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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

An atomic-scale view of single-site Pt catalysis for low-temperature CO oxidation

Single-atom catalysts have attracted great attention in recent years due to their high efficiencies and cost savings. However, there is debate concerning the nature of the active site, interaction with the support, and mechanism by which single-atom catalysts operate. Here, using a combined surface science and theory approach, we designed a model system in which we unambiguously show that individual Pt atoms on a well-defined Cu 2 O film are able to perform CO oxidation at low temperatures. Isotopic labelling studies reveal that oxygen is supplied by the support. Density functional theory rationalizes the reaction mechanism and confirms X-ray photoelectron spectroscopy measurements of the neutral charge state of Pt. Scanning tunneling microscopy enables visualization of the active site as the reaction progresses, and infrared measurements of the CO stretch frequency are consistent with atomically dispersed Pt atoms. These results serve as a benchmark for characterizing, understanding and designing other single-atom catalysts.

Therrien, Andrew J.↗
DOE OSTI2019

Methanol to high-octane gasoline within a market-responsive biorefinery concept enabled by catalysis

Biofuels production from lignocellulosic biomass is hindered by high conversion costs in the generation of high-quality fuels, driving research towards the development of new pathways with less severe conditions, higher yields and higher-quality products. In this report, we present a market-responsive biorefinery concept based on methanol as the key intermediate, which generates high-octane gasoline (HOG) and jet fuel blendstocks from biomass. Process models and techno-economic analysis are linked with both fundamental and applied catalyst development research to quantify the impact of catalyst advancements on process economics. By facilitating reincorporation of C 4 by-products during dimethyl ether homologation, a Cu-modified beta zeolite catalyst enabled a 38% increase in yield of the HOG product and a 35% reduction in conversion cost compared to the benchmark beta zeolite catalyst. Alternatively, C 4 by-products were directed to a synthetic kerosene that met five specifications for a typical jet fuel, with a small increase in the fuel synthesis cost versus the HOG-only case.

09 BIOMASS FUELS↗
DOE OSTI2024

CO 2 fixation into carbon nanofibres using electrochemical–thermochemical tandem catalysis

Carbon dioxide (CO 2 ) fixation into value-added solid carbon such as carbon nanofibres (CNF) for longer-term storage represents a promising avenue for achieving net-negative carbon emissions. However, directly converting CO 2 to CNF via thermocatalytic approaches faces thermodynamic constraints, while electrocatalytic methods typically lead to amorphous carbon with limited yields or require energy-intensive conditions (>720 °C). Here, we present an electrocatalytic-thermocatalytic tandem strategy for CNF production, which circumvents the aforementioned thermodynamic limitations by integrating the co-electrolysis of CO 2 and water into syngas (CO and H 2 ) with a subsequent thermochemical process at relatively mild conditions (370-450 °C, 1 atm), yielding CNF at a high production rate (average 2.5 g carbon g metals -1 h -1 ). Further, the optimal coordinated actions of FeCo alloy and extra metallic Co were ascertained to enhance the dissociative activation of syngas and favour the carbon-carbon bond formation to produce CNF. This tandem strategy opens a door to leverage renewable energy for decarbonizing CO 2 into valuable solid carbon products while producing renewable H 2 .

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

Architecture, catalysis and regulation of methylthio-alkane reductase for bacterial sulfur acquisition from volatile organic compounds

Bacteria utilize methylthio-alkane reductase (MAR) to acquire sulfur from volatile organic sulfur compounds. Reductive cleavage of methylthio-ethanol and dimethylsulfide liberates methanethiol for methionine synthesis and concomitantly releases ethylene and methane, respectively. Here we show that the native MAR of Rhodospirillum rubrum is a two-component system composed of a MarH ATP-dependent reductase and a MarDK catalytic core, whose architecture parallels nitrogenase. MarS complexes with MarDK to downregulate MAR activity during cellular sulfate influx, based on chromatographic and activity analyses. MarDK possesses complex metallocofactors resembling, but not identical to, nitrogenase P- and iron-only M-clusters, designated as mar1 and mar2 clusters based on metal, spectroscopic and mutagenesis analyses. They exhibit electronic features similar to the iron-only nitrogenase under turnover and, remarkably, are matured by MarB or nitrogenase NifB, resulting in maturase-dependent activity profiles. Altogether, this suggests a broader scope of reactivity, mechanisms and regulation in microbial metabolism for the nitrogenase-like family of enzymes than previously considered.

