical mixture of Pt and Pd catalysts prepared using a raspberry-colloid-templating (RCT) method. The RCT method produced Pt/Al 2 O 3 and Pd/Al 2 O 3 catalysts with partially embedded NPs to inhibit surface-mediated sintering pathways. As validated using an industry-defined emission control test protocol, aging a physical mixture of Pt/Al 2 O 3 and Pd/Al 2 O 3 at high temperature produced an alloyed PtPd/Al 2 O 3 catalyst that outperformed the fresh catalyst mixture and both individual catalysts for hydrocarbon conversion, while exhibiting high catalytic stability and resistance to sintering and to SO 2 poisoning. X-ray photoelectron spectroscopy revealed that in the aged catalyst mixture, half of the Pd content existed in the more active metallic state, compared to the less active oxide forms in the fresh mixture and both individual catalysts, explaining the unusual activity enhancement. Our results represent a practical approach to producing active and stable PtPd/Al 2 O 3 diesel oxidation catalysts for emission control applications.

Lim, Kang Rui Garrick [Harvard University, Cambrid↗
DOE OSTI2026

Simultaneous Determination of Halogens and Metals in Waste Plastic Pyrolysis Oil by Inductively Coupled Plasma Mass Spectrometry

A major barrier to integrating pyrolysis-derived oil into conventional refinery technology is the presence of impurities, particularly halogens and metals, that can deactivate catalysts. This study presents a novel, cost-effective approach for the simultaneous analysis of a subset of halogens, metals, nonmetals, and metalloids in complex, industrially relevant distilled pyrolysis oil samples, this was previously achievable only through multiple techniques. Excellent results were obtained using a widely accessible inductively coupled plasma mass spectrometry (ICP-MS) method with helium gas mode and standard laboratory consumables, enabling high-throughput analysis and efficient evaluation of adsorbent performance. Sample preparation is straightforward, requiring only dilution in a compatible matrix, and provides accurate and precise quantification, with 75%–137% spike recovery for Be, Ti, V, Cr, Fe, Ni, Co, Cu, As, Se, Mo, Cd, Sb, Tl, and Pb, and 62%–65% spike recovery for Cl and 109%–133% spike recovery for Br. Additionally, an enhanced version of the method using ICP-MS/MS and hydrogen gas is described, which has higher accuracy with 69%–112% spike recovery for Be, B, Ti, V, Fe, Co, Ni, Cu, As, Se, Mo, Cd, Sb, Tl, and Pb, with 85%–102% spike recovery for Cl and 63%–93% spike recovery for Br. Helium mode detection limits for industrially relevant elements (V, Fe, Ni, Cu, As, and Pb) are less than 1.7 µg/kg, and less than 0.2 mg/kg for Br and Cl. Furthermore, this methodology facilitates rapid systematic evaluation of adsorption capacities of materials under time-on-stream conditions and supports robust comparisons across diverse operating environments.

Lazarcik, James [University of Wisconsin-Madison, ↗
DOE OSTI2022

Conservative solute transport processes and associated transient storage mechanisms: Comparing streams with contrasting channel morphologies, land use and land cover

Abstract Land use within a watershed impacts stream channel morphology and hydrology and, therefore, in‐stream solute transport processes and associated transient storage mechanisms. This study evaluated transport processes in two contrasting stream sites where channel morphology was influenced by the surrounding land use, land cover, climate and geologic controls: Como Creek, CO, a relatively undisturbed, high gradient, forested stream with a gravel bed and complex channel morphology, and Clear Creek, IA, an incised, low‐gradient stream with low‐permeability substrate draining an agricultural landscape. We performed conservative stream tracer injections at these sites to address the following questions: (1) How does solute transport vary between streams with differing morphologies? and (2) How does solute transport at each stream site change as a function of discharge? We analysed in‐stream tracer time series data and compared results quantifying solute attenuation in surface and subsurface transient storage zones. Significant trends were observed in these metrics with varying discharge conditions at the forested site but not at the agricultural site. There was a broad range of transport mechanisms and evidence of substantial exchange with both surface and hyporheic transient storage in the relatively undisturbed, forested stream. Changing discharge conditions activated or deactivated different solute transport mechanisms in the forested site and greatly impacted advective travel time. Conversely in the simplified agricultural stream, there was a narrow range of solute transport behaviour across flows and predominantly surface transient storage at all measured discharge conditions. These results demonstrate how channel simplification inhibits available solute transport mechanisms across varying discharge conditions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Selective Catalytic Behavior Induced by Crystal–Phase Transformation in Well–Defined Bimetallic Pt–Sn Nanocrystals

