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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Directing the Rate‐Enhancement for Hydronium Ion Catalyzed Dehydration via Organization of Alkanols in Nanoscopic Confinements

Abstract Alkanol dehydration rates catalyzed by hydronium ions are enhanced by the dimensions of steric confinements of zeolite pores as well as by intraporous intermolecular interactions with other alkanols. The higher rates with zeolite MFI having pores smaller than those of zeolite BEA for dehydration of secondary alkanols, 3‐heptanol and 2‐methyl‐3‐hexanol, is caused by the lower activation enthalpy in the tighter confinements of MFI that offsets a less positive activation entropy. The higher activity in BEA than in MFI for dehydration of a tertiary alkanol, 2‐methyl‐2‐hexanol, is primarily attributed to the reduction of the activation enthalpy by stabilizing intraporous interactions of the C β ‐H transition state with surrounding alcohol molecules. Overall, we show that the positive impact of zeolite confinements results from the stabilization of transition state provided by the confinement and intermolecular interaction of alkanols with the transition state, which is impacted by both the size of confinements and the structure of alkanols in the E1 pathway of dehydration.

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

Highly Stable Subnanometric PtIn Clusters for the Selective Dehydrogenation of Alkanes

Abstract Subnanometric PtIn clusters have been synthesized within pure silica MFI zeolites by post‐synthetic incorporation of In to Pt@K‐MFI. The optimized PtIn@K‐MFI catalyst outcompetes state‐of‐the‐art PtSn formulations in ethane and propane dehydrogenations, avoiding the need of large excess of Pt promoters and harsh reductive conditions.

Li, Chengeng↗
DOE OSTI2021

Transition state stabilization depends on solvent identity, pore size, and hydrophilicity for epoxidations in zeolites

Ti-silicates activate H 2 O 2 to form Ti-hydroperoxo and Ti-peroxo intermediates that can react with alkenes to form epoxide products. Comparisons of kinetics for 1-octene epoxidation with H 2 O 2 on Ti-BEA and Ti-MFI catalysts with different hydrophilicities in methanol (CH 3 OH) or acetonitrile (CH 3 CN) solvents show the significance of the solvent for stabilizing catalytically-relevant species and the complex interdependencies between solvent, catalyst topology, and hydrophilicity. Epoxidation turnover rates are higher in CH 3 CN than CH 3 OH for Ti-BEA, but the opposite trend is observed for Ti-MFI. Ti-silicates with greater silanol densities, however, give greater epoxidation turnover rates than their hydrophobic counterparts in both solvents. Kinetic, spectroscopic, and thermodynamic analyses show that differences in turnover rates mainly arise from changes in the stabilization of reactive surface species by solvent mediated interactions, because the mechanism of the reaction and stability of the fluid-phase reactants remain similar in CH 3 CN and CH 3 OH. Specifically, apparent activation free energy values ($ΔG^{‡}_{App}$) indicate that surface intermediates responsible for alkene epoxidation are stabilized to a greater extent in CH 3 CN on Ti-BEA and in CH 3 OH on Ti-MFI. Hydrophilic Ti-silicates present lower ($ΔG^{‡}_{App}$) values regardless of solvent identity, which suggests that these differences correspond to the number of hydrogen-bonding solvent molecules found near reactive species bound to Ti active sites. Finally, taken together, these findings demonstrate the role of solvent molecules in allowing reactive intermediates to recognize the properties of active sites beyond the length-scale of covalent bonds, which carry implications for epoxidation but also other reactions within solvent-filled pores of microporous materials.

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

Reversible Formation of Silanol Groups in Two-Dimensional Siliceous Nanomaterials under Mild Hydrothermal Conditions

Monitoring the effects of mild hydrothermal conditions, in situ, on siliceous materials remains challenging using surface science techniques, which often require electrically conductive substrates. The emergence of two-dimensional (2-D) siliceous nanomaterials deposited on metal single crystals overcomes this limitation. Here, we use infrared reflection absorption spectroscopy (IRRAS) to study the effects of mild hydrothermal conditions, in situ, on 2-D model systems, namely, all-Si MFI nanosheets supported on Au(111) and a polymorphous bilayer silicate supported on Ru(0001). We find that the formation of silanol groups (SiOH) occurs at 473 and 573 K under a H 2 O pressure of 3 mbar in the MFI nanosheets, but not in the polymorphous bilayer silicate. The effects of mild hydrothermal conditions are reversible in the MFI nanosheets and do not result in framework degradation. Implications shown here provide a fundamental understanding of the impact of mild hydrothermal conditions on the 2-D siliceous nanomaterials and serve as a starting point when considering these effects on three-dimensional (3-D) ones.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

