Atm O2 Research Articles

Aerobic Ammoxidation of Cyclic Ketones to Dinitrile Products with Copper-Based Catalysts.

Adiponitrile (ADN) has wide applications, especially in the polymer industry. With the substantial and increasing global demand for ADN, effective production of ADN using safe and abundant starting materials is highly desirable but very challenging. Herein, we discovered that CuBr, combined with 1,10-phenanthroline (phen), could effectively promote the ammoxidation reaction of cyclohexanone to ADN with a yield of >99% using aqueous ammonia as the nitrogen source and O2 as the terminal oxidant under mild reaction conditions (80 °C, 5 atm O2). Moreover, cyclic ketones with various carbon numbers and substituent groups could also be converted into the corresponding dinitrile products with high yields. A detailed mechanistic study revealed that the reaction proceeded through a radical-mediated pathway, and the reason for the high selectivity to ADN was discussed. This study offers a new, simple, and cost-effective route to produce ADN and other dinitrile products.

Facile Interfacial Reduction Suppresses Redox Chemical Expansion and Promotes the Polaronic to Ionic Transition in Mixed Conducting (Pr,Ce)O2-δ Nanoparticles.

Mixed ionic/electronic conductors (MIECs) are essential components of solid-state electrochemical devices, such as solid oxide fuel/electrolysis cells. For efficient performance, MIECs are typically nanostructured, to enhance the reaction kinetics. However, the effect of nanostructuring on MIEC chemo-mechanical coupling and transport properties, which also impact cell durability and efficiency, has not yet been well understood. In this work, Pr0.2Ce0.8O2-δ (PCO20) nanopowders were prepared by coprecipitation, then sintered in a modified dilatometer at three different temperatures (600, 725, and 850 °C) for microstructure evolution, resulting in three samples with different average particle sizes (23, 30, and 53 nm). The chemical strain and electronic/ionic conductivity were then measured simultaneously on stable nanostructures in four isotherms from 550 to 400 °C with steps in pO2 (1 to 10-4 atm O2). A microcrystalline bar was prepared and measured for comparison. Particle size reduction led to a monotonically decreasing isothermal redox chemical strain, confirmed by in situ high-temperature, controlled-atmosphere XRD measurements. The corresponding conductivity measurements provided defect chemical insight into the particle size-dependent chemical expansion behavior. The significant weakening of the pO2 dependence and decreased activation energy for electrical conduction with decreasing particle size indicated a decrease in the reduction enthalpy of PCO, shifting the transition from (Pr) polaronic to ionic behavior to higher pO2. STEM-EELS measurements confirmed the majority of Pr was reduced to 3+ in the nanoparticles, while Ce remained 4+. These results demonstrate suppression of deleterious chemical expansion and tailoring of the dominant charge carrier simply through controlling the particle size, providing insights for MIEC microstructural design.

Effect of N2/I2 atmosphere annealing sensitization on PbSe-based photodetector for NIR photodetection

Lead selenide (PbSe) detectors have garnered widespread utility in infrared detection due to their advantages of low-Russian compounding and uncooled operation. In this study, PbSe thin films were firstly deposited on glass using selenourea (SeC(NH2)2) as the selenium source by chemical bath deposition. The changes in morphology, composition, structure, and photoelectric properties of PbSe films thermally sensitized in 4 atm of O2, N2, O2/I2, and N2/I2 were investigated. It was discovered that PbI2 was supplied to the film surface following thermal sensitization in the I2 atmosphere to create a PbSe/PbI2 separation model, promoting photogenerated charge separation and enhancing PbSe optoelectronics' performance. The device's dark current is decreased to 1/136 before annealing, the on-off ratio is increased by 18.7 times, the reaction time is only a few tens of μs, and the response speed is increased by 105 times after N2/I2 thermal sensitization.

Photosensitizer-free singlet oxygen generation via a charge transfer transition involving molecular O2 toward highly efficient oxidative coupling of arylamines to azoaromatics.