The Pt-Sn bimetallic system is a much studied and commercially used catalyst for propane dehydrogenation. The traditionally prepared catalyst, however, suffers from inhomogeneity and phase separation of the active Pt–Sn phase. Colloidal chemistry offers a route for the synthesis of Pt–Sn bimetallic nanoparticles (NPs) in a systematic, well-defined, tailored fashion over conventional methods. Here, the successful synthesis of well-defined ≈2 nm Pt, PtSn, and Pt 3 Sn nanocrystals with distinct crystallographic phases is reported; hexagonal close packing (hcp) PtSn and fcc Pt 3 Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed. Moreover, face centred cubic (fcc) Pt 3 Sn/Al 2 O 3 , which exhibited the highest stability compared to hcp PtSn, shows a unique phase transformation from an fcc phase to an L1 2 -ordered superlattice. Contrary to PtSn, H 2 cofeeding has no effect on the Pt 3 Sn deactivation rate. Finally, the results reveal structural dependency of the probe reaction, propane dehydrogenation, and provide a fundamental understanding of the structure–performance relationship on emerging bimetallic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effects of moisture and aging upon decomposition of methyl iodide by reduced silver mordenite

Abstract Reduced silver mordenite has been considered as a sorbent for the capture of organic iodides, especially methyl iodide, from off-gases produced by aqueous used nuclear fuel reprocessing operations. The adsorption capacity of this material has been unpredictable especially when NO x and water are present. Previous work has found that a catalytic decomposition reaction is occurring on the surface but few determinations have been made of the kinetics of this reaction. The work presented tested the adsorption behavior and apparent catalytic reaction rate in humid conditions and compared those to dry conditions testing. Both experiments observed a first order reaction with rate constants of 0.0847 L/g sorbent/s and 0.1202 L/g sorbent/s respectively. Such a reduction in apparent rate constant is possibly due to either water obstructing methyl iodide adsorption or product desorption limitation. Changes in the adsorption profile were also apparent between these two, with the humid conditions experiment reaching saturation sooner than the dry conditions experiment. Additionally, an experiment into the effects of sorbent storage in a controlled laboratory environment was performed. The performance of the sorbent materials that were stored with silver in the zerovalent state was slightly inferior to those materials that were stored in ionic form (Ag + ) and reduced to zerovalent silver immediately prior to subjecting them to sorption test. The materials stored with silver in the ionic form (and reduced just prior to application) behaved essentially similarly to the freshly synthesized (and reduced) sorbents in the sorption tests. This suggests that zerovalent silver experiences some oxidation resulting in deactivation of some sites.

Goettsche, Heinrik↗
DOE OSTI2022

Furfural Upgrading by Aldol Condensation with Ketones over Solid-Base Catalysts

Aldol condensation reactions between furfural and various ketones were studied in a flow reactor at 373 K and 100 psi for application to upgrading of furfural. Specific rates for the reaction of acetone and furfural were measured on MgAl 2 O 4 , Al 2 O 3 , CaO/MgAl 2 O 4 and MgO/MgAl 2 O 4 and found to be highest on CaO/MgAl 2 O 4 . While the presence of CO 2 and H 2 O did not affect the stability of the CaO/MgAl 2 O 4 catalyst, the catalyst deactivated over a period of a few hours due to the production of 2-furoic acid formed by the Cannizzaro reaction. While aldol condensation rates between furfural and either 2-pentanone and decanal approached that of acetone, rates for 4-heptanone and 2,5-heptanedione were significantly lower because the α-hydrogens of the carbonyl compounds are less easily attacked in these molecules. The selectivity to aldol products is affected by the relative rates of the aldol-condensation and the Cannizzaro reactions. Possible strategies for maximizing production of the aldol products with larger ketones are discussed.

