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NASA NTRS1992

Oxidation of the N-terminal methionine of lens alpha-A crystallin

Antiserum against the N-terminal peptide of bovine alpha-A crystallin has been used to monitor purification of two different seropositive peptides (i.e. T1a and T1b) from a tryptic digest of bovine lens proteins. Both these peptides have similar amino acid compositions, but peptide T1b has a molecular weight 16 atomic mass units larger than T1a, suggesting posttranslational modification. Analysis of ionization fragments of the T1b peptide by mass spectrometry demonstrates that this difference in molecular weight is due to the in vivo oxidation of the N-terminal met residue of the alpha-A crystallin molecule.

NASA Discipline Cell Biology↗

DOE OSTI2025

Direct Study of Changes in Catalyst Structure-Kinetic Properties During Redox Transitions

The Temporal Analysis of Products (TAP) pulse response methodology is a transient technique that provides the time resolution needed to deconvolve reaction steps from the complex networks typical in industrial catalytic processes. Traditionally, TAP measurements observe gas phase dynamics at the reactor exit but lack direct measurements of changes in the catalyst itself. Recently, a new operando technique was developed that couples gas phase transients to dynamic changes in metal centers with the precise TAP methodology for nanomole titration. Using an industrial CrOx/Al2O3 catalyst used for propane dehydrogenation, we demonstrate the capabilities of this unique device to reveal key catalytic processes: 1) total propane oxidation not associated with chromia centers, 2) reduction of Cr6+ to Cr3+ correlated with selective product formation, and 3) subsequent carbon accumulation. By utilizing incremental pulsing in a diffusion-only transport regime, the spectrokinetic device allows us to resolve detailed changes in catalyst structure, composition, and kinetic function that are otherwise indistinguishable in conventional operando devices. The unification of the TAP methodology with time-resolved spectroscopic measurements offers new and unique insights into the complex kinetic phenomena regulated by solid catalyst surfaces.

03 - NATURAL GAS↗

DOE OSTI2022

Activation of Transition Metal (Fe, Co and Ni)-Oxide Nanoclusters by Nitrogen Defects in Carbon Nanotube for Selective CO 2 Reduction Reaction

The electrochemical carbon dioxide reduction reaction (CO2RR), which can produce value-added chemical feedstocks, is a proton-coupled-electron process with sluggish kinetics. Thus, highly efficient, cheap catalysts are urgently required. Transition metal oxides such as CoO x , FeO x , and NiO x are low-cost, low toxicity, and abundant materials for a wide range of electrochemical reactions, but are almost inert for CO 2 RR. Here, we report for the first time that nitrogen doped carbon nanotubes (N-CNT) have a surprising activation effect on the activity and selectivity of transition metal-oxide (MO x where M = Fe, Ni, and Co) nanoclusters for CO 2 RR. MO x supported on N-CNT, MOx/N-CNT, achieves a CO yield of 2.6–2.8 mmol cm -2 min -1 at an overpotential of -0.55V, which is two orders of magnitude higher than MO x supported on acid treated CNTs (MOx/O-CNT) and four times higher than pristine N-CNT. The faraday efficiency for electrochemical CO 2 -to-CO conversion is as high as 90.3% at overpotential of 0.44V. Both in-situ XAS measurements and DFT calculations disclose that MO x nanoclusters can be hydrated in CO 2 saturated KHCO 3 , and the N defects of N-CNT effectively stabilize these metal hydroxyl species under carbon dioxide reduction reaction conditions, which can split the water molecules and provide local protons to inhibit the poisoning of active sites under carbon dioxide reduction reaction conditions.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Enhancement of polyhydroxyalkanoate production by co-feeding lignin derivatives with glycerol in Pseudomonas putida KT2440

