Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “aerobic oxidation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Heterogeneous Fe‐N‐C Cocatalyst for Hydroquinone Oxidation Enables Aerobic Oxidation of Primary Alcohols to Aldehydes

Abstract Benzoquinone (BQ) is commonly used as a cocatalyst in multi‐component catalyst systems for aerobic oxidation of organic molecules. Such methods often proceed by a redox cascade in which a secondary catalyst supports aerobic oxidation of hydroquinone (HQ) to BQ. The present study shows that a commercially available non‐precious metal heterogeneous catalyst, PAJ‐Fe‐N‐C, is much more efficient than established homogeneous catalysts for aerobic oxidation of HQ to BQ, and this improved reactivity is crucial to support aerobic oxidation of primary alcohols to aldehydes with the homogeneous iridium catalyst, [Ir(trop 2 DAD]OTf (trop 2 DAD= N , N ‐bis(5‐ H ‐dibenzo[ a , d ]cycloheptene‐5‐yl)‐1,4‐diazabuta‐1,3‐diene). The combination of this heterogeneous/homogeneous catalyst system operates with Ir catalyst loadings as low as 0.05 mol % and turnover frequencies ≥350 h −1 .

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

Heterogeneous Fe‐N‐C Cocatalyst for Hydroquinone Oxidation Enables Aerobic Oxidation of Primary Alcohols to Aldehydes

Abstract Benzoquinone (BQ) is commonly used as a cocatalyst in multi‐component catalyst systems for aerobic oxidation of organic molecules. Such methods often proceed by a redox cascade in which a secondary catalyst supports aerobic oxidation of hydroquinone (HQ) to BQ. The present study shows that a commercially available non‐precious metal heterogeneous catalyst, PAJ‐Fe‐N‐C, is much more efficient than established homogeneous catalysts for aerobic oxidation of HQ to BQ, and this improved reactivity is crucial to support aerobic oxidation of primary alcohols to aldehydes with the homogeneous iridium catalyst, [Ir(trop 2 DAD]OTf (trop 2 DAD= N , N ‐bis(5‐ H ‐dibenzo[ a , d ]cycloheptene‐5‐yl)‐1,4‐diazabuta‐1,3‐diene). The combination of this heterogeneous/homogeneous catalyst system operates with Ir catalyst loadings as low as 0.05 mol % and turnover frequencies ≥350 h −1 .

Asmaul Hoque, Md [Department of Chemistry Universi↗
DOE OSTI2020

The Role of Co-ZSM-5 Catalysts in Aerobic Oxidation of Ethylbenzene

Various forms of cobalt catalysts have been studied extensively for selective aerobic oxidation of hydrocarbons. However, it remains unclear whether cobalt can directly activate molecular oxygen under mild reaction conditions. Here we investigated the catalytic roles of cobalt in ethylbenzene oxidation with and without a hydroperoxide initiator. The contribution of different cobalt species was studied by varying the metal loading on Co-impregnated ZSM-5 samples. Quantitative EPR was used to determine the impact of cobalt catalysts on the free radical concentrations. Furthermore, this work provided strong evidence that cobalt, in several different forms, catalyzes hydrocarbon oxidation by facilitating peroxy bond cleavage, instead of direct oxygen activation.

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

Optimizing the Synthetic Potential of O 2 : Implications of Overpotential in Homogeneous Aerobic Oxidation Catalysis

Molecular oxygen is the quintessential oxidant for organic chemical synthesis, but many challenges continue to limit its utility and breadth of applications. Extensive historical research has focused on overcoming kinetic challenges presented by the ground-state-triplet electronic structure of O 2 and the various reactivity and selectivity challenges associated with reactive oxygen species derived from O 2 reduction. This Perspective will analyze thermodynamic principles underlying catalytic aerobic oxidation reactions, borrowing concepts from the study of the oxygen reduction reaction (ORR) in fuel cells. This analysis is especially important for "oxidase"-type liquid-phase catalytic aerobic oxidation reactions, which proceed by a mechanism that couples two sequential redox half-reactions: (1) substrate oxidation, and (2) oxygen reduction, typically affording H 2 O 2 or H 2 O. The catalysts for these reactions feature redox potentials that lie between the potentials associated with the substrate oxidation and oxygen reduction reactions, and changes in the catalyst potential lead to variations in effective overpotentials for the two half reactions. Catalysts that operate at low ORR overpotential retain more thermodynamic driving force for the substrate oxidation step, enabling O 2 to be used in more challenging oxidations. While catalysts that operate at high ORR overpotential have less driving force available for substrate oxidation, they often exhibit different or improved chemoselectivity relative to the high-potential catalysts. The concepts are elaborated in a series of case studies to highlight their implications for chemical synthesis. Examples include comparisons of (a) NO x /oxoammonium and Cu/nitroxyl catalysts, (b) high-potential quinones and amine oxidase biomimetic quinones, and (c) Pd aerobic oxidation catalysts, with or without NO x cocatalysts. In addition, we show how reductive activation of O 2 provides a means to access potentials not accessible with conventional oxidase-type mechanisms. Altogether, this analysis highlights the central role of catalyst overpotential in guiding the development of aerobic oxidation reactions.

