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Tuning OH binding energy enables selective electrochemical oxidation of ethylene to ethylene glycol
Abstract not provided
Evaluation of selected refractory oxide materials for use in high-temperature pebble- bed wind-tunnel heat exchangers
Refractory oxide materials for use in high temperature pebble-bed wind tunnel heat exchangers
A study of select ceramic oxide compositions as high temperature /1600-2100 deg k/ thermal energy storage materials final report. feb. 1962 - feb. 1963
Ceramic oxide compositions as high temperature thermal energy storage materials
Oxidation-chlorination of binary Ni-Cr alloys in flowing Ar-O2-Cl2 gas mixtures at 1200 K
Nickel-chromium alloys are resistant to oxidation because of the selective oxidation of chromium to form a protective Cr2O3 scale. In chlorine-containing environments, volatile corrosion products can also be formed. The mixed oxidation-chlorination of Ni-4.5Cr, Ni-13.8Cr, and Ni-26.5Cr (by weight) alloys in Ar-O2-Cl2 gas mixtures is investigated using thermogravimetric analysis and atmospheric-pressure-sampling mass spectrometry, followed by examination of the corrosion products using scanning electron microscopy and X-ray diffraction analysis. The overall kinetics of the corrosion are affected by the relative amounts of oxides and chlorides formed and the composition of the oxide corrosion products.
Bulk Preparation of Holey Graphene via Controlled Catalytic Oxidation
A scalable method allows preparation of bulk quantities of holey carbon allotropes with holes ranging from a few to over 100 nm in diameter. Carbon oxidation catalyst nanoparticles are first deposited onto a carbon allotrope surface in a facile, controllable, and solvent-free process. The catalyst-loaded carbons are then subjected to thermal treatment in air. The carbons in contact with the carbon oxidation catalyst nanoparticles are selectively oxidized into gaseous byproducts such as CO or CO.sub.2, leaving the surface with holes. The catalyst is then removed via refluxing in diluted nitric acid to obtain the final holey carbon allotropes. The average size of the holes correlates strongly with the size of the catalyst nanoparticles and is controlled by adjusting the catalyst precursor concentration. The temperature and time of the air oxidation step, and the catalyst removal treatment conditions, strongly affect the morphology of the holes.
ANALYSIS OF RADIOLYTIC HYDROGEN GENERATION FROM WATER ADSORBED ON SELECTED PLUTONIUM OXIDES
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Methanol Partial Oxidation on Cu(111) and PtCu(111) Single-Atom Alloy Surfaces: Effect of Surface Oxygen Coverage on Selectivity
The selective oxidation of methanol to formaldehyde on Cu surfaces is an important and well-studied reaction. However, a systematic analysis of product selectivity as a function of oxygen coverage on Cu(111) and Cu-based single-atom alloys (SAAs) has not been previously reported. In this work, we present a comprehensive investigation of deuterated methanol (CD 3 OH) partial oxidation on Cu(111) and 1% PtCu(111) SAA surfaces as a function of preadsorbed oxygen coverage. Temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) reveal that isolated Pt atoms inhibit the initial surface oxidation of Cu(111) under low oxygen exposures. Despite this difference in oxidation kinetics, the product selectivity remains largely unaffected: on both Cu(111) and PtCu(111), formaldehyde (CD 2 O) is the predominant partial oxidation product over a broad range of oxygen coverages. The selectivity toward formaldehyde peaks at intermediate oxygen coverages (∼0.3 monolayers, ML), indicating the existence of an optimal oxygen loading for partial oxidation. Notably, the similar product selectivities on Cu(111) and PtCu(111) over a range of surface oxygen coverage indicate that Pt single atoms do not significantly alter the reaction pathway or shift the optimal oxygen coverage for formaldehyde formation. Control experiments confirm that Cu(111) is unreactive toward methanol in the absence of oxygen, while PtCu(111) surfaces produce a small amount of formaldehyde even when oxygen is not preadsorbed, indicating that isolated Pt atoms facilitate O−H activation at below 150 K, leading to H 2 desorption, followed by C−D activation at higher temperatures (∼350 K). Density functional theory (DFT)-based calculations show that Pt atoms increase the O 2 dissociation barrier relative to Cu(111), consistent with the observed inhibition of oxidation at low exposures. Overall, this work provides the first detailed selectivity map for methanol oxidation on oxidized Cu(111) and PtCu(111) SAA surfaces. By linking classical mechanistic insights such as methoxy- and formate-mediated pathways with single-atom alloy catalyst design, this work demonstrates that while Pt substitution modulates the oxidation kinetics and oxygen binding, the overall selectivity toward formaldehyde is governed primarily by oxygen coverage. These findings underscore the potential of isolated dopants to tune surface oxidation behavior without compromising the intrinsic partial oxidation selectivity of copper-based catalysts.