The picasso map-making code: application to a simulation of the QUIJOTE northern sky survey

ABSTRACT Map-making is an important step for the data analysis of cosmic microwave background (CMB) experiments. It consists of converting the data, which are typically a long, complex, and noisy collection of measurements, into a map, which is an image of the observed sky. We present in this paper a new map-making code named picasso (Polarization and Intensity CArtographer for Scanned Sky Observations), which was implemented to construct intensity and polarization maps from the Multi Frequency Instrument (MFI) of the QUIJOTE (Q-U-I Joint TEnerife) CMB polarization experiment. picasso is based on the destriping algorithm, and is suited to address specific issues of ground-based microwave observations, with a technique that allows the fit of a template function in the time domain, during the map-making step. This paper describes the picasso code, validating it with simulations and assessing its performance. For this purpose, we produced realistic simulations of the QUIJOTE-MFI survey of the northern sky (approximately ∼20 000 deg2), and analysed the reconstructed maps with picasso, using real and harmonic space statistics. We show that, for this sky area, picasso is able to reconstruct, with high fidelity, the injected signal, recovering all the scales with ℓ > 10 in TT, EE, and BB. The signal error is better than 0.001 per cent at 20 < ℓ < 200. Finally, we validated some of the methods that will be applied to the real wide-survey data, like the detection of the CMB anisotropies via cross-correlation analyses. Despite that the implementation of picasso is specific for QUIJOTE-MFI data, it could be adapted to other experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Influence of Ti‐incorporated Zeolite Topology and Pore Condensation on Vapor Phase Propylene Epoxidation Kinetics with Gaseous H 2 O 2

Abstract Vapor‐phase propylene (C 3 H 6 ) epoxidation kinetics with hydrogen peroxide (H 2 O 2 ) strongly reflects the physical properties of Ti‐incorporated zeolite catalysts and the presence of spectating molecules (“solvent”) near active sites even without a bulk liquid phase. Steady‐state turnover rates of C 3 H 6 epoxidation and product selectivities vary by orders of magnitudes, depending on the zeolite silanol ((SiOH) x ) density, pore topology (MFI, *BEA, FAU), and the quantity of condensed acetonitrile (CH 3 CN) molecules nearby active sites, under identical reaction mechanisms sharing activated H 2 O 2 intermediates on Ti surfaces. Individual kinetic analyses for propylene oxide (PO) ring‐opening, homogeneous diol oxidative cleavage, and homogeneous aldehyde oxidation reveal that secondary reaction kinetics following C 3 H 6 epoxidation responds more sensitively to the changes in zeolite physical properties and pore condensation with CH 3 CN. Thus, higher PO selectivities achieved in hydrophilic Ti‐MFI at steady‐state reflect the preferential stabilization of transition states for C 3 H 6 epoxidation (a primary reaction) relative to PO ring‐opening and oxidative cleavage (secondary reactions) that solvation effects that reflect interactions among condensed CH 3 CN within pores and the extended pore structure.

Kwon, Ohsung↗
DOE OSTI2020

Deactivation of Cu-Exchanged Automotive-Emission NH 3 -SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X-ray Microscopy

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NO x with an ammonia reductant, we employed scanning transmission X-ray microscopy (STXM) to study Cu-exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000-mile aging. X-ray absorption near-edge structure (XANES) measurements were performed at the Al K- and Cu L-edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi-factor-induced catalytic deactivation. In Cu-exchanged MFI, a transformation of Cu II to Cu I and Cu x O y was observed. We also found a spatial correlation between extra-framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of CuI and tri-coordinated Al. By inspecting both Al and Cu in fresh and aged Cu-exchanged zeolites, we conclude that the importance of the preservation of isolated Cu II sites trumps that of Brønsted acid sites for NH 3 -SCR activity.

