CO Precursor Research Articles

Reactivity Determinants in Electrodeposited Cu Foams for Electrochemical CO2 Reduction.

CO2 reduction is of significant interest for the production of nonfossil fuels. The reactivity of eight Cu foams with substantially different morphologies was comprehensively investigated by analysis of the product spectrum and in situ electrochemical spectroscopies (X-ray absorption near edge structure, extended X-ray absorption fine structure, X-ray photoelectron spectroscopy, and Raman spectroscopy). The approach provided new insight into the reactivity determinants: The morphology, stable Cu oxide phases, and *CO poisoning of the H2 formation reaction are not decisive; the electrochemically active surface area influences the reactivity trends; macroscopic diffusion limits the proton supply, resulting in pronounced alkalization at the CuCat surfaces (operando Raman spectroscopy). H2 and CH4 formation was suppressed by macroscopic buffer alkalization, whereas CO and C2 H4 formation still proceeded through a largely pH-independent mechanism. C2 H4 was formed from two CO precursor species, namely adsorbed *CO and dissolved CO present in the foam cavities.

Kinetics of plasma-assisted oxidation of highly diluted hydrocarbon mixtures excited by a repetitive nanosecond pulse discharge

Plasma-assisted oxidation of atmospheric pressure hydrogen- and hydrocarbon-oxygen mixtures diluted in argon is analyzed by kinetic modeling, over a wide range of temperatures. In the experiments, preheated reactant mixtures are excited by a repetitively pulsed, double dielectric barrier ns discharge in plane-to-plane geometry, at near-isothermal conditions. Plasma images and temperature distributions in the discharge indicate that the reactant flow is nearly uniform, justifying the use of quasi-0D approximation in kinetic modeling. The kinetic model is based on a plasma chemistry mechanism combined with a conventional combustion reaction mechanism. The model does not contain adjustable parameters such as reduced electric field in the plasma, used in a number of previous 0D modeling studies. Comparison of the modeling predictions with the experimental data for hydrogen and methane oxidation exhibits good agreement between measured and predicted fuel concentrations over a wide range of temperatures, showing that the yield of primary radicals generated in the plasma is predicted accurately. Concentrations of intermediate hydrocarbon species predicted by the model are also in good agreement with the experiments, with the exception of acetylene below the hot ignition point. For ethylene and propane oxidation, the model overpredicts fuel consumption at low temperatures, also overpredicting concentration of CO, the dominant oxidation product, and underpredicting acetaldehyde concentration. This indicates that low-temperature pathways of formaldehyde formation, a major precursor for CO, as well as low-temperature reactions of several radicals which are precursors for formaldehyde and acetaldehyde, are not represented accurately in both conventional reaction mechanisms used. Although concentrations of intermediate hydrocarbon species in ethylene and propane are predicted relatively well, kinetics of formation and decay of acetylene remains not understood. This may be due to inaccurate branching ratio for dissociative quenching of metastable argon by heavy hydrocarbon species, as well as deficiencies of the conventional reaction mechanisms.

Highly Active Ni-Based Catalyst Derived from Double Hydroxides Precursor for Low Temperature CO2 Methanation

The Ni nanoparticles supported on Al2O3 metal oxides with different Ni2+/Al3+ molar ratios from 1/1 to 6/1 (denoted as NixAL-MO) derived from Ni–Al hydrotalcite precursors (NixAl-LDHs) were prepared and applied to CO2 methanation at a low temperature. By adjusting the Ni2+/Al3+ ratios, the alkaline and reducibility of the catalysts were designed, and the catalysts showed efficient catalytic performance at a low temperature. The Ni5AL-MO catalyst demonstrated the highest CO2 conversion of 89.4% at 250 °C. The superior catalytic property was related to the basic property, readily reducible NiO species, and the cooperation of metal nanoparticles and basic sites. The reaction intermediate species formed on the catalyst surface were identified by in situ FTIR analysis, and the reduction mechanism of CO2 was revealed. Moreover, the Ni5Al-MO catalyst had excellent resistance to carbon deposition and metal sintering after a long reaction duration. The NixAl-LDHs as the catalyst precursor show a promising potentia...

Visible-light-activated photoCORMs: rational design of CO-releasing organic molecules absorbing in the tissue-transparent window.