09 BIOMASS FUELS↗
DOE OSTI2023

Mapping the determinants of catalysis and substrate specificity of the antibiotic resistance enzyme CTX-M β-lactamase

Abstract CTX-M β-lactamases are prevalent antibiotic resistance enzymes and are notable for their ability to rapidly hydrolyze the extended-spectrum cephalosporin, cefotaxime. We hypothesized that the active site sequence requirements of CTX-M-mediated hydrolysis differ between classes of β-lactam antibiotics. Accordingly, we use codon randomization, antibiotic selection, and deep sequencing to determine the CTX-M active-site residues required for hydrolysis of cefotaxime and the penicillin, ampicillin. The study reveals positions required for hydrolysis of all β-lactams, as well as residues controlling substrate specificity. Further, CTX-M enzymes poorly hydrolyze the extended-spectrum cephalosporin, ceftazidime. We further show that the sequence requirements for ceftazidime hydrolysis follow those of cefotaxime, with the exception that key active-site omega loop residues are not required, and may be detrimental, for ceftazidime hydrolysis. These results provide insights into cephalosporin hydrolysis and demonstrate that changes to the active-site omega loop are likely required for the evolution of CTX-M-mediated ceftazidime resistance.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Activity of N-coordinated multi-metal-atom active site structures for Pt-free oxygen reduction reaction catalysis: Role of *OH ligands

We report calculated oxygen reduction reaction energy pathways on multi-metal-atom structures that have previously been shown to be thermodynamically favorable. We predict that such sites have the ability to spontaneously cleave the O₂ bond and then will proceed to over-bind reaction intermediates. In particular, the *OH bound state has lower energy than the final 2 H₂O state at positive potentials. Contrary to traditional surface catalysts, this *OH binding does not poison the multi-metal-atom site but acts as a modifying ligand that will spontaneously form in aqueous environments leading to new active sites that have higher catalytic activities. These *OH bound structures have the highest calculated activity to date.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2014

Size selected clusters and particles: from physical chemistry and chemical physics to catalysis

When changing the size of metals from single atoms to monodispersed subnanometer clusters to well defined nanoparticles, their properties may change dramatically, as the type and fraction of their atoms gradually shifts from being dominantly under-coordinated to those organized in crystalline facets. Taking into account the one- to three-dimensional particle shapes, structural fluxionality and attachment of particles to a support where interfaces form and changes in electronic properties of the particles may take place, there is a further modification to the intrinsic size- and composition dependent properties in supported particles which add to the complexity of the system.

van Bokhoven, Jeroen A.↗
DOE OSTI2014

The effect of host structure on the selectivity and mechanism of supramolecular catalysis of Prins cyclizations

The effect of host structure on the selectivity and mechanism of intramolecular Prins reactions is evaluated using K 12 Ga 4 L 6 tetrahedral catalysts. The host structure was varied by modifying the structure of the chelating moieties and the size of the aromatic spacers. While variation in chelator substituents was generally observed to affect changes in rate but not selectivity, changing the host spacer afforded differences in efficiency and product diastereoselectivity. An extremely high number of turnovers (up to 840) was observed. Maximum rate accelerations were measured to be on the order of 10 5 , which numbers among the largest magnitudes of transition state stabilization measured with a synthetic host-catalyst. Host/guest size effects were observed to play an important role in host-mediated enantioselectivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