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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Pyrophosphate-free glycolysis in Clostridium thermocellum increases both thermodynamic driving force and ethanol titers

Background: Clostridium thermocellum is a promising candidate for production of cellulosic biofuels, however, its final product titer is too low for commercial application, and this may be due to thermodynamic limitations in glycolysis. Previous studies in this organism have revealed a metabolic bottleneck at the phosphofructokinase (PFK) reaction in glycolysis. In the wild-type organism, this reaction uses pyrophosphate (PP i ) as an energy cofactor, which is thermodynamically less favorable compared to reactions that use ATP as a cofactor. Previously we showed that replacing the PP i -linked PFK reaction with an ATP-linked reaction increased the thermodynamic driving force of glycolysis, but only had a local effect on intracellular metabolite concentrations, and did not affect final ethanol titer. Results: In this study, we substituted PP i -pfk with ATP-pfk, deleted the other PPi-requiring glycolytic gene pyruvate:phosphate dikinase (ppdk), and expressed a soluble pyrophosphatase (PPase) and pyruvate kinase (pyk) genes to engineer PP i -free glycolysis in C. thermocellum. We demonstrated a decrease in the reversibility of the PFK reaction, higher levels of lower glycolysis metabolites, and an increase in ethanol titer by an average of 38% (from 15.1 to 21.0 g/L) by using PP i -free glycolysis. Conclusions: By engineering PP i -free glycolysis in C. thermocellum, we achieved an increase in ethanol production. These results demonstrate that optimizing the thermodynamic landscape through metabolic engineering can enhance product titers. While further increases in ethanol titers are necessary for commercial application, this work represents a significant step toward engineering glycolysis in C. thermocellum to increase ethanol titers.

09 BIOMASS FUELS↗
DOE OSTI2026

Powders and pellets – Extrusion engineering for a Cu/BEA syngas-to-hydrocarbons catalyst

Converting high-performing powder catalysts from the laboratory reactor scale into effective extruded catalysts at the industrial scale remains a hurdle for advancing sustainable catalytic processes, such as the conversion of biogenic syngas into high octane gasoline. Recently, a process-intensified syngas-to-hydrocarbons (STH) reaction in a single reactor under relatively mild conditions (220–250 ºC, 0.75–2.0 MPa) was reported, enabled by the development of a dimethyl ether (DME) homologation catalyst, Cu-modified H-BEA (Cu/BEA) zeolite. In this study, we explore approaches for synthesizing engineered Cu/BEA catalysts for use in the STH reaction to retain the high performance observed with the powder catalyst. We demonstrate that changes to the order of manufacturing steps (i.e., Cu deposition, alumina binder addition, and extrusion) result in observable changes to key active sites (Brønsted acid sites and zeolitic Cu + species), and ultimately, catalyst performance. When the Cu precursor was added directly to BEA before extrusion, both types of active sites were stabilized, preserving the activity of the powder catalyst. However, when the Cu precursor was added after extrusion, the resulting Cu species were mobile, destabilizing Brønsted acid sites and leading to near-zero activity.

09 BIOMASS FUELS↗
DOE OSTI2024

Theoretical Investigation of the Adsorbate and Potential–Induced Stability of Cu Facets During Electrochemical CO 2 and CO Reduction

The activity and product selectivity of electrocatalysts for reactions like the carbon dioxide reduction reaction (CO 2 RR) are intimately dependent on the catalyst's structure and composition. While engineering catalytic surfaces can improve performance, discovering the key sets of rational design principles remains challenging due to limitations in modeling catalyst stability under operating conditions. Herein, we perform first-principles density functional calculations adopting implicit solvation methods with potential control to study the influence of adsorbates and applied potential on the stability of different facets of model Cu electrocatalysts. Using coverage dependencies extracted from microkinetic models, we describe an approach for calculating potential and adsorbate-dependent contributions to surface energies under reaction conditions, where Wulff constructions are used to understand the morphological evolution of Cu electrocatalysts under CO 2 RR conditions. Here we identify that CO*, a key reaction intermediate, exhibits higher kinetically and thermodynamically accessible coverages on (100) relative to (111) facets, which can translate into an increased relative stabilization of the (100) facet during CO 2 RR. Our results support the known tendency for increased (111) faceting of Cu nanoparticles under more reducing conditions and that the relative increase in (100) faceting observed under CO 2 RR conditions is likely attributed to differences in CO* coverage between these facets.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Structure and Interactions of HIV-1 gp41 CHR-NHR Reverse Hairpin Constructs Reveal Molecular Determinants of Antiviral Activity

