Search NASA⌕ Search

SEARCH · Search NASA

Results for “hydrothermal synthesis”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Early Evolution of Earth's Geochemical Cycle and Biosphere: Implications for Mars Exobiology

Carbon (C) has played multiple key roles for life and its environment. C has formed organics, greenhouse gases, aquatic pH buffers, redox buffers, and magmatic constituents affecting plutonism and volcanism. These roles interacted across a network of reservoirs and processes known as the biogeochemical C cycle. Changes in the cycle over geologic time were driven by increasing solar luminosity, declining planetary heat flow, and continental and biological evolution. The early Archean C cycle was dominated by hydrothermal alteration of crustal rocks and by thermal emanations of CO2 and reduced species (eg., H2, Fe(2+) and sulfides). Bioorganic synthesis was achieved by nonphotosynthetic CO2-fixing bacteria (chemoautotrophs) and, possibly, bacteria (organotrophs) utilizing any available nonbiological organic C. Responding both to abundant solar energy and to a longterm decline in thermal sources of chemical energy and reducing power, the blaspheme first developed anoxygenic photosynthesis, then, ultimately, oxygenic photosynthesis. O2-photosynthesis played a central role in transforming the ancient environment and blaspheme to the modem world. The geochemical C cycles of early Earth and Mars were quite similar. The principal differences between the modem C cycles of these planets arose during the later evolution of their heat flows, crusts, atmospheres and, perhaps, their blasphemes.

DesMarais, David J.↗
DOE OSTI2022

Chapter 11: Biochar Production

In production of biochar, thermochemical processes that can be used to treat biomass include pyrolysis, gasification, hydrothermal processing, and combustion. Each of these processes is defined by specific operating conditions (e.g., temperature, presence of oxygen) and feedstock requirements for optimal conversion to the product of primary interest. Each process results in varying fractions of gaseous, liquid, and solid products. Though other publications have emphasized the gaseous bio-energy products of such processes (e.g., bio-oil, synthesis gas or "syngas") with biochar as a co-product, in this discussion, we focus primarily on biochar as the In production of biochar, thermochemical processes that can be used to treat biomass include pyrolysis, gasification, hydrothermal processing, and combustion. Each of these processes is defined by specific operating conditions (e.g., temperature, presence of oxygen) and feedstock requirements for optimal conversion to the product of primary interest. Each process results in varying fractions of gaseous, liquid, and solid products. Though other publications have emphasized the gaseous bio-energy products of such processes (e.g., bio-oil, synthesis gas or "syngas") with biochar as a co-product, in this discussion, we focus primarily on biochar as the main product, with heat and electrical energy as co-products of secondary interest. The reasons for this are as follows: when producing biochar, heat is the simplest form of energy to capture and utilize, electrical energy can be generated from heat energy with a wide range of available technologies small and large; rather than immediately combusting the gases released from biomass, there is potential to refine the gases into bio-oil and syngas. However, much larger investments of capital are needed to build facilities for which gaseous fuel production is the primary goal, as compared to those focused on biochar production with heat and electrical energy co-products. While the economic viability of biochar production will be improved by production of high-value co-products (e.g., wood acids for use in pesticides), the simplest production scheme is one in which biochar and heat are the primary products. Here we aim to provide a broader overview of thermochemical processes and technologies most relevant to biochar production in its current state of commercialization. All biochar is a result of pyrolysis (the reaction) but not all biochar is made with a dedicated pyrolysis reactor (the technology type). Further, all biochar is the result of a lack of complete combustion (the reaction), even biochar produced in a combustion or gasification reactor (the technology type). This is an important distinction to acknowledge in the following sections in which we discuss both thermochemical conversion reactions and technology types.

biochar↗
DOE OSTI2022

Robust hierarchical three dimensional nickel cobalt tungstate-MXene nanocomposite for high performance symmetric coin cell supercapacitors