Surface chlorination of IrO2(110) by HCl
The ability to controllably chlorinate metal-oxide surfaces can provide opportunities for designing selective oxidation catalysts. In the present study, we investigated the surface chlorination of IrO2(110) by HCl using temperature programmed reaction spectroscopy (TPRS), x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. We find that exposing IrO2(110) to HCl, followed by heating to 650 K in ultrahigh vacuum, produces nearly equal quantities of on-top and bridging Cl atoms on the surface, Clt and Clbr, where the Clbr atoms replace O-atoms that are removed from the surface by H2O formation. After HCl adsorption at 85 K, only H2O desorbs at low Cl coverages during TPRS, but HCl begins to desorb in increasing yields as the Cl coverage is increased above about 0.5 monolayer (ML). The desorption of Cl2 was not observed under any conditions, in good agreement with the high barrier for this reaction predicted by DFT. A maximum Cl coverage of 1 ML, with nearly equal coverages of Clt and Clbr atoms, could be generated by reacting HCl with IrO2(110) in UHV. Our results suggest that a kinetic competition between recombinative HCl and H2O desorption under the conditions studied limits the saturation Cl coverage to a value less than the 2 ML maximum predicted by thermodynamics. XPS further shows that the partitioning of Cl between the Clt and Clbr states can be altered by subjecting partially chlorinated IrO2(110) to reductive or oxidative treatments, demonstrating that the Cl site population can change dynamically in response to the gas environment. Our results provide insights for understanding the chlorination of IrO2(110) by HCl and can enable future experimental studies to determine how Cl-modification alters the surface chemical reactivity of IrO2(110) and potentially enhances selectivity toward partial oxidation chemistry.
Predicting the oxidative lifetime of beta NiAl-Zr alloys
Nickel aluminides containing 40 to 50 at. pct Al and 0.1 at. pct Zr were studied following cyclic oxidation at 1400 C. The selective oxidation of Al resulted in the formation of protective Al2O3 scales on each alloy composition. However, repeated cycling eventually resulted in the gradual formation of less-protective NiAl2O4, first appearing on the 40Al alloys followed at longer times on the 45Al alloys. The appearance of the NiAl2O4, signaling the end of the protective scale-forming capability of the alloy, was related to the presence of gamma-prime (Ni3Al) which formed as a result of the loss of Al from the sample. A diffusion model, based on finite-difference techniques, was developed to predict the protective life of beta Ni-Al alloys. This model predicts Ni and Al concentration profiles after various oxidation exposures. The model can predict the oxidative lifetime due to Al depletion when the Al concentration decreases to a critical concentration. Measured Al concentration profiles on two alloys after various oxidation exposures are compared to those predicted by the diffusion model. The time to the appearance of the NiAl2O4 and that predicted by the diffusion model are compared and discussed.