Engineered reverse hairpin constructs containing a partial C-heptad repeat (CHR) sequence followed by a short loop and full-length N-heptad repeat (NHR) were previously shown to form trimers in solution and to be nanomolar inhibitors of HIV-1 Env mediated fusion. Their target is the in situ gp41 fusion intermediate, and they have similar potency to other previously reported NHR trimers. However, their design implies that the NHR is partially covered by CHR, which would be expected to limit potency. An exposed hydrophobic pocket in the folded structure may be sufficient to confer the observed potency, or they may exist in a partially unfolded state exposing full length NHR. Here, in this study, we examined their structure by crystallography, CD and fluorescence, establishing that the proteins are folded hairpins both in crystal form and in solution. We examined unfolding in the milieu of the fusion reaction by conducting experiments in the presence of a membrane mimetic solvent and by engineering a disulfide bond into the structure to prevent partial unfolding. We further examined the role of the hydrophobic pocket, using a hairpin-small molecule adduct that occluded the pocket, as confirmed by X-ray footprinting. The results demonstrated that the NHR region nominally covered by CHR in the engineered constructs and the hydrophobic pocket region that is exposed by design were both essential for nanomolar potency and that interaction with membrane is likely to play a role in promoting the required inhibitor structure. The design concepts can be applied to other Class 1 viral fusion proteins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

iNovo479: Metabolic Modeling Provides a Roadmap to Optimize Bioproduct Yield from Deconstructed Lignin Aromatics by Novosphingobium aromaticivorans

Lignin is an abundant renewable source of aromatics and precursors for the production of other organic chemicals. However, lignin is a heterogeneous polymer, so the mixture of aromatics released during its depolymerization can make its conversion to chemicals challenging. Microbes are a potential solution to this challenge, as some can catabolize multiple aromatic substrates into one product. Novosphingobium aromaticivorans has this ability, and its use as a bacterial chassis for lignin valorization could be improved by the ability to predict product yields based on thermodynamic and metabolic inputs. In this work, we built a genome-scale metabolic model of N. aromaticivorans, iNovo479, to guide the engineering of strains for aromatic conversion into products. iNovo479 predicted product yields from single or multiple aromatics, and the impact of combinations of aromatic and non-aromatic substrates on product yields. We show that enzyme reactions from other organisms can be added to iNovo479 to predict the feasibility and profitability of producing additional products by engineered strains. Thus, we conclude that iNovo479 can help guide the design of bacteria to convert lignin aromatics into valuable chemicals.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Active oxygen species in heterogeneously catalyzed oxidation reactions

Active oxygen species generation in heterogeneously catalyzed hydrocarbon oxidation reactions have not been fully characterized. There is little consensus as to which the most active or selective species are. However, electron localization at a single oxygen atom—rather than shared over several—is necessary to activate very stable hydrocarbons like methane. This paper presents an overview of oxygen species formed on various catalytic surfaces and their role in hydrocarbon oxidation reactions. Since limitations of analytical methods are a significant bottleneck for understanding and engineering active oxygen species, approaches for characterizing and quantifying active oxygen are discussed. While several methods are effective for describing certain oxygen species, there is no method that comprehensively characterizes all active oxygen species. Here, the most promising approach is oxygen isotope exchange coupled with infrared spectrometry and inline mass spectrometry.