Abstract Background Efficient utilization of all available carbons from lignocellulosic biomass is critical for economic efficiency of a bioconversion process to produce renewable bioproducts. However, the metabolic responses that enable Pseudomonas putida to utilize mixed carbon sources to generate reducing power and polyhydroxyalkanoate (PHA) remain unclear. Previous research has mainly focused on different fermentation strategies, including the sequential feeding of xylose as the growth stage substrate and octanoic acid as the PHA-producing substrate, feeding glycerol as the sole carbon substrate, and co-feeding of lignin and glucose. This study developed a new strategy—co-feeding glycerol and lignin derivatives such as benzoate, vanillin, and vanillic acid in Pseudomonas putida KT2440—for the first time, which simultaneously improved both cell biomass and PHA production. Results Co-feeding lignin derivatives (i.e. benzoate, vanillin, and vanillic acid) and glycerol to P. putida KT2440 was shown for the first time to simultaneously increase cell dry weight (CDW) by 9.4–16.1% and PHA content by 29.0–63.2%, respectively, compared with feeding glycerol alone. GC–MS results revealed that the addition of lignin derivatives to glycerol decreased the distribution of long-chain monomers (C10 and C12) by 0.4–4.4% and increased the distribution of short-chain monomers (C6 and C8) by 0.8–3.5%. The 1 H– 13 C HMBC, 1 H– 13 C HSQC, and 1 H– 1 H COSY NMR analysis confirmed that the PHA monomers (C6–C14) were produced when glycerol was fed to the bacteria alone or together with lignin derivatives. Moreover, investigation of the glycerol/benzoate/nitrogen ratios showed that benzoate acted as an independent factor in PHA synthesis. Furthermore, 1 H, 13 C and 31 P NMR metabolite analysis and mass spectrometry-based quantitative proteomics measurements suggested that the addition of benzoate stimulated oxidative-stress responses, enhanced glycerol consumption, and altered the intracellular NAD + /NADH and NADPH/NADP + ratios by up-regulating the proteins involved in energy generation and storage processes, including the Entner–Doudoroff (ED) pathway, the reductive TCA route, trehalose degradation, fatty acid β -oxidation, and PHA biosynthesis. Conclusions This work demonstrated an effective co-carbon feeding strategy to improve PHA content/yield and convert lignin derivatives into value-added products in P. putida KT2440. Co-feeding lignin break-down products with other carbon sources, such as glycerol, has been demonstrated as an efficient way to utilize biomass to increase PHA production in P. putida KT2440. Moreover, the involvement of aromatic degradation favours further lignin utilization, and the combination of proteomics and metabolomics with NMR sheds light on the metabolic and regulatory mechanisms for cellular redox balance and potential genetic targets for a higher biomass carbon conversion efficiency.

09 BIOMASS FUELS↗

DOE OSTI2025

Modeling a High-Temperature Electrochemically Driven Water-Gas-Shift Process Using a Mixed-Conducting Membrane without External Electrical Power

This paper develops a model to predict and interpret the performance of an elevated-temperature, electrochemical, membrane-assisted, water-gas-shift process. The process uses separated feed streams of H 2 O and CO to produce separated streams of H 2 and CO 2 , without an external electrical power source. The dense ceramic membrane is mixed ionic-electronic-conducting (MIEC) gadolinium-doped ceria (GDC) and the porous composite electrodes are Ni-YSZ. At elevated temperature, GDC conducts both oxygen ions and small polarons. The present process uses chemical potential to drive the process. Electrochemical oxidation of CO proceeds within the composite anode and H 2 O reduction proceeds within the composite cathode. At high temperature (e.g., T > 700 °C), GDC has significant electronic leakage in the form of a reduced-cerium small polaron, which supports the charge-transfer reactions. In a typical electrolyzer or fuel cell, this leakage is significantly problematic. However, the present process depends on the leakage current to complete the electrochemical circuit. Model development and validation is based on measured material properties and reactor performance. Potential applications include using CO-rich blast-furnace off gases in steel processing, producing separated streams of H 2 and CO 2 .

Zhu, Huayang↗

DOE OSTI2022

Cation-Dependent Multielectron Kinetics of Metal Oxide Splitting

We report direct electrolytic extraction of metals from metal oxides is a promising process for the sustainable production of metals. In this work, we elucidate the inherent thermodynamic driving forces behind the reduction of metal oxides to metals (M-OER). It is shown that the thermodynamics of M-OER can be systematically tuned via the interactions of oxygen with the participating metal cations as a function of metal–oxygen covalency, oxygen–oxygen covalency, and metal–oxygen ionicity. We screen both group 1 elements and metals that are able to exist in the +2 oxidation state for M-OER thermodynamics. Li, Fe, and Co are identified as having low thermodynamic overpotentials for electrolytic extraction from their metal oxides due to interactions between oxygen and these metals being neither too strong (covalent) nor too weak (ionic). We further show that the bulk formation energies are predictive of M-OER reaction energetics on surfaces by developing unified design principles for tuning the thermodynamics of these reduction reactions both in bulk oxides and on surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

The Reductive Leaching of Chalcopyrite by Chromium(II) Chloride for the Rapid and Complete Extraction of Copper

