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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Catalyst Deactivation Modes of PdO/γ-Al 2 O 3 Catalysts for Lean Methane Oxidation

PdO/γ-Al 2 O 3 catalysts are one of the most active catalytic components for the complete oxidation of methane. Under reaction conditions, especially in a wet feed, the catalysts suffer severe performance degradation. This study establishes a series of testing protocols to systematically investigate the causes of catalyst deactivation under methane oxidation reaction conditions. Four distinct catalyst deactivation modes are identified. Two of the deactivation modes are directly related to H 2 O, either from the feed gas or as a part of the reaction products, with one (Mode 2) being attributed to the formation of surface hydroxyl groups and the other (Mode 3) to the competitive adsorption of H 2 O on the catalysts. The impact of the two deactivation modes is acute and severe but reversible. In contrast, the other two deactivation modes are gradual and persistent but irreversible. Both modes are induced by CH 4 oxidation reaction, with the impact of a wet feed (Mode 4) being substantially more severe than that of a dry feed (Mode 1). The major cause of the irreversible catalyst deactivation is attributed to surface reconstruction of PdO nanoparticles, which behaves as a passivation layer lowering the number of coordinately unsaturated Pd sites for CH 4 activation. Although the passivation layer is relatively stable against thermal or hydrothermal treatment, it is not completely inert. Formation and partial regeneration of the passivation layer is a highly dynamic process and heavily depends on the reaction temperature: a lower reaction temperature (≤ 450 ℃) can lead to quicker catalyst deactivation; but a higher reaction temperature (between 500 – 550 ℃) can result in a greater extent of catalyst deactivation.

PdO/γ-Al2O3↗
DOE OSTI2021

Catalytic decomposition of methane into hydrogen and high-value carbons: combined experimental and DFT computational study

Thermocatalytic decomposition (TCD) of methane can produce hydrogen and valuable nanocarbon co-products with low to near-zero CO2 emission. In this study, a series of Pd promoted Ni catalysts, prepared with various Ni/Pd ratios on a CNT support, were evaluated for methane TCD performance. Characterization and calculations using density functional theory (DFT) were carried out to elucidate the activity–structure relationship and growth mechanism of carbon nanomaterials. It was found that the methane conversion and stability of the catalysts were highly dependent on the Ni/Pd ratio and reaction temperature. DFT calculations revealed that the diffusion of carbon in the metal sublayer required for CNT growth was more favorable in the Ni–Pd alloy lattice suggesting that the buildup of carbon in the metal alloy sublayer facilitated the formation of CNTs and CNFs. A cyclic reaction–regeneration process for self-sustained TCD was experimentally demonstrated. In each cycle, a portion of the separated CNT product was used to re-synthesize the Ni–Pd/CNT catalyst for use in the next reaction cycle. After five cycles of operation, the CH4 conversion, morphology and crystallinity of the carbon product remained unchanged.

Wang, I-Wen↗
DOE OSTI2021

Oxygen Electrocatalysis on Mixed-Metal Oxides/Oxyhydroxides: From Fundamentals to Membrane Electrolyzer Technology

