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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Structural and Chemical Evolution of an Inverse CeO x /Cu Catalyst under CO 2 Hydrogenation: Tunning Oxide Morphology to Improve Activity and Selectivity

Small nanoparticles of ceria deposited on a powder of CuO display a very high selectivity for the production of methanol via CO 2 hydrogenation. CeO 2 /CuO catalysts with ceria loadings of 5%, 20%, and 50% were investigated. Among these, the system with 5% CeO x showed the best catalytic performance at temperatures between 200 and 350 °C. The evolution of this system under reaction conditions was studied using a combination of environmental transmission electron microscopy (E-TEM), in situ X-ray absorption spectroscopy (XAS), and time-resolved X-ray diffraction (TR-XRD). For 5% CeO x /Cu, the in situ studies pointed to a full conversion of CuO into metallic copper, with a complete transformation of Ce 4+ into Ce 3+ . Images from E-TEM showed drastic changes in the morphology of the catalyst when it was exposed to H 2 , CO 2 , and CO 2 /H 2 mixtures. Under a CO 2 /H 2 feed, there was a redispersion of the ceria particles that was detected by E-TEM and in situ TR-XRD. Finally, these morphological changes were made possible by the inverse oxide/metal configuration and facilitate the binding and selective conversion of CO 2 to methanol.

03 NATURAL GAS↗
DOE OSTI2023

A review of in situ/operando studies of heterogeneous catalytic hydrogenation of CO 2 to methanol

Repurposing CO 2 into chemicals, one of the Carbon Dioxide Removal (CDR) strategies, still faces significant challenges in conversion and energy efficiency due to the lack of effective catalysts and processes. Fundamental understanding through in situ/operando investigations of the reaction mechanisms and catalyst structures is pivotal for developing the efficient catalysts. This paper reviews the past and recent in situ/operando studies of methanol synthesis from heterogeneous CO 2 hydrogenation over a few typical catalysts including Cu-based, oxide-based, and noble-metal-based catalysts. With the development of high-pressure reactors, in situ/operando IR, X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), neutron diffraction and imaging have been used to reveal the surface intermediates and structures of working catalysts under CO 2 hydrogenation conditions. On the one hand, the combined operando techniques shed light on working mechanisms for some catalytic systems. On the other hand, due to the complexity of selective CO 2 hydrogenation reaction and limited sensitivity of current accessible operando techniques to the surface structure of catalysts, it is still murky about the exact nature of the active sites at the surface/interface and how different sites promote different reaction paths. Furthermore, it is concluded that new methodologies for differentiating signals from different sites, and the development of surface-sensitive techniques for high pressure reactions are needed for providing structural descriptors of highly active and selective CO 2 conversion catalysts.

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

Novel, Middle and Long Wave Infrared Laser Sources For Accelerator Applications

The main accomplishment during Years 2020-2024 of the DOE Accelerator Stewardship Program is proof-of-principle demonstration of amplification of an ultrashort 10 µm seed pulse in a multiatmosphere CO 2 laser optically pumped by nanosecond pulses of either a ~4.3 µm Fe:ZnSe laser or a 2.8 µm electro-optically (EO) Q-switched Er: Laser. This has been accomplished at the UCLA Neptune Laboratory by using about 100 mJ, ~100 ns long pulses generated by the pump laser built for this purpose by the UAB team. Implementation of EO Q-switching regime in the solid-state Er:laser system made possible nanosecond synchronization between the pump pulse and the 0.5 ps seed pulse produced by a commercial Ti:sapphire laser based mid-IR OPA/DFG. The injection mode-locking regime realized in a compact Mult atmosphere 3 Hz CO 2 -He regenerative amplifier enabled generation of a train of ultrashort pulses separated by the cavity round-trip time of ~3.2 ns. The measured gain lifetime of ~1 µs at a total pressure of ~12-15 atm indicates that lifetime of the upper laser level is a critical limiting factor in designing high-pressure CO 2 amplifiers. A single picosecond 10 mm pulse with an energy 0.1-0.2 mJ was extracted from the amplifier’s cavity using an ultrafast Ge semiconductor switch whose reflectivity was photo-induced by a femtosecond 800 nm pulse. For direct amplification regime, nonlinear absorption in Ge at 10 mm at GW/cm 2 intensities limited the extracted energy. Therefore, the generated energy could be further increased by minimizing losses in the switch and optimizing the cavity mode size. Based on the obtained data in collaboration with BNL colleagues, we have designed a high-pressure CO 2 amplifier to be used as a preamplifier for the future experiments at the ATF BNL. The latter work is the subject of funding availability.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