Photosensitizer (PS)-mediated generation of singlet oxygen, O2 (a1Δg) is a well-explored phenomenon in chemistry and biology. However, the requirement of appropriate PSs with optimum excited state properties is a prerequisite for this approach which limits its widespread application. Herein, we report the generation of O2 (a1Δg) via direct charge-transfer (CT) excitation of the solvent-O2 (X3Σg -) collision complex without any PS and utilize it for the catalyst-free oxidative coupling of arylamines to azoaromatics under ambient conditions in aqueous medium. Electron paramagnetic resonance (EPR) spectroscopy revealed the formation of O2 (a1Δg) upon direct excitation with 370 nm light. The present approach shows broad substrate scope, remarkably fast reaction kinetics (90 and 40 min under an open and O2 atm, respectively), high selectivity (100%), and excellent yields (up to 100%), and works well for both homo- and hetero-coupling of arylamines. The oxidative coupling of arylamines was found to proceed through the generation of amine radicals via electron transfer (ET) from amines to O2 (a1Δg). Notably, electron-rich amines show higher yields of azo products compared to electron-deficient amines. Detailed mechanistic investigations using various spectroscopic tools revealed the formation of hydrazobenzene as an intermediate along with superoxide radicals which subsequently transform to hydrogen peroxide. The present study is unique in the way that molecular O2 simultaneously acts as a light-absorbing chromophore (solvent-O2 complex) as well as an efficient oxidant (O2 (a1Δg)) in the same reaction. This is the first report on the efficient, selective, and sustainable synthesis of azo compounds in aqueous medium under an ambient atmosphere without any PCs/PSs and paves the way for further in-depth understanding of the chemical reactivity of O2 (a1Δg) generated directly via CT excitation of the solvent-O2 complex toward various photochemical and photobiological transformations.

Anderson-type polyoxometalate-based metal-organic framework as an efficient heterogeneous catalyst for selective oxidation of benzylic C-H bonds.

Oxidative transformation of benzylic C-H bonds into functional carbonyl groups under mild conditions represents an efficient method for the synthesis of aromatic carboxylic acids and ketones. Here we report a high-efficiency catalyst system constructed from an Anderson-type polyoxometalate-based metal-Organic framework (POMOF-1) and N-hydroxyphthalimide (NHPI) for selective oxidation of methylarenes and alkylarenes under 1 atm O2 atmosphere. POMOF-1 exerted a synergistic effect originating from the well-aligned Anderson {CrMo6} clusters and Cu centers within the framework, and this entailed good cooperation with NHPI to catalyze the selective oxidation. Accordingly, the reactions exhibit good tolerance and chemical selectivity for a wide range of substrates bearing diverse substituent groups, and the corresponding carboxylic acids and ketones were harvested in good yields under mild conditions. Mechanism study reveals that POMOF-1 worked synergistically with NPHI to activate the benzylic C-H bonds of substrates, which are sequentially oxidized by oxygen and HOO˙ to give rise to the products. This work may pave a way to design high-efficiency catalysts by integration of polyoxometalate-based materials with NPHI for challenging C-H activation.

Room‐Temperature Aerobic Oxidation of Amines to Nitriles over Ruthenium Oxide Supported on CeO2 Derived from MOFs

AbstractHeterogenous BPDC−RuO2−CeO2 catalyst derived from Ce−BPDC MOFs can successfully enable the oxidation of amines to nitriles under mild conditions (1 atm O2, H2O as a solvent, room temperature). The catalytic system has the good compatibility with benzylic and aliphatic amines. Lewis acid‐base pairs [Ru−O−Ce−Vö] formed by the combination of acidic oxygen vacancy and basic oxygen pair Ru−O−Ce on the surface of the catalyst is the key factor for the catalytic activity. The mechanical experiments indicate that amines adopt the step‐by‐step dehydrogenation process to nitriles in this transformation. Moreover, the catalyst could be recycled up to six times without the evident loss of catalytic activity and the change of morphology.

