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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

A general mechanism for gel layer formation on borosilicate glass under aqueous corrosion

Mineral and glass dissolution is a scientific topic deeply investigated but incompletely understood and of a great interest for the geochemical and materials science communities. If the interfacial dissolution/reprecipitation mechanism seems to be applicable to most of silicate minerals, the debate remains open concerning glass. Here we studied two model glasses, a ternary borosilicate (CJ1) and the same glass doped with 4.1 mol% of Al2O3 (CJ2). The two glasses were altered at 90°C, pH 9, and in conditions far and close to saturation with respect to amorphous silica, to determine the initial and residual rates. Moreover, a specific experiment was conducted for a short duration with a solution highly enriched with 18O and 29Si isotopes to understand how passivating gels form. SEM, TEM and ToF-SIMS characterization, along with Monte Carlo simulations were used to understand the rate limiting reactions at play and infer the role of Al. We show that Al yields a slower matrix dissolution in dilute conditions. However, it slows down he formation and the maturation of the passivating gel and favors alteration by partial hydrolysis of Si and Al entities followed by in-situ reorganization/relaxation into a porous network. Unexpectedly, CJ1 experienced both interfacial dissolution/reprecipitation and partial hydrolysis followed by in situ reorganization of the silicate network during the course of a single experiment. This study offers a unified concept that can pave the way for the future development of a predictive kinetic model based on a detailed description of bond breaking and bond forming as a function of glass composition and alteration conditions.

Gin, Stephane↗
DOE OSTI2017

Structural Emergence in Particle Dispersions

Particle dispersions, such as pigment-based inks, comprise weakly bound, milled nanoparticles. The properties of these pigments depend on both their chemical composition and a rather complex structural hierarchy which emerges from these dispersions. The emergence of structure under semidilute conditions is related to the structure of the dilute particles, the particle spacing (mesh size), processing history, and the interaction potential. Kinetic simulations could predict such emergence using these input parameters. In this paper, organic pigments are studied as an example of the importance of emergent structure to predict properties such as brilliance and opacity. Organic pigments are used to impart color to commercial inks, plastics, coatings, and cosmetics. In many cases, dilute pigments are mass fractal structures consisting of aggregated nanoparticles held together by weak van der Waals forces. In water, surfactant is added to create a pigment dispersion (an ink). The final properties of a pigment emerge from a complex interplay between aggregation and dispersion of aggregates as a function of concentration. Samples of the organic pigment yellow 14, PY14, were milled to four primary particle sizes to study the effect on structural emergence. The interaction between surfactant-stabilized PY14 aggregates in an aqueous medium was quantified by the second virial coefficient, A 2 , which reflects long-range interactions. The degree of aggregation is associated with short-range attractive interactions between primary particles. In this series of pigments, the degree of aggregation increases dramatically with reduction in primary particle size. Concurrently, the second-order virial coefficient, A 2 , increases reflecting stronger long-range repulsive interactions with particle size. Structural emergence can be understood through the percolation concentration and the filler mesh size. A 2 is translated into a repulsive interaction potential for use in dissipative particle dynamics simulations to enable predictive modeling. Furthermore, this description of the interactions between dispersed pigment aggregates allows for a more scientific and predictive approach to understand structural emergence.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Nanorod Mobility within Entangled Wormlike Micelle Solutions