High-temperature carbon dioxide capture in a porous material with terminal zinc hydride sites

Carbon capture can mitigate point-source carbon dioxide (CO 2 ) emissions, but hurdles remain that impede the widespread adoption of amine-based technologies. Capturing CO 2 at temperatures closer to those of many industrial exhaust streams (>200°C) is of interest, although metal oxide absorbents that operate at these temperatures typically exhibit sluggish CO 2 absorption kinetics and instability to cycling. Here, in this study, we report a porous metal–organic framework featuring terminal zinc hydride sites that reversibly bind CO 2 at temperatures above 200°C—conditions that are unprecedented for intrinsically porous materials. Gas adsorption, structural, spectroscopic, and computational analyses elucidate the rapid, reversible nature of this transformation. Extended cycling and breakthrough analyses reveal that the material is capable of deep carbon capture at low CO 2 concentrations and high temperatures relevant to postcombustion capture.

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

Mitigation Methods for Piperazine Oxidation in Post-Combustion Carbon Capture

Piperazine is a promising second-generation solvent for amine scrubbing in post-combustion CO2 capture. However, the oxidative degradation of PZ can cause environmental problems and economic loss. This work presents the effects of two mitigation methods: carbon treating and N2 sparging, on the PZ oxidation in long-term operations. The species and their respective quantities adsorbed by the activated carbon were tested in a bench-scale device. The carbon was then tested in the High Temperature Oxidation Reactor (HTOR), where the solvent oxidizes at a reasonably fast rate. Pilot plant campaigns were also performed at the UT Austin SRP and the National Carbon Capture Center (NCCC) and the effects were verified. When dissolved Fe is removed by carbon treating or other methods, available soluble Fe in the system dissolves and replaces the dissolved Fe. Therefore, all available Fe and ligands need to be removed for the mitigation to be effective. The sources of soluble Fe include fly ash and the corrosion of stainless steel, and the ligands are degradation products. 8 All PZ degraded solvents have two absorbance peaks at 320 nm and 538 nm. The 320 nm peak is caused by dissolved metals, especially Fe, complexed by degradation products. The 320 nm peak is related to the amine degradation level and can be used as a simple and efficient method to estimate the amine degradation rate. The pilot plant data suggest that NO2 can oxidize PZ significantly, possibly through radical reactions. 0.01 mmol/kg-hr absorption of NO2 increased the PZ oxidation rate from 1.2 mmol/kg-hr to 2.5 mmol/kg-hr.

Yuying, Wu↗
DOE OSTI2024

Sulfur-Enriched Nanoporous Carbon: A Novel Approach to CO 2 Adsorption

Carbon dioxide (CO 2 ) intake plays a vital role in sustaining the environmental balance by influencing global carbon dynamics and climatic stability. This work addresses the production of sulfur-doped porous nanocarbons (SDCs) as prospective sorbents for CO 2 capture. SDCs were fabricated by utilizing coconut shell as a carbon precursor and potassium persulfate as both a chemical activating agent and a sulfur dopant. The incorporation of sulfur functionalities into carbon matrices creates structural variability and active sites, boosting CO 2 absorption capabilities. Sulfur's peculiar electrical structure allows greater intermolecular interactions with CO 2 , enhancing adsorption affinities. According to the experimental data, the CO 2 uptake was best measured as 3.37 mmol/g at 0(degrees)C and 1 bar and 2.56 mmol/g at 25 C-degrees and 1 bar. The results show that the higher porosity of SDC materials adds to a large amplification in the CO 2 uptake capability. The work underlines the delicate interaction between sulfur doping, morphological porosity, and surface reactivity in enhancing the effectiveness of CO 2 sequestration. SDC materials hold considerable promise in tackling the present ecological concerns and developing CO 2 collection techniques. The suggested single-step synthesis technique described here provides a sustainable and environmentally friendly method for synthesizing SDCs for carbon capture applications.

