Carbon Dioxide Molecules Research Articles

Quantum Chemical Study of Supercritical Carbon Dioxide Effects on Combustion Kinetics.

In oxy-fuel combustion, the pure oxygen (O2), diluted with CO2 is used as oxidant instead air. Hence, the combustion products (CO2 and H2O) are free from pollution by nitrogen oxides. Moreover, high pressures result in the near-liquid density of CO2 at supercritical state (sCO2). Unfortunately, the effects of sCO2 on the combustion kinetics are far from being understood. To assist in this understanding, in this work we are using quantum chemistry methods. Here we investigate potential energy surfaces of important combustion reactions in the presence of the carbon dioxide molecule. All transition states and reactant and product complexes are reported for three reactions: H2CO + HO2 → HCO + H2O2 (R1), 2HO2 → H2O2 + O2 (R2), and CO + OH → CO2 + H (R3). In reaction R3, covalent binding of CO2 to the OH radical and then the CO molecule opens a new pathway, including hydrogen transfer from oxygen to carbon atoms followed by CH bond dissociation. Compared to the bimolecular OH + CO mechanism, this pathway reduces the activation barrier by 5 kcal/mol and is expected to accelerate the reaction. In the case of hydroperoxyl self-reaction 2HO2 → H2O2 + O2 the intermediates, containing covalent bonds to CO2 are found not to be competitive. However, the spectator CO2 molecule can stabilize the cyclic transition state and lower the barrier by 3 kcal/mol. Formation of covalent intermediates is also discovered in the H2CO + HO2 → HCO + H2O2 reaction, but these species lead to substantially higher activation barriers, which makes them unlikely to play a role in hydrogen transfer kinetics. The van der Waals complexation with carbon dioxide also stabilizes the transition state and reduces the reaction barrier. These results indicate that the CO2 environment is likely to have a catalytic effect on combustion reactions, which needs to be included in kinetic combustion mechanisms in supercritical CO2.

Evolution of disturbances in the shock layer on a flat plate in the flow of a mixture of vibrationally excited gases

The results of the numerical and experimental investigations of the evolution of the disturbances in a hypersonic shock layer on a flat plate streamlined by a flow of the mixture of vibrationally excited gases are presented. The experimental study was conducted in the hot-shot high-enthalpy wind tunnel IT-302 of the ITAM SB RAS. The numerical simulation was carried out with the aid of the ANSYS Fluent package using the solution of the unsteady two-dimensional Navier−Stokes equations with the incorporation of the user-created modules and enabling the consideration of the vibrational non-equilibrium of the carbon dioxide molecules within the framework of the model of the two-temperature aerodynamics. It was obtained that an increase in the carbon dioxide concentration in the mixture with air leads to a reduction of the intensity of pressure disturbances on the surface. The efficiency (up to 20 %) of the method of sound absorbing coatings in the vibrationally excited flows of the mixture of the carbon dioxide and air has been shown.

Density functional calculations of graphene-based humidity and carbon dioxide sensors: effect of silica and sapphire substrates

We present dispersion-corrected density functional calculations of water and carbon dioxide molecules adsorption on graphene residing on silica and sapphire substrates. The equilibrium positions and bonding distances for the molecules are determined. Water is found to prefer the hollow site in the center of the graphene hexagon, whereas carbon dioxide prefers sites bridging carbon-carbon bonds as well as sites directly on top of carbon atoms. The energy differences between different sites are however minute – typically just a few tenths of a millielectronvolt. Overall, the molecule-graphene bonding distances are found to be in the range 3.1–3.3Å. The carbon dioxide binding energy to graphene is found to be almost twice that of the water binding energy (around 0.17eV compared to around 0.09eV). The present results compare well with previous calculations, where available. Using charge density differences, we also qualitatively illustrate the effect of the different substrates and molecules on the electronic structure of the graphene sheet.

Ion-ion coincidence imaging at high event rate using an in-vacuum pixel detector.