To date, most known molecules that release carbon monoxide by the action of light are based on carbonyl complexes of metals. However, they suffer from several disadvantages, so the focus of this perspective is on photoactivatable metal-free CO precursors. The development and design of these systems from the starting point of deep-UV-absorbing hydrophobic molecules and leading to hydrophilic biocompatible visible-light-absorbing CO-releasing molecules (photoCORMs) is described with mechanistic details for several structural motifs. The possibilities of this development are not exhausted and here we discuss the design of new biologically interesting candidates.

Experimental study and chemical reactor network modeling of the high heating rate devolatilization and oxidation of pulverized bituminous coals under air, oxygen-enriched combustion (OEC) and oxy-fuel combustion (OFC)

Experimental and numerical investigations of the combustion of 2 bituminous coals under air, oxygen-enriched and oxy-fuel combustion conditions have been performed. 7 pulverized coal jet flames have been stabilized using a specifically designed flat flame reactor (FFR) allowing industrial heating rates to be reproduced. The investigated reacting media have been fully characterized in terms of temperature fields, fuel residence time, devolatilization rates and concentration profiles of O2, CO2, CO, NO and SO2. Obtained data have then been compared with predictions derived from a chemical reactor network (CRN) modeling approach. This latter incorporates a detailed reaction mechanism the formulation of which has been defined by comparing the results obtained through the implementation of 3 different detailed gas-phase combustion reaction schemes. On the whole, obtained numerical results show a good agreement with experimental data. By analyzing the reaction paths relying on the CRN predictions, the present study allowed highlighting and further exploring the influence played by the combustion atmosphere on the chemical pathways leading to species like CO, NO, SO2 or soot precursors. The main findings drawn through this work especially led to trace the increased CO concentrations measured under oxy-fuel combustion (OFC) to heightened HCO production and tar oxidation. Alternative NO formation pathways arising under OFC conditions (like the HCN → HNCO → NH → NO and HCN → NCO → HNCO → HNO → NO routes) have, moreover, been highlighted. While the SO2 production has been found to mainly depend on the quantity of fuel-S emitted during the devolatilization and on the local oxygen partial pressure (the main SO2 formation pathway being indeed not truly affected by the nature of the combustion atmosphere), the analysis of the main routes involved in the oxidation of aromatics such as benzene, naphthalene and phenanthrene has been found well insightful in order to explain some reduced soot productions recently reported in the literature under OFC.

Theoretical study of the CO formation mechanism in the CO2 gasification of lignite

Reactive force field (ReaxFF) molecular dynamics simulations of lignite and lignite-CO2 models were performed to investigate the CO formation mechanism of CO2 gasification process of lignite. A C++ program was developed to assess ReaxFF trajectories and to analyze elementary reactions involved in the mechanism. Calculated product distribution and relative amounts of main gas products show good agreement with reported experimental observations. We found that the CO formation pathways in the CO2 gasification of lignite begin with the chain carbon radical (Rn), which is formed by CH/CC bond cleavage reactions of aromatic moieties in the lignite or produced semicoke at high temperatures. These chain carbon radicals can react with CO2, forming oxidized carbon radicals, such as Rn-O-C-O, Rn-CO2 and Rn-O. Among these radicals, Rn-O and Rn-O-C-O are important precursors of CO. They produce CO molecules by releasing their C-O moieties at the end. The thermodynamic properties of these elementary reactions were obtained by density functional theory calculations at the B3LYP/6-311+G(2d,2p) level. The calculated overall enthalpy and entropy changes could clearly explain the experimental data. The density functional theory results show that most of these elementary reactions are endothermic and entropy increasing. High gasification temperatures are favorable for the reactions.