A hydrometallurgical process is developed to lower the costs of copper production and thereby sustain the use of copper throughout the global transition to renewable energy technologies. The unique feature of the hydrometallurgical process is the reductive treatment of chalcopyrite, which is in contrast to the oxidative treatment more commonly pursued in the literature. Chalcopyrite reduction by chromium(II) ion is described for the first time and superior kinetics are shown. At high concentrate loadings of 39, 78, and 117 gL –1 , chalcopyrite reacted completely within minutes at room temperature and pressure. The XRD, SEM-EDS, and XPS measurements indicate that chalcopyrite reacts to form copper(I) chloride (CuCl). After the reductive treatment, the mineral products are leached by iron(III) sulfate to demonstrate the complete extraction of copper. The chromium(II) ion may be regenerated by an electrolysis unit inspired by an iron chromium flow battery in a practical industrial process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Processing iridium foil targets for the production of radioplatinum isotopes

Dissolving noble metals remains challenging because of their high reduction potentials and tendency to passivate as oxides. This barrier is acute for iridium metal targets used to produce platinum radioisotopes, where post-irradiation processing is costly and hazardous with conventional routes. Here, we report a rapid alkali-fusion method that converts Ir metal directly into chloride media compatible with downstream separations. In the process, an Ir foil is fused with Na 2 O 2 and KCl at temperatures above the KCl melting point; the molten salt enhances heat transfer and facilitates O 2− /Na + transport to the Ir surface, overcoming Ir's oxidation resistance. The fused cake is then cooled and leached in 10 M HCl, yielding Ir in solution without specialized microwave digestion or HF. Pt separation from bulk Ir was evaluated using extraction-chromatography resins. A newly formulated ionic-liquid resin containing Cyphos IL 104 (E104) was compared with two commercial resins (TrisKem TK200 and TK201). All resins achieved >90 % Ir recovery. Pt co-recovery depended on resin chemistry: TK200 recovered 85.9 % Pt, TK201 recovered 54.1 % Pt, and E104 recovered 72.9 % Pt. This study introduces a fast, scalable dissolution route for solid Ir targets and demonstrates resin choices that tune Ir/Pt separation, lowering the barrier to routine production and purification of Pt radioisotopes.

07 ISOTOPE AND RADIATION SOURCES↗

NASA NTRS1992

Water reclamation technology development for future long range missions

This paper covers the development of computer simulation models of the Vapor Compression Distillation (VCD) process, the Super Critical Water Oxidation (SCWO) process, and two versions of a Vapor Phase Catalytic Ammonia Reduction (VPCAR) process. These process level models have combined into two Integrated Water Reclamation Systems (IWRS). Results from these integrated models, in conjunction with other data sources, have been used to develop a preliminary comparison of the two systems. Also discussed in this paper is the development of a Vapor Phase Catalytic Ammonia Reduction teststand and the development of a new urine analog for use with the teststand and computer models.

Flynn, Michael T.↗

NASA NTRS1995

Superconductivity devices: Commercial use of space

The work described in this report covers various aspects of the Rainbow solid-state actuator technology. It is presented in six parts dealing with materials, processing, fabrication, properties and associated phenomena. The Rainbow actuator technology is a relatively new materials development which had its inception in 1992. It consists of a new processing technology for preparing piezoelectric and electrostrictive ceramic materials. It involves a high temperature chemical reduction process which leads to an internal pre-stressing of the oxide wafer, thus the name Rainbow, an acronym for Reduced And INternally Biased Oxide Wafer. Ceramics fabricated by this method produce bending-mode actuator devices which possess several times more displacement and load bearing capacity than present-day benders (unimorphs, bimorphs). It is anticipated that these solid-state, electromechanical actuators which can be used in a number of applications in space such as cryopump motors, anti-vibration active structures, autoleveling platforms, telescope mirror correctors and autofocusing devices. When considering any of these applications, the key to the development of a successful device is the successful development of a ceramic material which can produce maximum displacement per volt input; hence, this initiative involving a solid-state means for achieving unusually high electromechanical displacement can be significant and far reaching. An additional benefit obtained from employing the piezoelectric effect in these actuator devices is the ability to also utilize them as sensors; and, indeed, they can be used as both motor (actuator) and generator (sensor) in multifunction devices.

