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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

High-performance of CrOx/HZSM-5 catalyst on non-oxidative dehydrogenation of C 2 H 6 to C 2 H 4 : Effect of supporting materials and associated mechanism

Ethane (C 2 H 6 ) is an important inexpensive and widely available fuel resource. High-value use of C 2 H 6 has become increasingly important. Catalytic dehydrogenation of C 2 H 6 to ethylene (C 2 H 4 ) has attracted much attention in recent years due to its high energy efficiency. The direct non-oxidative ethane dehydrogenation (EDH) to ethylene is a promising strategy to produce ethylene and hydrogen at the same time. In this research, Cr/HZSM-5 catalyst with superior stability was synthesized and exhibited an C 2 H 6 converting activity of 1.47 µmol/(g·s) with the corresponding C 2 H 6 conversion and C 2 H 4 selectivity of 37.3% and 90%, respectively. Herein, the synergistic effects of Si and Al in supporting materials were investigated by comparing Cr/HZSM-5 with SBA-15, SiO 2 and Al 2 O 3 supported ones, which contains either Al or Si with different structures. Characterization results indicated that the intimate interactions between Cr and support significantly improved the catalytic performance. The presence of Al in the support promoted the formation of more active Cr 6+ species by forming the aluminum-chromium-chromate (Cr-O-Al) structures which were more efficient to active C-H bond and form (Cr, Al)-OH groups during the reaction. Meanwhile, the formation of internal silanol group with the dissociative adsorbed H* could stabilized the active Cr phase to achieve a stable dehydrogenation activity.

03 NATURAL GAS↗
DOE OSTI2025

A review on advances in oxidative coupling of methane (OCM) for industrial use and prospects of CO 2 –H 2 O splitting integration

The discovery of shale gas reserves has encouraged the development of direct methods for methane conversion into valuable chemicals, offering an alternative to indirect approaches that involve an energy-intensive and intermittent syngas production step, leading to high CO 2 emissions. Amongst the direct methods, the oxidative coupling of methane (OCM) is a potential pathway to reduce CO 2 emissions and can produce commodity chemicals such as ethylene, a chemical regarded as central to the petrochemical industry. Even though OCM has been studied for over four decades, the technology still has not found commercial application. Amongst the challenges regarding industrial deployment of OCM, the most significant one is the requirement of a high ethylene yield of 30 % which is currently reported to be around 20 %. Moreover, the highly exothermic nature of the process and controlling the carbon selectivity over oxides of carbon (COx) is the heart of the problem. Numerous researchers have presented promising results in terms of catalysts, reactor designs and feeding strategies for OCM. However, due to lack of inclusiveness in the results, none of the combination of catalysts, reactors and system optimizations has been able to bring about its industrial viability. The current paper presents an extensive review of the noteworthy attempts to achieve industrial targets for OCM. Moreover, a comprehensive criteria is presented which highlights the desired end state for the industrial deployment of OCM technology. Furthermore, the criteria is based on literature survey and a comparison with industrially deployed ethylene production plants i.e., naphtha or ethane steam cracker plants. Finally, a novel integration technology is presented which includes a combination of OCM and CO 2 -H 2 O splitting in a chemical looping reactor design to enable efficient energy utilization and minimal heat losses to the environment.

CO2 Splitting↗
DOE OSTI2023

Earth Abundant Oxidation Catalysts for Removal of Contaminants of Emerging Concern from Wastewater: Homogeneous Catalytic Screening of Monomeric Complexes