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

TEA of a Unique Two-Pathways Process for Post-Combustion CO 2 Capture

A unique two-Pathways process using aqueous sodium glycinate for CO 2 capture from a split flue gas stream emitted from 600 MWe post-combustion coal power plant was developed in Aspen Plus v.10. The split gas flow rate used was 44.75 ton/h and contained 0.0023 mol% SO 2 and 13.33 mol% CO 2 . The process includes a washing unit, a CO 2 absorption unit, a reverse osmosis unit, and a solvent regeneration unit or an ultrafiltration unit. The washing unit uses deionized water to completely remove SO 2 and the CO 2 absorption unit uses SGS to capture at least 90 mol% of the CO 2 in the split flue gas stream. Upon CO 2 and SGS reactions, the resulting liquid products exhibit phase-separation into CO 2 -lean phase and CO 2 -rich phase, allow two distinct pathways. Pathway (i) is to regenerate mostly the CO 2 -rich phase, collect the released CO 2 , and compress it for sequestration purposes. Pathway (ii) is to send the liquid stream from the CO 2 absorption unit to the ultrafiltration unit to separate the solid nanomaterials. The hydraulics and mass transfer characteristics in the washing and CO 2 absorption units were obtained; and techno-economic analysis (TEA) for Pathways (i) and (ii), including Capital Expenditure (CAPEX), Operating Expenditure (OPEX), and Levelized Cost of CO 2 Captured (LCOC), were calculated and compared. The simulation results revealed that the CAPEX, OPEX, and LCOC for Pathway (i) were ($\$12,039,251$), (261 dollar/h), and (54.01 dollar/ton-CO 2 captured), respectively, and those for Pathway (ii) were ($\$5,908,000$), (237.2 dollar/h), and (39.90 dollar/ton-CO 2 captured), respectively. Moreover, in Pathway (ii), 8.19 ton/h of CO 2 were captured to produce 15.62 ton/h NaHCO 3 nanomaterials, which were sold to offset the overall process cost. The LCOC values indicate that Pathway (ii) is more cost-effective than Pathway (i) because LCOC values for Pathway (ii) are much lower than those for Pathway (i).COC values for Pathway (ii) are much lower than those for Pathway (i).

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2023

Surface‐modified Ag@Ru‐P25 for photocatalytic CO 2 conversion with high selectivity over CH 4 formation at the solid–gas interface

Systematic optimization of the photocatalyst and investigation of the role of each component is important to maximizing catalytic activity and comprehending the photocatalytic conversion of CO 2 reduction to solar fuels. A surface-modified Ag@Ru-P25 photocatalyst with H 2 O 2 treatment was designed in this study to convert CO 2 and H 2 O vapor into highly selective CH 4 . Ru doping followed by Ag nanoparticles (NPs) cocatalyst deposition on P25 (TiO 2 ) enhances visible light absorption and charge separation, whereas H 2 O 2 treatment modifies the surface of the photocatalyst with hydroxyl (–OH) groups and promotes CO 2 adsorption. High-resonance transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure techniques were used to analyze the surface and chemical composition of the photocatalyst, while thermogravimetric analysis, CO 2 adsorption isotherm, and temperature programmed desorption study were performed to examine the significance of H 2 O 2 treatment in increasing CO 2 reduction activity. The optimized Ag 1.0 @Ru 1.0 -P25 photocatalyst performed excellent CO 2 reduction activity into CO, CH 4 , and C 2 H 6 with a ~95% selectivity of CH 4 , where the activity was ~135 times higher than that of pristine TiO 2 (P25). For the first time, this work explored the effect of H 2 O 2 treatment on the photocatalyst that dramatically increases CO 2 reduction activity.

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

Carbonic anhydrase textile structured packing for efficient CO 2 absorption in methyldiethanolamine solvent

Carbonic anhydrase (CA) is an attractive biodegradable catalyst for CO 2 absorption in solvent–based CO 2 capture. However, maintaining the stability of CA as a homogeneous component of the solvents is a challenge. Solvent regeneration temperature typically exceeds the enzyme thermal tolerance, which leads to CA deactivation. To reduce the need for frequent CA replenishment and to avoid inactive CA accumulation in the solvent, this work shows the benefits of an immobilization strategy where CA is fixed in a second–generation design of textile structured packing (CATSP–2) modules. The enzyme–immobilized packing showed 1.5 times better performance in CO 2 separation compared with traditional structured packing with a corresponding increased CO 2 loading in the rich solvent. The modules exhibited good CA activity retention of ~80% during the tests without any CA replenishment. As a result, applying CATSP–2 could potentially decrease the packing height and absorber column size for a lower cost per amount of CO 2 captured.