A new ion-ion coincidence imaging spectrometer based on a pixelated complementary metal-oxide-semiconductor detector has been developed for the investigation of molecular ionization and fragmentation processes in strong laser fields. Used as a part of a velocity map imaging spectrometer, the detection system is comprised of a set of microchannel plates and a Timepix detector. A fast time-to-digital converter (TDC) is used to enhance the ion time-of-flight resolution by correlating timestamps registered separately by the Timepix detector and the TDC. In addition, sub-pixel spatial resolution (<6 μm) is achieved by the use of a center-of-mass centroiding algorithm. This performance is achieved while retaining a high event rate (104 per s). The spectrometer was characterized and used in a proof-of-principle experiment on strong field dissociative double ionization of carbon dioxide molecules (CO2), using a 400 kHz repetition rate laser system. The experimental results demonstrate that the spectrometer can detect multiple ions in coincidence, making it a valuable tool for studying the fragmentation dynamics of molecules in strong laser fields.

Исследование реакции ионосферы на продукты горения топлива при работе двигателей транспортных грузовых кораблей серии «Прогресс» по данным Иркутского радара некогерентного рассеяния

The FSUE Central Research Institute of Machine Building (TsNIIMash), Rocket and Space Corporation “Energia”, and Institute of Solar-Terrestrial Physics of Siberian Branch of Russian Academy of Sciences (ISTP SB RAS) jointly conducted the active space experiment “Radar-Progress” in 2007–2015. During this experiment, we used the Irkutsk Incoherent Scatter Radar to study space-time characteristics of ionospheric disturbances generated by exhaust products of “Progress” cargo spacecraft engines. As the basic effect during exhaust product injection we consider the formation of new centers for recombination of ambient ionospheric ions O+ on molecules of water and carbon dioxide. This produces an ionization “hole” in the region of injection. In nighttime conditions when the majority of experiments were performed, this hole was filled by hydrogen ions from the plasmasphere, thus the ion composition in the vicinity of the hole and incoherent scatter spectra were changed. For successful observation of the ionization hole dynamics, the critical factors are the degree of radar antenna diagram filling by exhaust products and the velocity of the thermospheric neutral wind, which makes exhaust gases move from the antenna diagram. These two factors lead to poor repeatability of successful experiments. Successful experiments recorded a decrease in electron density up to 35 % in the hole that existed for 30 min. The lifetime of the region with high concentration of H+ ions can be as long as one hour.

Collision-induced dissociation processes of protonated benzoic acid and related compounds: competitive generation of protonated carbon dioxide or protonated benzene.

Upon activation in the gas phase, protonated benzoic acid (m/z 123) undergoes fragmentation by several mechanisms. In addition to the predictable water loss followed by a CO loss, the m/z 123 ion more intriguingly eliminates a molecule of benzene to generate protonated carbon dioxide (H - O+ ═ C ≡ O, m/z 45), or a molecule of carbon dioxide to yield protonated benzene (m/z 79). Experimental evidence shows that the incipient proton ambulates during the fragmentation processes. For the CO2 or benzene loss, protonated benzoic acid transfers the charge-imparting proton initially to the ortho position and then to the ipso position to generate a transient species which dissociates to form an ion-neutral complex between benzene and protonated CO2 . The formation of the m/z 45 ion is not a phenomenon unique to benzoic acid: spectra from protonated isophthalic acid, terephthalic acid, trans-cinnamic acid and some aliphatic acids also displayed a peak for m/z 45. However, the m/z 45 peak is structurally diagnostic only for certain benzene polycarboxylic acids because the spectra of compounds with two carboxyl groups on adjacent ring carbons do not produce a peak at m/z 45. For the m/z 79 ion to be formed, an intramolecular reaction should take place in which protonated CO2 within the ion-neutral complex acts as the attacking electrophile to transfer a proton to benzene. Copyright © 2017 John Wiley & Sons, Ltd.