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

Enhanced Water Interaction at Dual Cu Sites Within the Defects on a Copper Sulfide Layer

Electrochemical transformations of stable molecules and water into fuels and value-added chemicals require efficient catalyst surfaces. Introducing controlled defects at atomic scales can offer promising routes to enhance catalyst performance. In this study, we found novel dual copper site (-Cu-Cu-) defects within a copper sulfide (Cu-S) layer supported on Cu(111). Using scanning tunneling microscopy (STM) and density functional theory (DFT), we found these dual copper sites enhance molecular adsorption strength, specifically for water molecules, compared to intact Cu-S layer or pristine copper surfaces. This discovery highlights the potential of engineered dual-site copper defects to advance electrochemical catalytic materials, particularly for reactions involving water activation.

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

Revealing protonation states and tracking substrate in serine hydroxymethyltransferase with room-temperature X-ray and neutron crystallography

Pyridoxal 5’-phosphate (PLP)-dependent enzymes utilize a vitamin B 6 -derived cofactor to perform a myriad of chemical transformations on amino acids and other small molecules. Some PLP-dependent enzymes, such as serine hydroxymethyltransferase (SHMT), are promising drug targets for the design of small-molecule antimicrobials and anticancer therapeutics, while others have been used to synthesize pharmaceutical building blocks. Understanding PLP-dependent catalysis and the reaction specificity is crucial to advance structure-assisted drug design and enzyme engineering. Here we report the direct determination of the protonation states in the active site of Thermus thermophilus SHMT (TthSHMT) in the internal aldimine state using room-temperature joint X-ray/neutron crystallography. Conserved active site architecture of the model enzyme TthSHMT and of human mitochondrial SHMT (hSHMT2) were compared by obtaining a room-temperature X-ray structure of hSHMT2, suggesting identical protonation states in the human enzyme. The amino acid substrate serine pathway through the TthSHMT active site cavity was tracked, revealing the peripheral and cationic binding sites that correspond to the pre-Michaelis and pseudo-Michaelis complexes, respectively. At the peripheral binding site, the substrate is bound in the zwitterionic form. By analyzing the observed protonation states, Glu53, but not His residues, is proposed as the general base catalyst, orchestrating the retro-aldol transformation of L-serine into glycine.

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

Virtual Volumetric Additive Manufacturing (VirtualVAM)

Abstract Tomographic volumetric additive manufacturing (VAM) produces arbitrary 3D geometries by exposure of a rotating volume of photopolymer resin to tomographically‐patterned illumination. This enables high speed, layer‐less printing of parts from a wide range of photopolymers not amenable to layer‐by‐layer processes. Since the entire geometry is produced at once over the course of a few seconds to minutes, molecular diffusion length scales become significant to the printing process. Understanding these molecular reaction and diffusion processes is imperative for advancing VAM to a usable technology. These processes are experimentally very difficult to monitor and measure. Herein, VirtualVAM ‐ a simulation framework for modeling the tomographic VAM process, is developed and experimentally validated. VirtualVAM simulates reaction, diffusion, and heat generation processes over the course of a print with single‐voxel resolution. From a few experimentally‐determined input parameters and a set of images for projection, VirtualVAM is able to generate a large spatio‐temporal data set for any given tomographic VAM print. Using VirtualVAM, a number of experimentally‐unattainable aspects of the VAM process are investigated such as single‐voxel conversion profiles, effect of molecular oxygen, and stopping time determination. VirtualVAM also enables the optimization of exposure patterns to further improve contrast between in‐part and out‐of‐part delivered dose.

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

Regulation of Cathode Mass and Charge Transfer by Structural 3D Engineering for Protonic Ceramic Fuel Cell at 400 °C

Abstract Lowering the operating temperature (ideally below 400 °C) for solid oxide fuel cell (SOFC) technology deployment has been an important transition that introduces the benefit of reduced operational costs and system durability. However, the key technical issue limiting the transition is the sluggish cathodic performance, namely the oxygen reduction reaction (ORR) rate of the conventional sponge‐like cathode dramatically drops as the temperature reduces. In this paper, 3D engineering of a cathode is conducted on a protonic ceramic fuel cell to obtain an enhanced ORR between 400 and 600 °C. Compared with a cell using a conventional sponge‐like cathode, 3D engineering improves the cathode ORR by 41% at 400 °C with a peak power density of 0.410 W cm −2 . A phase field simulation is applied to assist the engineering by understanding the competition between the cathode mass and charge transfer with different cathode porosities. The results show that structural engineering of existing well‐developed cathodes is a simple and effective method to promote cathode ORR for low temperature SOFC by regulating the mass and charge transfer.