Perspectives of Single-Wall Carbon Nanotube Production in the Arc Discharge Process

<p>Single-wall carbon nanotubes (SWNTs) promise wide applications in many technical fields. As a result purified SWNT material is sold now on the West market at more than $1000 per 1 gram. Thus developing an effective technology for SWNTs production rises to a very important scientific problem. The perspectives of three existing methods providing raw material in the technology of SWNT production have been analyzed. They are i) pulsed laser evaporation of graphite/metal composites, ii) evaporation of graphite electrodes with metal content in the arc discharge process, and iii) catalytic decomposition of the mixture of CO and metal carbonyl catalyst precursor. The observed dynamics of SWNT market points to replacing the laser method of SWNTs production by the arc process. The conclusion has been made that the technology based on the arc process will be the major one for the fabrication of purified SWNTs at least for the next five years. A reliable estimation of a low price limit of SWNTs was derived from a comparison of two technologies based on the arc discharge process: the first one is the production of SWNTs and the second one is the production of a fullerene mixture С<sub>60</sub> + С<sub>70</sub>. The main conclusion was made that the price of purified SWNTs should always be more by 2-3 times the price of fullerene mixture. The parameters of a lab-scale technology for the production of purified SWNTs are listed. A large-scale application of the developed technology is expected to reduce the price of purified SWNTs by approximately ten times. The methods now employed for the characterization of products containing SWNTs are briefly observed. It is concluded that electron microscopy, thermogravimetric analysis, absorption and Raman spectroscopy, measurement of the specific surface aria, optical microscopy – each in separation is not enough for extensive characterization of a sample containing SWNTs, and all these methods should be used together.</p>

Palladium catalyzed aroylation of NH-sulfoximines with aryl halides using chloroform as the CO precursor

Abstract A palladium-catalyzed aroylation of NH-sulfoximines for the efficient synthesis of N -aroyl sulfoximines from aryl halides and chloroform has been developed. The mild reaction conditions (temperature, catalyst loading) and the use of a CO surrogate render this transformation a useful method for the synthesis of N -aroyl sulfoximines from available feedstock.

Boron Nitride‐supported Sub‐nanometer Pd6 Clusters for Formic Acid Decomposition: A DFT Study

AbstractA periodic, self‐consistent planewave DFT study was carried out to explore the potential use of Pd6 clusters supported on a boron nitride sheet as a catalyst for the selective decomposition of formic acid (HCOOH) to CO2 and H2. The competition between formate (HCOO) and carboxyl (COOH) paths on catalytic sites, with different proximities to the support, was studied. Based on energetics alone, the reaction may mainly follow the HCOO route. Slightly lower activation energies were found at the lateral sites of the cluster as compared to top face sites. This is particularly true for the bidentate to monodentate HCOO conversion. Through comparison of results with similar studies on HCOOH decomposition on extended Pd surfaces, it was demonstrated that the existence of undercoordinated sites in the sub‐nanometer cluster could play a key role in preferentially stabilizing HCOO over COOH, which is a common CO precursor in this reaction. A hydrogen spillover mechanism was also investigated; migration toward the boron nitride support is not favorable, at least in the early stages of the reaction. However, hydrogen diffusion on the cluster has low barriers compared to those involved in formic acid decomposition.

Fabrication and electrochemical performance of La0.5Sr0.5CoO3 impregnated porous YSZ cathode

La0.5Sr0.5CoO3-yttria-stabilized zirconia (LSCO-YSZ) composite cathode for solid oxide fuel cell (SOFC) has been fabricated by wet impregnation method. Nitrate precursors of La, Sr, and Co have been impregnated into the pre-sintered porous YSZ matrix, which is converted into LSCO phase after calcination at 850 °C in the presence of glycine as confirmed from X-ray diffraction. LSCO of 5, 7, and 10 wt% impregnated porous YSZ have been electrochemically characterized using 2-probe AC conductivity method. Maximum ionic conductivity of 0.27 S/cm at 800 °C and activation energy of 0.15 eV between 600 and 800 °C have been observed for 10 wt% LSCO-YSZ cathode. Area-specific resistance of 1.01 Ω cm2 at 800 °C is estimated for the electrolyte-supported half-cell (10 wt% LSCO-YSZ/YSZ). After testing the LSCO-YSZ cathode matrix, the electrolyte-supported full cell (10 wt% LSCO-YSZ/YSZ/NiO-YSZ) has been tested and produced maximum power density 51.12 mW/cm2 (109.38 mA/cm2) at 800 °C. The electrolyte-supported full cell exhibited 6 Ω cm2 electrode polarization at 800 °C in H2, which is in higher side leading to low performance. LSCO-YSZ/YSZ/NiO-YSZ SOFC found to give stable performance up to 2 h and scanning electron microscopy analysis has been carried out before and after cell testing to assess the morphological changes.

