Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “model compounds”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Synthesis and Structure–Activity Characterization of a Single-Site MoO 2 Catalytic Center Anchored on Reduced Graphene Oxide

Molecularly derived single-site heterogeneous catalysts can bridge the understanding and performance gaps between conventional homogeneous and heterogeneous catalysis, guiding the rational design of next-generation catalysts. While impressive advances have been made with well-defined oxide supports, the structural complexity of other supports and the nature of the grafted surface species present an intriguing challenge. In this study, single-site Mo(=O) 2 species grafted onto reduced graphene oxide (rGO/MoO 2 ) are characterized by XPS, DRIFTS, powder XRD, N 2 physisorption, NH 3 -TPD, aqueous contact angle, active site poisoning assay, Mo EXAFS, model compound single-crystal XRD, DFT, and catalytic performance. NH 3 -TPD reveals that the anchored MoO 2 moiety is not strongly acidic, while Mo 3d 5/2 XPS assigns the oxidation state as Mo(VI), and XRD shows little rGO periodicity change on MoO 2 grafting. Contact angle analysis shows that MoO 2 grafting consumes rGO surface polar groups, yielding a more hydrophobic surface. The rGO/MoO 2 DRIFTS assigns features at 959 and 927 cm –1 to the symmetric and antisymmetric Mo=O stretching modes, respectively, of an isolated cis-(O=Mo=O) moiety, in agreement with DFT computation. Moreover, the Mo EXAFS rGO/MoO 2 structural data are consistent with isolated (C–O) 2– Mo(=O) 2 species having two Mo=O bonds and two Mo–O bonds at distances of 1.69(3) and 1.90(3) Å, respectively. rGO/MoO 2 is also more active than the previously reported AC/MoO 2 catalyst, with reductive carbonyl coupling TOFs approaching 1.81 × 10 3 h –1 . rGO/MoO 2 is environmentally robust and multiply recyclable with 69 ± 2% of the Mo sites catalytically significant. Altogether, rGO/MoO 2 is a structurally well-defined and versatile single-site Mo(VI) dioxo heterogeneous catalytic system.

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

Can the Hock Process Be Used to Produce Phenol from Polystyrene?

Polystyrene (PS) is a widely used thermoplastic polymer, but its very low recycling rate has motivated consideration of chemical conversion strategies to convert waste PS into value-added products. Oxidation methods have been widely studied, but they typically generate benzoic acid, a product with a relatively low market demand. Phenol is a higher volume chemical that would be an appealing target, but no methods currently exist for the conversion of PS into phenol. The repeat unit in PS closely resembles cumene, the primary feedstock used to produce phenol through the Hock process. Here, we investigate prospects for adapting the Hock process to PS, generating hydroperoxides through the autoxidation of benzylic C–H bonds followed by the acid-promoted rearrangement of the hydroperoxides to afford phenol and a partially oxygenated polymer. Experimental and computational studies of dimeric and trimeric PS model compounds show that neighboring phenyl rings impose conformational constraints that raise the barrier to hydrogen-atom transfer from the tertiary benzylic C–H bond. These effects are also evident with PS and contribute to lower yields of phenol when PS is subjected to Hock process conditions. Furthermore, these results provide valuable insights that have important implications for other efforts that seek to adapt small-molecule reactivity to polymeric feedstocks.