Bian, Wenjuan↗
DOE OSTI2021

Improved photosynthetic capacity and photosystem I oxidation via heterologous metabolism engineering in cyanobacteria

Significance Cyanobacteria have been increasingly explored as a biotechnological platform, although their economic feasibility relies in part on the capacity to maximize their photosynthetic, solar-to-biomass energy conversion efficiency. Here we show that cyanobacterial photosynthetic capacity can be increased by diverting cellular resources toward heterologous, energy-storing metabolic pathways and by reducing electron flow to photoprotective, but energy-dissipating, oxygen reduction reactions. We further show that these heterologous sinks can partially contribute to photosystem I (PSI) oxidation, suggesting an engineering strategy to improve both energy storage capacity and robustness by selective diversion of excess photosynthetic capacity to productive processes.

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

Grain boundary engineering for efficient and durable electrocatalysis

Grain boundaries in noble metal catalysts have been identified as critical sites for enhancing catalytic activity in electrochemical reactions such as the oxygen reduction reaction. However, conventional methods to modify grain boundary density often alter particle size, shape, and morphology, obscuring the specific role of grain boundaries in catalytic performance. This study addresses these challenges by employing gold nanoparticle assemblies to control grain boundary density through the manipulation of nanoparticle collision frequency during synthesis. We demonstrate a direct correlation between increased grain boundary density and enhanced two-electron oxygen reduction reaction activity, achieving a significant improvement in both specific and mass activity. Additionally, the gold nanoparticle assemblies with high grain boundary density exhibit remarkable electrochemical stability, attributed to boron segregation at the grain boundaries, which prevents structural degradation. This work provides a promising strategy for optimizing the activity, selectivity, and stability of noble metal catalysts through precise grain boundary engineering.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Chapter 4: What We Can Learn from Measuring Metabolic Fluxes in Cyanobacteria

Cyanobacteria with the capability of oxygen-evolving photosynthesis play a vital role in the global carbon, oxygen, and nitrogen cycles. From a biochemical perspective, all phenotypic traits and functions of cyanobacteria are derived from the potential of their metabolism and mirrored in metabolic fluxes through an integrated metabolic network. Metabolic flux, the rate of turnover of molecules through a metabolic pathway, is therefore of great importance for an in-depth understanding of the role of cyanobacteria in the biosphere. Recent interest in cyanobacteria metabolic fluxes is also motivated by the prospect to utilize their light-driven CO2 fixation for sustainable production of valuable chemicals and biofuels. Valorization of cyanobacterial metabolism will require engineering of the native metabolic network - a challenge that can benefit from a quantitative understanding of metabolic reactions taking place intracellularly. In this chapter, we will discuss some intriguing questions relevant to metabolic fluxes in cyanobacteria: How are metabolic fluxes predicted or measured? What do we know about the fluxome inside various cyanobacteria thus far? How are they different between strains as well as in different conditions? And how can we use fluxomics information to guide metabolic engineering and synthetic biology? This chapter will highlight updated knowledge on cyanobacterial metabolism. Specifically, we will focus on providing readers a quantitative vision to understand how this photosynthetic model works.

BASIC BIOLOGICAL SCIENCES,INORGANIC, ORGANIC, PHYS↗
DOE OSTI2020

Single-phase Ru 1- x-y Mn x Co y O 2 nanoparticles as highly effective oxygen reduction electrocatalysts in alkaline media with enhanced stability and fuel-tolerance