La and Ca-Doped A-Site Deficient Strontium Titanates Anode for Electrolyte Supported Direct Methane Solid Oxide Fuel Cell

Nickel-yttria stabilized zirconia (Ni-YSZ) cermet anodes for solid oxide fuel cells (SOFC) possesses excellent catalytic properties and stability for H2 oxidation but not for hydrocarbons as it results in fast carbon deposition in absence of excess steam. In the present work, A-site deficient porous LSCTA- (La0.2Sr0.25Ca0.45TiO3) anode has been fabricated using the environment friendly, aqueous tape casting method followed by the same procedure for the dense YSZ electrolyte and YSZ porous scaffold as cathode matrix. The anode, electrolyte, and porous cathode matrix have been laminated together and sintered up to 1350°C. After sintering, nitrate precursors of La, Sr, Co and Fe are infiltrated inside the porous YSZ cathode matrix to form the perovskite phases of La0.8Sr0.2CoO3 (LSC) and La0.8Sr0.2FeO3 (LSF). The as fabricated electrolyte supported SOFCs have been tested in H2 and CH4 fuel at 800°C. The electrolyte supported cell 15%LSF-5% LSC-YSZ/YSZ/4%Ni-6%CeO2-LSCTA- gives maximum power density of 328 mW cm−2 for 3 h in H2, but in CH4 the performance decreased to 165 mW cm−2 even though a sustained open circuit voltage of ∼1 V obtained during H2 and CH4 operation. The morphology of the anode before and after cell testing has been analyzed using scanning electron microscope followed by X-ray diffraction studies to understand phase changes during fabrication and testing.

Density functional investigation of CO and NO adsorption on TM-decorated C60 fullerene

We have analysed the adsorptions of CO and NO molecules on pristine, TM (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) in TM-doped fullerene C60 by using density functional theory (DFT) calculations at B3LYP/6-31g(d) theoretical level. This work revealed that the transition metal doped fullerenes were more highly sensitive to CO and NO adsorption than that of pure fullerene C60. The Fe-doped fullerenes C60 displayed the strongest interaction with C and N atoms of CO and NO molecules respectively. The nature of charge transfer between the d-orbitals of TM, and the π* orbital of the nearby C and N of CO and NO are clarified. Natural bond orbital (NBO) analysis reveals that the electronic configuration of the doped TM metal represents a qualitative change with respect to that of the free-metal. The binding of CO and NO precursor is mostly dominated by the metal E(i)(XO..TM) pairwise additive contributions, and the role of the C60 is not restricted to supporting the metal.

Controllable synthesis of nitrogen-doped hollow carbon nanospheres with dopamine as precursor for CO2 capture

Nitrogen-doped hollow carbon nanospheres are synthesized by using dopamine as carbon and nitrogen sources and tetraethyl orthosilicate as structure-assistant agent.

Iron-catalyzed carbonylation of aryl halides with arylborons using stoichiometric chloroform as the carbon monoxide source

The highly effective iron-catalyzed carbonylative Suzuki–Miyaura coupling using stoichiometric chloroform as the CO precursor has been developed.

ChemInform Abstract: Palladium‐Catalyzed One‐Pot Carbonylative Sonogashira Reaction Employing Formic Acid as the CO Source.

A convenient palladium-catalyzed carbonylative coupling of aryl iodides and terminal alkynes with formic acid as the CO precursor has been developed. A variety of alkynones were obtained in good yields in a one-pot manner for the first time.

CO and CN− syntheses by [FeFe]-hydrogenase maturase HydG are catalytically differentiated events

The synthesis and assembly of the active site [FeFe] unit of [FeFe]-hydrogenases require at least three maturases. The radical S-adenosyl-l-methionine HydG, the best characterized of these proteins, is responsible for the synthesis of the hydrogenase CO and CN(-) ligands from tyrosine-derived dehydroglycine (DHG). We speculated that CN(-) and the CO precursor (-):CO2H may be generated through an elimination reaction. We tested this hypothesis with both wild type and HydG variants defective in second iron-sulfur cluster coordination by measuring the in vitro production of CO, CN(-), and (-):CO2H-derived formate. We indeed observed formate production under these conditions. We conclude that HydG is a multifunctional enzyme that produces DHG, CN(-), and CO at three well-differentiated catalytic sites. We also speculate that homocysteine, cysteine, or a related ligand could be involved in Fe(CO)x(CN)y transfer to the HydF carrier/scaffold.