Catalyzing the oxygen evolution reaction (OER) is important for key energy-storage technologies, particularly water electrolysis and photoelectrolysis for hydrogen fuel production. Under neutral-to-alkaline conditions, first-row transition-metal oxides/(oxy)hydroxides are the fastest-known OER catalysts and have been the subject of intense study for the past decade. Critical to their high performance is the intentional or accidental addition of Fe to Ni/Co oxides that convert to layered (oxy)hydroxide structures during the OER. Unraveling the role that Fe plays in the catalysis and the molecular identity of the true “active site” has proved challenging, however, due to the dynamics of the host structure and absorbed Fe sites as well as the diversity of local structures in these disordered active phases. In this Account, we highlight our work to understand the role of Fe in Ni/Co (oxy)hydroxide OER catalysts. We first discuss how we characterize the intrinsic activity of the first-row transition-metal (oxy)hydroxide catalysts as thin films by accounting for the contributions of the catalyst-layer thickness (mass loading) and electrical conductivity as well as the underlying substrate’s chemical interactions with the catalyst and the presence of Fe species in the electrolyte. We show how Fe-doped Ni/Co (oxy)hydroxides restructure during catalysis, absorb/desorb Fe, and in some cases degrade or regenerate their activity during electrochemical testing. We highlight the relevant techniques and procedures that allowed us to better understand the role of Fe in activating other first-row transition metals for OER. We find several modes of Fe incorporation in Ni/Co (oxy)hydroxides and show how those modes correlate with activity and durability. We also discuss how this understanding informs the incorporation of earth-abundant transition-metal OER catalysts in anion-exchange-membrane water electrolyzers (AEMWE) that provide a locally basic anode environment but run on pure water and have advantages over the more-developed proton-exchange-membrane water electrolyzers (PEMWE) that use platinum-group-metal (PGM) catalysts. We outline the key issues of introducing Fe-doped Ni/Co (oxy)hydroxide catalysts at the anode of the AEMWE, such as the oxidative processes triggered by Fe species traveling through the polymer membrane, pH-gradient effects on the catalyst stability, and possibly limited catalyst utilization in the compressed stack configuration. We also suggest possible mitigation strategies for these issues. Lastly, we summarize remaining challenges including the long-term stability of Fe-doped Ni/Co (oxy)hydroxides under OER conditions and the lack of accurate models of the dynamic active surface that hinder our understanding of, and thus ability to design, these catalysts.

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

Combined Cyclohexene Dehydrogenation and Oxygenation over VO x /CeO 2 with O 2 and Vaporized H 2 O 2 as Oxidants

Selective oxidation of hydrocarbons over metal oxide catalysts frequently invokes Mars-van Krevelen (MvK) mechanisms involving lattice oxygens. At typical reaction temperatures, oxidative dehydrogenation reactions predominate and compete with total oxidation; production of more useful oxygenates is challenging. However, because regeneration of lattice oxygens has been previously hypothesized to involve transient formation of surface hydroperoxides or peroxides, MvK cycles should be capable of forming products derived from both lattice oxygen and surface (hydro)peroxide species, under certain conditions. In this report, we study the low temperature reaction of cyclohexene with O 2 over CeO 2 -supported VO x catalysts. Below 150°C and for higher VO x loading, cyclohexene converts to benzene and trans-1,2-cyclohexanediol with no appreciable CO 2 formation. Control experiments show similar behavior in other supported vanadia catalysts. Conversely, using vaporized H 2 O 2 as oxidant exclusively gives 1,2-cyclohexanedione, suggesting that MvK reoxidation cycles do not directly involve H 2 O 2 . Furthermore, these findings contribute to the current understanding of selective oxidation mechanisms, and demonstrate routes to the formation of industrially useful oxygenates with O 2 or vaporized H 2 O 2 over metal oxide catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Improved Self-Assembly of P3HT with Pyrene-Functionalized Methacrylates

A block copolymer with discotic liquid crystalline behavior was synthesized using Grignard metathesis polymerization (GRIM) and initiators for continuous activator regeneration atom transfer radical polymerization (ICAR-ATRP). A novel discotic liquid crystalline mesogen, 6-(pyren-1-yloxy)hexyl methacrylate (PyMA), comprises a block that is attached to regioregular poly(3- hexylthiophene) (rr-P 3 HT) generated by GRIM and subjected to end-group modification. Due to the continuous regeneration of Cu + in the reaction mixture in ICAR-ATRP compared to conventional methods, the synthesis was successfully performed with less catalyst. The purity and yield of the final product are increased by eliminating rigorous post-synthesis purification. Stacked pyrene units have contributed to the enhanced long-range π-π interactions and aligning of the P 3 HT block as observed in thin-film X-ray diffraction (XRD). Furthermore, field-effect mobilities in the order of 10 -2 cm 2 V -1 s -1 in bottom-gate, top-contact organic field-effect transistors (OFETs) suggest an enhancement in charge transport due to the discotic electron-rich pyrene units that help mitigate the insulating effect of the methacrylate backbone. The formation of uniform microdomains of P 3 HT-bpoly(PyMA) observed with tapping mode atomic force microscopy (TMAFM) on the channel regions of OFETs indicates the unique packing of the block copolymer in comparison to pristine P 3 HT. Thermotropic properties of the novel discotic mesogen in the presence and absence of P3HT were observed with both the poly(3-hexylthiophene)-b-poly(6-(pyren-1-yloxy)hexyl methacrylate) (P3HT-b-poly(PyMA)) block copolymer and poly(6-(pyren-1-yloxy)hexyl methacrylate) (poly(PyMA)) homopolymer using polarized optical microscopy (POM) and differential scanning calorimetry (DSC).