In the semi-dilute regime, wormlike micelles form an isotropic entangled microstructure that is similar to that of an entangled polymer solution with a characteristic, nanometer-scale entanglement mesh size. We report a combined x-ray photon correlation spectroscopy (XPCS) and rheology study to investigate the translational dynamics of gold nanorods in semi-dilute solutions of entangled wormlike micelles formed by the surfactant cetylpyridinium chloride (CPyCl) and the counter-ion sodium salicylate (NaSal). The CPyCl concentration is varied to tune the entanglement mesh size over a range that spans from approximately equal to the nanorod diameter to larger than the nanorod length. The NaSal concentration is varied along with the CPyCl concentration so that the solutions have the maximum viscosity for given CPyCl concentration. On short time scales the nanorods are localized on a length scale matching that expected from the high-frequency elastic modulus of the solutions as long as the mesh size is smaller than the rod length. On longer time scales, the nanorods undergo free diffusion. At the highest CPyCl concentrations, the nanorod diffusivity approaches the value expected based on the macroscopic viscosity of the solutions, but it increases with decreasing CPyCl concentration more rapidly than expected from the macroscopic viscosity. A recent model by Cai et al. [Cai, L.-H.; Panyukov, S.; Rubinstein, M. Macromolecules 2015, 48, 847-862.] for nanoparticle “hopping” diffusion in entangled polymer solutions accounts quantitatively for this enhanced diffusivity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Prolonged Stability of Pb-Catalyzed CO 2 Electroreduction to Methyl Formate in Acidic Methanol

Electrochemical CO 2 reduction from renewable energy is a promising route to mitigate greenhouse gas emissions from waste sources while generating value-added products. CO 2 electroreduction in methanol is particularly interesting due to the increased CO 2 solubility compared to water and the propensity to form methyl formate, a product absent in aqueous electrolysis. Here, four factors have been identified as critical to achieving prolonged high selectivity for methyl formate production on a Pb cathode in methanol: high pH near the electrode, low bulk pH, low water content, and regeneration of Pb 2+ sites. Increasing concentration of the formic acid product was observed to induce a selectivity shift towards hydrogen, which was mitigated by the in-situ conversion of the formic acid to methyl formate via an esterification reaction. Furthermore, co-electrolysis of CO 2 with dilute molecular oxygen (4% O 2 ) led to Pb catalyst repair through in-situ surface oxidation. Using CO 2 and dilute O 2 along with single-pass catholyte flow to maintain a low formic acid concentration, sustained high selectivity for methyl formate was attained at ~60% faradaic efficiency at -20 mA cm -2 for over 72 hours.

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

Understanding Inlet Concentration Effects on the Electrocatalytic Conversion of CO 2 to Formic Acid in Gas-Fed Electrolyzers

The electrochemical CO 2 reduction reaction (CO2RR) to produce value-added products remains a developing technology for utilizing waste CO 2 streams. Most device-level CO2RR studies use pure CO 2 gas feeds; however, the effect of dilute CO 2 on the electrolyzer performance is an important consideration for large-scale electrolyzer operation, single-pass conversion, and real-world CO 2 source utilization. This work investigates the effect that the CO 2 concentration has on the performance of formic acid (HCOOH) producing tin oxide (SnO 2 ) and bismuth oxide (Bi 2 O 3 ) catalysts in an electrolyzer device setting. Surprisingly, SnO2 demonstrated an approximately 20% increase in HCOOH selectivity (Faradaic efficiency) when the CO 2 concentration decreased from 100 to 20%. In contrast, Bi 2 O 3 consistently demonstrated high selectivity toward HCOOH across the same CO 2 concentration range. The effects of the CO 2 concentration on selectivity were further investigated with half-cell experiments and in situ Raman spectroscopy, which revealed dynamic changes in the cathodic overpotential and chemical state of the catalyst that depended on the CO 2 concentration. Density functional theory calculations showed how changes in the surface oxidation state of Sn, varying from fully oxidized SnO 2 to metallic Sn(0), affect the thermodynamic barriers of the three main observed products: HCOOH, CO, and H 2 . Our results indicate that dilute CO 2 concentrations required larger cathodic overpotentials to sustain a fixed current density, which, in turn, pushed the Sn-based catalyst toward a more reduced surface that was favorable to HCOOH formation. On the other hand, the Bi-based catalyst remained in a metallic state at CO2RR-relevant potentials and demonstrated a consistent product selectivity regardless of CO 2 concentration. These findings highlight how varying the CO 2 inlet gas concentrations affects the chemical state of catalysts and the resulting performance metrics.

