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DOE OSTI2024

Converting Carbon Dioxide into Carbon Nanotubes by Reacting with Ethane

In this study, the urgency to mitigate environmental impacts from anthropogenic CO 2 emissions has propelled extensive research efforts on CO 2 reduction. The current work reports a novel approach involving transforming CO 2 and ethane into carbon nanotubes (CNTs) using earth-abundant metals (Fe, Co, Ni) at 750 °C. This route facilitates long-term carbon storage via generating high-value CNTs and produces valuable syngas with adjustable H 2 /CO ratios as byproducts. Without CO 2 , direct pyrolysis of ethane undergoes rapid deactivation. The participation of CO 2 not only enhances the durability of the catalyst, but also contributes about 30 % of the CNTs production, presenting a viable solution to CO 2 challenges. The CNT morphology depends on the catalyst used. Co- and Ni-based catalysts produce CNT with a 20 nm diameter and micrometer length, whereas Fe-based catalysts yield bamboo-like structures. This work represents a pioneering effort in utilizing CO 2 and ethane for CNT production with potential environmental and economic benefits.

09 BIOMASS FUELS↗

DOE OSTI2024

3D‐Printed Carbon Nanoneedle Electrodes for Dopamine Detection in Drosophila

In vivo electrochemistry in small brain regions or synapses requires nanoelectrodes with long straight tips for submicron scale measurements. Nanoelectrodes can be fabricated using a Nanoscribe two-photon printer, but annealed tips curl if they are long and thin. We propose a new pulling-force strategy to fabricate a straight carbon nanoneedle structure. A micron-width bridge is printed between two blocks. The annealed structure shrinks during pyrolysis, and the blocks create a pulling force to form a long, thin, and straight carbon bridge. Parameterization study and COMSOL modeling indicate changes in the block size, bridge size and length affect the pulling force and bridge shrinkage. Electrodes were printed on niobium wires, insulated with aluminum oxide, and the bridge cut with focused ion beam (FIB) to expose the nanoneedle tip. Annealed needle diameters ranged from 400 nm to 5.25 μm and length varied from 50.5 μm to 146 μm. The electrochemical properties are similar to glassy carbon, with good performance for dopamine detection with fast-scan cyclic voltammetry. Nanoelectrodes enable biological applications, such as dopamine detection in a specific Drosophila brain region. Long and thin nanoneedles are generally useful for other applications such as cellular sensing, drug delivery, or gas sensing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Metal–Organic Frameworks at the Edge of Stability: Mediating Node Distortion to Access Metastable Nanoparticle Polymorphs

Metal-organic frameworks (MOFs) are emerging as unconventional precursors for nanoparticle synthesis, with potential to leverage their tunable structures and chemistry to achieve nanomaterials with structures and compositions inaccessible via traditional synthetic routes. Here we use in situ synchrotron X-ray diffraction and pair distribution function (PDF) measurements to investigate how the dynamic structure of MOFs at the edge of stability influences their transformation into different metastable polymorphs. Our study reveals that the local structural features of metal-oxo MOF nodes at elevated temperatures are linked to the resulting nanoparticle structures formed under mild conditions. Focusing on the titanium-based MOF MIL-125, we demonstrate that manipulating the chemical environment to facilitate transformation of the Ti8 node geometry promotes formation of metastable, nanometer-scale TiO2 brookite rather than the more common anatase and rutile TiO2 polymorphs typically produced through MOF pyrolysis at high temperature. These findings highlight the potential to harness the MOF topology and chemical environment to design and control node distortions and enable access to exotic metastable nanoparticle states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Upcycling of Waste Plastics into Carboxylic Acids for Biodegradable Surfactants