Impact of Particle Size on the Vapor-Phase Oxidative Coupling of Methanol and Dimethylamine over Palladium–Gold Nanoparticles
Oxidative coupling of methanol and dimethylamine in the presence of O 2 in the vapor phase over dilute Pd in Au bimetallic catalysts occurs via the dissociation of O 2 on Pd and selective oxidation of methanol on Au. Here, we synthesize a series of silica-supported PdAu alloy nanoparticle catalysts of varied Pd:Au ratios with ~5 nm particle diameter and show that these catalysts have increased selectivity to dimethylformamide across all Pd:Au ratios (~95%), distinct from observations over larger PdAu nanoparticles (~15–25 nm diameter) of similar Pd:Au ratios. Small monometallic Pd particles are more selective than large monometallic Pd particles, and small Au nanoparticles are reactive and selective for oxidative coupling (while large Au nanoparticles are inactive). Rates per surface metal atom were similar over PdAu nanoparticles of all sizes and increased monotonically with increasing Pd content for the small nanoparticles. Further, apparent reaction kinetics demonstrate distinct apparent methanol reaction order and apparent activation energy relative to those reported over larger nanoparticles of similar Pd:Au ratios. Unlike larger PdAu nanoparticles, the rate of dimethylformamide formation is not promoted by cofed water over small PdAu nanoparticles. The results of the kinetic studies are used to propose a series of elementary steps, derive a plausible rate expression, and regress rate and equilibrium constants. These results suggest high coverages of surface methoxy species and low coverages of adsorbates derived from dimethylamine. Taken together, these results demonstrate the sensitivity of the rates, selectivities, and kinetics of oxidative coupling reactions to the size of bimetallic nanoparticles.
Mechanism of O 2 /NO-Promoted Oxidative C–C Bond Cleavage in Linear Alkanes
Selective oxidation of alkanes to oxygenated products remains a fundamental challenge, particularly if the goal is to promote C−C bond cleavage while minimizing formation of CO 2 . Oxidation conditions that use O 2 and nitrogen oxides (NO x ) have been shown to be very effective in promoting radical-mediated functionalization and oxidative carbon−carbon cleavage in saturated hydrocarbon polymers, such as polyethylene. Here, we investigate the mechanism of O 2 /NO-mediated oxidation of ndecane as a prototypical linear alkane substrate. These reactions enable identification and quantification of reactive intermediates, including nitrites, nitrates, alcohols, and ketones. Under the reaction conditions, these species convert into common ketone intermediates that evolve into α-diketones and other α-functionalized ketones, which undergo further conversion into carboxylic acids. Infrared (IR) spectroscopy indicates that HDPE oxidation proceeds through similar key intermediates. Together, these findings establish a mechanistic framework for NO x -mediated alkane oxidation and provide a foundation for the development of broadly applicable oxidative transformations.
Mesoporous silica-encapsulated gold core–shell nanoparticles for active solvent-free benzyl alcohol oxidation
Silica-encapsulated gold core@shell nanoparticles (Au@SiO2 CSNPs) were synthesized via a bottom-up procedure and used to catalyze the selective oxidation of benzyl alcohol. The pore size, morphology, crystallinity and composition of Au@SiO2 was evaluated using non-local density functional theory, transmission electron microscopy, high-energy x-ray diffraction and inductively coupled plasma-mass spectroscopy, respectively. The nanoparticles exhibit a mesoporous shell with an average thickness of 25.5 Å which can enhance selectivity via preferential transport of the desired product (i.e., benzaldehyde) relative to larger, undesired products (i.e, benzoic acid/benzyl benzoate). GC-FID analysis revealed the addition of potassium carbonate to the solvent-free oxidation of benzyl alcohol increased conversion from 17.3 to 60.4% while decreasing selectivity from 98.7 to 75.0%. Under equivalent conditions, a bare gold nanoparticle control catalyst deposited on a silica support with a similar gold surface area took 6 times as long to reach the same conversion, achieving only 49.4% selectivity. These results suggest that the pore size distribution within the inert silica shell of Au@SiO2 CSNPs inhibits the formation of undesired products to facilitate the selective oxidation of benzaldehyde despite a basic environment, which reduces selectivity under typical conditions. The CSNPs demonstrated a much lower activation energy than the Au-SiO2 control catalyst, 37 ± 1.9 kJ/mol and 72 ± 7.1 kJ/mol, respectively. Thiele modulus analysis indicates the CSNP pore structure does not create a mass transport limitation due to the nano-scale path of diffusion through the pore structure to the active surface. The lower activation energy and mesopore distribution together suggest the Au@SiO2 catalyst demonstrates higher activity through beneficial in-pore orientation, both reducing competitive adsorption and promoting a single, lower activation energy mechanistic pathway.