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

Heterogeneous M-N-C Catalysts for Aerobic Oxidation Reactions: Lessons from Oxygen Reduction Electrocatalysts

Nonprecious metal heterogeneous catalysts composed of first-row transition metals incorporated into nitrogen-doped carbon matrices (M-N-Cs) have been studied for decades as leading alternatives to Pt for the electrocatalytic O 2 reduction reaction (ORR). More recently, similar M-N-C catalysts have been shown to catalyze the aerobic oxidation of organic molecules. Here, this Focus Review highlights mechanistic similarities and distinctions between these two reaction classes and then surveys the aerobic oxidation reactions catalyzed by M-N-Cs. As the active-site structures and kinetic properties of M-N-C aerobic oxidation catalysts have not been extensively studied, the array of tools and methods used to characterize ORR catalysts are presented with the goal of supporting further advances in the field of aerobic oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Holey Lamellar High-Entropy Oxide as an Ultra-High-Activity Heterogeneous Catalyst for Solvent-free Aerobic Oxidation of Benzyl Alcohol

The development of noble-metal-free heterogeneous catalysts is promising for selective oxidation of aromatic alcohols; however, the relatively low conversion of non-noble metal catalysts under solvent-free atmospheric conditions hinders their industrial application. Now, a holey lamellar high entropy oxide (HEO) Co 0.2 Ni 0.2 Cu 0.2 Mg 0.2 Zn 0.2 O material with mesoporous structure is prepared by an anchoring and merging process. The HEO has ultra-high catalytic activity for the solvent-free aerobic oxidation of benzyl alcohol. Furthermore, up to 98% conversion can be achieved in only 2 h, to our knowledge, the highest conversion of benzyl alcohol by oxidation to date. By regulating the catalytic reaction parameters, benzoic acid or benzaldehyde can be selectively optimized as the main product. Analytical characterizations and calculations provide a deeper insight into the catalysis mechanism, revealing abundant oxygen vacancies and holey lamellar framework contribute to the ultra-high catalytic activity.

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

Cu‐Catalyzed Aerobic Oxidative C─C Cleavage in Lignin‐Derived Oligomers and Biological Funneling of the Monomeric Products

Existing methods for lignin deconstruction to aromatic monomers primarily cleave carbon–oxygen bonds within the polymer, resulting in sub-optimal monomer yields and formation of oligomers that retain intact carbon–carbon bonds. Here, we demonstrate that copper-catalyzed aerobic oxidation under aqueous alkaline conditions promotes oxidative cleavage of carbon–carbon bonds in lignin oligomers derived from reductive catalytic fractionation (RCF) of pine and poplar biomass. Fundamental insights are gained from reactions of model compounds that resemble subunits present in RCF oligomers. Optimal results are achieved in a flow reactor that provides precise control over O2 delivery, temperature, and reaction residence time. The Cu-catalyzed aerobic oxidation conditions access aromatic monomers in 19 and 34 wt% monomer yields, respectively, from pine- and poplar-derived RCF oligomers. Overall, the sequence consisting of biomass RCF into monomers and oligomers followed by oxidative deconstruction of the RCF oligomers generates substantially higher yields of aromatic monomers from lignin. Engineered strains of Pseudomonas putida support biological funneling of the oligomer-derived oxygenated aromatic compounds into cis,cis-muconic acid from pine or 2-pyrone-4,6-dicarboxylic acid from poplar.