This work outlines a process for producing high‐purity (>95%) carboxylate surfactants from post‐consumer recycled high‐density polyethylene (PCR‐HDPE). The approach involves the thermal depolymerization of PCR‐HDPE via pyrolysis, followed by fractional distillation to isolate C9–C14 olefins. These olefins undergo hydroformylation using cobalt carbonyl catalysts to generate aldehydes, which are subsequently oxidized to carboxylic acids using Pinnick oxidation under mild aqueous‐phase conditions. Neutralization of the resulting carboxylic acids with sodium hydroxide produces plastic‐derived carboxylate surfactants (PDCs) in the form of sodium carboxylates. Subsequent purification steps ensure surfactant‐grade purity and enable accurate assessment of physicochemical properties. The resulting PDCs are evaluated for critical micelle concentration (CMC), foamability, surface tension reduction, and calcium ion tolerance, demonstrating competitive behavior with conventional anionic carboxylate surfactants. This route provides a sustainable alternative for surfactant production, reducing reliance on fossil‐derived feedstocks and valorizing plastic waste streams through chemical upcycling.

Biodegradable surfactants↗

DOE OSTI2017

Drop-in biofuel production via conventional (lipid/fatty acid) and advanced (biomass) routes. Part I

Drop-in biofuels that are 'functionally identical to petroleum fuels and fully compatible with existing infrastructure' are needed for sectors such as aviation where biofuels such as bioethanol/biodiesel cannot be used. The technologies used to produce drop-in biofuels can be grouped into the four categories: oleochemical, thermochemical, biochemical, and hybrid technologies. Commercial volumes of conventional drop-in biofuels are currently produced through the oleochemical pathway, to make products such as renewable diesel and biojet fuel. However, the cost, sustainability, and availability of the lipid/fatty acid feedstocks are significant challenges that need to be addressed. In the longer-term, it is likely that commercial growth in drop-in biofuels will be based on lignocellulosic feedstocks. However, these technologies have been slow to develop and have been hampered by several technoeconomic challenges. For example, the gasification/Fischer-Tropsch (FT) synthesis route suffers from high capital costs and economies of scale difficulties, while the economical production of high quality syngas remains a significant challenge. Although pyrolysis/hydrothermal liquefaction (HTL) based technologies are promising, the upgrading of pyrolysis oils to higher specification fuels has encountered several technical challenges, such as high catalyst cost and short catalyst lifespan. Biochemical routes to drop-in fuels have the advantage of producing single molecules with simple chemistry. Moreover, the high value of these molecules in other markets such as renewable chemical precursors and fragrances will limit their use for fuel. In the near-term, (1-5 years) it is likely that, 'conventional' drop-in biofuels will be produced predominantly via the oleochemical route, due to the relative simplicity and maturity of this pathway.

09 BIOMASS FUELS↗

DOE OSTI2019

Facile Synthesis of Fe/N/S‐Doped Carbon Tubes as High‐Performance Cathode and Anode for Microbial Fuel Cells

Abstract As a renewable energy technology, microbial fuel cell (MFC) has been attracting increasing attention in recent decades. However, practical applications of MFCs has been hampered by the unsatisfactory electrode performance, in particular, at the cathode. Herein, Fe/N/S‐doped carbon hollow tubes were prepared by a facile two‐stage procedure involving hydrothermal treatment and pyrolysis at controlled temperatures. Electrochemical studies showed that the obtained samples exhibited an apparent electrocatalytic activity towards oxygen reduction reaction in both alkaline and acidic media, a performance comparable to that of commercial Pt/C, and the sample prepared at 800 °C stood out as the best among the series with a half‐wave potential of +0.81 V vs. RHE and an electron transfer number of 3.98 at +0.6 V vs. RHE. The Fe/N/S‐doped carbon tubes also exhibited a remarkable performance as an MFC anode by facilitating bacterial growth and electron transfer between the biofilm and electrode. In fact, an MFC based on the carbon tubes as both cathode and anode showed a markedly higher performance (maximum power density 479 W m −3 ) than the control MFC based on a graphene aerogel anode and Pt/C cathode (359 W m −3 ). These results suggest that Fe/N/S‐doped carbon composites can be used for the fabrication of high‐efficiency MFC electrodes.

