337 Search Results

Experiments of in-situ DRIFTS combined with modulation excitation (ME) spectroscopy showed a rich surface chemistry associated with the adsorption of CO₂ on nanocubes and nanospheres of ceria. The nanocubes exposed faces with a (100) orientation, with the edges and corners displaying (110) and (111) orientations, respectively. Here, the nanospheres mainly contained ceria (111) and (110) planes. DFT calculations showed that CO₂ is a multidentate adsorbate on ceria that can undergo changes in its bonding configuration depending on the chemical environment. At 250 °C, a temperature typically used for the conversion of CO₂ into oxygenates, alkanes and olefins, CO₂ reacted withmore » O centers or OH groups present on the nanocubes and nanospheres to yield bi- and tri-dentate carbonates, hydroxycarbonates, and formates. Both nanostructures were highly reactive and a dynamic equilibrium was established: carbonate species were rapidly generated upon the injection of CO₂ and they decomposed upon the removal of CO₂ from the gas phase. In the case of the ceria nanocubes, the adsorption/desorption processes were essentially reversible, opening the door to catalytic transformations. A larger concentration of defects in the ceria nanospheres led to strongly bound carbonates and formates that may be spectators, site blockers, or surface modifiers in catalytic processes. In the ME studies, additional intermediates were detected, and it was clear that the response of surface species to the presence/absence of CO₂ was highly dependent on the morphology of the ceria nanostructures.« less

Geological carbon storage (GCS) is recognized as a critical technology for achieving large-scale reductions in anthropogenic carbon dioxide (CO₂) emissions. Ensuring long-term containment and safety requires robust risk assessment frameworks that account for geological uncertainty and identify potential failure scenarios. Among various indicators, the area of review (AoR) serves as a key metric for evaluating storage performance, regulatory compliance, and monitoring design, as it delineates the spatial extent impacted by pressure buildup and plume migration. However, conventional AoR-based risk assessments typically perturb parameters within narrow uncertainty bounds, potentially overlooking rare but high-impact events arising from extreme geological conditions. In thismore » study, we present a failure analysis–informed risk assessment framework for large-scale GCS projects to improve site prescreening and monitoring design. A suite of 300 numerical simulations was generated using stochastic geological models that vary five key parameters: net-to-gross ratio, anisotropy azimuth, porosity multiplier, permeability multiplier, and vertical-to-horizontal permeability ratio. Among these, 200 realizations represent normal geological uncertainty, while 100 additional cases explore extreme yet plausible conditions for failure-case analysis. The AoR was simulated and computed from pressure and CO₂ saturation fields, where the baseline AoR boundary, representing the extent predicted under typical geological uncertainty, was defined as the union of 200 normal-range simulations, and failure was identified when extreme-range cases exceeded this baseline. Results show that incorporating broader parameter uncertainty produces significantly larger AoR extents, underscoring the potential underestimation of risk under conventional uncertainty ranges. Furthermore, spatial probability maps derived from failure-induced AoR exceedance identify regions requiring enhanced monitoring attention. Various machine learning (ML)–based classifiers were developed to predict failure occurrence from geological parameters, with the random forest model achieving the highest performance (F1-score of 0.986). Consistent findings from correlation coefficient, feature importance, and Sobol sensitivity analyses reveal that low net-to-gross ratios and permeability multipliers are the dominant risk drivers, reflecting reduced reservoir connectivity and limited pressure dissipation. Altogether, these results provide a novel framework for risk-informed site prescreening and monitoring design that explicitly considers rare but high-impact geological scenarios in GCS projects.« less