09 BIOMASS FUELS↗
DOE OSTI2023

Mechanistic Studies to Enable Aerobic Oxidation of C-H Bonds by Manganese Catalysts (Final Report)

The project Mechanistic Studies to Enable Aerobic Oxidation of C-H Bonds by Manganese Catalysts provided fundamental new insight into the factors affecting hydrocarbon oxidation reactions by manganese-oxo complexes. These insights stem from the development of a structure-function relationship, whereby particular molecular properties of manganese(IV)-oxo complexes were shown to correlate to their efficacy in hydrocarbon oxidation reactions. This work is important, as manganese oxidation catalysts have seen increasing use in synthetic transformations, including reactions relevant to the synthesis of pharmaceuticals and other value-added chemicals. The desirability of developing new manganese catalysts stems from the inexpensive nature and low toxicity of the metal manganese, which contrasts with the high cost and toxicity of many other metals. The work carried out by this project was disseminated to the scientific community in the form of 14 peer-reviewed publications and over twenty presentations. In addition, the research results were incorporated into graduate and undergraduate courses at the University of Kansas, providing additional means of dissemination.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Heterogenization of polyoxometalates as solid catalysts in aerobic oxidation of glycerol

A series of heterogeneous catalysts based on phosphomolybdic salts with different metals in counter or substituent positions, L n PMo 12 O 40 (L = Al 3+ , Fe 3+ , Cr 3+ , Ti 4+ , Zr 4+ and Zn 2+ , abbreviated as LPMo 12 ) and H x PMo 11 LO 39 (L = Zn 2+ , Cr 3+ , Fe 3+ , Al 3+ , Ti 4+ , for Ti 4+ ; the amount of O is 40, abbreviated as HPMo 11 L), were prepared using a simple calcination treatment and were evaluated in aerobic oxidation of glycerol. After calcination at about 250 °C for 4 h, homogeneous Ln P Mo 12 O 40 ·nH 2 O and H x PMo 11 LO 39 ·mH 2 O became heterogeneous. Their specific surface areas were also enhanced as well as their activity and reusability. Similar to the homogeneous catalysts, AlPMo 12 treated at 400 °C (AlPMo 12 -400) was found to be the most active catalyst in glycerol oxidation to lactic acid, with 96.1% yield and 98.6% conversion at 60 °C for 5 h with 1 MPa of O 2 ; it gave a turnover number (TON; TON = [LA]/[catalyst]) of 2.4 × 10 2 , higher than that of AlPMo 12 -250 treated at 250 °C (TON = 2.0 × 10 2 ). AlPMo 12 behaved as a heterogeneous catalyst in glycerol oxidation and could be reused at least 12 times. AlPMo 12 -400 also performed well in crude glycerol oxidation, affording lactic acid yields as high as 86.8%.

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

Mechanistic investigation of the aerobic oxidation of 2-pyridylacetate coordinated to a Ru(ii) polypyridyl complex

A new ruthenium polypyridyl complex, [Ru(bpy) 2 (acpy)] + (acpy = 2-pyridylacetate, bpy = 2,2'-bipyridine), was synthesized and fully characterized. Distinct from the previously reported analog, [Ru(bpy) 2 (pic)] + (pic = 2-pyridylcarboxylate), the new complex is unstable under aerobic conditions and undergoes oxidation to yield the corresponding α-keto-2-pyridyl-acetate (acpyoxi) coordinated to the Ru II center. The reaction is one of the few examples of C–H activation at mild conditions using O 2 as the primary oxidant and can provide mechanistic insights with important implications for catalysis. Theoretical and experimental investigations of this aerobic oxidative transformation indicate that it takes place in two steps, first producing the α-hydroxo-2-pyridyl-acetate analog and then the final product. The observed rate constant for the first oxidation was in the order of 10 -2 h -1 . The reaction is hindered in the presence of coordinating solvents indicating the role of the metal center in the process. Theoretical calculations at the M06-L level of theory were performed for multiple reaction pathways in order to gain insights into the most probable mechanism. Our results= indicate that O 2 binding to [Ru(bpy) 2 (acpy)] + is favored by the relative instability of the six-ring chelate formed by the acpy ligand and the resulting Ru III -OO˙- superoxo is stabilized by the carboxylate group in the coordination sphere. C–H activation by this species involves high activation free energies (ΔG ‡ = 41.1 kcal mol -1 ), thus the formation of a diruthenium μ-peroxo intermediate, [(Ru III (bpy) 2 (O-acpy)) 2 O 2 ] 2+ via interaction of a second [Ru(bpy) 2 (acpy)] + was examined as an alternative pathway. The dimer yields two Ru IV =O centers with a low ΔG ‡ of 2.3 kcal mol -1 . The resulting Ru IV =O species can activate C–H bonds in acpy (ΔG ‡ = 23.1 kcal mol -1 ) to produce the coordinated α-hydroxo-2-pyridylacetate. Further oxidation of this intermediate leads to the α-keto-2-pyridyl-acetate product. The findings provide new insights into the mechanism of C–H activation catalyzed by transition-metal complexes using O 2 as the sole oxygen source.