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

CO2-Utilization Facilitated by Solid Reaction Mediums—A Review

Abstract This short review examines solid reaction mediums—specifically oxygen, CO 2 , and carbon carriers—within the framework of Chemical Looping (CL) to illuminate various CO 2 utilization pathways. The thermodynamic consideration for carrier selection is first discussed. This is followed by a summary of the key carrier types investigated to date, with an emphasis on elucidating the roles of compositional, structural, and surface properties of the various carriers toward their reactive performances. Besides assessing the performances of various oxygen carriers, their long-term performance, potential deactivation mechanism in the presence of CO 2, and strategies for their reactivation are also discussed in the context of chemical looping dry reforming of methane (CLDRM). While relatively underexplored, the current status of development, advantages, and potential limitations of CO 2 carriers in sorbent looping dry reforming of methane (SLDRM) and carbon carriers in chemical looping methane cracking (CLMC) are also reviewed and discussed. Emerging topics such as combined carriers are also covered along with a perspective for future research directions. Overall, this review aims to offer insights into the sustainable use of CO 2 through chemical looping, emphasizing the potential of solid reaction mediums across different carriers and the challenges associated with these solid reaction mediums.

Iftikhar, Sherafghan↗
DOE OSTI2020

Nanoarray-Based Monolithic Adsorbers for SO 2 Removal

Nanoarray-based monolithic catalysts have been developed for various applications, including CO oxidation, hydrocarbon combustion, lean NO x trapping, and low-pressure CO 2 hydrogenation. In this work, SO 2 adsorption properties have been explored and evaluated on the cordierite honeycomb monoliths grown with zinc oxide nanoarray (ZnO), zinc oxide nanoarray washcoated by BaCO 3 nanoparticles (ZnO/BaCO 3 ), and manganese oxide nanowire array with cryptomelane structure (MnO x ) at a temperature range from 50 to 425 °C. All samples show temperature-dependent SO 2 adsorption behaviors. The adsorption results reveal the performance order: MnO x > ZnO/BaCO 3 > ZnO, with ~ 90% SO 2 adsorbed in MnO x at 425 °C. Washcoated BaCO 3 contributes to the improvement of SO 2 adsorption in ZnO nanoarray, and the best performance displayed in MnO x may be attributed to their high specific surface area. After regeneration, nanoarrays all exhibit good thermal stability during test-regeneration cycles. No additional phase is formed in regenerated ZnO nanoarrays (ZnO-R), while BaCO 3 is converted to BaSO 4 in the regenerated ZnO/BaCO 3 nanoarrays (ZnO/BaCO 3 -R), and the sulfur species (possibly MnSO 4 ) and Mn 2 O 3 are found in regenerated MnO x nanoarrays (MnO x -R). It is noted that a small amount of sulfur species (possibly MnSO 4 ) may promote the SO 2 adsorption of MnO x -R at a lower temperature, while the formed Mn 2 O 3 contributes to the deactivation of MnO x -R.

36 MATERIALS SCIENCE↗
DOE OSTI2024

The stability of single-atom catalysts in thermocatalysis

Abstract Single-atom catalysts (SACs) featuring 100% atom utilization and uniform isolated active sites have been receiving sustainable attention over the last decade, as they offer exceptional performance in various catalytic applications. The motivation behind studying SACs is to develop highly active, selective, and stable catalysts for industrial applications with desirable economic and ecological benefits. Despite their promising potential, SACs face challenges related to stability, which need to be addressed for practical implementation. In this mini-review we discuss the existing stability issues of SACs, and summarize the deactivation mechanism and behaviors, protective strategies, and regeneration methods of SACs. We highlighted the challenges and prospects of future SACs study, aiming to pave the way for their widespread application in industrial processes.