Twenty novel Mn, Fe, and Cu complexes of ethylene cross-bridged tetraazamacrocycles with potentially copolymerizable allyl and benzyl pendant arms were synthesized and characterized. Multiple X-ray crystal structures demonstrate the cis-folded pseudo-octahedral geometry forced by the rigidifying ethylene cross-bridge and show that two cis coordination cites are available for interaction with substrate and oxidant. The Cu complexes were used to determine kinetic stability under harsh acidic and high-temperature conditions, which revealed that the cyclam-based ligands provide superior stabilization with half-lives of many minutes or even hours in 5 M HCl at 50–90 °C. Cyclic voltammetry studies of the Fe and Mn complexes reveal reversible redox processes indicating stabilization of Fe 2+ /Fe 3+ and Mn 2+ /Mn 3+ /Mn 4+ oxidation states, indicating the likelihood of catalytic oxidation for these complexes. Finally, dye-bleaching experiments with methylene blue, methyl orange, and rhodamine B demonstrate efficient catalytic decolorization and allow selection of the most successful monomeric catalysts for copolymerization to produce future heterogeneous water purification materials.

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

Silver(I) Supported Liquid Membranes for Selective Ethylene Recovery from Mixed-Gas Streams of Tandem CO 2 Electrolysis

Large-scale olefin separations from unreacted paraffins and other byproduct gases are primarily done by energy-intensive cryogenic distillation processes at refineries. Silver(I) supported liquid membranes (Ag SLMs) can be implemented at smaller production scales of ethylene (C 2 H 4 ), a critical industrial chemical, such as its electrocatalytic (EC) production from CO 2 . Challenges of EC C 2 H 4 production mainly stem from reducing gases like hydrogen (H 2 ), where the redox reactions pertinent to Ag(I) facilitators diminish olefin transport. Herein we report that aqueous Ag(I) solution in a composite Ag SLM can operate in mixed-gas conditions containing H 2 gas utilizing reduced titania compounds, such as titanium(III) oxide (Ti 2 O 3 ). Embedding Ti 2 O 3 in the polydimethylsiloxane layer of Ag SLM assisted in selectively separating C 2 H 4 from mixed-gas feed streams related to CO 2 electrolysis containing H 2 . The direct exposure of a mixed-gas stream containing C 2 H 4 , CO 2 , CO, N 2 , and CH 4 with as high as 50 vol % H 2 maintained excellent C 2 H 4 separations for 7 days of continuous operation. The Ag SLM provided effective separations of C 2 H 4 from CO (at detection limits), CH 4 (selectivity ratio (α) = 20–30), and H 2 (α = ∼20), but C 2 H 4 from CO 2 (α = 2–4) revealed a slightly lower separation. These data show that aqueous Ag(I) solution(s) used in the SLMs can separate C 2 H 4 for extended periods, even under highly reducing gas conditions. Also, we report C 2 H 4 recovery from the gas mixture produced in the EC CO 2 reduction process. In conclusion, the Ag SLM gave C 2 H 4 selective separation from a five-component complex mixed-gas stream, relevant to tandem CO 2 electrolysis.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2023

Electrosynthesis of ethylene glycol from C 1 feedstocks in a flow electrolyzer

Ethylene glycol is a widely utilized commodity chemical, the production of which accounts for over 46 million tons of CO 2 emission annually. Here we report a paired electrocatalytic approach for ethylene glycol production from methanol. Carbon catalysts are effective in reducing formaldehyde into ethylene glycol with a 92% Faradaic efficiency, whereas Pt catalysts at the anode enable formaldehyde production through methanol partial oxidation with a 75% Faradaic efficiency. With a membrane-electrode assembly configuration, we show the feasibility of ethylene glycol electrosynthesis from methanol in a single electrolyzer. The electrolyzer operates a full cell voltage of 3.2 V at a current density of 100 mA cm -2 , with a 60% reduction in energy consumption. Further investigations, using operando flow electrolyzer mass spectroscopy, isotopic labeling, and density functional theory (DFT) calculations, indicate that the desorption of a *CH 2 OH intermediate is the crucial step in determining the selectively towards ethylene glycol over methanol.