Oxygen Non-Stoichiometry and Point Defect Equilibria in (La1/6Pr1/6Nd1/6Gd1/6Ba1/6Sr1/6)MnO3- δ

Compositionally complex oxides (CCOs), also referred to as high entropy oxides, have several different cations (typically 5 or more) occupying a single site. CCOs have shown unique dielectric, ionic conductivity, and thermal conductivity properties, in addition to promising electrochemical properties for solid oxide fuel cells (SOFCs) [1,2]. In this work, the A-site of the common SOFC cathode La0.8Sr0.2MnO3-δ (LSM) is modified with additional lanthanide and alkali elements, resulting in the composition (La1/6Pr1/6Nd1/6Gd1/6Ba1/6Sr1/6)MnO3- δ. Typically, the average lattice parameter is correlated with bond length and strength, and thus energetics of oxygen vacancy formation energy. In the compositionally complex system, there is a wide range of cation radii on the A-site and so bond strengths are expected to vary significantly, resulting in a distribution of oxygen vacancy formation energies. Initial results have shown that the amount of oxygen released during reduction is significantly greater for the studied CCO in comparison with La2/3Sr1/3MnO3-δ, the latter having the same amount of total acceptor dopant and with a similar lattice parameter as the CCO. The significant enhancement in oxygen loss is an indicator of a lower reduction enthalpy and suggests a significant impact from atomic structure that is not captured in long-range structure parameters (i.e., average lattice parameter). The oxygen non-stoichiometry measured by thermogravimetric analysis in ~10-5 – 1 atm O2 at 1200 oC – 1450 oC will be presented and the point defect equilibria analysis will be discussed. Comparisons with existing high temperature experimental and modeling studies on LSM will also be discussed.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525References[1] Xu, Y., et al., J. Adv. Ceram., 11 (2022) 794, DOI:10.1007/s40145-022-0573-7[2] J. Dabrowa, et al., J. Mater. Chem. A, 8 (2020) 24455; DOI:10.1007/s40145-022-0573-7

Dayglow O2 Atm emission observations at equatorial and low latitudes by WINDII

Observations of the dayglow O2 Atm (0,0) band emission by the WINDII experiment on the UARS for 1992 and 1993 have been employed to study the emission's temporal and spatial variability at equatorial and low latitudes encompassing the latitude range of 30°N to 30°S. The WINDII O2 Atm (0,0) dayglow volume emission rates (VER) allowed day-to-day examination of their morphology over the altitude range from 80 km to 120 km altitude. The dayglow O2 Atm (0,0) VER revealed double-layered structures with peaks at about 88 km and at 98 km. Most of the O2 Atm (0,0) VER had their peak altitude at 88–92 km and their zonal variability to a great extent reflected the effect of diurnal tides, both seen in the elevated single peak on individual days and asymmetric with respect to the local noon. The upper peak at 98 km exhibited strong dependence on the local time and solar zenith angle, often centred around local noon, but independent of season as it became dominant or comparable to the lower peak for 12 LT ± 3 h. No upper peaks were observed before 8 LT and after 16 LT. Distinct wave-4 like signatures were observed embedded in the lower peak layer, at 88–90 km altitude. The double-layered structures when present often indicate a wave-4 like perturbations, more pronounced at the upper peak at 98 km. In the context of the double-layered structures observed and reported herein the ubiquitous presence of wave-4 perturbations suggest that these signatures result from tidal advection of [O] and the background atmosphere (N2, O2 and temperature).

Accelerated Perovskite Oxide Development for Thermochemical Energy Storage by a High‐Throughput Combinatorial Approach