Yang, Wei↗

DOE OSTI2017

Metal-organic-framework-derived carbons: Applications as solid-base catalyst and support for Pd nanoparticles in tandem catalysis

Here, the facile pyrolysis of a bipyridyl metal-organic framework, MOF-253, produces N-doped porous carbons (Cz-MOF-253), which exhibit excellent catalytic activity in the Knoevenagel condensation reaction and outperform other nitrogen-containing MOF-derived carbons. More importantly, by virtue of their high Lewis basicity and porous nature, Cz-MOF-253-supported Pd nanoparticles (Pd/Cz-MOF-253-800) show excellent performance in a one-pot sequential Knoevenagel condensation-hydrogenation reaction.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Synthesis of Host‐Guest Hematite Photoelectrodes for Solar Water Splitting

Abstract Hematite (α‐Fe 2 O 3 ) is a promising semiconductor for photoelectrochemical (PEC) water splitting, due to its abundance, low‐cost and excellent stability. However, the efficiency of α‐Fe 2 O 3 photoelectrodes has been limited by its low hole mobility and fast electron‐hole recombination. Host‐guest architectures have emerged as a suitable design, which involves the use of a nanostructured collector for high solar absorption while maintaining an ultrathin absorber layer for better charge transport. In this study, a thin mesoporous SiO 2 host template coated with a conductive thin layer of TiO 2 was optimized to support the α‐Fe 2 O 3 film. The α‐Fe 2 O 3 thin layer was deposited by spray pyrolysis and then coated with a FeNiOOH co‐catalyst. A photocurrent improvement of ca . 85% over planar α‐Fe 2 O 3 thin film reference was registered demonstrating the potential of this host‐guest approach.

Francisco, Filipe↗

DOE OSTI2020

Controlled One‐pot Synthesis of Nickel Single Atoms Embedded in Carbon Nanotube and Graphene Supports with High Loading

Abstract Single‐atom catalysts (SACs) have attracted much attentions due to the advantages of high catalysis efficiency and selectivity. However, the controllable and efficient synthesis of SACs remains a significant challenge. Herein, we report a controlled one‐pot synthesis of nickel single atoms embedded on nitrogen‐doped carbon nanotubes (NiSA−N−CNT) and nitrogen‐doped graphene (NiSA−N−G). The formation of NiSA−N−CNT is due to the solid‐to‐solid rolling up mechanism during the high temperature pyrolysis at 800 °C from the stacked and layered Ni‐doped g‐C 3 N 4 , g‐C 3 N 4 −Ni structure to a tubular CNT structure. Addition of citric acid introduces an amorphous carbon source on the layered g‐C 3 N 4 −Ni and after annealing at the same temperature of 800 °C, instead of formation of NiSA−N−CNT, Ni single atoms embedded in planar graphene type supports, NiSA−N−G were obtained. The density functional theory (DFT) calculation indicates the introduction of amorphous carbon source substantially reduces the structure fluctuation or curvature of layered g‐C 3 N 4 ‐Ni intermediate products, thus interrupting the solid‐to‐solid rolling process and leading to the formation of planar graphene type supports for Ni single atoms. The as‐synthesized NiSA−N−G with Ni atomic loading of ∼6 wt% catalysts shows a better activity and stability for the CO 2 reduction reaction (CO 2 RR) than NiSA−N−CNT with Ni atomic loading of ∼15 wt% due to the open and exposed Ni single atom active sites in NiSA−N−G. This study demonstrates for the first time the feasibility in the control of the microstructure of carbon supports in the synthesis of SACs.