09 BIOMASS FUELS↗
DOE OSTI2021

Effects of CO and H2O Co-Feed on the Adsorption and Oxidation Properties of a Pd/BEA Hydrocarbon Trap

Hydrocarbon traps for exhaust emissions control adsorb hydrocarbons in low temperature exhaust and release them as the exhaust warms up. In this work, a Pd/BEA hydrocarbon trap was tested under lean exhaust conditions using ethylene and dodecane as model hydrocarbons. Ethylene uptake was partially inhibited by CO and H2O when fed separately. When both were added, the loss in ethylene uptake was 90% relative to the condition with no H2O or CO. Dodecane uptake was unchanged under all conditions tested. During a temperature ramp, ethylene desorbed and was combusted to CO2 and H2O over active Pd centers. Further, oxidation light-off of dodecane generated an exotherm which caused rapid desorption of the remaining hydrocarbon species from the zeolite. For both hydrocarbons, CO co-feed led to a decreased oxidation light-off temperature, and therefore lower desorption temperature. By pretreating the catalyst in CO and H2O at 80 °C, and even after removing CO from the feed, the enhanced oxidation light-off behavior was observed. DRIFTS characterization shows that some form of oxidized Pd was reducible to Pd0 by CO at 80 °C only in the presence of H2O. Further, this reduction appears reversible by high temperature oxygen treatment. We speculate that this reduced Pd phase serves as the active site for low temperature hydrocarbon oxidation.

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

Au/Pt Bimetallic Nanowires with Stepped Pt Sites for Enhanced C–C Cleavage in C2+ Alcohol Electro-oxidation Reactions

Efficient C–C bond cleavage and oxidation of alcohols to CO 2 is the key to developing highly efficient alcohol fuel cells for renewable energy applications. In this work, we report the synthesis of core/shell Au/Pt nanowires (NWs) with stepped Pt clusters deposited along the ultrathin (2.3 nm) stepped Au NWs as an active catalyst to effectively oxidize alcohols to CO 2 . The catalytic oxidation reaction is dependent on the Au/Pt ratios, and the Au 1.0 /Pt 0.2 NWs have the largest percentage (~75%) of stepped Au/Pt sites and show the highest activity for ethanol electro-oxidation, reaching an unprecedented 196.9 A/mg Pt (32.5 A/mg Pt+Au ). This NW catalyst is also active in catalyzing the oxidation of other primary alcohols, such as methanol, n-propanol, and ethylene glycol. In situ X-ray absorption spectroscopy and infrared spectroscopy are used to characterize the catalyst structure and to identify key reaction intermediates, providing concrete evidence that the synergy between the low-coordinated Pt sites and the stepped Au NWs is essential to catalyze the alcohol oxidation reaction, which is further supported by DFT calculations that the C–C bond cleavage is indeed enhanced on the undercoordinated Pt–Au surface. Here, our study provides important evidence that a core/shell structure with stepped core/shell sites is essential to enhance electrochemical oxidation of alcohols and will also be central to understanding electro-oxidation reactions and to the future development of highly efficient direct alcohol fuel cells for renewable energy applications.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Rhodium-Catalyzed Oxidative Alkenylation of Anisole: Control of Regioselectivity

We report the conversion of anisole and olefins to alkenyl anisoles via a transition metal-catalyzed arene C–H activation and olefin insertion mechanism. The catalyst precursor, [(η 2 -C 2 H 4 ) 2 Rh(μ-OAc)] 2 , and the in situ oxidant Cu(OPiv) 2 (OPiv = pivalate) convert anisole and olefins (ethylene or propylene) to alkenyl anisoles. When ethylene is used as the olefin, the o/m/p ratio varies between approximately 1:3:1 (selective for 3-methoxystyrene) to 1:5:10 (selective for 4-methoxystyrene). When propylene is the olefin, the o/m/p regioselectivity varies between approximately 1:8:20 to 1:8.5:1. The o/m/p ratios depend on concentration of pivalic acid and olefin. For example, when using ethylene, at relatively high pivalic acid concentrations and low ethylene concentrations, the o/m/p regioselectivity is 1:3:1. Conversely, again for use of ethylene, at relatively low pivalic acid concentrations and high ethylene concentrations, the o/m/p regioselectivity is 1:5:10. Mechanistic studies of the conversion of anisole and olefins to alkenyl anisoles provides evidence that the regioselectivity is likely under Curtin-Hammett conditions.