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

Microwave heated chemical looping ammonia synthesis over Fe and CoMo particles

Chemical looping ammonia synthesis (CLAS) materials were subjected to a three cycle ammonia synthesis test under both conventional thermal heating and microwave heating. Microwave heating was found to outperform conventional heating for the first cycle on both Fe and CoMo materials. Principles of microwave catalysis and the heating of metallic particles may be generalized from this study; the dielectric loss tangent for optimum heating must fall within a realtively small range, ~0.8–1.4, and the penetration depth of the microwave into the particle must be considered and optimized for efficient heating, penetration depth should be on the same order as the particle size. The active phases of both catalysts, Fe 4 N and Co 3 Mo 3 N, were found to be responsive to microwave irradiation. Lastly, the deactivation and regeneration of the materials was studied by examining the BET surface areas by reforming surfaces with a low concentration gas phase oxidation reaction. This study sheds light on more general principles of microwave catalysis and on the scale-up of CLAS reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Understanding Degradation Mechanisms in SrIrO 3 Oxygen Evolution Electrocatalysts: Chemical and Structural Microscopy at the Nanoscale

Designing acid-stable oxygen evolution reaction electrocatalysts is key to developing sustainable energy technologies such as polymer electrolyte membrane electrolyzers but has proven challenging due to the high applied anodic potentials and corrosive electrolyte. This work showcases advanced nanoscale microscopy techniques supported by complementary structural and chemical characterization to develop a fundamental understanding of stability in promising SrIrO 3 thin film electrocatalyst materials. Cross-sectional high-resolution transmission electron microscopy illustrates atomic-scale bulk and surface structure, while secondary ion mass spectrometry imaging using a helium ion microscope provides the nanoscale lateral elemental distribution at the surface. After accelerated degradation tests under anodic potential, the SrIrO 3 film thins and roughens, but the lateral distribution of Sr and Ir remains homogeneous. A layer-wise dissolution mechanism is hypothesized, wherein anodic potential causes the IrO x -rich surface to dissolve and be regenerated by Sr leaching. Finally, the characterization approaches utilized herein and mechanistic insights into SrIrO 3 are translatable to a wide range of catalyst systems.

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

Recent Advances and Future Perspectives of Low-Concentration CO 2 Enrichment and Emerging Applications

Low-concentration carbon dioxide (LCCO 2 ) streams, ranging from ambient air to industrial flue gas, represent a significant yet underutilized carbon resource. This review examines recent advances in technologies for enriching LCCO 2 and enabling its integration into a wide range of applications. It covers emerging materials and processes for CO 2 capture, including immobilized amines, metal oxides, polymers, porous carbons, and zeolites, with a focus on performance metrics, regeneration strategies, and process intensification. Beyond capture, the review explores the direct utilization of LCCO 2 through reactive capture pathways enabled by novel catalysts and processes, as well as nonreactive applications, such as greenhouse cultivation, enhanced weathering, and sustainable agriculture. Additionally, this review highlights the role of LCCO 2 in enhancing critical metal recovery. Finally, the review outlines crucial future research directions necessary to fully realize LCCO 2 enrichment’s potential within circular carbon economies and critical material supply chains, paving the way toward a more energy-innovative and resource-resilient industrial sector. The findings are significant for researchers in academia, industry, and government, as well as the public interested in extending the value of LCCO 2 .

atmospheric chemistry↗
DOE OSTI2020

Critical roles of Cu(OH)2 in low-temperature moisture-induced degradation of Cu-SAPO-34 SCR catalyst: Correlating reversible and irreversible deactivation

