95 Search Results

Efficient carbon capture and utilization require strategies that minimize energy penalties of CO₂ regeneration and compression. Reactive capture and conversion (RCC) address this challenge by integrating capture with direct electrochemical conversion. Here, we show an NH3-mediated tandem RCC system that couples capture of CO₂ from simulated flue gas (10% v/v CO₂ in N₂) with electroreduction of NH₄HCO₃ to CO over a Ni single-atom catalyst (Ni-SAC). Speciation modeling and capture experiments revealed that a deep CO₂ capture with C/N ratio of 0.65 was achieved using 2.5 M NH₃ from simulated flue gas. Electrolysis of the resulting NH₄HCO₃ on the Ni- SACmore » delivered an 85% CO Faradaic efficiency at 100 mA/cm² with excellent tolerance to NH₃/NH₄⁺ as confirmed by DFT calculations and ab initio molecular dynamics (AIMD) simulations. Further, the technoeconomic analysis established a levelized total cost of CO manufacturing of $25.43/kmol, gauging the practical viability. Overall, this study holds great potential to decarbonize the chemical manufacturing industry while reducing synthetic production costs.« less

A catalyst architecture with mesoporous silica coating Ru nanoparticles on reduced graphene oxide (mSiO2/Ru/rGO) localizes the 2 nm Ru solely at the closed bottoms of 2.9 nm diameter mesopores. mSiO2/Ru/rGO catalyzes the rapid, selective hydrogenolysis of polyolefins at wax formation rates (νwax) up to 1700 gwax·gRu–1·h–1 and a turnover frequency (TOF) for C–C bond cleavage of 130 ± 8 min–1. The νwax and TOF for mSiO2/Ru/rGO are 23× and 16× those of non-porous Ru/rGO, indicating faster chain cleavage is also more selective inside mesopores. The methane yield from mSiO2/Ru/rGO is ca. 30% of the value obtained from Ru/rGO. Methane decreasesmore » and wax selectivity improves with narrow-pore (2.3 nm) mSiO2/Ru/rGO. The reaction rate decreases at lower and higher H2 pressures from its maxi-mum at 37 bars. Log(TOF)-log(PH2) plots reveal rate ∝ [PH2]2.8 or [PH2]–2.1 in the lower and higher pressure ranges, re-spectively. Corresponding plots for Ru/C give rate ∝ [PH2]1 or [PH2]–2.4. Ru is hydrocarbon-covered at low pressure, thus the higher H2 order for mSiO2/Ru/rGO indicates that mesopores increase the density of cleavable unsaturated moieties on the Ru surface. The lower H2 order on Ru/C implies a lower density of cleavable groups because saturated segments occupy a larger fraction of the Ru surface. Higher surface occupancy by the hydrocarbon reactant correlates with more methane formation. Therefore, pore confinement, narrower pore diameter in mSiO2/Ru/rGO, or higher H2 pressure lead to lower methane yields. Ru nanoparticles in mSiO2/Ru/rGO maintain equivalent activity and selectivi-ty over five recycling tests.« less

Metal-free heteroatom-doped carbocatalysts are promising alternatives to precious metals for alkane direct dehydrogenation/hydrogenation and reversible hydrogen storage, yet the nature of their active sites remains poorly understood. This study investigates a nitrogen assembly carbocatalyst (NAC) for efficient and selective hydrocarbon dehydrogenation. For ethylbenzene, NAC maintains a selectivity of >99% towards styrene at a conversion of >20% for 120 hours at a weight hourly space velocity of 0.4 h⁻¹. Theoretical studies suggest that closely spaced graphitic nitrogen sites are the active sites for the chemisorption and dehydrogenation of ethylbenzene, and the robustness of these sites is supported by ambient-pressure X-ray photoelectronmore » spectroscopy. Kinetic analysis reveals a temperature-dependent reaction profile, with distinct activation energies and reaction orders at 300 and 500 °C. Isotope-labeling studies indicate that dehydrogenation primarily proceeds via initial cleavage of the benzylic C–H bond, and the faster desorption of ethylbenzene at higher temperatures contributes to the difference in kinetic behavior. Importantly, the NAC catalyst also enables efficient hydrogenation of styrene back to ethylbenzene at 250 °C, allowing for reversible hydrogen storage using a single catalyst at moderate temperatures. These findings underscore the significance of constructing high densities of closely spaced graphitic nitrogen in carbocatalysts for enhanced activity and selectivity.« less