Haertling, Gene↗

NASA NTRS2001

Sulfate- and Sulfur-Reducing Bacteria as Terrestrial Analogs for Microbial Life on Jupiter's Satellite Io

Observations from the Voyager and Galileo spacecraft have revealed Jupiter's moon Io to be the most volcanically active body of our Solar System. The Galileo Near Infrared Imaging Spectrometer (NIMS) detected extensive deposits of sulfur compounds, elemental sulfur and SO2 frost on the surface of Io. There are extreme temperature variations on Io's surface, ranging from -130 C to over 2000 C at the Pillan Patera volcanic vent. The active volcanoes, fumaroles, calderas, and lava lakes and vast sulfur deposits on this frozen moon indicate that analogs of sulfur- and sulfate-reducing bacteria might inhabit Io. Hence Io may have great significance to Astrobiology. Earth's life forms that depend on sulfur respiration are members of two domains: Bacteria and Archaea. Two basic links of the biogeochemical sulfur cycle of Earth have been studied: 1) the sulfur oxidizing process (occurring at aerobic conditions) and 2) the process of sulfur-reduction to hydrogen sulfide (anaerobic conditions). Sulfate-reducing bacteria (StRB) and sulfur-reducing bacteria (SrRB) are responsible for anaerobic reducing processes. At the present time the systematics of StRB include over 112 species distributed into 35 genera of Bacteria and Archaea. Moderately thermophilic and mesophilic SrRB belong to the Bacteria. The hyperthermophilic SrRB predominately belong to the domain Archaea and are included in the genera: Pyrodictium, Thermoproteus, Pyrobaculum, Thermophilum, Desulfurococcus, and Thermodiscus. The StRB and SrRB use a wide spectrum of substrates as electron donors for lithotrophic and heterotrophic type nutrition. The electron acceptors for the StRB include: sulfate, thiosulfate, sulfite, sulfur, arsenate, dithionite, tetrathionate, sulfur monoxide, iron, nitrite, selenite, fumarate, oxygen, carbon dioxide, and chlorine-containing phenol compounds. The Sulfate- and Sulfur-reducing bacteria are widely distributed in anaerobic ecosystems, including extreme environments like hot springs, deepsea hydrothermal vents, soda and high salinity lakes, and cryo-environments. Furthermore, the StRB and SrRB have Astrobiological significance as these anaerobic extremophiles may represent the dominant relic life forms that inhabited our planet during the extensive volcanic activity in the Earth's early evolutionary period.

Pikuta, Elena V.↗

DOE OSTI2020

Overcoming Oxidation State-Dependent Spectral Interferences: Online Monitoring of U(VI) Reduction to U(IV) via Raman and UV–vis Spectroscopy

Analytical characterization of chemical processes is an essential component of both industrial processes and fundamental studies. Applicable techniques abound, but optical spectroscopy has the unique combination of being easily incorporated into on-line (in-situ) monitoring probes and can also provide abundant chemical information (concentration, oxidation state, speciation). However, this abundance of chemical information can make applying optical spectroscopy to complex chemical processes challenging. This is particularly evident in the bulk electrolysis of U(VI) to U(IV), an essential preparatory step in some nuclear fuel recycling schemes. Starting and product materials have interfering spectral signatures in both electronic and vibrational spectroscopies, making accurate and real-time analysis difficult to achieve. In this paper, we discuss the application of optical spectroscopy to the on-line monitoring of a bulk electrolysis process and the methods utilized to analyze data as well as characterize the efficiency and mechanism of U(IV) generation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Techno-economic Analysis for a Low Cost and Recyclable Oxygen Carrier

The novelty of a chemical looping combustion (CLC) process is its ability to oxidize solid or gaseous fuels in a nitrogen-free environment eliminating the need for post combustion carbon dioxide capture. The technology is based on the oxygen carrier (OC); a metal oxide that at high temperatures can undergo a reduction reaction with a fuel, followed by an oxidation reaction with air. Successful development of CLC processes is dependent on the OC having: low cost, high attrition resistance under CLC conditions, and high reactivity for coal. In this paper, we discuss the development of a novel iron-based OC formulation produced from low cost and abundant raw materials. The active OC components are recyclable, with reformulated material performance comparable to the virgin OC, even when reformulated with ash contents of up to 10%. Furthermore, we discuss a techno-economic analysis for a centrally located OC facility for the novel OC, with a production capacity of 1 million metric tonnes per year. The facility serves a hypothetical market comprising 25 chemical looping combustion facilities, averaging 5 tonnes per hour OC replacement per facility. Estimates for the cost of the OC are around $150/tonne, and include an energy-to-power option to improve process economics.