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

Field Scale Testing of the Thermocatalytic Ethylene Production Process Using Ethane and Actual Coal Fired Flue Gas Co 2

This report provides a summary of the work performed and results obtained from a project supported by the US DOE (DE-FE0031713). In this study, Southern Research (SR) completed field-scale demonstration of a rationally designed novel nano-engineered catalyst driven thermochemical process to produce high yield of ethylene by using CO 2 derived from actual coal-fired flue gas and ethane. This process, referred to here as “CO 2 -ODH” due to CO 2 use via oxidative dehydrogenation (ODH) mechanism, follows a modified pathway to classical steam cracking (SC) process of ethylene production thus paving the way for significantly reduced CO 2 footprint, marginally improved thermodynamics, higher product selectivity and lower reaction temperatures.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2021

A Nitroxide Containing Organic Molecule in a Deep Eutectic Solvent for Flow Battery Applications

The nitroxide radical redox organic molecule, 2-phenyl-4,4,5,5-tetrame- thylimidazoline-1-oxyl-3-oxide (PTIO), was investigated for the first time in a deep eutectic solvent (DES)-like system consisting of a 1:4 molar ratio of choline chloride and ethylene glycol(Ch1EG4) as a redox flow battery electrolyte. PTIO is a single molecule with three oxidation states, and can provide both positive and negative redox couples for a flow battery. A flow battery using the PTIO/Ch1EG4 electrolyte demonstrated nearly 50% roundtrip efficiency with an approximately 1 V open circuit potential. Inefficiencies were primarily due to membrane resistance which can be significantly lowered with increased temperature. While PTIO appears stable over short periods (hours), the oxidized form is not stable in the DES-like electrolyte over longer times. Molecular modeling was performed to investigate the relative stability of PTIO in DES as compared to the previously studied 4-hydroxy-TEMPO (4HT). It was found that the oxoammonium cation 4HT + exhibits a noticeably larger nucleophilic reactive cloud as compared to PTIO + , indicating a higher reactivity. This method to predict stability of the oxoammonium cation shows promise to inform the design and synthesis of promising redox systems based on nitroxide radicals in DES electrolytes to identify new chemistries for large scale energy storage.

25 ENERGY STORAGE↗
DOE OSTI2024

Stabilizing LiCoO 2 at 4.6 V by regulating anti-oxidative solvents

For LiCoO 2 (LCO) operating at high voltages (>4.5 V vs. Li/Li + ), the intensive side reactions between LCO and traditional ethylene carbonate (EC)-based electrolytes with LiPF 6 salts can produce plenty of corrosive species (such as HF and HPO 2 F 2 ), causing severe surface degradation. Herein, anti-oxidative fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC) were selected as co-solvents to reduce the generation of corrosive species. Besides, PF 6 − anions enrich the Helmholtz plane of the LCO/electrolyte interface and promote the formation of a robust cathode/electrolyte interphase (CEI) featuring LiF/Li x PO y F z /Li 3 PO 4 inorganics and P-containing organics under the synergy of fluorinated solvents, which significantly inhibits the catalysis of highly oxidative Co 4+ /O n− (0 < n < 2). Benefiting from the reduced corrosive species and reinforced CEI, the layered structure of the LCO surface is well preserved during long-term cycling, with a highly reversible O3/H1-3 phase transition. Consequently, a LCO||graphite pouch cell exhibits a remarkable capacity retention of 85.7% after 500 cycles in 3.0–4.55 V. Furthermore, this work provides a new insight into developing advanced functional electrolytes for high-voltage lithium-ion batteries.