Design of rational electrode materials with hierarchically structured pseudocapacitive materials has been identified as a successful strategy for revamping the electrochemical characteristics of supercapacitors. However, the simultaneous assurance of strong electrical conductivity and higher specific capacitance via a simple and cost-effective synthesis protocol is of concern today. In this work, Ni-CoWO 4 incorporated MXene nanocomposite has been successfully prepared by a facile hydrothermal process. The structure, morphology, stoichiometry, and chemical characterization of the prepared Ni-CoWO 4 , Ti 3 C 2 T x , and Ni-CoWO4@MXene nanocomposite were explored extensively. MXene demonstrated a layered 2D nanoscale structure whereas pure Ni-CoWO 4 was composed of spherical nanoparticles. The composite Ni-CoWO 4 @MXene revealed the morphology of spherical Ni-CoWO 4 nanoparticles decorated on MXene sheets. Furthermore, a series of electrochemical characterizations illustrated the contribution of the delightful morphology of Ni-CoWO 4 @MXene composite to excellent electrochemistry. The resultant Ni-CoWO 4 @MXene electrode exhibited high specific capacitance of 582 Fg -1 at 1 A g -1 and 93.5 % capacitance retention over the 10,000 cycles., which is higher than that of the individual counterparts Ni-CoWO 4 and MXene. The excellent electrochemical performance of Ni-CoWO 4 @MXene is attributed to the synergistic interaction between Ni-CoWO4 nanoparticles and nanolayered MXene that may create new active sites that enhanced the charge transfer, charge/discharge kinetics and the electrical conductivity. Significantly, the unique Ni-CoWO 4 @MXene supercapacitor prototype delivered a higher energy density of 85.7 Wh kg -1 and power density of 0.85 kW kg -1 establishing its superiority over other Cosingle bondW based supercapacitors. A theoretical study was also performed to correlate the improved charge storage capacity of the prepared Ni-CoWO 4 @MXene composite.

25 ENERGY STORAGE↗
NASA NTRS2010

N channel JFET based digital logic gate structure

A circuit topography is presented which is used to create usable digital logic gates using N (negatively doped) channel Junction Field Effect Transistors (JFETs) and load resistors, level shifting resistors, and supply rails whose values are based on the direct current (DC) parametric distributions of those JFETs. This method has direct application to the current state of the art in high temperature, for example 300.degree. C. to 500.degree. C. and higher, silicon carbide (SiC) device production. The ability to produce inverting and combinatorial logic enables the production of pulse and edge triggered latches. This scale of logic synthesis would bring digital logic and state machine capabilities to devices operating in extremely hot environments, such as the surface of Venus, near hydrothermal vents, within nuclear reactors (SiC is inherently radiation hardened), and within internal combustion engines. The basic logic gate can be configured as a driver for oscillator circuits allowing for time bases and simple digitizers for resistive or reactive sensors. The basic structure of this innovation, the inverter, can be reconfigured into various analog circuit topographies through the use of feedback structures.

Krasowski, Michael J.↗
DOE OSTI2020

Iron-Doped Sodium Vanadium Oxyflurophosphate Cathodes for Sodium-Ion Batteries—Electrochemical Characterization and In Situ Measurements of Heat Generation

Sodium-ion batteries (NaIBs) are increasingly being envisioned for grid-scale energy-storage systems because of cost advantages. However, implementation of this vision has been challenged by the low-energy densities delivered by most NaIB cathodes. Toward addressing this challenge, the authors report the synthesis and characterization of a new iron-doped Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 cathode using a novel facile hydrothermal route. The synthesized material was characterized using scanning electron microscopy, X-ray diffraction, and Mössbauer spectroscopy techniques. The obtained discharge capacity in the half-cell configuration lies from 119 to 125 to 130 mA h/g at C/10 while tested using three different electrolyte formulations, dimethyl carbonate–ethylene carbonate (EC)–propylene carbonate (PC), diethyl carbonate–EC, and EC–PC, respectively. The synthesized cathodes were also evaluated in full-cell configurations, which delivered an initial discharge capacity of 80 mA h/g with NaTi 2 (PO 4 ) 3 MWCNT as the anode. Ionic diffusivity and interfacial charge transfer kinetics were also evaluated as a function of temperature and sodium concentration, which revealed that electrochemical rate performances in this material were limited by charge-transfer kinetics. To understand the heat generation mechanism of the Na/Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 half-cell during charge and discharge processes, an electrochemical isothermal calorimetry measurement was carried out at different current rates for two different temperatures (25 and 45 °C). The results showed that the amount of heat generated was strongly affected by the operating charge/discharge state, C-rate, and temperature. Altogether, this work provides a new synthesis route for the development of iron-doped Na 3 Fe 0.3 V 1.7 O(PO 4 ) 2 F 2 -based high-performance sodium cathode materials aimed at providing a viable pathway for the development and deployment of large-scale energy-storage based on sodium battery systems.