Cu-SAPO-34 selective catalytic reduction (SCR) catalyst deactivates upon exposure to water vapor at temperatures lower than 100 °C, which deteriorates its application prospects. The deactivation under cycled aging-regeneration conditions can be categorized into two stages, namely reversible and irreversible deactivation. Based on SCR reaction tests, and characterizations with diffuse reflection infrared Fourier transform spectroscopy (DRIFTS), NH3 temperature-programmed desorption (NH3-TPD) and H2 temperature-programmed reduction (H2-TPR), it is concluded that the transformation of SCR active isolated Cu(II) ions to Cu(OH)2 is critical to both types of deactivation. Within the frame of reversible deactivation, Cu(OH)2 is converted back to SCR active Cu(II) ions by interacting with Brønsted acid sites during high-temperature regeneration. However, interactions between Cu(OH)2 and hydrolyzed framework Al lead to the formation of CuAl2O4-like species, causing permanent loss of active Cu(II) ions and thus, irreversible deactivation. The authors from Tsinghua University would like to acknowledge the financial support from projects of China Science and Technology Exchange Centre (No. 2016YFE0126600) and the National Key R&D Program of China (No. 2017YFC0211102). YM also acknowledges Tsinghua Scholarship for Overseas Graduate Studies for a visit to the Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the US Department of Energy (DOE) under contract DE-AC05-76RL01830. FG is supported by DOE, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office.

Cu-SAPO-34, low-temperature deactivation, reversib↗
DOE OSTI2023

Mechanistic insights to drive catalytic hydrogenation of formamide intermediates to methanol via deaminative hydrogenation

Amine-promoted hydrogenation of CO 2 to methanol typically proceeds via a formamide intermediate when amines are used as additives or if the hydrogenation is performed in carbon capture solvents. The catalysts used for the hydrogenation of the formamide intermediate dictate the selectivity of the products formed: 1) Deoxygenative hydrogenation (C–O bond cleavage) resulting in N-methylation of amine and deactivation of the solvent, 2) Deaminative hydrogenation (C–N bond cleavage) resulting in formation of methanol and regeneration of the solvent. To date, catalytic reductions of CO 2 with amine promoters suffer from poor selectively for methanol which we attribute to the limiting formamide intermediate, though to date, the conditions that favor C–N cleavage have yet to be fully understood. To better understand the reactivity of the formamide intermediates, a range of heterogenous catalysts were used to study the hydrogenation of formamide. Well-known gas phase CO 2 hydrogenation catalysts catalyze the hydrogenation of formamide to N-methyl product via C–O bond cleavage. However, the selectivity can be readily shifted to selective C–N bond cleavage by addition of an additive with sufficient basicity for both homogenous and heterogeneous catalytic systems. The base additive shifts the selectivity by deprotonating a hemiaminal intermediate formed in situ during the formamide hydrogenation. This prevents dehydration process leading to N-methylated product, which is a key capture solvent deactivation pathway that hinders amine use in carbon capture, utilization, and storage (CCUS). The findings from this study provide a roadmap on how to improve the selectivity of known heterogenous catalysts, enabling catalytic reduction of captured CO 2 to methanol.

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

Tuning the hydrogenation of CO 2 to CH 4 over mechano-chemically prepared palladium supported on ceria

CO 2 methanation reactivity, reaction mechanism, and surface structure were investigated on a mechanochemically prepared Pd/CeO 2 catalyst (PdAcCeO 2 -M), where an oxidative pretreatment (-o) increased methane yield by a factor of two compared to a reductive pretreatment (-h). Methanation rates were maintained for over 48 h and further increased upon oxidative regeneration treatments. The surface species of both PdAcCeO 2 -M-o and PdAcCeO 2 -M-h were explored via in situ CO 2 and CO hydrogenation DRIFTS, where CO hydrogenation effectively models the dissociative CO 2 mechanism (CO 2 → CO → CH 4 ). PdAcCeO 2 -M-o yielded distinct Pd-CO adsorption and the absence of monodentate carbonate at ~ 1400 cm -1 , while AP-XPS showed that PdAcCeO 2 -M-o yielded a unique Pd δ+ contribution at 335.9 eV. By gaining insights from various in situ spectroscopic techniques, and by breaking the CO 2 hydrogenation mechanism into piecewise steps, a deeper understanding of the direct CO 2 reduction towards methane and CO over mechanochemically prepared Pd/CeO 2 catalysts was obtained.