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

Tighter Confinement Increases Selectivity of d-Glucose Isomerization Toward l-Sorbose in Titanium Zeolites

Aqueous-phase isomerization of D-glucose to D-fructose and L-sorbose is catalyzed in parallel by Lewis acidic Ti sites in siliceous frameworks. Glucose isomerization rates (per Ti, 373 K) are undetectable when Ti sites are confined within mesoporous voids (Ti-MCM-41, TiO 2 -SiO 2 ) and increase to detectable values when Ti sites are confined within the smaller 12-membered ring (12-MR) micropores of Ti-Beta. Furthermore, isomerization rates decrease to lower values (by ≈20×) with further decreases in micropore size as Ti sites are confined within 10-MR pores (Ti-MFI, Ti-CON), likely because of intrapore reactant diffusion restrictions, and reach undetectable values within the 8-MR pores of Ti-CHA as size exclusion prevents glucose from accessing active sites. Remarkably, the selectivity toward l -sorbose over d -fructose increases systematically as spatial constraints around Ti sites become tighter, and is >10 on Ti-MFI. These findings demonstrate the marked influence of confinement around Ti active sites on the selectivity between parallel stereoselective sugar isomerization pathways.

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

Influence of Ti‐incorporated Zeolite Topology and Pore Condensation on Vapor Phase Propylene Epoxidation Kinetics with Gaseous H 2 O 2

Vapor-phase propylene (C 3 H 6 ) epoxidation kinetics with hydrogen peroxide (H 2 O 2 ) strongly reflects the physical properties of Ti-incorporated zeolite catalysts and the presence of spectating molecules (“solvent”) near active sites even without a bulk liquid phase. Steady-state turnover rates of C 3 H 6 epoxidation and product selectivities vary by orders of magnitudes, depending on the zeolite silanol ((SiOH) x ) density, pore topology (MFI, *BEA, FAU), and the quantity of condensed acetonitrile (CH 3 CN) molecules nearby active sites, under identical reaction mechanisms sharing activated H 2 O 2 intermediates on Ti surfaces. Individual kinetic analyses for propylene oxide (PO) ring-opening, homogeneous diol oxidative cleavage, and homogeneous aldehyde oxidation reveal that secondary reaction kinetics following C 3 H 6 epoxidation responds more sensitively to the changes in zeolite physical properties and pore condensation with CH 3 CN. Thus, higher PO selectivities achieved in hydrophilic Ti-MFI at steady-state reflect the preferential stabilization of transition states for C 3 H 6 epoxidation (a primary reaction) relative to PO ring-opening and oxidative cleavage (secondary reactions) that solvation effects that reflect interactions among condensed CH 3 CN within pores and the extended pore structure.

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

Climate change is intensifying rainfall erosivity and soil erosion in West Africa

Soil erosion is a critical environmental challenge with significant implications for agriculture, water quality, and ecosystem stability. Understanding its dynamics is essential for sustainable environmental management and societal welfare. Here, we analyze rainfall erosivity and erosion patterns across West Africa (WAF) during the historical (1982–2014), near future (2028–2060), and far future (2068–2100) periods under Shared Socioeconomic Pathways (SSPs 370 and 585). Using bias-corrected-downscaled (BCD) climate models validated against reference data, we ensure an accurate representation of rainfall—a key driver of erosivity (R-factor) and soil erosion. We compare Renard's approach and the Modified Fournier Index (MFI) to calculate the R-factor and note a strong correlation. However, Renard's method shows slightly lower accuracy in Sierra Leone, Guinea, and The Gambia, likely due to its inability to capture high-intensity, short-duration rainfall events. In contrast, the MFI, utilizing continuous rain gauge data, proves more reliable for these regions. We also attribute fluctuations in erosivity, such as those seen during the 2003 West Africa floods, to synoptic weather patterns influenced by multiple climate processes. Furthermore, our analysis reveals regions where future soil erosion could exceed 20 t/ha/yr due to climate change. Under the SSP 370 scenario, soil erosion in WAF is projected to rise by 14.84 % in the near future and 18.65 % in the far future, increasing further under SSP 585 to 19.86 % and 23.49 %, respectively. The most severe increases are expected in Benin and Nigeria, with Nigeria potentially facing a 66.41 % rise in erosion by the far future under SSP 585. These findings highlight the region's exposure to intensified climatic conditions and underscore the urgent need for targeted soil management and climate adaptation strategies to mitigate erosion's ecological and socioeconomic impacts.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Effect of Solvent on the Interaction of Lignin with a Zeolite Nanosheet in the Condensed Phase