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

Polyethylene Upcycling to Liquid Alkanes in Molten Salts under Neat and External Hydrogen Source-Free Conditions

Development of facile approaches to convert plastic waste into liquid fuels under neat conditions is highly desired but challenging, particularly without noble metal catalysts and an external hydrogen source. Herein, highly efficient and selective polyethylene-to-gasoline oil (branched C 6 –C 12 alkanes) conversion was achieved under mild conditions (<170 °C) using commercially available AlCl 3 -containing molten salts as reaction media and to provide catalytic sites (no extra solvents, additives, or hydrogen feeding). The high catalytic efficiency and selectivity was ensured by the abundant active Al sites with strong Lewis acidity (comparable to the Al type in acidic zeolite) and highly ionic nature of the molten salts to stabilize the carbenium intermediates. Dynamic genesis of the Al sites was elucidated via time-resolved Al K-edge soft X-ray and 27 Al NMR, confirming the tricoordinated Al 3+ as active sites and its coordination with the as-generated alkene/aromatic intermediates. Further, the carbenium formation and polyethylene chain variation was illustrated by inelastic neutron scattering (INS) and an isotope-labeling experiment. Theoretical simulations further demonstrated the successive hydride abstraction, β-scission, isomerization, and internal hydrogen transfer reaction pathway with AlCl 3 as active sites. This facile catalytic system can further achieve the conversion of robust, densely assembled, and high molecular weight plastic model compounds to liquid alkane products in the diesel range.

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

A unique Co@CoO catalyst for hydrogenolysis of biomass-derived 5-hydroxymethylfurfural to 2,5-dimethylfuran

The development of precious-metal-free catalysts to promote the sustainable production of fuels and chemicals from biomass remains an important and challenging target. Here, we report the efficient hydrogenolysis of biomass-derived 5-hydroxymethylfurfural to 2,5-dimethylfuran over a unique core-shell structured catalyst, Co@CoO that affords the highest productivity among all catalysts, including noble-metal-based catalysts, reported to date. Surprisingly, we find that the catalytically active sites reside on the shell of CoO with oxygen vacancies rather than the metallic Co. The combination of various spectroscopic experiments and computational modelling reveals that the CoO shell incorporating oxygen vacancies not only drives the heterolytic cleavage, but also the homolytic cleavage of H 2 to yield more active H δ- species, resulting in the exceptional catalytic activity. Co@CoO also exhibits excellent activity toward the direct hydrodeoxygenation of lignin model compounds. This study unlocks, for the first time, the potential of simple metal-oxide-based catalysts for the hydrodeoxygenation of renewable biomass to chemical feedstocks.

09 BIOMASS FUELS↗
DOE OSTI2021

A multiplexed nanostructure-initiator mass spectrometry (NIMS) assay for simultaneously detecting glycosyl hydrolase and lignin modifying enzyme activities

Lignocellulosic biomass is composed of three major biopolymers: cellulose, hemicellulose and lignin. Analytical tools capable of quickly detecting both glycan and lignin deconstruction are needed to support the development and characterization of efficient enzymes/enzyme cocktails. Previously we have described nanostructure-initiator mass spectrometry-based assays for the analysis of glycosyl hydrolase and most recently an assay for lignin modifying enzymes. Here we integrate these two assays into a single multiplexed assay against both classes of enzymes and use it to characterize crude commercial enzyme mixtures. Application of our multiplexed platform based on nanostructure-initiator mass spectrometry enabled us to characterize crude mixtures of laccase enzymes from fungi Agaricus bisporus (Ab) and Myceliopthora thermophila (Mt) revealing activity on both carbohydrate and aromatic substrates. Using time-series analysis we determined that crude laccase from Ab has the higher GH activity and that laccase from Mt has the higher activity against our lignin model compound. Inhibitor studies showed a significant reduction in Mt GH activity under low oxygen conditions and increased activities in the presence of vanillin (common GH inhibitor). Ultimately, this assay can help to discover mixtures of enzymes that could be incorporated into biomass pretreatments to deconstruct diverse components of lignocellulosic biomass.

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

OH radical reactions with the hydrophilic component of sphingolipids

In this article, using the example of model compounds, we studied the reactions resulting from the interaction of OH radicals with the hydrophilic part of sphingolipids. We compared the stopped-flow EPR spectroscopy and pulse radiolysis with optical detection methods to characterize radical intermediates formed in the reaction of OH radicals with glycerol, serinol and N-boc-serinol. Quantum chemical calculations were also performed to help interpret the observed experimental data. It was shown that H-abstraction from the terminal carbon atom is the main process that is realized for all the studied compounds. The presence of the unsubstituted amino group (–NH 2 ) is seen to completely change the reaction properties of serinol in comparison with those observed in glycerol and N-boc serinol.