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 OSTI2024

Direct conversion of methane to aromatics and hydrogen via a heterogeneous trimetallic synergistic catalyst

Abstract Non-oxidative methane dehydro-aromatization reaction can co-produce hydrogen and benzene effectively on a molybdenum-zeolite based thermochemical catalyst, which is a very promising approach for natural-gas upgrading. However, the low methane conversion and aromatics selectivity and weak durability restrain the realistic application for industry. Here, a mechanism for enhancing catalysis activity on methane activation and carbon-carbon bond coupling has been found to promote conversion and selectivity simultaneously by adding platinum–bismuth alloy cluster to form a trimetallic catalyst on zeolite (Pt-Bi/Mo/ZSM-5). This bimetallic alloy cluster has synergistic interaction with molybdenum: the formed CH 3 * from Mo 2 C on the external surface of zeolite can efficiently move on for C-C coupling on the surface of Pt-Bi particle to produce C 2 compounds, which are the key intermediates of oligomerization. This pathway is parallel with the catalysis on Mo inside the cage. This catalyst demonstrated 18.7% methane conversion and 69.4% benzene selectivity at 710 °C. With 95% methane/5% nitrogen feedstock, it exhibited robust stability with slow deactivation rate of 9.3% after 2 h and instant recovery of 98.6% activity after regeneration in hydrogen. The enhanced catalytic activity is strongly associated with synergistic interaction with Mo and ligand effects of alloys by extensive mechanism studies and DFT calculation.

03 NATURAL GAS↗
DOE OSTI2025

Manipulating the Second Coordination Shell of Single-Atom Fe for Enhanced Fenton Reaction

While current methods use oxidizable metals as electron donors to effectively reduce Fe 3+ , they suffer from the irreversible oxidation of these metals, ultimately compromising the catalyst’s longevity. To address this challenge, we engineered the second coordination shell of a single-atom Fe center by doping boron (B) onto a graphene-based support (Fe 1 /B-graphene) and utilized H 2 O 2 as the electron source for efficient Fe 2+ regeneration. Experimental results, supported by theoretical calculations, revealed that the Fe–O–B motif functions like a micro galvanic cell, with intermediary O atoms facilitating electron transfer between electrodes. Specifically, electrons consumed during H 2 O 2 activation at Fe 1 sites (positive electrode) are replenished by electrons extracted from H 2 O 2 at B atoms (negative electrode), where the activation energy for H 2 O 2 oxidation is significantly lower than that at Fe 1 sites. This study offers inspirational insights into the design of Fenton catalysts through precise regulation of the second coordination shell, demonstrating the potential of tailoring the outer coordination environment of single-atom catalysts to enhance catalytic performance across various reactions.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Selective CO 2 Reduction by Bis(bipyridine)cobalt(II) Catalysts: The Role of Pendant Pyridine as a Proton Acceptor

Electrochemical CO 2 reduction reaction (CO 2 RR) catalyzed by molecular earth-abundant metal catalysts is a promising strategy to convert CO 2 into value-added products. One recent trend in this field has been focusing on the rational design of catalysts by incorporating redox-active ligands and modifying the secondary coordination sphere (SCS) to achieve efficient and selective CO 2 RR. Herein, we report a series of Co bis­(bipyridine) catalysts featuring various dangling groups, such as pyridine, tertiary amine, or butyl, in the secondary coordination sphere (Co-PyMe, Co-Py, Co-PrN, and Co-Bu). Efficient, selective electrocatalytic CO 2 RR was achieved by the complexes after the generation of triply reduced intermediate consisting of a Co I center and a dianionic ligand, producing CO as the major product and trace amount of H 2 . Strong correlations with the identity of dangling groups and turnover frequency (TOF) have been observed, in which Co-PyMe displayed the highest TOF (1086 s –1 in MeCN/H 2 O). Mechanistic studies indicated that the acceleration of CO 2 RR with pyridine-functionalized catalysts were derived from the protonation of pyridine dangling groups which participated as weak acids in the H-bonding network with exogenous proton sources, stabilizing CO 2 -bound intermediates and facilitating proton transfer. In addition, precatalytic CO 2 binding and activation at the third reduction (−2.1 V) was revealed by CV and SEC-IR studies. The resultant doubly reduced CO-bound species acted as a trapping state which inhibited CO 2 RR electrocatalysis. Regeneration of active species was accessed via reductive dissociation of CO at a more negative potential. In conclusion, this study highlights the combined effects of redox-active ligands and pyridine/pyridinium as SCS groups on CO 2 RR catalysis and provides design principles for future development of CO 2 RR catalysts utilizing pyridine/pyridiniums as SCS functional groups to fine-tune the catalytic activity.