Wheat gluten, a bio-polymer to monitor carbon dioxide in food packaging: Electric and dielectric characterization

The use of wheat gluten as sensing material to detect carbon dioxide is a promising approach. The dielectric properties of wheat gluten are modified in contact with carbon dioxide gas at high relative humidity (90%) and at a temperature of 25°C due to a structural change in the sensing material, where amino groups act as receptors to carbon dioxide molecules. In the present study, the effects of carbon dioxide on the electrical and dielectric properties of wheat gluten at 20% and 90% of relative humidity (usually found in food packaging) are determined and discussed. At 90% of relative humidity, a linear increase of the dielectric permittivity and dielectric loss was observed with a significant hysteresis which increased with the number of carbon dioxide treatment cycles. One of the significant results is the increase in the dielectric permittivity from 7.01±0.07 to 12.02±0.03 with a sensitivity of 31.38±0.06fF/%CO2 measured at 868MHz. The developed sensor is sought to be integrated in the design of UHF-RFID (ultra-high frequency − radio frequency identification) systems working at 868MHz.

Enhancing CO2 electrolysis through synergistic control of non-stoichiometry and doping to tune cathode surface structures

Sustainable future energy scenarios require significant efficiency improvements in both electricity generation and storage. High-temperature solid oxide cells, and in particular carbon dioxide electrolysers, afford chemical storage of available electricity that can both stabilize and extend the utilization of renewables. Here we present a double doping strategy to facilitate CO2 reduction at perovskite titanate cathode surfaces, promoting adsorption/activation by making use of redox active dopants such as Mn linked to oxygen vacancies and dopants such as Ni that afford metal nanoparticle exsolution. Combined experimental characterization and first-principle calculations reveal that the adsorbed and activated CO2 adopts an intermediate chemical state between a carbon dioxide molecule and a carbonate ion. The dual doping strategy provides optimal performance with no degradation being observed after 100 h of high-temperature operation and 10 redox cycles, suggesting a reliable cathode material for CO2 electrolysis.

Laser-induced electron diffraction: inversion of photo-electron spectra for molecular orbital imaging

ABSTRACTIn this paper, we discuss the possibility of imaging molecular orbitals from photoelectron spectra obtained via laser -induced electron diffraction in linear molecules. This is an extension of our recent work to the case of the HOMO-1 orbital of the carbon dioxide molecule. We show that such an imaging technique has the potential to image molecular orbitals at different internuclear distances in a sub-femtosecond time scale and with a resolution of a fraction of an Angström.

Synthesis and crystal structure analysis of a novel microporous barium-containing silicate AES-20

A novel microporous barium-containing silicate AES-20 was successfully synthesized, and its crystal structure was determined based on the ab-initio structure analysis from powder X-ray diffraction data. AES-20 was composed of unique silicate layers having 8- and 5-rings and interlayer barium atoms pillaring the silicate layers. AES-20 was obtained through the hydrothermal synthesis in the presence of lithium cations, which were involved in AES-20 as extra-framework species. The 8-ring micropore in AES-20 is smaller than a nitrogen molecule but larger than a carbon dioxide molecule, suggesting the application to a size-selective adsorbent for carbon dioxide removal.

Amine-functionalized poly(ionic liquid) brushes for carbon dioxide adsorption

Amine-functionalized imidazolium-based poly(ionic liquid) brushes on titanate nanotubes are synthesized using a convenient “grafting through” technique. The carbon dioxide adsorption performance of the synthesized polymer brushes is evaluated using temperature programmed desorption (TPD) process. TPD profiles of the synthesized polymer brushes after carbon dioxide adsorption reveal that carbon dioxide molecules can adsorb on the synthesized polymer brushes through physical adsorption, reaction with 2-position carbon of imidazole rings, and chemical reaction with amine groups. The total carbon dioxide adsorption capacity of the synthesized poly(ionic liquid) brushes with polymer content of 46wt.% achieves 2.43mmolg−1 at 25°C under carbon dioxide partial pressure of 0.2 bar, higher than that of the corresponding free polymer powders (1.28mmolg−1) under the same conditions. The total adsorption capacity decreases to 1.46mmolg−1 after two TPD adsorption/desorption cycles and it however remains almost constant in the later cycles.