Lignin is the essential building block of lignocellulosic biomass, an excellent renewable source of different aromatic monomers for the polymer and biofuel industry. The depolymerization of lignin into value-added chemicals and fuels through the catalytic process poses a significant challenge due to the complex structure of lignin. Understanding lignin’s conformational diversity and dynamics in the liquid phase is crucial to designing an effective depolymerization process. Here, we conducted all-atom molecular dynamics simulations to understand the conformation and dynamics of softwood lignin on the all-silica zeolite nanosheet based on the MFI topology in a binary mixture of water–methanol at three different molar compositions (0%, 50%, and 100% methanol). We observed that the methanol–surface interaction is stronger than the water–surface interaction, and methanol readily diffused into the MFI core. Lignin surface contacts decrease with increasing methanol composition due to higher solubility and dynamics. Lignin dynamics on the surface in neat water is an order of magnitude smaller than methanol. Here, we also found that lignin adopts a slightly extended conformation when it stays on the surface than in the bulk solution phase for the pure water case, whereas for pure methanol and the binary solution structures are statistically similar.

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

Confinement-Controlled Rearrangements in Dioxolane Upgrading on H-ZSM-5 Revealed by Periodic DFT

Zeolitic Brønsted acid sites catalyze carbocation rearrangements central to upgrading biomass-derived oxygenates. Here we elucidate the mechanism of dioxolane conversion to methyl ethyl ketone and isobutanal on H-ZSM-5 using periodic density functional theory on the MFI model, complemented by ab initio molecular dynamics to probe confinement effects. Dioxolane adsorption at the Brønsted site is followed by protonation-assisted ring opening to form an oxocarbenium intermediate stabilized by the deprotonated framework. From this common intermediate, selectivity is governed by two competing rearrangements, namely, the 1,2-hydride shift with a free-energy barrier of 18.05 kcal mol –1 at 498 K leading toward MEK, and the 1,2-methyl shift with a higher barrier of 25.40 kcal mol –1 leading toward isobutanal. The hydride-shift channel is kinetically preferred over the methyl-shift channel, lowering the isobutanal/MEK ratio below the 3:1 limit expected for equal branching. Adsorption thermodynamics further indicate stronger stabilization of MEK than isobutanal within ZSM-5 channels, suggesting that confinement-controlled binding can bias product distributions in addition to intrinsic rearrangement barriers. These results highlight how Brønsted acidity and pore confinement jointly shape the rearrangement landscape in MFI zeolites.

adsorption↗
DOE OSTI2021

Differences in Mechanism and Rate of Zeolite-Catalyzed Cyclohexanol Dehydration in Apolar and Aqueous Phase

The rate of acid-base catalyzed dehydration of alcohols strongly depends on the solvent and the environment of the acid sites. In this work, we find that Brønsted acidic sites in large-pore zeolites, but not in medium-pore zeolites, catalyze cyclohexanol dehydration in decalin at significantly higher rates than hydrated hydronium ions in aqueous phase. Specifically, the difference in turnover rates between the two solvents amounts to two to three orders of magnitude on H-BEA and H-FAU, while being very modest (within a factor of 2) for H-MFI. Combining kinetic, isotopic tracer and 2H NMR measurements, it is established that cyclohexanol dehydration generally follows an E1-elimination pathway in decalin. A notable exception is the monomer dehydration route on H-MFI, which exhibits a much lower activation energy and a substantially negative activation entropy that appear to be associated with an E2-type mechanism. The C-O bond cleavage displays a dominant degree of rate control in decalin, which stands in contrast to deprotonation (C-H cleavage) being rate-limiting in aqueous-phase dehydration.