25 ENERGY STORAGE↗
DOE OSTI2021

Synthesis and Single Crystals of Refractory Oxides of Lanthanides and Thorium

At the completion of this program, we can report that we developed a considerable degree of technical improvements in our ability to perform hydrothermal reactions at high temperatures and pressures. We can now routinely perform reactions at 700-750°C and 200 MPa. Currently we are in the process of exploiting this new technology synthesizing a range of exotic new materials investigating relatively poorly understood materials. Our initial efforts focused on the chemistry of rare earth oxides with tetravalent and pentavalent oxides. We recently published a study of the lanthanides with Nb 5+ and Ta 5+ ions, where we grew oxides such as RENdO 4 and RETaO 4 as high quality single crystals. These compounds were targeted as potential hosts for luminescent and scintillation materials, particularly given that they are among the densest oxide hosts and hence have good potential as absorbers for high energy radiation like X-rays and gamma rays. We also isolated a range of unusual new rare earth tantalates with very complex structures. indicating that the chemistry is very sensitive to conditions. We performed some fairly comprehensive examinations of the solid-state chemistry of rare earth ions with various tetravalent metal ions especially Si 4+ , Ge 4+ , Sn 4+ and Ti 4+ . Given the potential role of rare earth silicates in immobilizing radioactive waste elements in long-term storage, and the similarity of our hydrothermal fluids with known geological conditions, this chemistry continues to be relevant. We prepared an extensive series of new lanthanide germanates (e.g. RE 13 Ge 6 O 31 (OH), BaRE 10 (GeO 4 ) 4 O 8 ). and found that there is there is almost no overlap between the chemistry of the rare earth silicates. Stannic oxide (SnO 2 ) is much more refractory and requires higher temperatures and of mineralizer concentrations. One significant result is the growth of RE 2 Sn 2 O 7 pyrochlore single crystals. These are of interest because the rare earth stannate pyrochlores are known to display a wide range of magnetic frustration such as spin ice behavior. We grew high quality single crystals of rare earth germanate and stannate pyrochlores and this led to a collaboration with Professor Kate Ross at Colorado State. Preliminary measurements, indicate that the crystals contain no detectable defects or site disorder. Initial neutron diffraction on single crystals was performed at Oak Ridge, and more detailed experiments involving the Ross group are underway at both NIST and ORNL. This particular chemistry has turned out to be the most potentially significant work on this project and the collaborative effort with Prof. Ross is the topic of a DoE renewal project on quantum materials. Our initial foray into the hydrothermal chemistry of rare earth titanates has also been very promising and a range of cubic and polar ferroic phases of the light rare earths RE 2 Ti 2 O 7 (RE = La - Pr) in the P2 1 phase. We also discovered an interesting new phase Ce 2 Ti 4 O 11 that can have implications in heavy metal immobilization and storage. along with a series of new rare earth titanates (La 5 Ti 4 O 15 (OH) Sm 3 TiO 5 (OH) 3 and Lu 5 Ti 2 O 11 (OH) with exceptionally complex structures. One interesting sidelight has been high temperature hydrothermal chemistry terbium, including the growth of large crystals of TbO(OH). This is not a new compound but it is the first time it has been grown as large single crystals. The Tb atom density is almost as high as that in Tb 2 O 3 and has a very high Verdet constant (ca. 70), making it a very attractive candidate as a Faraday rotator. Unfortunately it is not in a cubic structure but he material is hard, stable, pure and inexpensive, so should still be an attractive Faraday oscillator. We recently received a patent on this material. We also synthesized K 2 Tb(Ge 2 O 7 ) containing stable octahedral Tb 4+ ions, which appears to be the first example of a well-characterized Tb 4+ complex. Given that Tb 4+ has been proposed as a benign surrogate for more treacherous tetravalent ions such as Cf 4+ and Bk 4+ , we think that Tb 4+ silicates can be a particularly useful study for actinide immobilization and related work. We also began reaction studies with rare earths and both ReO 2 and RuO 2 . These resulted in large single crystals of species like RE 5 Ru 2 O 12 , RE 4 Re 2 O 11 , REReO 4 and RE 2 ReO 5 . Several of these samples have already been sent to ORNL for magnetic and neutron diffraction studies.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Divergent Responses of Carbon Nitride Dot‐Based Amorphous Species and Small Molecule Hybrids to Trace Level Analytes