42 ENGINEERING↗
DOE OSTI2022

Microemulsions as Emerging Electrolytes: The Correlation of Structure to Electrochemical Response

We describe the structural studies of microemulsions (μEs) prepared from water, toluene, butanol, and polysorbate 20 (PS20) that we recently used as electrolytes. Small-angle neutron scattering was used to monitor the development of the bicontinuous system as a function of the water-to-surfactant mass ratio on a constant oil-to-surfactant dilution line, revealing how the domain size, correlation length, amphiphilicity factor, and bending moduli change with composition. Kratky and Porod analyses are also employed, providing further structural detail of the scattering domains. Here, we demonstrate that controlling the water-to-surfactant ratio with a constant oil-to-surfactant dilution affects the bicontinuous phase, reveals a sizeable compositional region with structural similarities, and provides insight into the correlation of structure to physical properties. Voltammetric results are presented to examine how the evolution of the bicontinuous structure formed in a μE prepared from water, toluene, butanol, and PS20 contributes to the electrochemical response. These findings, therefore, provide essential information that will guide the formulation of μEs as electrolytes for energy storage.

25 ENERGY STORAGE↗
DOE OSTI2019

Investigation of the Microstructure and Rheology of Iridium Oxide Catalyst Inks for Low-Temperature Polymer Electrolyte Membrane Water Electrolyzers

Here, we present an investigation of the structure and rheological behavior of catalyst inks for low-temperature polymer electrolyte membrane water electrolyzers. The ink consists of iridium oxide (IrO 2 ) catalyst particles and a Nafion ionomer dispersed in a mixture of 1-propanol and water. The effects of ionomer concentration and catalyst concentration on the microstructure of the catalyst ink were studied. Studies on dilute inks (0.1 wt % IrO 2 ) using zeta potential and dynamic light scattering measurements indicated a strong adsorption of the ionomer onto the catalyst particles which resulted in an increase in the ..zeta..-potential and the z-average diameter. Steady-shear and dynamic-oscillatory-shear rheological measurements of concentrated IrO 2 dispersions (35 wt % IrO 2 ) indicated that the particles are strongly agglomerated in the absence of the ionomer. The addition of even a small amount of the ionomer (2.4 wt % with respect to total solids) caused the rheology to transition from shear thinning to Newtonian because of the reduction in agglomerated structure due to stabilization of the aggregates by the ionomer, consistent with the behavior of dilute inks. At intermediate ionomer loadings, between 2.4 and 9 wt %, the viscosity increased with increasing ionomer wt %, though remained Newtonian, predominantly due to the increasing ionomer volume fraction in the ink. For ionomer loadings greater than 9 wt %, the particles were found to be flocculated, likely induced by a dispersed ionomer. The flocculated inks exhibited strong shear-thinning and gel-like behaviors in steady-shear and oscillatory-shear rheology. The onset of flocculation was found to be sensitive to the catalyst concentration, where below 35 wt % of IrO 2 , flocculation was not observed. The rheological observations were further verified by ultra-small-angle X-ray scattering.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A First-Principles Approach to Modeling Surface Site Stabilities on Multimetallic Catalysts