AbstractThe structural and compositional flexibility of perovskite oxides and their complex yet tunable redox properties offer unique optimization opportunities for thermochemical energy storage (TCES). To improve the relatively inefficient and empirical‐based approaches, a high‐throughput combinatorial approach for accelerated development and optimization of perovskite oxides for TCES is reported here. Specifically, thermodynamic‐based screening criteria are applied to the high‐throughput density functional theory (DFT) simulation results of over 2000 A/B‐site doped SrFeO3−δ. 61 promising TCES candidates are selected based on the DFT prediction. Of these, 45 materials with pure perovskite phases are thoroughly evaluated. The experimental results support the effectiveness of the high‐throughput approach in determining both the oxygen capacity and the oxidation enthalpy of the perovskite oxides. Many of the screened materials exhibit promising performance under practical operating conditions: Sr0.875Ba0.125FeO3−δ exhibits a chemical energy storage density of 85 kJ kgABO3−1 under an isobaric condition (with air) between 400 and 800 °C whereas Sr0.125Ca0.875Fe0.25Mn0.75O3−δ demonstrates an energy density of 157 kJ kgABO3−1 between 400 °C/0.2 atm O2 and 1100 °C/0.01 atm O2. An improved set of optimization criteria is also developed, based on a combination of DFT and experimental results, to improve the effectiveness for accelerated development of redox‐active perovskite oxides.

Iron-incorporated metal-organic frameworks for oxidative cleavage of trans-anethole to p-anisaldehyde.

An iron-incorporated Zn-MOF catalyst Zn-bpydc·Fe was fabricated for the oxidative cleavage of trans-anethole to p-anisaldehyde under facile conditions, under 1 atm of O2. The Fe coordinated bipyridine serves as the catalytically active center inside the structural skeleton of Zn-MOFs. This work affords a new avenue for the mild oxidation of olefins.

Control of self-organization of drop-casted Nafion film for improving proton conduction in a polymer-electrolyte-membrane fuel cell to raise its output power density

A simple drop-cast method to directly deposit Nafion polymer electrolyte membrane (PEM) on nanostructured thin-film catalyst layer composed of stacked Pt nanoparticles prepared by pulsed laser deposition (PLD) was demonstrated. Through optimization of solvent composition and drying temperature of Nafion solution to control self-organization of Nafion, a uniform PEM with better bulk and interface microstructures could be produced, leading to a significant improvement in the output current density of a PEM fuel cell over that using reference commercial PEMs. The formation of facile proton conduction pathways in the bulk Nafion membrane resulted in a 35% reduction in ohmic resistance compared to that with the commercial membrane. Moreover, the infiltration of Nafion in the catalyst layer formed suitable proton transport network to render more catalyst nanoparticles effective and thus lower charge-transfer resistance. With the optimized PLD, drop-cast, and hot-pressing conditions, the current density of PEMFCs using drop-casted PEM reached 1902 mA cm−2 at 0.6 V at 2 atm H2 and O2 pressures with a cathode Pt loading of 100 μg cm−2, corresponding to a power density of 1.14 W cm−2 and a cathode mass-specific power density of 11.4 kW g−1.

Molten salt-induction of geometrically deformed ruthenium single atom catalysts with high performance for aerobic oxidation of alcohols

Recently, construction of single atom catalysts (SACs) for heterogeneous organic transformations has attracted great interest, but accomplishing high selectivity for a specific product under mild conditions remains challenging. Herein, we report a facile molten salt-induced strategy for creating Ru single atoms anchored onto a geometrically deformed nitrogen-doped carbon (Ru1/NC) support. This Ru catalyst is characterized by a range of methods, including advanced electron microscopy and X-ray absorption spectroscopy. The results show that the Ru single atom catalyst is highly effective for benzyl alcohol oxidation reaction, achieving an exceptional catalytic efficiency (1 atm O2 @ 90 °C) with more than 99 % selectivity for benzaldehyde under nearly 100 % conversion, along with a high initial turnover frequency up to 1213 h−1. Moreover, excellent recyclability and substrate tolerance ability are validated. Density functional theory calculations further indicate that the high catalytic reactivity stems from strong electronic metal-support interactions. This work provides a new avenue in designing single atom catalysts at the atomic level for organic transformations.