20 FOSSIL-FUELED POWER PLANTS↗

DOE OSTI2025

Thiol- and Disulfide-Functionalized Polycyclooctene: Metathesis Polymerization, Degradation, and Reformation

The enormous global production and use of polymers and plastics, combined with slower and less efficient disposal and recycling methods, have led to a worldwide growth in plastic waste. Here, we describe an approach that builds degradability into macromolecular polyolefins through the design of telechelic oligomers with reactive functional groups that enables control over polymer deconstruction and reconstruction. Our work exploits disulfide-containing polymers that have emerged as promising cyclable materials due to their dynamic reversibility (bond formation and cleavage) driven by redox chemistry under mild conditions. Specifically, we describe the synthesis of a telechelic α,ω-dithiopolycyclooctene (PCOE) by ring-opening metathesis polymerization using a dithioacetate chain transfer agent, followed by deprotection to convert the chain-end thioacetates to thiols. This process was studied towards control over the degree of oxidation to yield disulfide-containing PCOE, followed by an evaluation of reductive degradation and oxidative repolymerization. Overall, this approach facilitates the production of disulfide-containing unsaturated polyolefins and the integration of degradable and reformable moieties into soluble, processable, metathesis-derived polymers.

Lee, Kyoungwon↗

DOE OSTI2021

Synthetic and Mechanistic Implications of Chlorine Photoelimination in Nickel/Photoredox C(sp 3 )–H Cross-Coupling

In recent years, the development of light-driven reactions has contributed numerous advances in synthetic organic chemistry. A particularly active research area combines photoredox catalysis with nickel catalysis to accomplish otherwise inaccessible cross-coupling reactions. In these reactions, the photoredox catalyst absorbs light to generate an electronically excited charge-transfer state that can engage in electron or energy transfer with a substrate and the nickel catalyst. Our group questioned whether photoinduced activation of the nickel catalyst itself could also contribute new approaches to cross-coupling. Over the past 5 years, we have sought to advance this hypothesis for the development of a suite of mild and site-selective C(sp 3 )–H cross-coupling reactions with chloride-containing coupling partners via photoelimination of a Ni–Cl bond. On the basis of a report from the Nocera laboratory, we reasoned that photolysis of a Ni(III) aryl chloride species, generated by single-electron oxidation of a typical Ni(II) intermediate in cross-coupling, might allow for the catalytic generation of chlorine atoms. Combining this with the ability of Ni(II) to accept alkyl radicals, we hypothesized that photocatalytically generated chlorine atoms could mediate hydrogen atom transfer (HAT) with C(sp 3 )–H bonds to generate a substrate-derived alkyl radical that is captured by the Ni center in cross-coupling. A photoredox catalyst was envisioned to promote the necessary single-electron oxidation and reduction of the Ni catalyst to facilitate an overall redox-neutral process. Overall, this strategy would offer a visible-light-driven mechanism for chlorine radical formation enabled by the sequential capture of two photons. As an initial demonstration, we developed a Ni/photoredox-catalyzed α-oxy C(sp 3 )–H arylation of cyclic and acyclic ethers. This method was extended to a mild formylation of abundant and complex aryl chlorides through selective 2-functionalization of 1,3-dioxolane. Seeking to develop a suite of reactions that introduce carbon at all different oxidation states, we explored C(sp 3 )–H cross-coupling with trimethyl orthoformate, a common laboratory solvent. We found that trimethyl orthoformate serves as a source of methyl radical for a methylation reaction via β-scission from a tertiary radical generated upon chlorine-mediated HAT. Since chlorine radical is capable of abstracting unactivated C(sp 3 )–H bonds, our efforts have also been directed at cross-coupling with a range of feedstock chemicals, such as alkanes and toluenes, along with late-stage intermediates, using chloroformates as coupling partners. Overall, this platform enables access to valuable synthetic transformations with (hetero)aryl chlorides, which despite being the most ubiquitous and inexpensive aryl halide coupling partners, are rarely reactive in Ni/photoredox catalysis. Little is known about the photophysics and photochemistry of organometallic Ni complexes relevant to cross-coupling. We have conducted mechanistic investigations, including computational, spectroscopic, emission quenching, and stoichiometric oxidation studies, of Ni(II) aryl halide complexes common to Ni/photoredox reactions. These studies indicate that chlorine radical generation from excited Ni(III) is operative in the described C(sp 3 )–H functionalization methods. More generally, the studies illustrate that the photochemistry of cross-coupling catalysts cannot be ignored in metallaphotoredox reactions. We anticipate that further mechanistic understanding should facilitate catalyst design and lead to the development of new synthetic methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2005