Chae, Sudong↗
DOE OSTI2020

Enzyme interactions on lignocellulosic biomass structure

This chapter shows that, although well studied over the years, the cellulose enzymatic hydrolysis process has still many obstacles to be overcome or minimized. High enzyme loading and relatively long incubation periods are generally required for effective cellulose saccharification to be achieved. These limitations make the process unattractive from an economic perspective. Most studies show that the conversion rate of cellulose hydrolysis decreases over reaction time due to several factors that may inhibit, deactivate, or slow the work of enzymes. Some of these factors are inhibition by the product generated; inhibition/deactivation of enzymes by by-products generated during pretreatment (PT); limitation of mass transfer; shear stress by high stirring; air–liquid interfacial area; and unproductive adsorption on lignin or other compounds present in the biomass. The interaction between cellulases and the lignin present in these biomasses has a major negative impact on the process, with the source of the raw material and the type of PT used having a strong influence on it. Finally, the use of nonenzymatic proteins seems to be the best way to mitigate this problem.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2021

Ordering effects on deformation substructures and strain hardening behavior of a CrCoNi based medium entropy alloy

Here, a CrCoNi based medium entropy alloy with small additions of Ti, Al and Nb (denoted as (CrCoNi) 93 Al 4 Ti 2 Nb) in the as-quenched condition, exhibits tensile properties comparable to those of the equiatomic CrCoNi alloy at room temperature. Dark field transmission electron microscopy (TEM), atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) together with atom probe tomography (APT) show that spatially-localized long range ordering (LRO) L1 2 domains exist in this alloy. The evolution of deformation substructure with plastic deformation in this alloy was characterized using electron backscatter diffraction (EBSD), electron channeling contrast imaging (ECCI) and STEM based techniques including the recently developed weak beam dark field STEM imaging. Plastic deformation occurs by the slip of a/2<110>dislocations, which are narrowly dissociated into Shockley partial dislocations on {111} slip planes. Their dissociation distances in the (CrCoNi) 93 Al 4 Ti 2 Nb alloy are much smaller than the widths of the corresponding partials in the equiatomic CrCoNi alloy due to one or more of the minor alloying elements (Al, Ti, Nb). Dislocation slip in this alloy has a pronounced planar character. The leading dislocations in slip bands glide as pairs due to the existence of LRO domains. Multipoles were formed through the slip of dislocations with opposite signs on adjacent {111} slip planes. Those multipoles serve as building blocks for the formation of subgrain structures consisting of fine slip bands. The distances between slip bands were continuously refined during plastic deformation and dynamic refinement of slip bands plays a crucial role in strain hardening. The effects of LRO domains on planar dislocation slip, the deactivation of deformation twinning and strain hardening of this alloy are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Engineering the Composition of Bimetallic Nanocrystals to Improve Hydrodeoxygenation Selectivity for 2-Acetylfuran

Hydrodeoxygenation (HDO) of 2-acetylfuran (2-AF) was examined at 473 K and 33 bar over carbon-supported, bimetallic catalysts. Monodispersed, Pt-based (PtNi, PtCo, and PtCu) and Ni-based (NiCu) nanocrystals (NCs) with well-defined sizes and compositions were prepared via colloidal synthesis. Steady-state, flow-reactor measurements demonstrate that selectivities for the HDO reaction to 2-ethylfuran (2-EF) are strongly dependent on the alloy compositions. The HDO of 2-AF is shown to be sequential, where 2-EF can react further to form over-hydrogenated products. The NiCu 3 /C nanocatalyst was superior to the other bimetallics; with the optimal residence time, it was possible to achieve a selectivity of 75% 2-EF with 80% conversion of 2-AF, with good stability for up to at least 5 hours time-on-stream. Deactivation due to coking became an issue when the NCs were deposited on oxide supports with weak acidity (SiO 2 and γ-Al 2 O 3 ). Furthermore, this work provides insights into which bimetallic catalytic systems might be useful for HDO of 2-AF reaction.