Ionic liquid-modulated aerobic oxidation of isoeugenol and β-caryophyllene via nanoscale Cu-MOFs under mild conditions

Novel synergistic systems based on Cu-1,3,5-benzenetricarboxylate and ionic liquid are developed for the convenient conversion of renewable olefins, isoeugenol and β-caryophyllene, under very mild conditions (i.e. 313 K and 1 atm O2). Using acidic ionic liquid [C4mim][HSO4] (5.0 mol%) as co-catalyst, Cu3(BTC)2-Lauric acid (LA) afforded high selectivity (95.8%) and excellent yield (86.3%) for vanillin methyl ketone during the aerobic oxidation of isoeugenol. In comparison, 91.1% selectivity for vanillin together with 28.9% conversion of isoeugenol was obtained over Cu3(BTC)2-LA in the presence of amino acid ionic liquid, [C4mim][Ala]. Additionally, 91.3% selectivity and 86.5% yield for β-caryophyllene epoxide were provided by Cu3(BTC)2-LA with the aid of neutral [C4mim]Cl (5.0 mol%), indicating the importance of different types of ILs in tuning the microenvironments of designed Cu3(BTC)2-LA nanosystems. Simultaneously, Cu3(BTC)2-LA/IL showed superior stability during above-mentioned transformations, as verified by TEM, FT-IR and XRD analyses. Insights into the synergistic free radical routes were supported by fluorescence and DRUV-Vis characterizations.

Facile Synthesis of Single Iron Atoms over MoS2 Nanosheets via Spontaneous Reduction for Highly Efficient Selective Oxidation of Alcohols.

The facile creation of high-performance single-atom catalysts (SACs) is intriguing in heterogeneous catalysis, especially on 2D transition-metal dichalcogenides. An efficient spontaneous reduction approach to access atomically dispersed iron atoms supported over defect-containing MoS2 nanosheets is herein reported. Advanced characterization methods demonstrate that the isolated iron atoms situate atop of molybdenum atoms and coordinate with three neighboring sulfur atoms. This Fe SAC delivers exceptional catalytic efficiency (1 atm O2 @ 120°C) in the selective oxidation of benzyl alcohol to benzaldehyde, with 99% selectivity under almost 100% conversion. The turnover frequency is calculated to be as high as 2105 h-1 . Moreover, it shows admirable recyclability, storage stability, and substrate tolerance. Density functional theory calculations reveal that the high catalytic activity stems from the optimized electronic structure of single iron atoms over the MoS2 support.

Scaling behavior of four ternary Co-20Ni-based alloys containing 3/5 wt% Al or 8/15 wt% Cr in 1 Atm O2 at 800–900 °C

The oxidation in 1 atm O2 of two Co-20Ni-yAl (y = 3,5 wt%), two Co-20Ni-xCr (x = 8,15 wt%) and a Co-20Ni alloy was studied at 800–900 °C. Except for Co-20Ni-15Cr oxidized at 900 °C, all the ternary alloys oxidized more rapidly than the binary alloy Co-20Ni at both temperatures. A thin protective oxide layer formed only on the surface of the ternary alloy Co-20Ni-15Cr by oxidation at 900 °C. In all the other cases the scales contained an outer layer of Co-Ni oxide plus an inner layer of Co-Ni oxide mixed with spinels and a zone of internal oxidation.

Synthesis of 2-hydroxytetrahydrofurans by Wacker-type oxidation of 1,1-disubstituted alkenes.

1,1-Disubstituted alkenes feature high steric hindrance, which renders their Wacker-type oxidation difficult. We demonstrate the stereoselective synthesis of 2-hydroxytetrahydrofurans via the Wacker-type oxidation of 3-methyl-3-buten-1-ols by using a PdCl2(MeCN)2/NO/BQ catalyst system under 1 atm O2 in H2O or H2O/DMF.

Palladium‐Catalyzed Aerobic α,β‐Dehydrogenation of Carboxylic Acids

AbstractThe aerobic dehydrogenation of saturated carboxylic acids to α,β‐unsaturated carboxylic acids proceeded by a simple Pd(OAc)2/pyridine catalyst system under 1 atm of O2. β‐Acyloxylated carboxylic acids were also produced from propionic acid and butyric acid by the conjugate addition of the substrates to the formed α,β‐unsaturated carboxylic acids. When propionic acid was used as a substrate,trans‐Pd(OCOEt)2(pyridine)2was formedin situas a precatalyst. The kinetic experiments indicated that Pd(OCOR)2(pyridine) is a catalytically active species and that β‐C(sp3)−H bond activation in the carboxylate ligand is the turnover‐limiting step. The DFT calculations agreed with the mechanism.

