52 Search Results

Direct reduced iron (DRI) is an increasingly important feedstock for modern steelmaking. Fundamental research into DRI properties is limited by the discrepancy between the behavior of industrially produced pellets and laboratory‐produced pellets, leading to nongeneralizable conclusions from laboratory work. Here, in this study, a detailed nano‐computed tomographic characterization of ore pellets, hydrogen DRI reduced in a pilot‐scale shaft furnace, and laboratory‐reduced DRI is presented to better understand the microstructurally influenced property differences between the two. The shaft‐furnace‐reduced pellets show lower overall porosity but larger average pore volume thickness and solid volume thickness than the laboratory‐reduced pellets. This effect is attributedmore » to increased sintering behavior in the shaft furnace case. All pellet types show almost entirely connected pore volumes. The tortuosity of the pores is shown to increase with a degree of reduction, though the shaft furnace pellets show lower tortuosity than the laboratory‐reduced pellets. Again, this difference is attributed to the larger pore volume thickness for shaft‐furnace‐reduced pellets.« less

Although it has been established that covalent functionalization of the U–O bonds in the uranyl dication (UO₂²⁺) generally requires use of strong reductants and electrophiles, little work has examined how interactions between the individual reaction components could affect final outcomes in solution. Here, the patterns of such reactivity have been studied in a UO₂²⁺-containing model system supported by a workhorse pentadentate ligand, 2,2′-[(methylimino)bis(2,1-ethanediylnitrilomethylidyne)]bis-phenol. Oxo activation and functionalization have been tested with (i) electrochemical and chemical reduction, and (ii) coordinating and noncoordinating solvents. In acetonitrile, uranyl reduction was achieved cleanly, but treatment of the reduced species with tris(pentafluorophenyl)borane (BCF) resulted inmore » a mixture of products arising from direct electron transfer to BCF. In dichloromethane (CH₂Cl₂), electrochemical reduction of uranyl was achieved cleanly, but clean chemical reactivity was inaccessible. Despite these challenges, one trinuclear and oxo-deficient uranium-containing product was crystallized from CH₂Cl₂ solution and characterized; thus, desirable electrophilic reactivity can proceed to some degree in CH₂Cl₂ with BCF. Computational studies were used to investigate the properties of the trinuclear uranium product and the changes that could be inducible by further reduction. Here, taken together, the reactivity patterns identified here could inform design of improved systems for actinyl oxo functionalization.« less

The reduction of Hg^II to Hg^I or Hg⁰ can lead to significant changes in Hg toxicity and mobility in the environment. Photochemical reduction is the primary process for the reduction of Hg^II to Hg⁰ in sunlit environments; however, dark reduction of HgII can occur via microbial metabolic processes and/or reduction by reduced natural organic matter, Fe^II mineral phases, Fe^II sorbed to minerals, or aqueous Fe^II. Here, in this study, we demonstrate a novel Hg^II reduction pathway involving another environmentally relevant reductant, Mn^II. Abiotic reduction of Hg^IIO by Mn^II was studied as a function of pH and anion environment (perchlorate, sulfate,more » chloride) using X-ray absorption spectroscopy to characterize the solid-phase Hg and Mn species. At circumneutral pH of 7.5, about 70% of Hg^II was reduced to elemental Hg⁰ within 2 h. In contrast, 12 h were needed to achieve the same extent of reduction at pH 6.9. In the presence of sulfate and chloride, Hg^I species were formed. Hg^II reduction was initially rapid and coupled with the oxidation of soluble Mn^II-oxides to insoluble Mn^IV-oxides, followed by a significantly slower reduction of Hg^II during the Mn^II-catalyzed transformation of the Mn^IV-oxides to hydroxide and oxyhydroxide minerals. The observed reduction of Hg^II by Mn^II at circumneutral pH could be an important transformation pathway for environmental Hg, affecting its bioavailability and mobility under mildly reducing conditions.« less