Zhao, Shiyong↗

DOE OSTI2019

Reactivity of the Indenyl Radical (C 9 H 7 ) with Acetylene (C 2 H 2 ) and Vinylacetylene (C 4 H 4 )

The reactions of the indenyl radicals with acetylene (C 2 H 2 ) and vinylacetylene (C 4 H 4 ) is studied in a hot chemical reactor coupled to synchrotron based vacuum ultraviolet ionization mass spectrometry. These experimental results are combined with theory to reveal that the resonantly stabilized and thermodynamically most stable 1-indenyl radical (C 9 H 7 $^\bullet$) is always formed in the pyrolysis of 1-, 2-, 6-, and 7-bromoindenes at 1500 K. The 1-indenyl radical reacts with acetylene yielding 1-ethynylindene plus atomic hydrogen, rather than adding a second acetylene molecule and leading to ring closure and formation of fluorene as observed in other reaction mechanisms such as the hydrogen abstraction acetylene addition or hydrogen abstraction vinylacetylene addition pathways. While this reaction mechanism is analogous to the bimolecular reaction between the phenyl radical (C 6 H 5 $^\bullet$) and acetylene forming phenylacetylene (C 6 H 5 CCH), the 1-indenyl+acetylene→1-ethynylindene+hydrogen reaction is highly endoergic (114 kJ mol -1 ) and slow, contrary to the exoergic (-38 kJ mol -1 ) and faster phenyl+acetylene→phenylacetylene+hydrogen reaction. In a similar manner, no ring closure leading to fluorene formation was observed in the reaction of 1-indenyl radical with vinylacetylene. Finally, these experimental results are explained through rate constant calculations based on theoretically derived potential energy surfaces.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2018

Cascade Production of Lactic Acid from Universal Types of Sugars Catalyzed by Lanthanum Triflate

Abstract Lignocellulosic biomass conversion into value‐added platform chemicals in the non‐toxic, water‐tolerant Lewis acid, and water solutions bears the hallmark of green chemistry. Lactic acid derived from biomass is an important chemical building block for biodegradable polymers such as polylactide. Herein, a universal method of converting lignocellulosic sugars into lactic acid using catalytic amount of water‐stable Lewis acid La(OTf) 3 is demonstrated. The lignocellulosic sugars studied in this work include 1) pyrolytic sugars from pyrolysis oil, and 2) sugars derived from ionic liquid (IL)‐pretreated biomass. Under moderate conditions (250 °C, 1 h), levoglucosan (major pyrolytic sugar), glucose, and xylose were converted into lactic acid with carbon‐based molar yields of 75, 74, and 61 %, respectively. Furthermore, roughly 49 mol % (based on levoglucosan) and 74 wt % (relative to pretreated biomass) of lactic acid were obtained from the conversion of pyrolytic sugars and sugar‐rich fraction after lignin removal from switchgrass, respectively. To our knowledge, this is the first reported conversion of pyrolytic sugar into lactic acid by chemocatalysis and also lignocellulosic sugars are converted into lactic acid without hydrolysis. This approach could potentially be extended to other lignocellulosic sugars after simple removal of lignin from biomass pretreatment, rendering moderate to high yields of lactic acid.

Liu, Dajiang↗

DOE OSTI2021

Hybrid Chemo-Mechanical Plastics Recycling: Solvent-free, High-speed Reactive Extrusion of Low-Density Polyethylene

Low-Density Polyethylene (LDPE) is ubiquitous in the packaging industry due to its flexibility, toughness, and low cost. However, it is typically contaminated with other materials, seriously limiting options for mechanical recycling. Interest in chemical recycling techniques such as pyrolysis and hydrothermal liquefaction is growing, but most of these processes face technoeconomic challenges that have limited commercial deployment. We present a hybrid chemo-mechanical approach using reactive twin-screw extrusion (TSE) for tailoring the molecular weight and chain structure of reclaimed LDPE. Two types of zeolite catalysts at several loading levels were evaluated over a range of processing conditions. Structural, thermal, and rheological properties of the extruded samples were investigated and compared to virgin LDPE and LDPE extruded without the catalyst. A nuclear magnetic resonance spectroscopic technique was used to investigate changes in the structure of the polymer. LDPE extruded with microporous y-zeolite showed lower degradation temperature and increased short chain branching. Mesoporous MCM-41 also induced increased branching but had no effect on degradation temperature. The theoretical mechanical energy input for the chemical modification was calculated using process modeling. The demonstrated hybrid reactive extrusion process provides a potential low-cost, simple approach for repurposing LDPE-based flexible packaging as coatings and adhesives.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Chemical Recycling Processes of Waste Polyethylene Terephthalate Using Solid Catalysts