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

Coal-based Bricks & Blocks (CBBs): Process Development to Prototype Fabrication Coupled with Techno-Economic Analysis and Market Survey

The decline of coal use for energy production provides an abundance of local feedstock for new innovative uses and value-added products. Expanding the U.S. coal-value chain to manufacture high-value carbon products can strengthen the nation’s energy and mineral security, enhance the U.S. national defense security, increase the United States’ economic prosperity, while achieving U.S. environmental objectives. The primary project goal is a relatively light-weight composite product with superior (or comparable) compressive strength. Both virgin and, where available, post-consumer recycled thermoplastic versions are tested for each thermoplastic species. A useful attribute of thermoplastics as binders is that they can be heated to their melting point, cooled, and reheated again without significant degradation. A key advantage of thermoset CBBs is that they require only mixing and molding. CBB advantages include low cost, availability, binding ability and processability. Coal-based bricks and blocks (CBBs) weigh about 50% less than clay bricks and can be manufactured with an interlocking design to promote ease of use for the novice builder. CBB formulation is evaluated according to a design-of-experiments (DoE) approach. DoE variables are a) relative weight fractions of binder, b) relative proportions of large versus small (milled) anthracite size fractions, and c) additive percentage. Fabrication methods include hot-press molding and extrusion, the later being the most commercially viable. CBBs are tested for compressive strength, modulus of rupture (by flexure test) and water absorption per ASTM C67, with density determined by the Archimedes drainage method. Fractured interfaces are examined by SEM (Scanning Electron Microscopy) to resolve fracture dynamics and interior microstructure uniformity. Differential scanning calorimetry (DSC) is used to compare plastic transition temperatures i.e., glass and melting temperatures to contrast virgin with post-consumer recycled thermoplastics and optimize their usage. These results are used in the DoE analysis to identify the binder and relative weight percentages for optimum strength, density, and porosity. Overall, CBBs possess strength comparable to clay-based bricks but are non-permeable and hydrophobic, and hence resistant to degradation by freeze-fracturing, corrosion, and efflorescence. The strongest composites have been made with the following thermoplastic binders (in order of strength): thermoset, high-density polyethylene crosslink resin, high-density polyethylene, nylon 6/6, and polypropylene. Results from a techno-economic analysis TEA show economy of scale for CBBs by modularization and reveal the binder as the cost driver for material costs. Ideally, the incorporation of post-consumer recycled thermoplastic will decrease material acquisition costs and increase product sustainability. Notably, CBBs do not require the high temperature calcination needed to produce cement, nor do they require firing in the 1600-2400 °F range for three days using natural gas, as do clay brick equivalents. Instead, CBBs are heated to a modest <600 °F according to the melt flow index of the thermoplastic binder. Existing anthracite mines can be expanded to produce CBBs to reduce aggregate transportation costs and emissions that exist for clay bricks. TEA reflects this reduced energy cost while a comparative CO2 emission analysis quantifies the reduced environmental footprint. The market survey identifies several commercialization opportunities, dependent upon the brick classification.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2025

Restructuring of Benzimidazole-Based Copper Complexes during Electrochemical CO 2 Reduction

Copper-based molecular catalysts have been widely used for the electrochemical reduction of carbon dioxide (ERCO 2 ). However, establishing a correlation between structure and catalytic performance has been challenging due to the dynamic nature of these materials under ERCO 2 working conditions. Here, we report on the restructuring of the copper complexes [Cu(bzimpy)Cl 2 ] and [Cu(pyrben) 2 (NO 3 )]NO 3 during ERCO 2 in an acidic medium, evidencing its effects on the observed activity, selectivity, and stability. In situ X-ray absorption spectroscopy (XAS) suggested that, at sufficiently negative potentials, the Cu 2+ centers of both complexes are reduced to undercoordinated Cu 0 species. Pb underpotential deposition of post-ERCO 2 samples indicated that such Cu 0 species also present a dominant contribution of the (100) domain, which is in line with the high Faradaic efficiency toward C 2 products (∼45%) shown by both complexes at −1.24 V vs RHE. By combining online electrochemical mass spectrometry, in situ XAS, electron paramagnetic resonance (EPR), and quantitative product analysis, we found that [Cu(bzimpy)Cl 2 ] exhibits a partially reversible restructuring, regenerating the main complex moiety, [Cu(bzimpy)] 2+ , and its geometry.