2,2’-Bis(4-dimethylaminophenyl)- and 2,2'-dicyclohexyl-1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[ d ]imidazole ((N-DMBI) ₂ and (Cyc-DMBI) ₂ ) are quite strong reductants with effective potentials of ca. −2 V vs ferrocenium/ferrocene, yet are relatively stable to air due to the coupling of redox and bond-breaking processes. Here, we examine their use in accomplishing electron transfer-induced bond-cleavage reactions, specifically dehalogenations. The dimers reduce halides that have reduction potentials less cathodic than ca. −2 V vs ferrocenium/ferrocene, especially under UV photoexcitation (using a 365 nm LED). In the case of benzyl halides, the products are bibenzyl derivatives, whereas aryl halides are reduced to the corresponding arenes. The potentials ofmore » the halides that can be reduced in this way, quantum-chemical calculations, and steady-state and transient absorption spectroscopy suggest that UV irradiation accelerates the reactions via cleavage of the dimers to the corresponding radical monomers.« less

1,3-Dimethyl-2,3-dihydrobenzo[ d ]imidazoles, 1H , and 1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[ d ]imidazoles, 1 ₂ , are of interest as n-dopants for organic electron-transport materials. Salts of 2-(4-(dimethylamino)phenyl)-4,7-dimethoxy-, 2-cyclohexyl-4,7-dimethoxy-, and 2-(5-(dimethylamino)thiophen-2-yl)benzo[ d ]imidazolium ( 1g–i ⁺ , respectively) have been synthesized and reduced with NaBH ₄ to 1gH , 1hH , and 1iH , and with Na:Hg to 1g ₂ and 1h ₂ . Their electrochemistry and reactivity were compared to those derived from 2-(4-(dimethylamino)phenyl)- ( 1b ⁺ ) and 2-cyclohexylbenzo[ d ]imidazolium ( 1e ⁺ ) salts. E ( 1 ⁺ / 1 ^• ) values for 2-aryl species are less reducing thanmore » for 2-alkyl analogues, i.e., the radicals are stabilized more by aryl groups than the cations, while 4,7-dimethoxy substitution leads to more reducing E ( 1 ⁺ / 1 ^• ) values, as well as cathodic shifts in E ( 1 ₂ ^•+ / 1 ₂ ) and E ( 1H ^•+ / 1H ) values. Both the use of 3,4-dimethoxy and 2-aryl substituents accelerates the reaction of the 1H species with PC ₆₁ BM. Because 2-aryl groups stabilize radicals, 1b ₂ and 1g ₂ exhibit weaker bonds than 1e ₂ and 1h ₂ and thus react with 6,13-bis(triisopropylsilylethynyl)pentacene ( VII ) via a “cleavage-first” pathway, while 1e ₂ and 1h ₂ react only via “electron-transfer-first”. 1h ₂ exhibits the most cathodic E ( 1 ₂ ^•+ / 1 ₂ ) value of the dimers considered here and, therefore, reacts more rapidly than any of the other dimers with VII via “electron-transfer-first”. Crystal structures show rather long central C–C bonds for 1b ₂ (1.5899(11) and 1.6194(8) Å) and 1h ₂ (1.6299(13) Å).« less

Technetium-99 is a prevalent fission product from nuclear waste. The long half-life (211,000 yr) and environmental mobility of pertechnetate (TcO₄^-) render Tc particularly challenging to isolate and stabilize. Here, in this study, we present two approaches for development of potential wasteforms using titanium dioxide, TiO₂. Approach 1 is a low temperature chemical synthesis of TiO₂ doped with Tc(IV) from TcO₄^- intended to mimic the Tc waste stream from the UREX family of separations and removes 98.5 % of the Tc, mainly present as edge-shared Tc(IV) pairs. Approach 2 utilizes TiO₂ to photocatalytically reduce TcO₄^- to Tc(IV) stabilized on the surfacemore » of or within the TiO₂ lattice. The %Tc removed from solution and adsorbed to TiO₂ is pH dependent, with the maximum Tc(IV) adsorbed at pH 3–4 as either TcO₂ or edge-sharing Tc(IV) octahedra. The Tc(IV)-TiO₂ composites materials formed by both approaches are suitable for consolidation into a dense wasteform by Hot Isostatic Pressing (HIPing).« less