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

Evaluating the Origins of Aerobic Oxidation Catalysis with TAM-3, a MOF with Accessible Co(II) Sites and Large Pores

Metal-organic frameworks (MOFs) are attractive platforms that merge concepts of homogeneous and heterogeneous catalysis. Catalyst design and optimization are enabled by an array of synthetic methods that offer independent control over the local chemical structure of lattice-embedded metal ions (i.e., ligand identity and geometry) and the long-range materials properties (i.e., porosity). Establishing the origin of catalytic activity in MOF-promoted reactions remains a significant challenge: The relative rates of catalyst turnover and substrate diffusion dictate the extent to which interstitial sites are accessible and operational in catalysis. To minimize the contributions of surface sites in catalysis, materials with large pore dimensions are often sought, however, the impact of pore expansion on the origins of catalytic activity is similarly challenging to establish. Here, we describe TAM-3, a Co(II) based MOF with accessible metal sites supported by a facially coordinating tris-tetrazole ligand set. TAM-3 features large channel-like pores (17 × 23 Å) and promotes aerobic C−H oxidation and olefin epoxidation. Using a set of simple kinetics experiments, based on the analysis of kinetic isotope effects and olefin oxidation diastereoselectivities, we demonstrate that despite the large pores, interstitial metal ions do not significantly contribute to the observed substrate oxidation. This study highlights the importance of conducting kinetic experiments to assess the origin of apparent catalytic activity with MOFs and the challenge of harnessing reactive oxidants with microporous catalyst materials.

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

Enhanced Oxygen Activation Achieved by Robust Single Chromium Atom-Derived Catalysts in Aerobic Oxidative Desulfurization

Oxidative desulfurization (ODS) plays critical roles in the production of high-quality sulfur impurity-free fuels, especially procedures using molecular oxygen as the sole oxidant. However, the state-of-the-art systems still rely on noble metal nanocatalysts, with deactivation issues caused by coking and sintering still present. In this work, leveraging the merits of single-atom catalysts (SACs) with earth-abundant metal cores and robust nanoporous supports, a series of catalysts composed of homogeneously distributed single chromium atoms anchored on multiwalled carbon nanotubes were fabricated and deployed to catalyze the aerobic ODS transformation. Adopting aromatic sulfur compound (ASC)-containing alkanes as a model system with molecular oxygen as the oxidant, efficient oxygen-to-active O 2 •– transformation and subsequent ASCs-to-sulfone conversion have been achieved, with the former benefiting from the chromium-active sites and the latter arising from the robust, nanoporous, and π-conjugated architecture of the supports. The attractive catalytic performance and cycling stability of the chromium-based SACs make them promising candidates in practical sulfur species removal from liquid fuels, supplying an alternative guidance on the catalyst design toward cost-effective and energy-efficient ODS procedures.

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

Spontaneous N 2 formation by a diruthenium complex enables electrocatalytic and aerobic oxidation of ammonia

The electrochemical conversion of ammonia to dinitrogen in a direct ammonia fuel cell (DAFC) is a necessary technology for the realization of a Nitrogen Economy. Previous efforts to catalyze this reaction with molecular complexes require the addition of exogenous oxidizing reagents or application of potentials greater than the thermodynamic potential for the oxygen reduction reaction (ORR) – the cathodic process of a DAFC. We report a stable metal–metal bonded diruthenium complex that spontaneously produces dinitrogen from ammonia under ambient conditions. The resulting reduced diruthenium material can be re-oxidized with oxygen for subsequent reactions with ammonia, demonstrating its ability to spontaneously promote both half reactions necessary for a DAFC. Here, the diruthenium complex also acts as a redox mediator for the electrocatalytic oxidation of ammonia to dinitrogen at potentials as low as –255 mV vs Fc 0/+ and operates below the ORR potential in alkaline conditions, thus achieving a thermodynamic viability relevant for the future development of DAFCs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