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

Direct, efficient and selective capture of low concentration of CO 2 from natural gas flue gas using a high temperature tubular carbon capture membrane

Natural gas (NG) fired power plants emit low concentration (4–5%) of CO 2 , which presents additional technical and economic challenges to the current benchmark amine absorption technology. The newly emerged high-temperature multiphase membranes operated on molten carbonate (MC) chemistry for CO 2 capture/separation/conversion have been demonstrated with great potential to meet this challenge. In this study, we report on the CO 2 capture performance of such a membrane in tubular geometry from a mockup NG flue gas. The membrane is comprised of a mixture of Gd 0.20 Ce 0.80 O 1.95 (GDC) and MC, in which GDC forms a porous skeleton to contain MC. Here, we show that the membrane with a dimension of 6.1 mm in outer diameter, 5.1 mm in inner diameter and 5 cm in effective length (resulting in 4cm 2 effective surface area) can achieve a CO 2 flux density of 0.46–0.55 mL/min·cm 2 at 650°C, capturing 97% pure CO 2 at a rate of 37–42% from 5%CO 2 –N 2 using moistened Ar as the sweep gas. The level of performance demonstrated by this study suites the membrane well for stationary CO 2 capture from NG power plants.

03 NATURAL GAS↗
DOE OSTI2022

Efficient carbon capture using sub-textured polymer packing surfaces via 3D printing

Gas absorption is a common unit operation whose performance deeply relies on the gas liquid contact behavior. In this work, we report a solid polymeric surface feature containing microscale striation to improve the solid-liquid and gas-liquid contact and facilitate mass transfer. As a proof of concept, the surface feature is adopted for CO 2 capture absorber packing via 3D printing. Besides traditional embossing texture, an additional laminar striation is applied to the packing surface as a sub-texture. The packing shows notable CO 2 mass transfer increase without interfering with other key operating characteristics including pressure drop and liquid holdup. The improvement is based on the synergy of favorable wettability, thin liquid film and increased liquid mixing from rougher surface. In the demonstration test, the packing height could decrease by 33% using the advanced packing with same CO 2 removal, leading to a significant decrease in equipment size and capital expense for commercial CO 2 capture systems.

3D printing↗
DOE OSTI2025

Manufacturing of Continuous Microporous Polymeric Fibers for Separation Applications

Polyolefin plastic waste, particularly polypropylene, is one of the most prevalent components in the plastic waste stream generated globally. However, only a small fraction of this waste is recycled and reintegrated into second applications. These materials have significant embedded energy that could be used for additional productivity if recycled properly. Therefore, there is a critical need to develop scalable processing techniques with high throughput to effectively recycle it. We report the continuous manufacturing of microporous fibers using waste polypropylene plastic and melt-processable lignin, a plant biomass constituent produced as a byproduct in paper mills or biorefineries, as a template to create pores. Further, these filaments with hierarchical porosity─created by controlled microphase separation during high-speed extensional flow followed by removal of lignin─exhibit exceptional capillary action for hydrophobic liquids. The resulting porous fibers can be used for various separation applications. For example, the oil uptake of the fibers is 9.59 ± 0.82 g/g for applications in oil recovery in bodies of water. In addition, polyethylenimine infiltration within these nanoporous fibers introduces cyclic room temperature sorption and thermal desorption potential of acidic gases such as CO 2 in a bench-scale experiment. The fibers exhibit multiple cycles of CO 2 absorption, with a range of 0.15 to 0.17 mmol/g. Thus, these polyethylenimine-infiltered nanoporous polypropylene fibers can also be used in removing acidic gases from a gas mixture.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Understanding the dynamic evolution of atomically dispersed Cu catalyst for CO 2 electrochemical conversion using integrated XANES analysis and mechanistic studies

Direct electrochemical conversion of CO 2 to ethanol (CH 3 CH 2 OH) offers a promising strategy to lower CO 2 emission while storing energy from renewable electricity. Our recent study reported a carbon-supported atomically dispersed Cu catalyst that achieved the highest reported selectivity for CH 3 CH 2 OH formation (91%) at a relatively low potential (-0.6 V), however, the active site structure that is responsible for such high activity and selectivity has yet to be understood. Here, in this paper, we demonstrate a computational investigation combining X-ray absorption near edge structure (XANES) simulations and a mechanistic study via density functional theory (DFT) to understand the catalyst structures of this Cu catalyst during electrocatalysis and the corresponding reaction mechanisms of the key products. An integrated computational and experimental XANES analysis depicted the dynamic evolution of the catalytic site during electrocatalysis. The as-prepared, atomically dispersed Cu catalyst aggregates and forms metallic clusters/nanoparticles under electrochemical condition, which then break down to smaller oxidized clusters after electrocatalysis. The formed Cu clusters/nanoparticles showed distinct catalytic activity and selectivity as a function of particle size based on the mechanistic investigation using DFT, which is consistent with experimental observations for catalyst samples with different Cu loadings. This comprehensive study which combines experimental and computational XANES investigation, mechanistic study via DFT calculations, and experimental performance of the catalysts, provides unprecedented dynamic and mechanistic insights into the supported atomically dispersed metal catalysts for CO 2 reduction. Such strategy and details gained can further guide discovery of novel catalyst materials for CO 2 electrochemical reduction.