Polyethylene terephthalate (PET) is a non-degradable single-use plastic and a major component of plastic waste in landfills. Chemical recycling is one of the most widely adopted methods to transform post-consumer PET into PET's building block chemicals. Non-catalytic depolymerization of PET is very slow and requires high temperatures and/or pressures. Recent advancements in the field of material science and catalysis have delivered several innovative strategies to promote PET depolymerization under mild reaction conditions. Particularly, heterogeneous catalysts assisted depolymerization of post-consumer PET to monomers and other value-added chemicals is the most industrially compatible method. Here, this review includes current progresses on the heterogeneously catalyzed chemical recycling of PET. It describes four key pathways for PET depolymerization including, glycolysis, pyrolysis, alcoholysis, and reductive depolymerization. The catalyst function, active sites and structure-activity correlations are briefly outlined in each section. An outlook for future development is also presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Zeolitic-Imidazolate Framework Derived Intermetallic Nickel Zinc Carbide Material as a Selective Catalyst for CO 2 to CO Reduction at High Pressure

The conversion of CO 2 into CO is an important step in CO 2 utilization to achieve clean fuels and value-added chemicals. Herein, we explored the pyrolysis of zeolitic imidazolate framework-8 (ZIF-8) loaded with different amounts of Ni 2+ to obtain Ni-Zn carbide (Ni 3 ZnC) embedded in N-doped carbon. Ni is present in the intermetallic compound, while Zn excess remains on the N-doped carbon. The Ni 3 ZnC phase catalyzes the selective hydrogenation of CO 2 into CO via the reverse water gas shift reaction, reaching 100 % CO selectivity at ~30 % CO 2 conversion at 450 °C and atmosphere pressure (CO 2 :H 2 =1:4, GHSV=30000 mL g cat -1 h -1 ). The methanation reaction of CO 2 /CO, which is usually favored over Ni catalysts, is suppressed. The selectivity to CO at the expense of CH 4 is related to the stability of chemisorbed CO in the Ni 3 ZnC surface, which is lower compared to Ni surfaces. The Ni 3 ZnC@NC catalyst is selective towards CO over a wide range of conditions, including high pressure, that is usually required for the conversion of CO to hydrocarbons and alcohols via the Fisher-Tropsch synthesis (FTS) process. Contrarily, a classical Ni/SiO 2 catalyst prepared by impregnation produces CH 4 under high pressure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

Processing-Structure-Property Relationships for Lignin-Based Carbonaceous Materials Used in Energy-Storage Applications

Lignin, an abundant organic polymer and a byproduct of pulp and biofuel production, has potential applications owing to its high carbon content and aromatic structure. Processing structure relationships are difficult to predict because of the heterogeneity of lignin. Here, this work discusses the roles of unit operations in the carbonization process of softwood lignin, and their resulting impacts on the material structure and electrochemical properties in application as the anode in lithium-ion cells. The processing variables include the lignin source, temperature, and duration of thermal stabilization, pyrolysis, and reduction. Materials are characterized at the atomic and microscales. High-temperature carbonization, at 2000 °C, produces larger graphitic domains than at 1050 °C, but results in a reduced capacity. Coulombic efficiencies over 98 % are achieved for extended galvanostatic cycling. Consequently, a properly designed carbonization process for lignin is well suited for the generation of low-cost, high-efficiency electrodes.