Co/O loss↗
DOE OSTI2022

An Improved Pathway to Ethylene Glycol via CO 2

This report describes our efforts to develop a partial electrochemical oxidation process to produce formaldehyde selectively from methanol. The effort examined numerous potential anode materials in pursuit of 70% Faradaic efficiency for conversion of methanol to formaldehyde. Among the various electrode materials tested herein both Pt and PtRu were identified as the most promising catalysts in this process as the Faradaic efficiency obtained in these cases are 40% and >70% respectively. Several other 3d transition metals, Pt group metals and their alloys were also studied in which the Faradaic efficiency was obtained within 5-30%. In case of Pt and PtRu bulk metal electrode shows higher selectivity to formaldehyde compared to their nanostructured materials. Based on the literature, nanostructured Pt and PtRu are considered as active catalysts for methanol fuel cells, thus, lower selectivity to formaldehyde with nano Pt and PtRu in our case was attributed to their preferential oxidation of methanol to CO 2 . Severe catalyst deactivation was noted when 0.5 (M) sulfuric acid was used as the electrolyte irrespective of catalyst formulation. On the other hand, much higher activity and selectivity for formaldehyde was noted when alkaline electrolyte was employed during oxidation. Considering selective electrochemical oxidation of methanol to formaldehyde is an area which is underexplored as of today, our findings about catalyst formulation and process condition is noteworthy in this direction. Both bulk metal electrodes of Pt and PtRu may be cost prohibitive and thus present challenges to the scale up this technology. Therefore, we recognize that additional efforts are needed to develop catalysts with high activities and Faradaic efficiencies similar to bulk electrodes for the electrooxidation of methanol to formaldehyde.

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

Catalysis: Volume 36 (Preface)

This volume reviews the extensive literature published in the area of microwave-assisted catalytic approaches for waste conversion, non-reductive CO2 conversion, CO₂ utilization, heterogeneous catalysis and its integration with solid oxide electrolysis cell (SOEC) systems for chemical production, mechanistic pathways in ethylene epoxidation.

CO2 utilization↗
DOE OSTI2020

Critical Hydrogen Coverage Effect on the Hydrogenation of Ethylene Catalyzed by δ-MoC(001): An Ab Initio Thermodynamic and Kinetic Study

Highly selective oxidation of methane to methanol has long been challenging in catalysis. Here, we reveal key steps for the promotion by water when tuning the selectivity of a well-defined CeO 2 /Cu 2 O/Cu(111) catalyst from CO and CO 2 to methanol under a reaction environment with methane, oxygen, and water. Ambient-pressure x-ray photoelectron spectroscopy showed that water added to CH 4 and O 2 led to surface CH 3 O and accelerated methanol production. These results were consistent with density functional theory calculations and kinetic Monte Carlo simulations which showed that water preferentially dissociates over the active Ce ions at the CeO 2 -Cu 2 O/Cu(111) interface. The adsorbed OH blocked O-O bond cleavage that would dehydrogenate CH 3 O to CO and CO 2 , and it directly converted this species to methanol, while O 2 now reoxidized the reduced surface. Water adsorption also displaced the produced methanol into the gas phase.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Silica-copper catalyst interfaces enable carbon-carbon coupling towards ethylene electrosynthesis

Membrane electrode assembly (MEA) electrolyzers offer a means to scale up CO 2 -to-ethylene electroconversion using renewable electricity and close the anthropogenic carbon cycle. To date, excessive CO 2 coverage at the catalyst surface with limited active sites in MEA systems interferes with the carbon-carbon coupling reaction, diminishing ethylene production. With the aid of density functional theory calculations and spectroscopic analysis, here we report an oxide modulation strategy in which we introduce silica on Cu to create active Cu-SiO x interface sites, decreasing the formation energies of OCOH* and OCCOH*—key intermediates along the pathway to ethylene formation. We then synthesize the Cu-SiO x catalysts using one-pot coprecipitation and integrate the catalyst in a MEA electrolyzer. By tuning the CO 2 concentration, the Cu-SiO x catalyst based MEA electrolyzer shows high ethylene Faradaic efficiencies of up to 65% at high ethylene current densities of up to 215 mA cm -2 ; and features sustained operation over 50 h.