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

A mechanistic study of cellulase adsorption onto lignin

To explore the effect of lignin composition on cellulase adsorption, here dehydrogenation polymers (DHPs) were prepared from p-glucocoumaryl alcohol/coniferin/syringin, giving rise to H-DHP, G-DHP, and S-DHP, respectively. The structures of DHPs were thoroughly characterized and compared by GPC and NMR techniques, and the Langmuir isotherm protocol was applied to determine the cellulase adsorption behaviors of these different types of DHPs. The adsorption study indicated that the binding strength between the DHPs and cellulase varied in the following order: G-DHP > H-DHP > S-DHP. The inhibition of different types of DHPs on enzymatic hydrolysis of cellulose was in the same order as the cellulase adsorption, indicating that non-productive adsorption was the main way to influence cellulase. The correlation analysis results showed a positive association between the phenolic hydroxyl group content in DHPs and their maximum adsorption capacity toward enzymes. A negative correlation between the PDI and binding strength was also observed. It was also found that the adsorbed cellulase could be desorbed and retained normal enzyme activity, and so it was presumed that DHPs and cellulase were mainly linked by physisorption such as hydrogen bonding. This study clearly showed that the composition of lignin had a great impact on cellulase, and that G-type lignin exhibited the most detrimental effect. The results could provide useful information on the mechanism of cellulase adsorption onto lignin using DHPs as lignin model compounds.

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

Electrochemically induced metal- vs. ligand-based redox changes in mackinawite: identification of a Fe 3+ - and polysulfide-containing intermediate

Under anaerobic conditions, ferrous iron reacts with sulfide producing FeS, which can then undergo a temperature, redox potential, and pH dependent maturation process resulting in the formation of oxidized mineral phases, such as greigite or pyrite. A greater understanding of this maturation process holds promise for the development of iron-sulfide catalysts, which are known to promote diverse chemical reactions, such as H + , CO 2 and NO 3 - reduction processes. Hampering the full realization of the catalytic potential of FeS, however, is an incomplete knowledge of the molecular and redox processess ocurring between mineral and nanoparticulate phases. Here, we investigated the chemical properties of iron-sulfide by cyclic voltammetry, Raman and X-ray absorption spectroscopic techniques. Tracing oxidative maturation pathways by varying electrode potential, nanoparticulate n(Fe 2+ S 2- ) (s) was found to oxidize to a Fe 3+ containing FeS phase at -0.5 V vs. Ag/AgCl (pH = 7). In a subsequent oxidation, polysulfides are proposed to give a material that is composed of Fe 2+ , Fe 3+ , S 2- and polysulfide (S n 2- ) species, with its composition described as Fe 2+ 1-3x Fe 3+ 2x S 2- 1-y (S n 2- ) y . Thermodynamic properties of model compounds calculated by density functional theory indicate that ligand oxidation occurs in conjunction with structural rearrangements, whereas metal oxidation may occur prior to structural rearrangement. These findings together point to the existence of a metastable FeS phase located at the junction of a metal-based oxidation path between FeS and greigite (Fe 2+ Fe 3+ 2 S 2- 4 ) and a ligand-based oxidation path between FeS and pyrite (Fe 2+ (S 2 ) 2- ).