25 ENERGY STORAGE↗

DOE OSTI2019

Negative Emission Energy Production Technologies: A Techno‐Economic and Life Cycle Analyses Review

Negative emission technologies (NETs) are of growing importance for society to meet the atmospheric carbon levels required to maintain global temperatures under sustainable limits. A wide range of NETs have been proposed, but there are limited NET assessments that integrate life cycle analysis (LCA) and techno‐economic analysis (TEA). This Review gathers NET TEA/LCA findings and compares their costs and greenhouse gas emissions. Eight different NET‐producing transportation fuels and power‐generation technologies are considered: anaerobic digestion (lignocellulosic), fermentation, torrefaction, combustion, fast pyrolysis, gasification, and hydrothermal liquefaction. Most of these technologies sequester carbon either as carbon dioxide or as biochar. Some are carbon negative by virtue of avoided or displaced emissions. Overall, results indicate that NET energy production costs range between $20 and $80 GJ −1 and have emissions from −400 to 100 kg CO 2,eq GJ −1 . These results suggest that there are potential tradeoffs to consider when developing NETs. These results also show that future TEA/LCA studies of NETs are needed to decrease their uncertainty and improve their technology readiness level.

Li, Wenqin↗

DOE OSTI2020

Uncertainty analysis of correlated parameters in automated reaction mechanism generation

Abstract Uncertainty analysis is a useful tool for inspecting and improving detailed kinetic mechanisms because it can identify the greatest sources of model output error. Owing to the very nonlinear relationship between kinetic and thermodynamic parameters and computed concentrations, model predictions can be extremely sensitive to uncertainties in some parameters while uncertainties in other parameters can be irrelevant. Error propagation becomes even more convoluted in automatically generated kinetic models, where input uncertainties are correlated through kinetic rate rules and thermodynamic group values. Local and global uncertainty analyses were implemented and used to analyze error propagation in Reaction Mechanism Generator (RMG), an open‐source software for generating kinetic models. A framework for automatically assigning parameter uncertainties to estimated thermodynamics and kinetics was created, enabling tracking of correlated uncertainties. Local first‐order uncertainty propagation was implemented using sensitivities computed natively within RMG. Global uncertainty analysis was implemented using adaptive Smolyak pseudospectral approximations as implemented in the MIT Uncertainty Quantification Library to efficiently compute and construct polynomial chaos expansions to approximate the dependence of outputs on a subset of uncertain inputs. Cantera was used as a backend for simulating the reactor system in the global analysis. Analyses were performed for a phenyldodecane pyrolysis model. Local and global methods demonstrated similar trends; however, many uncertainties were significantly overestimated by the local analysis. Both local and global analyses show that correlated uncertainties based on kinetic rate rules and thermochemical groups drastically reduce a model's degrees of freedom and have a large impact on the determination of the most influential input parameters. These results highlight the necessity of incorporating uncertainty analysis in the mechanism generation workflow.

Gao, Connie W.↗

DOE OSTI2024

ReactionMechanismSimulator.jl: A modern approach to chemical kinetic mechanism simulation and analysis

Abstract We present ReactionMechanismSimulator.jl (RMS), a modern differentiable software for the simulation and analysis of chemical kinetic mechanisms, including multiphase systems. RMS has already been applied to problems in combustion, pyrolysis, polymers, pharmaceuticals, catalysis, and electrocatalysis. RMS is written in Julia, making it easy to develop and allowing it to take advantage of Julia's extensive numerical computing ecosystem. In addition to its extensive library of optimized analytic Jacobians, RMS can generate and use Jacobians computed using automatic differentiation and symbolically generated analytic Jacobians. RMS is demonstrated to be faster than Cantera and Chemkin in several benchmarks. RMS also implements an extensive set of features for analyzing chemical mechanisms, including a library of easy‐to‐call plotting functions, molecular structure resolved flux diagram generation, crash analysis, traditional sensitivity analysis, transitory sensitivity analysis, and an automatic mechanism analysis toolkit. RMS implements efficient adjoint and parallel forward sensitivity analyses. We also demonstrate the ease of adding new features to RMS.

Johnson, Matthew S.↗