Bottom-up synthesis of carbon nitride dots (CNDs) offers a versatile platform for the creation of diverse nanomaterials with tunable properties. Here, we report a facile hydrothermal approach using citric acid (CA) and urea (U) as precursors to synthesize CNDs with varying degrees of condensation and crystallinity. By carefully controlling reaction conditions and post-synthetic treatments, we obtained two distinct fractions: a polycrystalline fraction composed of small-molecule hybrids and an amorphous fraction containing CNDs. We then sought to understand how the dominant species in these fractions impact sensing abilities using trace-level explosive exemplars. In conclusion, the results have important implications for sensing and related applications where understanding the complex interplay between synthetic conditions and post-synthetic processing play vital roles in determining the final properties of CND materials.

carbon nitride dots↗
NASA NTRS2015

Amino Acid Stability in the Early Oceans

It is likely that a variety of amino acids existed in the early oceans of the Earth at the time of the origin and early evolution of life. "Primordial soup", hydrothermal vent, and meteorite based processes could have contributed to such an inventory. Several "protein" amino acids were likely present, however, based on prebiotic synthesis experiments and carbonaceous meteorite studies, non-protein amino acids, which are rare on Earth today, were likely the most abundant. An important uncertainty is the length of time these amino acids could have persisted before their destruction by abiotic and biotic processes. Prior to life, amino acid concentrations in the oceans were likely regulated by circulation through hydro-thermal vents. Today, the entire ocean circulates through vent systems every 10(exp 7) years. On the early Earth, this value was likely smaller due to higher heat flow and thus marine amino acid life-time would have been shorter. After life, amino acids in the oceans could have been assimilated by primitive organisms.

prebiotic synthesis↗
DOE OSTI2024

Synthesis of 2D layered transition metal (Ni, Co) hydroxides via edge-on condensation

Abstract Layered transition metal hydroxides (LTMHs) with transition metal centers sandwiched between layers of coordinating hydroxide anions have attracted considerable interest for their potential in developing clean energy sources and storage technologies. However, two-dimensional (2D) LTMHs remain largely understudied in terms of physical properties and applications in electronic devices. Here, for the first time we report > 20 μm α-Ni(OH) 2 2D crystals, synthesized from hydrothermal reaction. And an edge-on condensation mechanism assisted with the crystal field geometry is proposed to understand the 2D intra-planar growth of the crystals, which is also testified through series of systematic comparative studies. We also report the successful synthesis of 2D Co(OH) 2 crystals (> 40 μm) with more irregular shape due to the slightly distorted octahedral geometry of the crystal field. Moreover, the detailed structural characterization of synthesized α-Ni(OH) 2 are performed. The optical band gap energy is extrapolated as 2.54 eV from optical absorption measurements and the electronic bandgap is measured as 2.52 eV from reflected electrons energy loss spectroscopy (REELS). We further demonstrate its potential as a wide bandgap (WBG) semiconductor for high voltage operation in 2D electronics with a high breakdown strength, 4.77 MV/cm with 4.9 nm thickness. The successful realization of the 2D LTMHs opens the door for future exploration of more fundamental physical properties and device applications.

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

Electrochemical Synthesis of Zeolite Coatings with Controlled Crystal Polymorphism and Self-Regulating Growth

Zeolite coatings are studied as molecular sieves for membrane separation, membrane reactors, and chemical sensor applications. They are also studied as anticorrosive films for metals and alloys, antimicrobial and hydrophobic films for heating, ventilation, and air conditioning, and dielectrics for semiconductor applications. Zeolite coatings are synthesized by hydrothermal, ionothermal, and dry-gel conversion approaches, which require high process temperatures and lengthy times (ranging from hours to days). Here, we report the first zeolite coatings synthesized via electrochemical deposition on a cathodic electrode, with controlled crystal polymorphism achieved within subhourly duration. We demonstrate this approach by developing sodium zeolite (e.g., sodalite (SOD), NaA (LTA), and Linde Type N (LTN)) coatings on a titanium electrode and extending the synthesis method to porous stainless steel. The coating morphology and crystallinity depend on the temperature, time, and applied current. The coating thickness is independent of the applied current, showing the presence of a self-regulating mechanism to ensure a uniform coating thickness across the metal surface. The electrochemical zeolite growth mechanism was elucidated with high-resolution transmission electron microscopy, and applications of the resultant zeolite coatings for oil/water separation and ethanol/water pervaporation were exploited. Electrochemical synthesis represents a novel, simple, fast, and environmentally friendly approach to preparing zeolite coatings. It can potentially be generalized for developing zeolite materials with diverse framework structures, morphologies, and orientations for substrates with complicated geometries.