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

Carbon-efficient conversion of natural gas and natural-gas condensates to chemical products and intermediate feedstocks via catalytic metal–organic framework (MOF) chemistry

The net-zero carbon emission scenario of stopping hydrocarbon use as fuel is unlikely to end the extraction of fossil hydrocarbons. Remaining will be a sizable need for hydrocarbons as feedstocks for commodity chemicals destined for transformation into polymers, manufacturing-relevant intermediates, and value-added chemicals. Historically, the primary feedstock source has been oil. Over the past dozen years, however, fracking-based extraction of shale-trapped natural gas from known enormous reserves, in North America, has resulted in feedstock sourcing instead from wet shale gas. This shift has transformed the catalytic chemistry of commodity chemical manufacturing. In this paper, following a brief discussion of the merits and limitations of crystallographically well-defined metal–organic frameworks (MOFs) as model catalysts and catalyst-supports, we examined their applications for understanding and potentially enabling carbon-economical, catalytic transformation of C 1 , C 2 , C 3 , and C 4 components of natural gas to desirable commodity chemicals, intermediates, or model compounds.

03 NATURAL GAS↗
DOE OSTI2023

Mechanistic insights into the conversion of polyalcohols over Brønsted acid sites

Multi-layered plastic (MLP) films provide excellent properties for food packaging; however, because of the complicated chemistry of the hydrophobic substrates and tightly laminated hydrophilic layers, it is challenging to recycle the MLP films. The selective conversion of polar functional groups in hydrophilic layers with a minimal destruction of the carbon backbone of constituted polymers is considered a promising approach to improve the recyclability of MLP films. Here, in this study, we combine computational and experimental studies to investigate the acid-catalyzed conversion of functional groups in polyalcohols, through which we report potential reaction pathways involved in the conversion of ethylene vinyl alcohol (EVOH), a common copolymer used in MLP films as an oxygen barrier. Using 2,4-pentanediol as a model compound, we show that its conversion proceeds primarily through the dehydration of a hydroxyl group via either a stepwise or a concerted mechanism to form an unsaturated alcohol that can be further converted into a conjugated diene or a saturated ketone; this secondary reaction determines the product selectivity. The rate determining intermediates and transition states are identified, and the activation barriers are calculated, in agreement with experimentally observed product selectivities. This study thus provides insights for the selective conversion of EVOH.

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

Ambient mechanosynthesis of flexible two-dimensional covalent organic frameworks

We present the first ambient mechanosynthesis of 16 flexible covalent organic frameworks (COFs) within an hour. Notably, one representative COF exhibited a high iodine uptake capacity of ∼4.3 g g −1 from aqueous solutions and 5.97 g g −1 from vapor. Flexible two-dimensional covalent organic frameworks (2D COFs) constructed from nonplanar building blocks represent an emerging paradigm in COF design. Nevertheless, the prevailing solvothermal synthesis suffers from low time efficiency, environmental unfriendliness, and cumbersome protocols. Here, we address these challenges by developing the first ambient mechanosynthesis of a diverse library of flexible 2D COFs. Sixteen distinct triazine-cored Schiff-base COFs, including five as-yet-unreported ones, were rapidly synthesized via ball milling using 2,4,6-tris(4-aminophenoxy)-1,3,5-triazine (TPT-NH 2 ) and 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (TPT-CHO) as building blocks. Notably, the representative COF, MC-flexible-COF-1, was synthesized in as little as one hour under mechanosynthesis conditions, whereas it remained unattainable via the traditional solvothermal method, despite prolonged heating and extensive solvent screening. The highly dynamic nature of the imine linkage was unequivocally demonstrated through mechanochemical “scrambling” experiments using molecular model compounds. Furthermore, MC-flexible-COF-1 exhibited a high iodine uptake capacity of ∼4.30 g g −1 from aqueous solutions and 5.97 g g −1 from the vapor phase. This work underscores the immense potential of mechanochemistry as a powerful and sustainable tool for the rapid synthesis of advanced 2D COFs, including those inaccessible via conventional solution-based methods.