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

Supported Organochromium Ethylene Oligomerization Enabled by Surface Lithiation

Here, in this work, supported organochromium ethylene polymerization catalysts have been tuned to mediate ethylene oligomerization via surface lithiation, which provides a generalizable protocol to control stereoelectronics and redox states of surface organometallic active sites. The homoleptic chromium(IV) alkyl complex Cr(CH 2 SiMe 3 ) 4 was grafted on high-surface-area anatase titania (TiO 2 ) nanoparticles as well as on silica to produce Cr/TiO 2 and Cr/SiO 2 , respectively. Treatment of these materials with excess n-butyllithium led to the reduced chromium complexes Cr/Li x TiO 2 and Cr/Li/SiO 2 , each of which still retains one hydrocarbyl ligand on chromium. A set of heterogeneous complexes were studied by electron paramagnetic resonance and X-ray absorption spectroscopy, which indicate a reduction in the oxidation state of the major chromium species to Cr II upon lithiation. Cr/Li x TiO 2 converts ethylene to hexenes with a high selectivity (>80%), which was persistent over 10 days at 80 °C, achieving >950 turnovers. The exclusive formation of C 4 and C 6 olefins, preferring the trimerization product, without a statistical (Flory–Schulz) distribution is characteristic of the oxidative cyclization oligomerization mechanism rather than the traditional Cossee–Arlman mechanism, whereas Cr/Li/SiO 2 produced a mixture of trimerization and polymerization products, suggesting site heterogeneity in the silica-based material. On the other hand, the unreduced chromium(IV) materials as well as low lithium-containing Cr/Li x TiO 2 (x < 0.16) exclusively produced ultrahigh molecular weight polyethylene, determined by differential scanning calorimetry and gel permeation chromatography analysis, likely formed via a linear-insertion mechanism, with a crossover from the polymerization to oligomerization regime observed at ~16% Li intercalation.

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

Understanding and Mitigating the Dissolution and Delamination Issues Encountered with High-Voltage LiNi 0.5 Mn 1.5 O 4

In our initial study on the high-voltage 5 V cobalt-free spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode, we discovered a severe delamination issue in the laminates when cycled at a high upper cut-off voltage (UCV) of 4.95 V, especially when a large cell format was used. This delamination problem prompted us to investigate further by studying the transition metal (TM) dissolution mechanism of cobalt-free LNMO cathodes, and as a comparison, some cobalt-containing lithium nickel manganese cobalt oxides (NMC) cathodes, as the leachates from the soaking experiment might be the culprit for the delamination. Unlike other previous reports, we are interested in the intrinsic stability of the cathode in the presence of a baseline Gen2 electrolyte consisting of 1.2 M of LiPF 6 in ethylene carbonate/ethyl methyl carbonate (EC/EMC), similar to a storage condition. The electrode laminates (transition metal oxides, transition metal oxides, TMOs, coated on an Al current collector with a loading level of around 2.5 mAh/cm 2 ) or the TMO powders (pure commercial quality spinel LNMO, NMC, etc.) were stored in the baseline solution, and the transition metal dissolution was studied through nuclear magnetic resonance, such as 1 H NMR, 19 F NMR, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). Significant electrolyte decomposition was observed and could be the cause that leads to the TM dissolution of LNMO. To address this TM dissolution, additives were introduced into the baseline electrolyte, effectively alleviating the issue of TM dissolution. The results suggest that the observed delamination is caused by electrolyte decompositions that lead to etching, and additives such as lithium difluorooxalato borate and p-toluenesulfonyl isocyanate can alleviate this issue by forming a firm cathode electrolyte interface. This study provides a new perspective on cell degradation induced by electrode/electrolyte interactions under storage conditions.

25 ENERGY STORAGE↗