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

Ultra-Low Amounts of Transition Metals in Carbon-Based Catalysts Improve Their Alkaline OER Performance: A Systematic Study

The pursuit of green hydrogen production highlights a persistent gap in electrocatalyst research: while academic efforts prioritize cost-efficiency via activity enhancement, industrial viability demands greater emphasis on electrochemical stability. Carbon-based electrocatalysts, particularly those incorporating transition metals, have shown promise in alkaline oxygen evolution (OER) due to their high activity, cost-efficiency, and resource-efficiency. However, these catalysts suffer from insufficient stability under oxidizing conditions compared to pure transition metal catalysts due to erosion of the carbon support resulting from carbon corrosion, among other degradation mechanisms. In this systematic study, the influence of ultra-low amounts (<1 wt %) of iron, cobalt, nickel, and their most common combinations on the stability of a hydrothermally derived, N-doped carbon support and the overall catalyst performance during alkaline OER is systematically explored. By identifying critical stability descriptors and correlating them with synthesis conditions and catalyst properties, primary and secondary corrosion pathways are unraveled. Subsequently, through careful adjustment of carbonization temperature and composition of incorporated transition metals, overall catalyst corrosion can be suppressed immensely. Especially, the inclusion of Ni and Fe is paramount for the formation of stable catalyst materials under laboratory conditions (10 mA/cm 2 in 0.1 M KOH), which is surprisingly unconstrained by the degree of graphitization of the carbon support. Mixing this electrochemically stable material with a graphitic carbon powder results in an excellent stability of over 400 h at 100 mA/cm 2 in 1 M KOH, implying great potential for the future improvement of carbon-based electrodes under oxidizing conditions toward industrial application.

N-doped carbon↗
NASA NTRS2017

Smectite Formation in the Presence of Sulfuric Acid: Implications for Acidic Smectite Formation on Early Mars

The excess of orbital detection of smectite deposits compared to carbonate deposits on the martian surface presents an enigma because smectite and carbonate formations are both favored alteration products of basalt under neutral to alkaline conditions. We propose that Mars experienced acidic events caused by sulfuric acid (H2SO4) that permitted phyllosilicate, but inhibited carbonate, formation. To experimentally verify this hypothesis, we report the first synthesis of smectite from Mars-analogue glass-rich basalt simulant (66 wt% glass, 32 wt% olivine, 2 wt% chromite) in the presence of H2SO4 under hydrothermal conditions (approximately 200 degC). Smectites were analyzed by X-ray diffraction, Mossbauer spectroscopy, visible and near-infrared reflectance spectroscopy and electron microprobe to characterize mineralogy and chemical composition. Solution chemistry was determined by Inductively Coupled Plasma Mass Spectrometry. Basalt simulant suspensions in 11-42 mM H2SO4 were acidic with pH less than or equal to 2 at the beginning of incubation and varied from acidic (pH 1.8) to mildly alkaline (pH 8.4) at the end of incubation. Alteration of glass phase during reaction of the basalt simulant with H2SO4 led to formation of the dioctahedral smectite at final pH approximately 3 and trioctahedral smectite saponite at final pH approximately 4 and higher. Anhydrite and hematite formed in the final pH range from 1.8 to 8.4 while natroalunite was detected at pH 1.8. Hematite was precipitated as a result of oxidative dissolution of olivine present in Adirondack basalt simulant. Formation of secondary phases, including smectite, resulted in release of variable amounts of Si, Mg, Na and Ca while solubilization of Al and Fe was low. Comparison of mineralogical and solution chemistry data indicated that the type of smectite (i.e., dioctahedral vs trioctahedral) was likely controlled by Mg leaching from altering basalt and substantial Mg loss created favorable conditions for formation of dioctahedral smectite. We present a model for global-scale smectite formation on Mars via acid-sulfate conditions created by the volcanic outgassing of SO2 in the Noachian and early Hesperian.