Anodic Hydrogen Generation from Benzaldehyde on Au, Ag, and Cu: Rotating Ring-Disk Electrode Studies
Aldehydes are selectively oxidized to carboxylates on group 11 metals at low potentials (<0.4 V vs. RHE) in alkaline media. This process can occur by a pathway that generates H 2 gas from the aldehyde, known as electro-oxidative dehydrogenation (EOD) or anodic hydrogen production. The EOD process occurs with transfer of only one electron per aldehyde, whereas typical oxidation with discharge of hydrogen to form water is a two-electron process. Here, we study the catalytic activity and selectivity toward H 2 of Au, Ag, and Cu electrodes using benzaldehyde with rotating disk and ring-disk electrode (RDE/RRDE) techniques. The average number of electrons per benzaldehyde molecule obtained via H 2 detection by RRDE agrees with that obtained via Koutecký-Levich analysis conducted at various rotation rates. We find that Au and Ag have much higher H 2 and benzoate formation rates than Cu, but that Cu can perform the reaction at about 0.2 V lower overpotentials. On all three materials, benzaldehyde oxidation has high selectivity to anodic H 2 (one-electron pathway) below ∼0.5 V vs. RHE, but, with increasing potential, the selectivity shifts to H-oxidation forming water (two-electron pathway).
Separation of compounds
A method for separating liquids is disclosed. A feed stream is passed into a separator. The feed stream comprising an organic compound, carbon dioxide, and oxides selected from the group consisting of sulfur oxides, nitrogen oxides, ozone and combinations thereof. A portion an organic-rich stream is separated from a portion of an inorganic-rich stream through separation by gravity. The organic-rich stream contains a portion of the organic compound and a first portion of the carbon dioxide. The inorganic-rich stream contains a portion of the oxides and a second portion of the carbon dioxide.
Water-promoted interfacial pathways in methane oxidation to methanol on a CeO 2 -Cu 2 O catalyst
Highly selective oxidation of methane to methanol has long been challenging in catalysis. Here, we reveal key steps for the promotion of this reaction by water when tuning the selectivity of a well-defined CeO 2 /Cu 2 O/Cu(111) catalyst from carbon monoxide and carbon dioxide to methanol under a reaction environment with methane, oxygen, and water. Ambient-pressure x-ray photoelectron spectroscopy showed that water added to methane and oxygen led to surface methoxy groups and accelerated methanol production. These results were consistent with density functional theory calculations and kinetic Monte Carlo simulations, which showed that water preferentially dissociates over the active cerium ions at the CeO 2 –Cu 2 O/Cu(111) interface. The adsorbed hydroxyl species blocked O-O bond cleavage that would dehydrogenate methoxy groups to carbon monoxide and carbon dioxide, and it directly converted this species to methanol, while oxygen reoxidized the reduced surface. Water adsorption also displaced the produced methanol into the gas phase.
Mechanism of Chlorine-Mediated Electrochemical Ethylene Oxidation in Saline Water
Chlorine as a redox mediator allows for the selective oxidation of ethylene to 2-chloroethanol, which converts to ethylene oxide in alkaline aqueous electrolyte. This strategy utilizes abundant saline water as an electrolyte and source of oxygen atoms for functionalization. We present a mechanistic study of ethylene oxidation in saline water using cobalt oxide nanoparticle catalysts. Electrochemical kinetic analysis and in situ X-ray absorption spectroscopy suggest that the resting state of the catalyst and the rate-determining step differ for the chlorine evolution reaction in the presence and absence of ethylene. In 0.6 M NaCl pH 8 electrolyte, which resembles seawater, the average current density was ~60 mA/cm 2 with a Faradaic efficiency of ~41% toward ethylene functionalization. The use of synthetic and natural seawater achieved Faradaic efficiencies above 70%, while the partial current toward the product remained invariant. Further conversion of the initial product 2-chloroethanol into ethylene glycol was also demonstrated. Here, we present a broader vision of harnessing saline water in electrochemical functionalization of organic molecules and coproduction of hydrogen.