Theoretical Study of Enzyme Promiscuity: Mechanisms of Hydration and Carboxylation Activities of Phenolic Acid Decarboxylase

The cofactor-free phenolic acid decarboxylases (PADs) catalyze the nonoxidative decarboxylation of phenolic acids to their corresponding p-vinyl derivatives. Since these compounds are useful industrially, PADs have potential applications as biocatalysts. Recently, PADs have been reported to also catalyze the hydration and carboxylation of hydroxystyrenes, increasing further their biocatalytic utility. We have used quantum chemical methodology to investigate the detailed mechanisms of both promiscuous reactions. A large model of the active site is designed starting from the crystal structure of PAD from Bacillus subtilis. The calculations suggest new mechanisms, quite different from the literature proposals. For the carboxylation reaction, a carbon dioxide molecule is proposed to be generated from bicarbonate first and then act as the source for the carboxylate group of the product. For the hydration activity, the reaction is suggested to start with the formation of a quinone methide intermediate by proton...

Reaction dynamics of Al + CO2 → AlO + CO studied by a crossed-beam velocity map imaging technique.

The oxidation reaction of a gas-phase aluminum atom by a carbon dioxide molecule was studied by employing a crossed-beam technique at two collision energies: 27.9 and 52.8 kJ/mol. A (1 + 1) resonance-enhanced multiphoton ionization via the D2Σ+-X2Σ+ transition of AlO was applied to ionize the product. For several rotational levels of AlO in the vibrational ground state, time-sliced ion images were measured for the first time, and the angular-kinetic energy distributions were determined. All angular distributions showed forward and backward peaks; the forward peaks were more pronounced than the backward ones at the two collision energies. The product kinetic energy showed rather narrow distributions whose peaks appeared at near to the highest limit estimated from the available energies. The rotational distributions of the counter product CO, derived from the kinetic energy distributions, suggested that only a limited number of rotational states were formed and that a small amount of energies go into this mode. These results suggested that the reaction proceeds via a short-lived intermediate in which the O-C-O keeps a nearly linear structure.

Free Energy-Based Coarse-Grained Force Field for Binary Mixtures of Hydrocarbons, Nitrogen, Oxygen, and Carbon Dioxide.

The free energy based Lennard-Jones 12-6 (FE-12-6) coarse-grained (CG) force field developed for alkanes1 has been extended to model small molecules of light hydrocarbons (methane, ethane, propane, butane, and isobutane), nitrogen, oxygen, and carbon dioxide. The adjustable parameters of the FE-12-6 potential are determined by fitting against experimental vapor-liquid equilibrium (VLE) curves and heat of vaporization (HOV) data for pure substance liquids. Simulations using the optimized FE-12-6 parameters correctly reproduced experimental measures of the VLE, HOV, density, vapor pressure, compressibility, critical point, and surface tension for pure substances over a wide range of thermodynamic states. The force field parameters optimized for pure substances were tested on methane/butane, nitrogen/decane, and carbon dioxide/decane binary mixtures to predict their vapor-liquid equilibrium phase diagrams. It is found that for nonpolar molecules represented by different sized beads, a common scaling factor (0.08) that reduces the strength of the interaction potential between unlike beads, generated using Lorentz-Berthelot (LB) combination rules, is required to predict vapor-liquid phase equilibria accurately.

Improved Photocatalytic Air Cleaner with Decomposition of Aldehyde and Aerosol-Associated Influenza Virus Infectivity in Indoor Air