Polymerizable Ionic Liquid as Nitrogen-Doping Precursor for Co–N–C Catalyst with Enhanced Oxygen Reduction Activity

The Co–N–C catalyst with higher nitrogen content was fabricated with a polymerizable ionic liquid (PIL) of hydrolyzed vinyl imidazolium dihydrogen phosphate ([HVim]H2PO4) as N-doping precursor. The PIL was first prepared and then reacted with Co(NO3)2·6H2O. The N-doped Co-based catalyst was then obtained after carbonization process at 600 °C. The electrochemical characterization indicated that the electroactivity of catalyst prepared with PIL shows higher activity toward oxygen reduction reaction (ORR) than that of the sample prepared with non-IL precursor or nonpolymerizable IL under similar conditions. The ORR onset potential of the C1 (PIL as precursor) was approximately 100 mV higher than the counterpart prepared with C2 (non-IL precursor) or C3 (nonpolymerizable IL precursor) in basic electrolyte. The XPS results demonstrated that C1 contains higher nitrogen with more pyridinic and pyrrolic nitrogen groups, which was favorable for ORR.

Photofragmentation Mechanisms of Chlorosulfonyl Isocyanate, ClSO2NCO, Excited with Synchrotron Radiation between 12 and 550 eV.

The unimolecular photofragmentation mechanisms of chlorosulfonyl isocyanate, ClSO2NCO, excited with tunable synchrotron radiation between 12 and 550 eV, were investigated by means of time-of-flight (TOF) coincidence techniques. The main fragmentation mechanism after single ionization, produced by irradiation of an effusive beam of the sample with synchrotron light in the valence electron region, occurs through the breaking of the Cl-S single bond, giving a chloride radical and a SO2NCO(+) fragment. This mechanism contrasts with the one observed for the related FSO2NCO, in which the rupture of the S-N bond originates the FSO2(+) fragment. The energies of the shallow- (S 2p, Cl 2p, and S 2s) and core-shell (C 1s, N 1s, and O 1s) electrons were determined by X-ray absorption. Transitions between these shallow and core electrons to unoccupied molecular orbitals were also observed in the total ion yield (TIY) spectra. Fourteen different fragmentation mechanisms of the doubly charged parent ion, ClSO2NCO(2+), were inferred from the bidimensional photoelectron-photoion-photoion-coincidence (PEPIPICO) spectra. The rupture of the S-N bond can evolve to form NCO(+)/SO2(•+), NCO(+)/SO(•+), or S(•+)/NCO(+) pairs of ions. The Cl-S bond breaking originates different mechanisms, Cl(+)/SO(•+), Cl(+)/S(•+), CO(•+)/S(•+), O(•+)/SO(•+), O(•+)/Cl(+), O(•+)/S(•+), C(•+)/S(•+), and C(•+)/O(•+) pairs being detected in coincidence as the final species. Another three coincidence islands can only be explained with an initial atomic rearrangement forming ClNCO(2+), ONCO(2+), and ClCO(2+), as precursors of CO(•+)/Cl(+), O(•+)/CO(•+), and C(•+)/Cl(+) pairs, respectively. The formation of Cl(•) radical is deduced from several mechanisms.

Palladium-Catalyzed One-Pot Carbonylative Sonogashira Reaction Employing Formic acid as the CO Source.

A convenient palladium-catalyzed carbonylative coupling of aryl iodides and terminal alkynes with formic acid as the CO precursor has been developed. A variety of alkynones were obtained in good yields in a one-pot manner for the first time.

ChemInform Abstract: A Cp*CoI2‐Dimer as a Precursor for Cationic Co(III)‐Catalysis: Application to C—H Phosphoramidation of Indoles.

C2-selective indole C–H phosphoramidation was achieved through improved Cp*Co(III) catalysis. A cationic Co(III) species generated in situ from a Cp*CoI2-dimer showed the best catalytic activity, giving phosphoramidated indoles in 60–86% yield.