Scaling behavior of four Co-20Ni-xCr-yAl (x = 8,15 wt.%; y = 3,5 wt.%) alloys exposed to 1 atm O2 at 1000 °C and 1100 °C

The oxidation of four Co-20Ni-xCr-yAl (x = 8,15 wt.%; y=3,5 wt.%) alloys in 1 atm of pure oxygen was studied at 1000 °C and 1100 °C. All the alloys formed complex scales. The alloy with lowest Cr and Al contents corroded much more rapidly than the other three materials. Incomplete external alumina scales formed only on the alloys containing 5 wt.% Al (at 1100 °C for Co-20Ni-8Cr-5Al and at 1000 °C and 1100 °C for Co-20Ni-15Cr-5Al). More than 5 wt.% Al is required to form continuous external alumina layers on alloys with 8–15 wt.% Cr.

Oxidative Cleavage of Alkenes by O2 with a Non-Heme Manganese Catalyst.

The oxidative cleavage of C=C double bonds with molecular oxygen to produce carbonyl compounds is an important transformation in chemical and pharmaceutical synthesis. In nature, enzymes containing the first-row transition metals, particularly heme and non-heme iron-dependent enzymes, readily activate O2 and oxidatively cleave C=C bonds with exquisite precision under ambient conditions. The reaction remains challenging for synthetic chemists, however. There are only a small number of known synthetic metal catalysts that allow for the oxidative cleavage of alkenes at an atmospheric pressure of O2, with very few known to catalyze the cleavage of nonactivated alkenes. In this work, we describe a light-driven, Mn-catalyzed protocol for the selective oxidation of alkenes to carbonyls under 1 atm of O2. For the first time, aromatic as well as various nonactivated aliphatic alkenes could be oxidized to afford ketones and aldehydes under clean, mild conditions with a first row, biorelevant metal catalyst. Moreover, the protocol shows a very good functional group tolerance. Mechanistic investigation suggests that Mn–oxo species, including an asymmetric, mixed-valent bis(μ-oxo)-Mn(III,IV) complex, are involved in the oxidation, and the solvent methanol participates in O2 activation that leads to the formation of the oxo species.

Efficient Syntheses of Biobased Terephthalic Acid, p-Toluic Acid, and p-Methylacetophenone via One-Pot Catalytic Aerobic Oxidation of Monoterpene Derived Bio-p-cymene.

An efficient elevated-pressure catalytic oxidative process (2.5 mol % Co(NO3)2, 2.5 mol % MnBr2, air (30 bar), 125 °C, acetic acid, 6 h) has been developed to oxidize p-cymene into crystalline white terephthalic acid (TA) in ∼70% yield. Use of this mixed Co2+/Mn2+ catalytic system is key to obtaining high 70% yields of TA at relatively low reaction temperatures (125 °C) in short reaction times (6 h), which is likely to be due to the synergistic action of bromine and nitrate radicals in the oxidative process. Recycling studies have demonstrated that the mixed metal catalysts present in recovered mother liquors could be recycled three times in successive p-cymene oxidation reactions with no loss in catalytic activity or TA yield. Partial oxidation of p-cymene to give p-methylacetophenone (p-MA) in 55–60% yield can be achieved using a mixed CoBr2/Mn(OAc)2 catalytic system under 1 atm air for 24 h, while use of Co(NO3)2/MnBr2 under 1 atm O2 for 24 h gave p-toluic acid in 55–60% yield. Therefore, access to these simple catalytic aerobic conditions enables multiple biorenewable bulk terpene feedstocks (e.g., crude sulfate turpentine, turpentine, cineole, and limonene) to be converted into synthetically useful bio-p-MA, bio-p-toluic acid, and bio-TA (and hence bio-polyethylene terephthalate) as part of a terpene based biorefinery.