Here, a series of single-phase binary and ternary ruthenium and transition metal oxide nanoparticles supported on Vulcan - Ru 1-x MnxO2/C, Ru1-xCoxO 2 /C, Ru 1-x-y MnxCo y O 2 /C, Ru 1-x Fe x O 2 /C, Ru 1-x Ni x O 2 /C and Ru 1-x V x O 2 /C, as well as RuO 2 /C, MnO 2 /C, Co 3 O 4 /C and Mn 3-x Co x O 4 /C - were synthesized via a facile method and studied for their oxygen reduction reaction (ORR) activity in alkaline media. Single-phase Ru 1-x Mn x O 2 /C, Ru 1-x-y Mn x Co y O 2 /C and Ru 1-x Co x O 2 /C catalysts significantly boosted ORR kinetics in alkaline media. Moreover, they were H 2 and methanol tolerant, and exhibited long term stability due to their single-phase structure. Ru 0.85 Mn 0.15 O 2 /C stood out as the most active catalyst among them. A volcano relationship of the ORR activity of these binary and ternary metal oxide catalysts vs. the O adsorption energy was found, with the maximum activity observed for the Ru 1-x Mn x O 2 /C, Ru 1-x-y Mn x Co y O 2 /C and Ru 1-x Co x O 2 /C catalysts due to their optimal O binding energy. These materials have potential applications as highly active ORR catalysts in alkaline fuel cells and metal-air batteries.

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

Conversion of Phenolic Oil from Biomass Pyrolysis into Phenyl Esters

Bio-oil is among the most economical approaches for advanced biofuel production. However, bio-oil faces several challenges including high acidity and viscosity, poor storage, and thermal stability. This study focuses on the upgradation of lignocellulosic (corn stover and yellow pine) bio-oil derived phenolic oil (PO), produced by the autothermal fast pyrolysis, through acid-catalyzed esterification reaction. Our strategy exploits a little recognized chemistry: the Fischer esterification of PO and carboxylic acids into carboxylic acid phenyl esters (CAPE) using Dean Stark distillation. Analyses by the Folin–Ciocalteu method, Karl Fischer titration, gas chromatography flame ionization detector, and the molecular weight determination by gel permeation chromatography suggest the conversion of 50 wt% added phenolics to their corresponding CAPE. The Fourier transform infrared spectroscopy analysis confirmed the formation of new C=O and two C–O stretching bands and decrease in the intensity of phenolic-OH bands in the CAPE. The 13 C NMR analysis supports the formation of CAPE together with some unreacted precursors. A base-catalyzed ester hydrolysis experiment and mass balance calculation show an excellent agreement (within 5% range) of the equivalent weight between the produced ester and the phenyl hexanoate. Brookfield analysis indicates that CAPE has 330-fold lower viscosity than starting PO. Heating values of CAPE were higher than PO, from which they were derived (42.2 and 43.6%, respectively, for PO from pyrolysis of corn stover and yellow pine), while moisture content decreased by 98.3 and 98.7%, respectively. The CAPE, which is a phenolic analogue of methyl esters used in biodiesel, has improved stability compared to PO from which it was derived.

42 ENGINEERING↗
DOE OSTI2021

Unusual Role of Point Defects in Perovskite Nickelate Electrocatalysts

Low-cost transition-metal oxide is regarded as a promising electrocatalyst family for an oxygen evolution reaction (OER). The classic design principle for an oxide electrocatalyst believes that point defect engineering, such as oxygen vacancies (VO .. ) or heteroatom doping, offers the opportunities to manipulate the electronic structure of material toward optimal OER activity. Oppositely, in this work, we discover a counterintuitive phenomenon that both VO .. and an aliovalent dopant (i.e., proton (H + )) in perovskite nickelate (i.e., NdNiO 3 (NNO)) have a considerably detrimental effect on intrinsic OER performance. Detailed characterizations unveil that the introduction of these point defects leads to a decrease in the oxidative state of Ni and weakens Ni-O orbital hybridization, which triggers the local electron-electron correlation and a more insulating state. Evidenced by first-principles calculation using the density functional theory (DFT) method, the OER on nickelate electrocatalysts follows the lattice oxygen mechanism (LOM). The incorporation of point defect increases the energy barrier of transformation from OO*(V O ) to OH*(V O ) intermediates, which is regarded as the rate-determining step (RDS). Furthermore, this work offers a new and significant perspective of the role that lattice defects play in the OER process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