The study of multimetallic alloys and the multitude of possible surface compositions have sparked a tremendous interest in engineering low-cost materials with high activity and selectivity in heterogeneous catalysis. Multimetallic systems provide complementary functionalities and an unprecedented tunability when designing catalyst formulations. However, due to their immense structural and compositional complexity, the investigation and identification of an optimal catalyst is a tedious and time-consuming process, both experimentally and theoretically. Therefore, theoretical design principles are highly desirable to accelerate the screening of catalyst structures across the vast compositional space. In this paper, we introduce a simple and general model for predicting the site stability of multimetallic surfaces and nanoparticles, which is based on physical principles. The model requires only a small set of density functional theory (DFT) calculations of metal atom binding energies on monometallic and dilute alloy surface slabs to optimize the parameters in the simple model. The resulting model allows for the quantification of the stability of any particular atom site in any conceivable chemical environment across a wide range of morphologies, sizes, and arrangements by interpolating the derived parameters from a monometallic system to a completely diluted alloyed system. Herein, we demonstrate the robustness of the model across an extensive data set of transition metal alloy surfaces and 147-atoms cuboctahedral nanoparticles (NPs) composed of IrRhRu and PtPdRu. In conclusion, our approach yields mean absolute errors of ≈0.15 (IrRhRu), 0.20 (PtPdRu), 0.19 (IrRhRu NP), and 0.26 (PtPdRu NP) eV relative to site binding energies calculated using DFT.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Challenges in Product Selectivity for Electrocatalytic Reduction of Amine-Captured CO 2 : Implications for Reactive Carbon Capture

CO 2 is a potential feedstock for carbon-based fuels or materials, but is only available in dilute streams. Integrated processes for CO 2 capture and conversion directly valorize the CO 2 captured by sorbent materials, skipping the energetically expensive sorbent regeneration step. Amines are the most heavily studied liquid-phase sorbent materials for CO 2 capture from dilute streams. Amines react with CO 2 in a 2:1 ratio to form the corresponding ammonium carbamate. Ammonium carbamate [NH 4 ][H 2 NCO 2 ] was tested as the substrate using the highly selective and robust CO 2 -to-formate reduction electrocatalyst [( tBu POCOP)Ir(H)(NCCH 3 ) 2 ], where ( tBu POCOP) is the tridentate pincer ligand 2,6-bis(di tert -butyl-phosphonito). When ammonium carbamate was used as the substrate instead of CO 2 , only hydrogen was produced. An equivalent electrolysis with ammonium hexafluorophosphate with CO 2 also resulted in primarily hydrogen. Methyl carbamate and urea were also tested as substrates as proxies for carbamate that do not contain an equivalent of ammonium, and there was also negligible reduction to carbon-based products. These results indicate that the loss of selectivity observed for aminecaptured CO 2 , or ammonium carbamate, is likely due to the generation of the acidic ammonium equivalent as well as the greater challenge of reducing carbamate compared to CO 2 . This study illustrates that catalysts with high selectivity for concentrated CO 2 can favor hydrogen evolution and loss of carbon-based products when amine-captured CO 2 is used instead.

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

Topology-Dependent Polymer Stretching and Scission in Solution at Extreme Shear Rates

There has been significant interest in the engineering of polymer topology to control rheology and mechanical stability in dilute solutions for applications involving extreme shear rate flows. However, methods to experimentally probe properties at relevant shear rates (≈ 10 4 –10 6 s –1 ) have remained ex situ, obscuring access to measures of polymer deformation and rheology that would otherwise provide mechanistic insight into the topology-dependent properties that control their behavior in extreme shear flows. In this study, we used novel in situ small angle neutron scattering measurements in a capillary rheometer (capillary rheo-SANS) to simultaneously measure solution viscosities and polymer deformations in high shear on a series of chemically homologous topology-defined polymers including linear, randomly branched, and star-shaped molecules. We demonstrate that differences in the onset of chain stretching and shear thinning of these polymers in dilute solution are controlled primarily by differences in their molecular relaxation time. These differences correlate with differences in chain scission inferred from ex situ measurements at more extreme shear rates. Together, the results demonstrate a direct coupling between chain deformation and scission, and suggest that the dominant effect of branching as a means to impart resilience against mechanical degradation is through differences in relaxation dynamics due to branching. We anticipate that these results will provide key insights to engineer topology-controlled polymers for rheological modification, mechanical stability, and controlled mechano-chemistry.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2015

Acidolysis of α-O-4 Aryl-Ether Bonds in Lignin Model Compounds: A Modeling and Experimental Study