The exponential increase in data produced over the last two decades has revolutionized the way we collect, store, process, analyze, model, and interpret information to improve profitability. Manufacturing is no exception. How- ever, Smart Manufacturing, the digital practice, organization, workforce, and infrastructure transformation for collection and deployment of data and models at scale and at all levels of manufacturing, is a complex, costly, and labor-intensive journey that is still seeing slow adoption. The Clean Energy Smart Manufacturing Innovation Institute (CESMII), a national Manufacturing USA public-private partnership sponsored by the Department of Energy, is addressing this scaled use of data andmore » modeling in manufacturing. CESMII has focused on how to col- lect and use operating data for numerous applications that improve productivity, precision, and performance of manufacturing operations from factory floor to supply chain using process simulation, predictive analytics, mon- itoring and control, and real-time optimization. Because contextualized data are key, CESMII has developed the Smart Manufacturing Innovation Platform (SMIP) to lower the barriers to the data that are needed to accelerate data-based model building, improve data visualization, and more quickly gain insights. Reusable, standards-based ways of doing data collection, ingestion, and contextualization are particularly important for scaling access and use of data. The SMIP uses a standards-based definition and construct for reusable information models called an SM Profile. When an SM Profile is used in conjunction with the SMIP, the SMIP ensures the availability of contextualized, operational data for model building. The present work demonstrates Smart Manufacturing and the application of the SMIP for building several data-centered models for the operation and control of an ex- perimental electrochemical reactor that reduces carbon dioxide (CO₂) gas to valuable liquid and gas chemicals, such as alcohols, olefins, and syngas. We describe how the SMIP plays a central role in more effective model building and we demonstrate how the electochemical reactor can be controlled and optimized for the desired products. Use of the SMIP involves the transmission of real-time sensor measurements to a cloud resource so that the operating data are available to all model building experts. The data collection and transmission process is fully automated to greatly reduce the need for manual manipulation of the data. Data-driven machine learning models are used for advanced real-time state estimation, real-time optimization, and model-based feedback control for the reactor. The application models are implemented as a system to monitor the data flow and control the electrochemical reactor with a single visualization interface. SM Profiles are used to demonstrate reusability of the information models for the reactor and the instrumentation. The application packages, algorithms, and user interfaces developed are cast as Docker images in a library to facilitate reusability of the application models.« less

Here the impacts of feed modulation (frequency, amplitude) and catalyst design (composition and architecture) parameters are reported for the conversion of methane and NO_x over a dual-layer Pt+Pd/Al₂O₃ + Mn_0.5Fe_2.5O₄/Al₂O₃ monolith. CH₄ and NO_x conversion data show that the dual-layer catalyst outperforms single-layer samples having the same catalyst loadings, with and without spinel. Close proximity of the PGM and MFO functions in the mixed-layer catalyst lowers the CH₄ conversion at high temperature while separating the PGM and spinel layers with an intermediate Al₂O₃ layer does not. Methane conversion enhancement is linked to its nonmonotonic dependence on O₂. The performance gainsmore » are tied to a transient activity spike that occurs during the lean-to-rich feed transition when water is present in the feed. The transient spike is attributed to the removal of CO and H₂ products via reactions with stored O₂ in the spinel, eliminating inhibition of methane steam reforming.« less

Biochars can remove potentially toxic elements, such as inorganic mercury [Hg(II)] from contaminated waters. However, their performance in complex water matrices is rarely investigated, and the combined roles of natural organic matter (NOM) and ionic composition in the removal of Hg(II) by biochar remain unclear. Here, we investigate the influence of NOM and major ions such as chloride (Cl^–), nitrate (NO₃^–), calcium (Ca²⁺), and sodium (Na⁺) on Hg(II) removal by a wood-based biochar (SWP700). Multiple sorption sites containing sulfur (S) were located within the porous SWP700. In the absence of NOM, Hg(II) removal was driven by these sites. Ca²⁺ bridgingmore » was important in enhancing removal of negatively charged Hg(II)-chloro complexes. In the presence of NOM, formation of soluble Hg-NOM complexes (as seen from speciation calculations), which have limited access to biochar pores, suppressed Hg(II) removal, but Cl^– and Ca²⁺ could still facilitate it. The ability of Ca²⁺ to aggregate NOM, including Hg-NOM complexes, promoted Hg(II) removal from the dissolved fraction (<0.45 μm). Hg(II) removal in the presence of Cl^– followed a stepwise mechanism. Weakly bound oxygen functional groups in NOM were outcompeted by Cl^–, forming smaller-sized Hg(II)-chloro complexes, which could access additional intraparticle sorption sites. Therein, Cl^– was outcompeted by S, which finally immobilized Hg(II) in SWP700 as confirmed by extended X-ray absorption fine structure spectroscopy. We conclude that in NOM containing oxic waters, with relatively high molar ratios of Cl^–: NOM and Ca²⁺: NOM, Hg(II) removal can still be effective with SWP700.« less