Nailwal, Yogendra↗
DOE OSTI2021

Probing the effect of magnetic field on charge order in the quasi-two-dimensional Mott insulator κ - (ET) 2 Hg(SCN) 2 Cl

Molecular-based quasi-two-dimensional charge-ordered Mott insulators can possess both spin S = 1/2 and an electric dipole degree of freedom residing on each (BEDT - TTF) 2 lattice site. There exists a theoretical proposal for a magnetoelectric effect in such a material, which can manifest itself as a sensitivity of charge distribution on (BEDT - TTF) 2 dimers to the magnetic field. Here in this work, we used Raman scattering spectroscopy in the magnetic field up to 31 T applied perpendicular to the two-dimensional triangular lattice planes to probe a magnetoelectric effect in $\kappa$ - (ET) 2 H g (SCN) 2 Cl. This is a model compound, which shows charge order and antiferromagnetic correlations at temperatures below 30 K. We discuss possible reasons for the absence of an observable magnetoelectric effect in the probed temperature and magnetic field ranges.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Chemical state mapping of simulant Chernobyl lava-like fuel containing material using micro-focused synchrotron X-ray spectroscopy

Uranium speciation and redox behaviour is of critical importance in the nuclear fuel cycle. X-ray absorption near-edge spectroscopy (XANES) is commonly used to probe the oxidation state and speciation of uranium, and other elements, at the macroscopic and microscopic scale, within nuclear materials. Two-dimensional (2D) speciation maps, derived from microfocus X-ray fluorescence and XANES data, provide essential information on the spatial variation and gradients of the oxidation state of redox active elements such as uranium. In the present work, we elaborate and evaluate approaches to the construction of 2D speciation maps, in an effort to maximize sensitivity to the U oxidation state at the U L 3 -edge, applied to a suite of synthetic Chernobyl lava specimens. Our analysis shows that calibration of speciation maps can be improved by determination of the normalized X-ray absorption at excitation energies selected to maximize oxidation state contrast. The maps are calibrated to the normalized absorption of U L 3 XANES spectra of relevant reference compounds, modelled using a combination of arctangent and pseudo-Voigt functions (to represent the photoelectric absorption and multiple-scattering contributions). We validate this approach by microfocus X-ray diffraction and XANES analysis of points of interest, which afford average U oxidation states in excellent agreement with those estimated from the chemical state maps. This simple and easy-to-implement approach is general and transferrable, and will assist in the future analysis of real lava-like fuel-containing materials to understand their environmental degradation, which is a source of radioactive dust production within the Chernobyl shelter.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synthesis of a new zinc phthalocyanine–benzoquinone rigid dyad

A new zinc phthalocyanine–benzoquinone rigid dyad, QnZnPc–G2 was synthesized as a model compound to study photo-induced charge separation mimicking natural photosynthesis. Compared to its previously reported analog, this dyad has an additional fused benzene ring between the zinc phthalocyanine (ZnPc) (donor) and benzoquinone (acceptor) moieties. The rigid structure of QnZnPc–G 2 (i.e. no rotamers) is designed to minimize the unusual electronic perturbation induced by the internal motions, which resulted in a significant increase in the lifetime of the charged separated state (from 40 ps to 252 ps). Finally, physical and photochemical properties of this new dyad were examined and discussed in this paper.

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

Tailored Bioblendstocks With Low Environmental Impact To Optimize MCCI Engines

This project seeks to overcome impediments to expansion of algae cultivation and conversion into fuels to displace petroleum and reduce greenhouse gas (GHG) emissions. The overall objective of the project is to develop and demonstrate a microalgae bio-blendstock with greater than 60% greenhouse gas reduction relative to petroleum diesel, reduce sooting propensity, increase cetane number, improve engine thermal efficiency relative to a baseline diesel engine operating on conventional fuel. These objectives are being accomplished by: Applying cultivation of algae polycultures to achieve robustness and productivity, Converting whole algae to bio-hydrocarbons via Hydrothermal Liquefaction (HTL) to make a biocrude and up-grading the biocrude via hydroprocessing to obtain tailored bioblendstocks for diesel fuel, Optimizing diesel (MCCI) combustion through blending model compounds into diesel fuel to represent the tailored bioblendstocks through experiments and numerical simulation.