Supported platinum nanoparticles are known to convert polyolefins to high-quality liquid hydrocarbons with hydrogen under relatively mild conditions. However, no systematic study has been undertaken using bimetallic catalysts for polyethylene upcycling. Specifically, a total of 98 monometallic and bimetallic combinations (Ag, Cr, Co, Cu, Fe, Ga, In, Mn, Ni, Pd, Pt, Rh, Ru, Zr) on alumina were synthesized utilizing surface organometallic chemistry (SOMC) technique via robotic platform. These were investigated at a small scale (10 mg of catalyst and 50 mg of polyethylene) for their activity for the hydrogenolysis of polyethylene in a high-throughput batch reactor. Combinations of Ni andmore » Co were selected as candidates with high activity toward conversion into paraffin oils. Reaction conditions were optimized with Ni/Co/Al₂O₃ catalyst at a larger scale (300 mg catalyst and 3 g polyethylene) to obtain a high yield (93.1%) of paraffin wax with desired properties (M_n = 380 Da) and low polydispersity (Đ = 1.2). Ni/Co/Al₂O₃ was compared against Co/Ni/Al₂O₃ to understand the role of the deposition sequence. When Co is deposited before Ni, a layer of cobalt aluminate is formed upon reduction, stabilizing the deposition of 5 nm metallic Ni particles. When nickel is deposited before Co, particles are larger (average >20 nm) and more oxidized (Ni^δ+ in NiAl₂O₄), decreasing the availability of the catalytically active metallic Ni. In conclusion, the difference in electronic environments was also described by DFT calculations, which revealed that smaller 3D clusters of Ni are preferred on CoAl2O4 over the 3D clusters on NiAl₂O₄ and that these smaller clusters are more reducible, as confirmed experimentally.« less

It was recently reported that boron monoxide (BO) is formed through the cross-linking of B₄O₂ structural building units. Multiple theoretical phases agree with this description. Using pycnometry, multidimensional ¹⁷O NMR spectroscopy, and plane-wave DFT calculations we determined the likely polymorph to be a one-dimensional polymer initially proposed in 1955.

Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a powerful technique for materials characterization, yet its application to air- and moisture-sensitive materials is often hindered by the difficulty in maintaining an inert environment during magic-angle spinning (MAS). This is particularly true for fast-MAS rotors that do not generally provide tight seals. Herein, we present a generalizable approach employing perdeuterated paraffin waxes—n-icosane-d42 and c-dodecane-d24—as protective embedding media to analyze sensitive organometallic catalysts using SSNMR. We demonstrate that these waxes significantly slow oxidative degradation under MAS conditions. Weak background ¹H and ¹³C NMR signals from the waxes are effectively suppressed using double-quantum filtrationmore » and cross-polarization techniques. In conclusion, these findings offer a robust method for expanding the scope of SSNMR to air-sensitive systems, with implications for the structural study of reactive materials and catalysts.« less

Here, the rotation frequencies of amido ligands are highly sensitive to the electronic structure of d⁰ transition metal complexes and have been used to study ligand donor properties. While attempting to study the donor properties of silanolate ligands in a silica-supported Cr complex, we observed highly restricted motions due to the added steric hindrance from the support, with only approximately half of the amides rotating on a 50 ms time scale. Surprisingly, when the same species is grafted into narrow 2.2 nm pores, all amido ligands are able to rotate. Density functional theory calculations suggest that confinement may limit themore » possible coordination sites and the configuration of the formed surface species, potentially enabling the formation of conformationally homogeneous surface site populations.« less