CO2 reduction↗
DOE OSTI2022

Biomimetic Metal-Free Hydride Donor Catalysts for CO 2 Reduction

The catalytic reduction of carbon dioxide to fuels and value-added chemicals is of significance for the development of carbon recycling technologies. One of the main challenges associated with catalytic CO 2 reduction is product selectivity: the formation of carbon monoxide, molecular hydrogen, formate, methanol, and other products occurs with similar thermodynamic driving forces, making it difficult to selectively reduce CO 2 to the target product. Significant scientific effort has been aimed at the development of catalysts that can suppress the undesired hydrogen evolution reaction and direct the reaction toward the selective formation of the desired products, which are easy to handle and store. Inspired by natural photosynthesis, where the CO 2 reduction is achieved using NADPH cofactors in the Calvin cycle, in this study we explore biomimetic metal-free hydride donors as catalysts for the selective reduction of CO 2 to formate. Here, we outline our recent findings on the thermodynamic and kinetic parameters that control the hydride transfer from metal-free hydrides to CO 2 . By experimentally measuring and theoretically calculating the thermodynamic hydricities of a range of metal-free hydride donors, we derive structural and electronic factors that affect their hydride-donating abilities. Two dominant factors that contribute to the stronger hydride donors are identified to be (i) the stabilization of the positive charge formed upon HT via aromatization or by the presence of electron-donating groups and (ii) the destabilization of hydride donors through the anomeric effect or in the presence of significant structural constrains in the hydride molecule. Hydride donors with appropriate thermodynamic hydricities were reacted with CO 2 , and the formation of the formate ion (the first reduction step in CO 2 reduction to methanol) was confirmed experimentally, providing an important proof of principle that organocatalytic CO 2 reduction is feasible. The kinetics of hydride transfer to CO 2 were found to be slow, and the sluggish kinetics were assigned in part to the large self-exchange reorganization energy associated with the organic hydrides in the DMSO solvent. Finally, we outline our approaches to the closure of the catalytic cycle via the electrochemical and photochemical regeneration of the hydride (R–H) from the conjugate hydride acceptors (R + ). We illustrate how proton-coupled electron transfer can be efficiently utilized not only to lower the electrochemical potential at which the hydride regeneration takes place but also to suppress the unwanted dimerization that neutral radical intermediates tend to undergo. Overall, this account provides a summary of important milestones achieved in organocatalytic CO 2 reduction and provides insights into the future research directions needed for the discovery of inexpensive catalysts for carbon recycling.

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

Ene Reactivity of an Fe=NR Bond Enables the Catalytic α-Deuteration of Nitriles and Alkynes

Herein, we report the reactions of an Fe(II) imido complex [Ph 2 B( t BuIm) 2 Fe=NDipp] – (1) with internal alkynes and isobutyronitrile, affording the Fe amido allenyl complexes [Ph 2 B( t BuIm) 2 Fe(NHDipp)((R 1 )C=C=C(R 2 )(H))] – (R 1 = Et or n Pr; R 2 = Me or Et, 2–5) and the Fe amido keteniminate complex [Ph 2 B( t BuIm) 2 Fe(NHDipp)(N=C=CMe 2 )K(THF)] n (8-K), respectively. These transformations represent the previously unknown ene-like reactivity of a metal–ligand multiple bond. Stoichiometric reactions of 2 and 8-K with DippNH 2 lead to the regeneration of 3-hexyne and isobutyronitrile, respectively, with concomitant formation of the bis(anilido) complex [Ph 2 B( t BuIm) 2 Fe(NHDipp) 2 ] – (9). These results provide the platform for 1 as an efficient catalyst for the selective α-deuteration of nitriles and alkynes by RND 2 . Furthermore, these results demonstrate a new reaction mode for metal imido complexes and suggest new avenues for using the imido ligand in catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