ABSTRACTAir pollution caused by fine particulate matter (PM2.5), volatile organic compounds, and bioaerosols is a major environmental risk to health. We developed a photocatalytic air cleaner for reducing the pollution levels of indoor air; we improved the photocatalytic system by using UV-LED for the removal of acetaldehyde and PM2.5 and by reducing the weight and size of the system. The efficiency of photocatalysis depends on the surface area and materials. Therefore, we prepared a nanosized titanium dioxide (TiO2)-coated aluminum plate irradiated by UV-LED lamps (wavelength: 375 nm) as a photocatalytic air cleaner. Passing air continuously through a TiO2-coated aluminum plate (5 × 10 × 1 cm) under black light for 200 min decomposed 90% of 5 ppm acetaldehyde (12.4 µmol h–1) and generated two carbon dioxide molecules (25.43 µmol h–1) at a molar ratio of 1:2, indicating complete decomposition of acetaldehyde with high efficiency. This photocatalytic air cleaner was applied to the decomposition of acetaldehyde and inactivation and removal of aerosol-associated influenza virus. Acetaldehyde (20 ppm) in a 1-m3 cubic space was eliminated in 60 min at a half-life of 8 min. The aerosol-associated infectivity and the RNA genome of influenza virus A/PR/8/1934 (H1N1) produced by a nebulizer in a 779-L cubic space were eliminated within 7 min; however, they were detectable for up to 28 minutes when the functional photocatalytic air cleaner was not used. The presence of intermediate breakdown products of influenza virus indicated that the virus was broken down by photocatalysis. Thus, the photocatalytic air cleaner efficiently decomposed and eliminated organic chemicals, acetaldehyde, and aerosol-associated influenza virus infectivity and viral RNA, indicating that it can clean and detoxify the indoor air in a closed space for maintaining a safer environment.

Cerium oxide as a catalyst for the ketonization of aldehydes: mechanistic insights and a convenient way to alkanes without the consumption of external hydrogen

The atom-efficient transformation of two aldehyde molecules into a linear alkane at the expense of one carbon dioxide molecule.

Computational study of the interplay between intermolecular interactions and CO2 orientations in type I hydrates.

Carbon dioxide (CO2) molecules show a rich orientation landscape when they are enclathrated in type I hydrates. Previous studies have described experimentally their preferential orientations, and some theoretical works have explained, but only partially, these experimental results. In the present paper, we use classical molecular dynamics and electronic density functional theory to advance in the theoretical description of CO2 orientations within type I hydrates. Our results are fully compatible with those previously reported, both theoretical and experimental, the geometric shape of the cavities in hydrate being, and therefore, the steric constraints, responsible for some (but not all) preferential angles. In addition, our calculations also show that guest-guest interactions in neighbouring cages are a key factor to explain the remaining experimental angles. Besides the implication concerning equation of state hydrate modeling approximations, the conclusion is that these guest-guest interactions should not be neglected, contrary to the usual practice.

Systematization of data sources with spectral line parameters for the carbon dioxide molecule and its isotopologues in the W@DIS information system

Systematization of data sources with spectral line parameters for the carbon dioxide molecule and its isotopologues in the W@DIS information system

Effect of organic substituents on the adsorption of carbon dioxide on a metal–organic framework

The adsorption of carbon dioxide on the MOF-5 metal–organic framework and modifications of it obtained by replacing the hydrogen atoms in the organic ligands with electron donor (–CH3,–OCH3) or electron acceptor groups (–CN,–NO2) is investigated using the grand canonical Monte Carlo (GCMC) method and density functional theory (DFT). It is shown that the adsorption of carbon dioxide molecules on the structures of metal–organic frameworks is most likely on Zn4O clusters, and that the adsorption of carbon dioxide is of a physical nature. The presence of substituents–CH3,–OCH3,–CN in metal–organic frameworks increases their capacity to adsorb carbon dioxide, while that of nitro groups (–NO2) has the opposite effect.

X-ray Diffraction Study on Simple Molecular Glasses Created by Low-Temperature Vapor Deposition

The structure of simple molecular glasses has been one of the central issues in the research of glasses. We tried to form the glasses of carbon dioxide (CO2), carbon monoxide (CO), and nitrogen (N2) molecules by slow vapor deposition at 3 K (deposition rate: ca. 10 nm/h). Glassy CO2 was successfully obtained and it crystallized on heating at 25 K, which is lower than the hypothetical glass transition temperature of CO2. The CO2 glass is the simplest molecular glass ever created. The X-ray diffraction patterns and derived pair distribution functions revealed that the glassy CO2 has a structure in which the intermolecular distance is shorter and the intermolecular correlation is much stronger than those of liquid CO2. Orientational glasses, which are positionally ordered and orientationally disordered, of CO and N2 were obtained and they were gradually ordered as the annealing temperature is increased.