Systems that sequentially capture and upgrade CO₂ from air to fuels/fuel-intermediates, such as syngas and ethylene, rely on an energy-intensive CO₂ release process. Electrified reactive capture systems transform CO₂ obtained directly from carbonate capture liquid into products. Previous reactive capture systems show a decline in Faradaic efficiencies (FE) at current densities above 200 mA/cm². Here we show the chemical origins of this problem, finding that prior electrocatalyst designs failed to arrest, activate, and reduce in situ-generated CO₂ (i-CO₂) before it traversed the catalyst layer and entered the tailgas stream. We develop a templated synthesis to define pore structures and themore » sites of Ni single atoms, and find that carbon-nitrogen-based nanopores are effective in accumulating i-CO₂ via short-range, non-electrostatic interactions between CO₂ molecules and the nanochannel walls. These interactions confine and enrich i-CO₂ within the pores, enhancing its binding and activation. We report as a result carbonate electrolysis at 300 mA/cm² with FE to CO of 50% ± 3%, and with <1% CO₂ in the tailgas outlet stream. This corresponds to a projected energy efficiency (EE) to 2:1 syngas of 46% at 300 mA/cm² when H₂ is added using a water electrolyzer.« less

Characterization of metal centers in metal–organic frameworks (MOFs) is critical for rational design and further understanding of structure–property relationships. The short-range structure about Zr atoms is challenging to properly elucidate in many Zr MOFs, particularly when local disorder is present. Static ⁹¹Zr solid-state NMR spectra of the seven zirconium MOFs UiO-66, UiO-66-NH₂, UiO-67, MOF-801, MOF-808, DUT-68 and DUT-69 have been acquired at high magnetic fields of 35.2 T and 19.6 T, yielding valuable information on the local structure, site symmetry and order about Zr. ⁹¹Zr NMR is very sensitive to differences in MOF short-range structure caused by guest molecules, linkermore » substitution and post-synthetic treatment. Complementary density functional theory (DFT) calculations assist in the interpretation and assignment of ⁹¹Zr solid-state NMR spectra, lend insight into structural origins of ⁹¹Zr NMR parameters and enable determination of local Zr coordination environments. This approach can be extended to many other materials containing zirconium.« less

Carbon reactive capture and conversion offers a sustainable route to valuable chemicals and fuels while aiding Green House Gas (GHG) reduction. Direct electrochemical conversion of capture solutions like bicarbonate avoids the energy demands of conventional CO₂ regeneration. Ammonium bicarbonate (NH₄HCO₃) is particularly attractive due to its low decomposition temperature and ability to supply in situ CO₂ from dilute sources without requiring purified CO₂. Meanwhile, single-atom catalysts (SACs) with nitrogen-coordinated metal sites further enhance CO₂ reduction efficiency using Earth-abundant materials. In this study, we demonstrate a nickel single-atom catalyst (Ni-SAC)-based electrolyzer that utilizes NH₄HCO₃ as the CO₂ source, achieving significantly improvedmore » CO production performance compared to the conventional silver cathodes used in the CO₂ reduction reaction (CO₂RR) to produce CO. The Ni-SAC cathode exhibited a Faradaic efficiency of 60.1% for CO production at −200 mA cm⁻², while the silver cathode achieved a Faradaic efficiency of only 2%, likely due to ammonium-induced poisoning. Furthermore, the integration of a customized microporous layer onto the electrode significantly increased the Faradaic efficiency from 64% to 83% at −100 mA cm⁻², emphasizing the crucial role of electrode structure optimization in enhancing CO selectivity. These findings demonstrate a sustainable and economically viable strategy for green CO production directly from CO₂ capture solutions.« less