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

Bioadaptive Ni single atoms unlock high rate microbial electrosynthesis of isopropanol from CO 2

Hybrid systems that integrate electrochemical CO 2 reduction with microbial upgrading offer a viable route to high value organic compounds from CO 2 at ambient conditions. However, electrocatalyst deactivation in microbial growth media remains a key barrier, limiting efficiency and increasing cost. Here we show that a bioadaptive single-atom nickel catalyst (Ni SAC), coupled with genetically engineered Clostridium ljungdahlii, enables robust electrosynthesis of isopropanol (IPA) from CO 2 via a CO-mediated pathway. Instead of relying on H 2 as an electron carrier, the system applies high-rate CO formation in complex growth media, maintaining a tunable CO Faradaic efficiency up to 92%, which is 9.4 to 52.7 times greater than conventional Ag catalysts. This performance supports stable IPA production at current density of 10.8 A/m 2 and production rate of 161.3 mg/L/day. In situ Raman and X-ray absorption spectroscopy, together with theoretical calculations, indicate that the Ni SAC can resist competing organic adsorption and retain its coordination structure during CO 2 reduction in bioelectrolytes, providing a mechanistic basis for the catalyst stability and integrated process performance.

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

Carbonation reaction of recycled concrete aggregates (RCA): CO 2 mass consumption under various treatment conditions

Concrete is a key building material around the world due to its excellent strength and durability. Recycling demolished concrete for new construction materials may play a significant role in sustainable development. Producing recycled concrete aggregates (RCA) from waste concrete is one approach for such an initiative. However, using RCA may pose challenges, such as reduced density, lower elastic modulus and strength, and increased water absorption. Recently, the carbonation of RCA has emerged as a method to address those concerns. This study explores the carbon sequestration capacity of RCA through carbonation, examining various parametric conditions, including initial CO 2 pressure, relative humidity, temperature, and pre-treatment approach. Both lab-scale and large-scale carbonation tests were conducted. Additionally, a cost analysis and CO 2 footprint assessment were performed. The findings showed that applying higher initial CO 2 pressures (e.g., 40–60 psi) and optimal relative humidity (~55 %) could significantly enhance the carbonation efficiency of RCA. Elevating temperature also led to accelerated CO 2 consumption, being more effective on the lab scale. The economic analysis presented potential cost benefits when substituting natural aggregates with CO 2 -treated RCA. All in all, these results suggest that the carbonation of RCA may provide significant environmental benefits through carbon sequestration, promoting sustainable construction practices.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Plasmonic Hot-Carrier Generation and Catalysis in Ti 3 C 2 O 2 from Real-Time TDDFT Simulations

Photoinduced hot electrons are central to plasmon-driven catalysis. Atomically thin Ti 3 C 2 O 2 , with high carrier density and broad optical absorption, offers a promising platform for plasmon-driven reactions. However, comprehensive investigations of its plasmon resonance, hot-carrier generation, and plasmonic catalytic performance remain limited. In this work, real-time time-dependent density functional theory (rt-TDDFT) was employed to study Ti 3 C 2 O 2 ’s plasmon excitation and hot-carrier generation from nonradiative plasmon damping. The temporal evolution of the dipole moment reveals plasmon resonance in Ti 3 C 2 O 2 , followed by strong plasmon damping that redistributes the stored energy to generate hot carriers. Ti 3 C 2 O 2 with low oxygen vacancy concentration (O v -Ti 3 C 2 O 2 ) exhibits plasmonic behavior resembling the pristine surface, and the plasmon-generated hot electrons can markedly reduce the dissociation barrier of CO 2 at the oxygen vacancy. These findings provide fundamental insights into the plasmonic properties of Ti 3 C 2 O 2 and how they drive its catalytic performance in surface reactions, which is valuable for advancing plasmon-driven catalysis.

CO2 reduction↗