09 BIOMASS FUELS↗
DOE OSTI2023

Design and Operation of a Multi-Bed Catalytic Micro-Reactor for the Study of Co-Processing of Bio-Oils with VGO

An industry wide shift from fossil-based fuel to renewable fuel sources including biomass, municipal waste, and plastics will require new process monitoring methods to minimize transitional risks including off specification product formation and catalyst deactivation. This project aims to provide a machine learning based process monitoring tool composed of online, slipstream mass spectra for use in biomass refineries and co-processing in existing refineries allowing operators to monitor product qualities and adjust process conditions accordingly. In order to maximize the robustness of the tool, large volumes of data must be collected to fine tune model parameters which consists of both micro and pilot scale mass spectral data. Micro-scale data is collected with a multi-tube micro-reactor housing up to six catalysts in horizontal beds, coupled with a molecular beam mass spectrometer. A pyrolizer equipped with an auto-sampler streamlines the micro-scale data collection process. This type of pyrolizer/micro-reactor configuration does not exist on the market, and therefore had to be created for the purposes of this project. The design and commissioning of this reactor will be presented in detail. This reactor set-up is highly flexible and increases throughput of analysis. For catalyst testing, each bed can be individually selected simply by turning valves. For catalyst reduction and regeneration, simultaneous flow through all six beds is used. The reproducibility of the system was first assessed with whole biomass pyrolysis along with pyrolysis of calibration standards. Initial work on this system evaluated two FCC catalysts, equilibrium catalyst (E-cat), and a proprietary catalyst from Johnson Matthey specifically design for co-processing of bio-oil with vacuum gas oil (VGO). This work used model compounds and VGO which illuminated differences in products produced by the catalysts.

biomass↗
DOE OSTI2023

2.3.4.100 - Lignin Utilization

Lignin depolymerization to aromatic monomers is a primary route for myriad lignin valorization strategies. To date, there are many strategies able to cleave aryl-ether linkages in lignin, but the lignin polymer, in both its native and processed forms, contains a substantial fraction of refractory carbon-carbon linkages between aromatic units, which typically limits aromatic monomer yields to -30-40 wt% or lower, depending on the feedstock. To that end, the Lignin Utilization (LigU) project addresses the critical challenge of lignin depolymerization catalysis with emphasis on C-C bond cleavage. Being able to achieve cost-effective C-C bond catalysis in lignin depolymerization would enable a substantial increase in accessible aromatic monomer yields from lignin. Among the catalysis strategies that have been investigated in the LigU project, we have made substantial progress in the use of autoxidation catalysis, inspired by the industrial conversion of p-xylene to terephthalic acid, for C-C bond cleavage in lignin. Using multiple substrates, we have demonstrated that autoxidation catalysis can produce mixtures of bio-available aromatic monomers for conversion to exemplary bioproducts, such as cis,cis-muconic acid, in collaboration with the Biological Lignin Valorization project. Prior to FY23, the LigU project also included lignin analytical chemistry method development, lignin analytics for BETO-funded projects, and model compound syntheses, which will also be presented.

BIOMASS FUELS↗
DOE OSTI2025

Analyzing Tradeoffs Associated with the Manufacture of Refined Fuels by Comparing Volatile Organic Compound (VOC) Emissions Model Results with Carbon Impacts

A first-of-its kind, publicly-available model for estimating emissions of volatile organic compounds from operations along the supply chain of liquid fuels and refinery products is presented and demonstrated. This standardized model permits comprehensive, reproducible, and comparable evaluation of the supply chain/life cycle VOC emissions of liquid fuels and refinery products.

09 BIOMASS FUELS↗