Lignocellulosic biomass offers a vast, renewable resource for the sustainable production of fuels and chemicals. To date, a commonly employed approach to depolymerize the polysaccharides in plant cell walls employs mineral acids, and upgrading strategies for the resulting sugars are under intense development. Although the behavior of cellulose and hemicellulose is reasonably well characterized, a more thorough understanding of lignin depolymerization mechanisms in acid environments is necessary to predict the fate of lignin under such conditions and ultimately to potentially make lignin a viable feedstock. To this end, dilute acid hydrolysis experiments were performed on two lignin model compounds containing the a-O-4 ether linkage at two temperatures concomitant with dilute acid pretreatment. Both primary and secondary products were tracked over time, giving insight into the reaction kinetics. The only difference between the two model compounds was the presence or absence of a methyl group on the a-carbon, with the former being typical of native lignin. It was found that methylation of the a-carbon increases the rate of reaction by an order of magnitude. Density functional theory calculations were performed on a proposed mechanism initiated by a nucleophilic attack on the a-carbon by water with a commensurate protonation of the ether oxygen. The values for the thermodynamics and kinetics derived from these calculations were used as the basis for a microkinetic model of the reaction. Results from this model are in good agreement with the experimental kinetic data for both lignin model compounds and provide useful insight into the primary pathways of a-O-4 scission reactions in acid-catalyzed lignin depolymerization. The distribution of primary and secondary products is interpreted as a function of two barriers of formation exhibiting opposite trends upon methylation of the a-carbon (one barrier is lowered while the other is increased). Such insights will be needed to construct a comprehensive model of how lignin behaves in a common deconstruction approach.

14 SOLAR ENERGY↗
DOE OSTI2016

Physiochemical Characterization of Lignocellulosic Biomass Dissolution by Flowthrough Pretreatment

Comprehensive understanding of biomass solubilization chemistry in aqueous pretreatment such as water-only and dilute acid flowthrough pretreatment is of fundamental importance to achieve the goal of valorizing biomass to fermentable sugars and lignin for biofuels production. In this study, poplar wood was flowthrough pretreated by water-only or 0.05% (w/w) sulfuric acid at different temperatures (220-270 °C), flow rate (25 mL/min), and reaction times (8-90 min), resulting in significant disruption of the lignocellulosic biomass. Ion chromatography (IC), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, and solid state cross-polarization/magic angle spinning (CP/MAS) 13C nuclear magnetic resonance (NMR) spectroscopy were applied to characterize the pretreated biomass whole slurries in order to reveal depolymerization as well as solubilization mechanism and identify unique dissolution structural features during these pretreatments. Results showed temperature-dependent cellulose decrystallization in flowthrough pretreatment. Crystalline cellulose was completely disrupted, and mostly converted to amorphous cellulose and oligomers by water-only operation at 270 °C for 10 min and by 0.05 wt % H2SO4 flowthrough pretreatment at 220 °C for 12 min. Flowthrough pretreatment with 0.05% (w/w) H2SO4 led to a greater disruption of structures in pretreated poplar at a lower temperature compared to water-only pretreatment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Identification and Mitigation of Inhibitory Substances Contained in High-Salinity Crude Glycerol Generated from Biodiesel Production for Polyhydroxyalkanoate Synthesis by Haloferax mediterranei

High-salinity crude glycerol generated from biodiesel production poses significant challenges to microbial valorization due to inhibitory ingredients that severely limit microbial growth. This study identified and mitigated inhibitory substances contained in high-salinity glycerol sludge to enable its conversion to polyhydroxyalkanoates (PHAs) by the extreme halophilic archaeon Haloferax mediterranei. The long-chain fatty acids (LCFAs) were consistently identified as the primary inhibitors by liquid chromatography−mass spectrometry, Fourier transform infrared spectroscopy, and ultraviolet−visible spectroscopy. Acid precipitation at pH 2 efficiently removed these LCFAs, substantially reducing the required feedstock dilution from 23 to 3 times, improving PHA titer by 40%. Furthermore, this dilution reduction also increased the feedstock salinity utilization, achieving a 46% reduction in external salt supplementation for H. mediterranei growth. In contrast, overliming and arrested anaerobic digestion were confirmed to be ineffective in inhibitor removal. This study provides deep insights into inhibitor chemistry and presents acid precipitation as an effective pretreatment strategy for waste valorization of highsalinity crude glycerol.