Smectite↗
DOE OSTI2025

Hydrothermal Growth of Magnetically Frustrated Crystals: Lanthanide Stannate Pyrochlores as a Prototype

One important test bed system for frustrated magnetism is the pyrochlore lattice with the formula A2B2O7 in the cubic space group Fd3(-)m. Both the A and B sites occupy crystallographic trigonal sites and both sites possess a tetrahedral relationship with the other similar metal ion sites. These symmetry relationships generate a 3 D frustrated structure. In frustrated magnetic systems, typically a trivalent lanthanide ion occupies the A site and a magnetically silent tetravalent ion (Ti, Zr, Sn, etc.) occupies the B site. A classical problem related to the crystal growth of these compounds is sample quality. As refractory oxides, the traditional synthesis and crystal growth techniques require high temperatures, which creates two problems that are quite common and endemic to the pyrochlores. One is oxide lattice defects and the other is A/B site disorder. Both issues often occur in the same crystals at the same time and can have a significant impact on the study of physical properties. A hydrothermal approach can be applied to this problem. The relatively low crystal growth temperatures (600-720˚C) greatly minimize nonstoichiometry, lattice defects and A/B site disorder. The reduction of these pervasive imperfections significantly increases the quality of the observed physical property data. This talk will focus on the lanthanide stannates Ln2Sn2O7 as a prototype test bed of these systems. The stannates are among the few building blocks that can stabilize the pyrochlore structure type for all the lanthanides and they serve as an excellent proving ground for a wide range of physical properties. The synthesis and crystal growth of the lanthanide stannates will be reviewed, along with a discussion of some of the physical properties that result from the frustrated magnetic states of these low defect crystals.

Hydrothermal, crystal growth↗
DOE OSTI2024

Influence of Carbon-Nitride Dot-Emitting Species and Evolution on Fluorescence-Based Sensing and Differentiation

Carbon dots have attracted widespread interest for sensing applications based on their low cost, ease of synthesis, and robust optical properties. We investigate structure–function evolution on multiemitter fluorescence patterns for model carbon-nitride dots (CNDs) and their implications on trace-level sensing. Hydrothermally synthesized CNDs with different reaction times were used to determine how specific functionalities and their corresponding fluorescence signatures respond upon the addition of trace-level analytes. Archetype explosives molecules were chosen as a testbed due to similarities in substituent groups or inductive properties (i.e., electron withdrawing), and solution-based assays were performed using ratiometric fluorescence excitation–emission mapping (EEM). Analyte-specific quenching and enhancement responses were observed in EEM landscapes that varied with the CND reaction time. We then used self-organizing map models to examine EEM feature clustering with specific analytes. Finally, the results reveal that interactions between carbon-nitride frameworks and molecular-like species dictate response characteristics that may be harnessed to tailor sensor development for specific applications.

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

Fe-Exchanged Small-Pore Zeolites as Ammonia Selective Catalytic Reduction (NH 3 -SCR) Catalysts

Cu-exchanged small-pore zeolites have been extensively studied in the past decade as state-of-the-art selective catalytic reduction (SCR) catalysts for diesel engine exhaust NOx abatement for the transportation industry. During this time, Fe-exchanged small-pore zeolites, e.g., Fe/SSZ-13, Fe/SAPO-34, Fe/SSZ-39 and high-silica Fe/LTA, have also been investigated but much less extensively. In comparison to their Cu-exchanged counterparts, such Fe/zeolite catalysts display inferior low-temperature activities, but improved stability and high-temperature SCR selectivities. Such characteristics entitle these catalysts to be considered as key components of highly efficient emission control systems to improve the overall catalyst performance. In this short review, recent studies on Fe-exchanged small-pore zeolite SCR catalysts are summarized, including (1) the synthesis of small-pore Fe/zeolites; (2) nature of the SCR active Fe species in these catalysts as determined by experimental and theoretical approaches, including Fe species transformation during hydrothermal aging; (3) SCR reactions and structure-function correlations; and (4) a few aspects on industrial applications.