2-acetylfuran↗
DOE OSTI2020

A critical literature review of the advances in methane dehydroaromatization over multifunctional metal-promoted zeolite catalysts

We report the drastic rise in shale gas production has encouraged the quest for alternative uses of methane as a chemical feedstock in the manufacturing industry. While two-step syngas routes for methane valorization are deployed commercially, direct one-step routes for methane conversion are attracting much attention. As steam cracking installations have shifted from using oil-based naphtha to shale-based natural gas liquids, production of aromatics has dropped. Methane dehydroaromatization (MDA) is a one-step reaction capable of valorizing methane to hydrogen and benzene. Challenges with the MDA reaction are two-fold: the reaction is thermodynamically limited with low one-pass methane conversion and even the best catalytic systems, Mo/zeolites, suffer rapid deactivation from coking. A catalyst design strategy to improve stability is the use of multifunctional Mo-X/zeolite systems where X is a dopant capable of modulating the stability. In this paper we provide a complete overview of the main Mo-X/zeolite systems used in MDA and critically draw connections among the different types of dopants (X) employed, as a function of the role they play in the reaction/deactivation pathway. We have also dedicated a section to emerging trends with non-Mo based catalysts. The goal of this review article is to establish a basis that will facilitate the identification of useful multifunctional catalytic systems, and recognize gaps in the knowledge of these systems that deserve more attention. Improving MDA systems to the point to which they can be commercially deployed requires a multifaceted approach that combines optimization of the designs of both the catalyst and the reactor configuration. We therefore also provide a brief overview of the most recent advances in process intensification strategies employed with different reactor configurations.

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

Structure sensitivity and its effect on methane turnover and carbon co-product selectivity in thermocatalytic decomposition of methane over supported Ni catalysts

We explore how thermocatalytic decomposition of methane (TCD) is a promising approach for producing CO 2 -free hydrogen and solid carbon co-product. In this study, a series of Al 2 O 3 - and MgAl 2 O 4 -based Ni catalysts, prepared with varying synthesis and pretreatment methods, were evaluated for methane TCD performance at 650°C and characterized before and after reaction to elucidate activity-structure relationships. We found that methane TCD turnover increases with Ni particle size. Further, large Ni particle sizes (i.e., >20 nm) are selective toward the formation of carbon nanotubes (CNTs), while small Ni particle sizes (i.e., <10 nm) are selective toward the formation of graphitic carbon layers. The formation of graphitic carbon layers block access to Ni active sites, thus rendering the catalyst inactive more quickly than when CNTs are produced. Additionally, the catalyst deactivation observed with time-on-stream is due to the fragmentation of Ni particles into smaller Ni particles followed by their encapsulation with graphitic carbon layers.

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

Assessment and comparison of ordered & non-ordered supported metal oxide catalysts for upgrading propane to propylene

Propylene is an important chemical feedstock that is largely produced via cracking of oil-derived naphtha. Direct conversion of propane into propylene may be a more attractive alternative. Specifically, propane dehydrogenation (DH) and oxidative dehydrogenation (ODH) are promising for this transformation, albeit only DH has been industrially implemented. However, even the best DH catalysts (Pt-based) still suffer from deactivation. VO x - and BO x -based ODH catalysts result in significant over-oxidation and lack a mechanistic understanding. A common challenge in developing these catalysts is the broad distribution of surface species caused by the use of non-ordered catalyst supports. This hampers clear structure-performance correlations. Recent progress in the preparation of well-defined active sites on ordered supports has brought about improved catalysts, as well as fundamental insight into the working mechanism. This review will highlight recent advancements in the development of these catalysts and provide direction on the use of ordered supports for propane upgrading.

03 NATURAL GAS↗