LC-MS↗
DOE OSTI2017

Butanol Separation from Humid CO 2 -Containing Multicomponent Vapor Mixtures by Zeolitic Imidazolate Frameworks

Butanol is a promising renewable fuel and feedstock. A major challenge in fermentative butanol production is to find a cost-effective butanol separation process from dilute aqueous solutions, usually an acetone-butanol-ethanol (ABE) mixture. Nanoporous zeolitic imidazolate frameworks (ZIFs) have shown potential for alcohol separation from dilute solutions. However, little is known about butanol separation from multicomponent mixtures using ZIFs, including the effects of the humid acid gas (CO 2 ) used to sparge the fermenter and generate the vapor product stream. We present a study of butanol separation by ZIF-8, ZIF-90, ZIF-71 and hybrid ZIF-8–90 and ZIF-8–71 adsorbents with binary butanol/water and multicomponent ABE feeds. To obtain reliable structure–property relations for ZIF adsorbents in realistic conditions, we combine multicomponent vapor breakthrough with structural, textural, and stability characterization techniques in humid CO 2 environments. In the absence of CO 2 , more hydrophobic materials such as ZIF-8, ZIF-8 55 -71 45 , ZIF-8 70 -90 30 , and ZIF-71 are found to be excellent candidates with butanol/water selectivities >10 and butanol capacities >3.5 mmol/g. However, in the presence of humid CO 2 , all the materials except ZIF-71 are found to degrade. The mechanistic aspects of this degradation are studied by FTIR spectroscopy and explained based upon acid gas attack of Zn–N coordinate bonds. ZIF-71 emerges as an excellent candidate owing to its acid gas stability, good butanol adsorption capacity, and selectivity. Vapor breakthrough with a model ABE solution demonstrates the high butanol selectivity of ZIF-71 relative to acetone, ethanol, and water and the recovery of a 65 mol % butanol product by desorption at 453 K. Finally, this study highlights the importance of determining structure–property relationships of MOF/ZIF materials in realistic multicomponent conditions, and the importance of acid gas stability in their applications.

09 BIOMASS FUELS↗
DOE OSTI2011

Effect of Acid, Alkali, and Steam Explosion Pretreatments on Characteristics of Bio-Oil Produced from Pinewood

Here, bio-oil produced from pinewood by fast pyrolysis has the potential to be a valuable substitute for fossil fuels. Pretreatment prior to the fast pyrolysis process has been shown to alter the structure and chemical composition of biomass. To determine the influence of biomass pretreatments on bio-oil produced during fast pyrolysis, we tested three pretreatment methods: dilute acid, dilute alkali, and steam explosion. Bio-oils were produced from untreated and pretreated pinewood feedstocks in an auger reactor at 450°C. The bio-oils physical properties including pH, water content, acid value, density, viscosity, and heating value were measured. Chemical characteristics of the bio-oils were determined by gas chromatographymass spectrometry. Results showed that bio-oil yield and composition were influenced by biomass pretreatment. Of the three pretreatment methods, 1% H 2 SO 4 pretreatment resulted in the highest bio-oil yield and best bio-oil quality.