Liquid organic hydrogen carriers (LOHCs) are an attractive fuel source due to their compatibility with existing transportation methods and ease of use. However, they suffer from sluggish (de)hydrogenation kinetics. One promising platform for developing next-generation catalysts is metal–organic frameworks (MOFs), which can enable systematic interrogation into the influence of metal identity and spatial arrangement. In this study, the effect of the coordination environment was investigated using Ni- and Co-based azolate MOFs: MFU-4l-OH (M_xZn_5–x(OH)₄(BTDD)₃; x = 4 for M = Co and x = 3 for M = Ni, H₂BTDD = bis(1H-1,2,3-triazolo[4,5-b][4′,5′-i])dibenzo[1,4]dioxin), composed of single-site nodes, and M(OH)₂BBTA (M = Ni,more » Co; H₂BBTA = 1H,5H-benzo(1,2-d:4,5-d’)bistriazole), composed of extended chain-type nodes. The catalysts were characterized by isotherms, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS) analysis. Acetylene hydrogenation activity under steady state conditions (150 °C, 1:1 C₂H₂:H₂) revealed higher turnover frequencies (TOFs) up 1.17 × 10^–2 mol C₂H₂ mol⁻¹ Ni min⁻¹ and 1.98 × 10^–3 mol C₂H₂ mol⁻¹ Co min⁻¹ for Ni-MFU-4l-OH and Co-MFU-4l-OH, respectively, compared to their BBTA analogues. However, the Co-based MOFs, particularly Co₂(OH)₂-BBTA, exhibited greater selectivity (up to 19%) for the fully hydrogenated ethane product. Isosteric heat of adsorption (Q_st) measurements for ethylene and ethane revealed that the BBTA framework had stronger binding to the products than MFU-4l. Furthermore, these findings demonstrate that metal identity and coordination environment may modulate acetylene hydrogenation performance, leading to design principles for tuning LOHC hydrogenation catalysts.« less

Insertion reactions play a central role in the catalytic synthesis of ethanol and higher alcohols. X-ray photoelectron and absorption spectroscopies have been used to follow migratory CO insertion and C─C coupling in a cis-[Ru(2,2′-bipyridine)₂(CO)(CH₃)]⁺ complex heated in a vacuum or exposed to CO. Heating of the Ru complex in a vacuum to temperatures above 50 °C induced spontaneous migration of CO into the Ru─CH₃ bond to yield a ─COCH₃ ligand. In conclusion, after adding CO to the background gas, the CO insertion reaction was seen at room temperature, opening the door for the synthesis of ethanol and more energy densemore » liquids.« less

The conversion of CO₂ into value-added chemicals, such as methanol, offers a promising pathway toward a renewable energy future. However, a precise kinetic control and a highly selective catalyst are necessary to overcome the thermodynamic preference for CO₂ hydrogenation to methane. Rhenium-based catalysts, particularly Re/TiO₂, demonstrate high activity and selectivity for methanol under high-pressure conditions. For example, at 100 bar and 200 °C, a methanol selectivity of 97−99% was obtained. Catalysts with 1 wt % Re and 5 wt % Re/ TiO₂ were used to study the effect of cluster sizes. At 250 °C, the 1 wt % catalyst achievesmore » 97% selectivity at 23% conversion, whereas 5 wt % Re/TiO₂ achieves 74% selectivity at 40% conversion, corresponding to a drop in space-time yield from 65 to 16 g_CH3OH·g_Re⁻¹·h⁻¹, respectively. X-ray absorption spectroscopy provided insights into the structure of the active sites, while density functional theory calculations revealed the effects of cluster size on the energy barriers for H₂ activation, CH₃OH dissociation, and CH₃OH desorption, all of which directly influence conversion and selectivity. These results underscore the importance of balancing cluster size for optimal catalyst performance and provide insights into the design of efficient and selective catalysts for renewable methanol production.« less

Atomically dispersed catalysts have drawn great interest lately, as they showcase a high density of active sites, selectivity, and high turnover frequencies in oxidation chemistry due to labile oxygen activation. In contrast, the applications of these catalysts have lagged in reduction reactions due to the ambiguity caused by the sintering and restructuring of active sites. To bridge this gap, the evolution of Pt⁴⁺ isomorphically substituted into an octahedral molecular sieve structure (OMS-2) under reductive conditions was correlatively characterized using multiple in-situ analytical techniques such as ambient pressure X-ray photoelectron spectroscopy, environmental transmission electron microscopy, and solid-state nuclear magnetic resonance. Themore » surface dynamics of the Pt single atoms were revealed during the Reverse Water Gas Shift (RWGS) reaction, where the active sites were identified as two-coordinated platinum single atoms. Under reaction, we show nonbinding atoms adjacent to the single atoms restructured the motif of the single atoms to Pt²⁺ via ion mobility of potassium, increasing the activation energy by 25.6 kJ/mol. Here, this work also highlights the potential for increased stability of the single atom sites via isomorphic substitution of the metal oxide support, since the Pt-OMS-2 catalyst retained activity for about 33 h before deactivation, after which nanoparticles were observed in TEM images. This work offers a new perspective in single atom synthesis using the metal oxide as the host for the single atom site, instead of adatoms on the surface« less