A Viable Scheme for Elemental Extraction and Purification Using In-Situ Planetary Resources

NASA's new strategic direction includes establishing a self-sufficient, affordable and safe human and robotic presence outside the low earth orbit. Some of the items required for a self-sufficient extra-terrestrial habitat will include materials for power generation (e.g. Si for solar cells) and habitat construction (e.g. Al, Fe, and Ti). In this paper we will present a viable elemental extraction and refining process from in-situ regolith which would be optimally continuous, robotically automated, and require a minimum amount of astronaut supervision and containment facilities, The approach is based on using a concentrated heat source and translating sample geometry to enable simultaneous oxide reduction and elemental refining. Preliminary results will be presented to demonstrate that the proposed zone refining process is capable of segregating or refining important elements such as Si (for solar cell fabrication) and Fe (for habitat construction). A conceptual scheme will be presented whereby such a process could be supported by use of solar energy and a precursor robotic mission on the surface of the moon.

Sen, S.↗

DOE OSTI2022

Midwest Regional Carbon Conversion/Utilization Procurement Grant Workshop

https://events.usea.org/events/midwest-regional-carbon-conversionutilization-procurement-grant-workshop As the U.S. economy moves toward clean energy and a lower carbon future, the U.S. Department of Energy (DOE) is seeking to partner with states, communities, and industries to support the procurement and development of carbon conversion products. These efforts have been enabled by provisions included in the Bipartisan Infrastructure Law (BIL). As part of the BIL, supporting the Administration’s goal to achieve a carbon-free power sector by 2035 and putting the United States on a path to a net-zero economy by 2050, a new initiative was established within DOE’s Office of Fossil Energy and Carbon Management through its Carbon Conversion/Utilization Program. The new initiative will establish a demonstration grant program to issue grants to eligible entities to procure commercial and industrial products derived from the conversion of anthropogenic carbon oxides and demonstrate a significant net reduction in life cycle greenhouse gas emissions compared to incumbent technologies, processes, and products. DOE-FECM will establish a demonstration grant program within the Carbon Conversion/Utilization Program to support eligible applicants that procure those commercial and industrial products derived from anthropogenic carbon oxides. Therefore, the Carbon Conversion/Utilization Program, with the assistance of the United States Energy Association (USEA), will conduct a series of workshops (both virtual and in-person) with relevant stakeholders, e.g., product manufacturers, eligible entities, or their representative national organizations (e.g., United States Conference of Mayors, etc.) to solicit input and ideas on challenges and opportunities for a potential grant program.

Larimore, Ryan↗

DOE OSTI2026

Role of Surface Hydroxyls and Lattice Oxygen in Governing Selectivity and Restructuring During Acetic Acid Conversion on Fe 3 O 4 (001)

Understanding the reactivity of carboxylic acids on metal oxide surfaces is critical for elucidating ketonization mechanisms relevant to biomass upgrading. Here, we investigate the adsorption and thermal decomposition of acetic acid (CH 3 COOH) on Fe 3 O 4 (001) using scanning tunneling microscopy (STM), temperature-programmed reaction spectroscopy (TPRS), and X-ray photoelectron spectroscopy (XPS). At room temperature, acetic acid adsorbs dissociatively to form ordered bidentate acetate (CH 3 COO) overlayer that lifts the (√2 × √2)R 45° surface reconstruction. TPRS reveals ketene (CH 2 CO) as the dominant product, along with CO, CO 2 , and H 2 O, the latter evolving via a Mars–van Krevelen (MvK) mechanism. Isotopic labeling shows preferential CO 2 formation from the carboxyl carbon and a more balanced CO/CO 2 ratio from the methyl carbon, suggesting distinct oxidation pathways. STM imaging reveals embedded acetate intermediates filling surface oxygen vacancies created in MvK steps. Upon product formation completion (~700 K), extensive surface etching is observed, with pits elongated along the octahedral Fe rows. Approximately 20% of the surface oxygen is removed, consistent with vacancy formation stoichiometry inferred from product distributions. These findings demonstrate that carboxylate-induced restructuring of Fe 3 O 4 (001) involves both surface healing and reduction processes, offering mechanistic insights relevant to ketonization and broader carboxylic acid chemistry on metal oxides.

acetic acid↗