09 BIOMASS FUELS↗
DOE OSTI2014

Polyacrylonitrile-Chalcogel Hybrid Sorbents for Radioiodine Capture

Powders of a Sn2S3 chalcogen-based aerogel (chalcogel) were combined with powdered polyacrylonitrile (PAN) in different mass ratios (SnS33, SnS50, and SnS70 in mass% of chalcogel), dissolved into dimethyl sulfoxide, and dropped into deionized water to form pellets of a porous PAN-chalcogel hybrid material. Pellets of these hybrid sorbents, along with pure powdered (SnSp) and granular (SnSg) forms of the chalcogel, were then used to adsorb iodine gas under both concentrated and dilute conditions. Both the SnSp and SnSg chalcogels showed very high maximum iodine loadings at 67.2 and 68.3 mass%. The maximum iodine loadings in the SnS33 and SnS50 were high at 32.8 and 53.5 mass%. In all cases, X-ray diffraction results showed the formation of Sn-I phases of SnI4 and SnI4(S8)2 revealing that the iodine binding in these materials is mainly due to a chemisorption process although some evidence also exists that supports a physisorption process.

chalcogel↗
DOE OSTI2022

Colloidal Platinum–Copper Nanocrystal Alloy Catalysts Surpass Platinum in Low-Temperature Propene Combustion

Low-temperature removal of noxious environmental emissions plays a critical role in minimizing the harmful effects of hydrocarbon fuels. Emission-control catalysts typically consist of large quantities of rare, noble metals (e.g., platinum and palladium), which are expensive and environmentally damaging metals to extract. Alloying with cheaper base metals offers the potential to boost catalytic activity while optimizing the use of noble metals. In this work, we show that Pt x Cu 100–x catalysts prepared from colloidal nanocrystals are more active than the corresponding Pt catalysts for complete propene oxidation. By carefully controlling their composition while maintaining nanocrystal size, alloys with dilute Cu concentrations (15–30% atomic fraction) demonstrate promoted activity compared to pure Pt. Complete propene oxidation was observed at temperatures as low as 150 °C in the presence of steam, and five to ten times higher turnover frequencies were found compared to monometallic Pt catalysts. Additionally, through DFT studies and structural and catalytic characterization, the remarkable activity of dilute Pt x Cu 100–x alloys was related to the tuning of the electronic structure of Pt to reach optimal binding energies of C* and O* intermediates. This work provides a general approach toward investigation of structure–property relationships of alloyed catalysts with efficient and optimized use of noble metals.

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

Solution and Active Site Speciation Drive Selectivity for Electrocatalytic Reactive Carbon Capture in Diethanolamine over Ni–N–C Catalysts

Direct conversion of captured forms of carbon, or reactive carbon capture (RCC), presents an opportunity to reduce the energy intensity and cost of direct CO 2 utilization from dilute sources. While amine-based sorbents effectively capture CO 2 , their use for RCC presents numerous challenges with typical pure metal catalysts used for electrochemical CO 2 reduction (CO 2 R). Here, using both theory and experiments, we find that Ni–N–C single atom catalysts are effective for RCC conversion to CO using a diethanolamine sorbent, in contrast to pure metal catalysts. Computational analysis reveals that RCC can proceed directly through direct reduction of the sorbent-CO 2 adduct or indirectly by C–N bond breaking facilitating CO 2 adsorption and subsequent reduction. We find that the latter mechanism is most prevalent at low overpotentials where we experimentally observe RCC selectivity. We also find experimentally that the rate of CO production for RCC with Ni–N–C catalysts can exceed pure bicarbonate solutions at intermediate sorbent concentration (0.1–0.5 M DEA) under dilute (10–25%) streams of CO 2 at low overpotentials. The coordination environment of Ni sites and the solution speciation influence their RCC activity, with changes in protonation to coordinating N/C atoms resulting in changing the RCC mechanism and consequent activity. In situ X-ray absorption spectroscopy and computational analysis reveal restructuring under RCC conditions due to hydrogen coadsorption with DEA that limits the stability of Ni–N–C catalysts. This work highlights the importance of carefully controlling the catalyst and solution environment to achieve active and stable RCC electrocatalysis.

Chemistry↗