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

Large-Scale Compatibilization of Postconsumer Polyolefins in the Presence of Paraffin Wax as a Rheology Modifier

Postconsumer polyolefins (r-POs) are leading plastic waste contributors today. This study reports, for the first time, the compatibilization of r-POs at a 50 kilogram (kg) scale with a styrene block copolymer compatibilizer in the presence of paraffin waxes as rheology modifiers (RMs). The addition of the rheological modifier (RM) and compatibilizer enhances the melt flow indices (MFIs) and mechanical properties, respectively. One aspect of this study is to compare the effectiveness of low-cost paraffin wax to that of specialized and expensive RMs in r-POs. The mechanical and rheological properties such as the melt flow index (MFI) of r-POs were compared in the presence of two types of RMs. Next, the study explores the challenges encountered when scaling the compatibilization of r-POs in the presence of paraffin wax from a 10-g to a 50-kg scale. The mechanical properties were determined and compared for samples at different scales. The study further investigated the effect of the method used for blending paraffin wax with r-PO and its impact on the value of their MFI and mechanical properties. This at-scale validation could pave the way for the commercialization of r-POs.

crystallinity↗
DOE OSTI2026

Design Principles for the Synthesis of Self-Pillared ZSM-5 Zeolite Nanosheets

The design of next-generation materials for emerging energy and environmental applications heavily relies on empirical approaches to direct nonclassical nucleation and crystal growth pathways, polymorphism, intercrystalline transformations, and seed-assisted growth processes. A long-standing obstacle to nanoporous materials design is the complexity of their crystallization, which hinders the development of predictive models and/or physical descriptors that can guide their synthesis. In this study, we use a combination of state-of-the-art synthesis, characterization, and computational design to prepare hierarchical MFI-type zeolites, which we couple with benchmark catalytic testing to assess structure-property-performance relationships. These hierarchical materials are intergrowths of two commercially relevant zeolite frameworks, MFI and MEL, prepared as self-pillared pentasil (SPP) zeolites through seed-assisted, organic-free syntheses for which little theoretical guidance existed. Here, by comparing a large library of zeolite seeds with different pore sizes, dimensions, and structural composite building units, we determined the relative impact of seed and silica source selection, among other synthesis variables. Combined experimental and computational studies are used to test several hypotheses in literature to rationalize the choice of seed structure and establish a more robust selection criteria for seed-assisted synthesis of zeolites. Specifically, we show that a data-driven approach to develop structural descriptors correlates to new, facile routes to rationally design SPP zeolites, addressing knowledge gaps in the fundamental understanding of (non)classical crystal growth mechanisms that are characteristic of nanoporous aluminosilicates.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Role of the ionic environment in enhancing the activity of reacting molecules in zeolite pores

Tailoring the molecular environment around catalytically active site allows the enhancement of catalytic reactivity via a hitherto unexplored pathway. In zeolites, the presence of water creates an ionic environment via the formation of hydrated hydronium ions and the negatively charged framework Al tetrahedra. The high density of cation-anion pairs determined by the aluminum concentration of a zeolite induces a high local ionic strength that increases the excess chemical potential of sorbed and uncharged organic reactants. Charged transition states (as for example, the carbenium ions in the discussed alcohol dehydration) are stabilized, reducing the energy barrier and leading to a higher reaction rate. Using the intramolecular dehydration of cyclohexanol on H-MFI in water, we show quantitatively the enhancement of the reaction rate by the presence of high ionic strength as well as potential limitations of this strategy. The approach opens a new pathway to systematically enhance catalytic reactivity rates and has wide-ranging implications for understanding catalysis in condensed phase.

Pfriem, Niklas↗
DOE OSTI2026

Collaborative: Fundamental studies of how water influences the synthesis and behavior of zeolite catalysts for reactions in the circular carbon economy (Final Technical Report)

This project established a computational framework to predict and interpret how synthesis conditions control active site location in MFI zeolites and how those site distributions influence catalytic reactivity. The Hibbitts Group led the theoretical effort, applying periodic DFT calculations to quantify (i) SDA–framework–heteroatom interactions during crystallization and (ii) the energetics and mechanisms of arene methylation reactions within distinct MFI environments.

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

Direct synthesis of high-aspect ratio zeolite nanosheets

An example material includes a planar layer of MFI zeolite. The planar layer has a thickness in a range between 4 nm and 10 nm for at least 70% of a basal area of the planar layer. In one embodiment, the planar layer includes an embedded particle of an MFI zeolite.

Tsapatsis, Michael↗