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

Complex Fluorine Chemical Potential Effects on the Shape and Compositional Heterogeneity of KTa 1– x Nb x O 3 Nanoparticles

When kinetic conditions dominate and dictate the growth in a nanoparticle synthesis, properties of the synthesis environment can have considerable effects on the properties of the products. Such effects were studied here, where the solution environment was changed via the addition of KF to the hydrothermal syntheses of KTa 1– x Nb x O 3 and KTaO 3 . One result demonstrated the straightforward cause-and-effect relationship between the solution and reaction kinetics: KF directly increased the solution stability of the Ta species and therefore decreased its reaction rate, resulting in a change in composition heterogeneity of Ta and Nb in the KTa 1– x Nb x O 3 particles. However, not all effects are so simple; changing the chemical potential of the solution with KF can also promote the formation of particles with anisotropic defect enhanced kinetic Wulff shapes instead of cuboidal shapes. The increased F chemical potential in the solution enabled the formation of planar defects in the bulk, which accelerated growth in-plane to form particles characterized by flat rectangular flake geometries. In this work, thermodynamic modeling with density functional theory calculations confirmed that sufficient KF concentrations can drive the formation of a defect phase K n +1 Ta n O 3 n F.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2012

Hydrogen Isotope Measurements of Organic Acids and Alcohols by Pyrolysis-GC-MS-TC-IRMS: Application to Analysis of Experimentally Derived Hydrothermal Mineral-Catalyzed Organic Products

We report results of experiments to measure the H isotope composition of organic acids and alcohols. These experiments make use of a pyroprobe interfaced with a GC and high temperature extraction furnace to make quantitative H isotope measurements. This work compliments our previous work that focused on the extraction and analysis of C isotopes from the same compounds [1]. Together with our carbon isotope analyses our experiments serve as a "proof of concept" for making C and H isotope measurements on more complex mixtures of organic compounds on mineral surfaces in abiotic hydrocarbon formation processes at elevated temperatures and pressures. Our motivation for undertaking this work stems from observations of methane detected within the Martian atmosphere [2-5], coupled with evidence showing extensive water-rock interaction during Mars history [6-8]. Methane production on Mars could be the result of synthesis by mineral surface-catalyzed reduction of CO2 and/or CO by Fischer-Tropsch Type (FTT) reactions during serpentization [9,10]. Others have conducted experimental studies to show that FTT reactions are plausible mechanisms for low-molecular weight hydrocarbon formation in hydrothermal systems at mid-ocean ridges [11-13]. Our H isotope measurements utilize an analytical technique combining Pyrolysis-Gas Chromatograph-Mass Spectrometry-High Temperature Conversion-Isotope Ratio Mass Spectrometry (Py-GC-MS-TC-IRMS). This technique is designed to carry a split of the pyrolyzed GC-separated product to a Thermo DSQII quadrupole mass spectrometer as a means of making qualitative and semi-quantitative compositional measurements of separated organic compounds, therefore both chemical and isotopic measurements can be carried out simultaneously on the same sample.

Socki, Richard A.↗
NASA NTRS2001

Catalysis in the 3rd Dimension: How Organic Molecules May be Formed

Catalysis is often little more than a word to phenomenologically describe the fact that a reaction follows a pat1 that leads to products of an unexpected kind or of unexpected yield. Low activation energy barriers for intermediates are recognized as the most likely cause why a system deviates from the thermodynamic pull towards minimizing its free energy and ends up in a metastable state. Seldom is the mechanism known. This i: particularly true for heterogeneous catalysis under hydrothermal conditions with minerals as catalysts. It is commonly assumed that catalytic action takes place across solid-fluid interfaces and that, on the atomic level, interfaces are just 2-dimensional contacts. This makes it difficult to understand, for instance, the assembly of long-chain carboxylic (fatty) acids. 3y studying single crystals that grew from a melt in the presence of H2O and CO2, we can show: (1) that numerals take up the fluid components into solid solution, (2) that some-thing happens converting them to -educedH and C, (3) that C atoms segregate into dislocations and tie C-C bonds. The products are medium-to-long chain Cn protomolecules, with some C-H attached, pre-assembled in the dislocations. Upon solvent extraction, these proto-molecules turn into carboxylic and dicarboxylic acids. This observation suggests that, in a very elementary step, catalysis under hydrothermal conditions leading to fatty acids involves the pre-assembly of Cn entities in the interface that is not 2-D but extends into the 3rd dimension, with dislocations as synthesis sites.

Freund, Friedemann↗