Electrochemical CO₂ reduction is a promising conversion process for producing value-added fuels and chemicals from electricity and CO₂ as a sustainable carbon feedstock to domestically produce fuels and chemicals from industrial waste. Having reached industrially viable performance metrics with small-scale CO₂ electrolysis cells, the field must now increasingly focus on extending the device durability of large stacks to achieve equivalent metrics for 35,000+ hours to decrease maintenance and capital costs. Reported device lifetimes have increased in recent years, with the longest stability studies for CO, ethylene, and formic acid production being published in 2024–2025 with operation times of 4500, 1000,more » and 5200 h, respectively. Unfortunately, significant extension of the device durability is still required. Here, we provide an overview of ion-exchange membranes (IEMs) and provide insight into the variety of degradation mechanisms that must be overcome to enable the community to meet durability targets. In an effort to accelerate the extension of device lifetimes, we propose a general approach for characterizing CO₂ electrolysis cell degradation before and after durability testing to better elucidate the mechanisms and failure modes of IEMs in zero-gap cells. Furthermore, we encourage the adoption of operando characterizations in tandem with accelerated stress and durability tests, postulating that their combined applications will be increasingly valuable. We hope that this perspective motivates future durability studies to evaluate degradation across the entire electrolysis cell.« less

Our group recently developed dual-function materials (DFMs) and reactive carbon capture (RCC) processes for the selective production of methanol (MeOH) or CO, offering two novel and unique pathways for MeOH production. This study conducted a comparative techno-economic analysis (TEA) of the two RCC pathways from exhaust CO₂: 1) a “Direct RCC-to-MeOH” pathway and 2) an “Indirect RCC-to-CO” pathway followed by MeOH synthesis. The “Direct RCC-to-MeOH” pathway produced a lower levelized cost of MeOH (LCOM) at $$\$$$$0.78/kg, compared to $$\$$$$0.84/kg for the “Indirect RCC-to-CO” pathway. The key difference is the need to recompress the syngas from RCC before MeOH synthesis inmore » “Indirect RCC-to-CO.” Nonetheless, with reduced catalyst costs and hydrogen requirements for “RCC-to-CO,” this pathway merits further study to produce syngas rather than MeOH. Both pathways are comparable in LCOM to baseline e-MeOH production from CO₂ hydrogenation ($$\$$$$0.72/kg) while having lower carbon intensities (0.45 and 0.51 kg-CO₂e/kg vs 0.54 kg-CO₂e/kg).« less

Gas fermentation enables the production of fuels, chemicals, and foods from gaseous carbon sources and could serve as a technology for valorizing carbon that may otherwise be emitted to the atmosphere. In this review, we focus on upstream feedstock considerations: the supply of carbon and the supply of electrical power. Electrical power serves a dual role, providing both process energy and biochemical redox potential (via hydrogen or reduced intermediates). We define gas fermentation as bioprocesses involving gaseous feedstocks metabolized by microbes, distinct from microbial electrosynthesis. Trends in CO₂ point sources and low-carbon electricity systems are analyzed, highlighting opportunities and challengesmore » for future deployment. This review synthesizes current knowledge and identifies key R&D priorities for process integration at industrial scale.« less

This study presents numerical investigations of the trapping characteristics of fold-and-thrust belt structures, defining three carbon capture and storage (CCS) play types that could be used to store commercial volumes (millions of tonnes) of CO₂. Specifically, we present simulations of CO₂ storage in three fold-and-thrust belt models comprising a thrust-ramp, duplex, and thrust-fold geometry. To constrain these play types in realistic geology, each model is based on a study site, including a novel investigation of a greenfield saline reservoir in Virginia, USA, being considered for commercial carbon storage and two well-characterized petroleum fields: the Wilburton field in Oklahoma, USA, andmore » the Incahuasi field in Bolivia. Our results provide insight into several key parameters, such as the long-term security of injected CO₂ in these geologies and injection strategies for maximizing storage efficiency while reducing pressure-related risk. These results improve the understanding of CCS in fold-and-thrust belt storage sites globally by describing general storage parameters that may be applied to site-specific projects. We find that thrust-ramp geometries may securely trap CO₂ through solubility and hydrodynamic trapping under suitable reservoir conditions, duplex structures may store some quantities of CO₂ but are pressure-constrained, and that thrust-ramp structures may store large quantities of CO₂ by maximizing fetch volume, which simultaneously lowers geomechanical risk by reducing pressure buildup along zones of weakness.« less