Dissociation Of CO2 Molecules Research Articles

Unveiling the charge migration-induced surface reconstruction of Cu2MoS4 catalyst for boosted CO2 reduction into olefiant gas

Understanding the charge dynamic behavior of the catalyst is crucial to unravel the underlying mechanism for photocatalytic CO2 reduction to C2+ products. However, the structure–activity relationships are not intuitive because of the dynamic evolution of electronic and atomic structures for catalysts under the excitation state. Herein, modeling on layered Cu2MoS4 nanosheets, we for the first time observe charge migration-induced evolution of electronic and atomic structure on Cu2MoS4 catalyst during the CO2 reduction process by combining synchronous-illumination X-ray photoelectron spectroscopy (SI-XPS) with X-ray diffraction (SI-XRD). During the dissociation of CO2 molecules as well as the charge migration process under the visible light irradiation condition, the surface S atoms return back to the lattice phase, leading to the valence-state normalization of Cu, Mo and S atoms and the increases of the interlayer lattice spacing. By virtue of the above unique characteristic changes, Cu2MoS4 nanosheets exhibit excellent activity enhancement (8.7 μmol g−1 h−1) for CO2 reduction to C2H4 under the visible light irradiation in comparison with the trace amount of Cu-doped MoS2 and pure MoS2.

On CO2 conversion in discharges in CO2–N2 mixtures

Recent results on the efficiency of CO2 conversion in discharges in CO2–N2 mixtures are discussed. Conditions are considered when the dominating conversion mechanism is dissociation of CO2 molecules in collisions with nitrogen molecules in several electronically excited states. Its efficiency is determined by the values of dissociation yields in these collisions. Knowledge of dissociation yields for various N2 excited states is rather poor. In this paper, the effects of variation of these yields on the conversion efficiency are evaluated. Comparison of the obtained estimates with available experimental data allows ascertaining the yield values.

A DFT study on the role of oxygen vacancy on m-ZrO2 ([formula omitted]) in adsorption and dissociation of CO2

The performance stability of a Catalytic Dry Reforming of Methane (CDRM) catalyst is primarily determined by its ability to resist coke formation. This is possible through removal of carbon deposited on the hydrogen production sites of the catalyst by mobile surface oxygen formed via CO2 dissociation. In this study, it is aimed to understand the role of oxygen vacancies in activation and dissociation of CO2 molecule on m-ZrO2, which has been widely studied as the support of CDRM catalysts. For this purpose, first, oxygen vacancy formation on m-ZrO2 (1¯11) surface was investigated. Two possible types of oxygen vacancies were determined based on the results of periodic DFT calculations. Then, CO2 adsorption onto both stoichiometric and nonstoichiometric m-ZrO2 (1¯11) surfaces were performed. The results revealed that the CO2 dissociation is possible only on the nonstoichiometric m-ZrO2 surfaces, and that presence of an oxygen vacancy, regardless of its type, significantly lowers the adsorption energy and increases adsorbate–metal oxide interaction. The study presented here theoretically proves at atomic scale that oxygen vacancies have a great influence on the dissociative CO2 adsorption ability of m-ZrO2, and confirms its clear potential as a support to be used in technical CDRM catalysts prepared for practical applications.

Modeling of CO2 conversion in low-pressure glow discharges in CO2-N2 mixtures

An approach for evaluation of plasma parameters and conversion factor in glow discharges in CO2–N2 mixtures at low pressures is presented. In the framework of this approach, analytical expressions relating plasma characteristics (the electric field, the gas temperature) in discharges in the mixtures with those in pure CO2 have been obtained. It is shown that dissociation of CO2 molecules in collisions with electronically excited N2 molecules gives substantial contribution to the conversion rate. Obtained dependences of the plasma parameters and conversion factor on the nitrogen molar fraction agree with available experimental data.

Enhanced performance of Ni catalysts supported on ZrO2 nanosheets for CO2 methanation: Effects of support morphology and chelating ligands

A series of Ni/ZrO2 catalysts was prepared by the impregnation method with modification of the morphology of ZrO2 support as well as the impregnation procedure and tested for CO2 methanation. The catalysts supported on the ZrO2 nanosheets displayed superior catalytic performance as compared with that on ZrO2 nanoparticles, which could be mainly attributed to the abundant oxygen vacancies promoting the adsorption and dissociation of CO2 molecules as well as the high dispersion of Ni species. With the introduction of ethylenediamine (En) in the impregnation procedure, the resulting Ni-15En/ZrO2-1.5 catalyst showed the optimal activity with CO2 conversion of 86% significantly higher than Ni/ZrO2-0 of 44% and Ni/ZrO2-1.5 of 79% at 0.5 MPa and 300 °C. The excellent performance was attributed to increased moderately basic sites for CO2 adsorption in ZrO2 nanosheets, as well as the enhanced dispersion of nickel caused by the complexation of Ni ions with En, which inhibited the aggregation of nickel particles in the subsequent thermal treatments. In conclusion, the synergistic effects of the morphology of ZrO2 nanosheets as well as the chelating behavior of En contributed to the enhanced performance of Ni-15En/ZrO2-1.5 in the CO2 methanation reaction. The strategy shows good prospects for controlling the size of active metals, especially those that were dispersed on the surface of the two-dimensional (2D) metal oxide materials.

First-principles study of co-adsorption behavior of O2 and CO2 molecules on δ-Pu(100) surface

First principles calculation is performed to study the co-adsorption behaviors of O2 and CO2 on δ-Pu(100) surface by using a slab model within the framework of density functional theory (DFT). The results demonstrate that the most favorable co-adsorption configurations are Tv-C4O7 and Tp1-C2O8, with adsorption energy of –17.296 eV and –23.131 eV for CO2-based and O2-based system, respectively. The C and O atoms mainly interact with the Pu surface atoms. Furthermore, the chemical bonding between C/O and Pu atom is mainly of ionic state, and the reaction mechanism is that C 2s, C 2p, O 2s, and O 2p orbitals overlap and hybridize with Pu 6p, Pu 6d, and Pu 5f orbital, resulting in the occurrence of new band structure. The adsorption and dissociation of CO2 molecule are obviously promoted by preferentially occupying adsorbed O atoms, therefore, a potential CO2 protection mechanism for plutonium-based materials is that in CO2 molecule there occurs complete dissociation of CO2 → C + O + O, then the dissociated C atom combines with O atom from O2 dissociation and produces CO, which will inhibit the O2 from further oxidizing Pu surface, and slow down the corrosion rate of plutonium-based materials.

Insight into CO2 Dissociation in Plasma from Numerical Solution of a Vibrational Diffusion Equation

The dissociation of CO2 molecules in plasmas is a subject of enormous importance for fundamental studies and the recent interest in carbon capture and carbon-neutral fuels. The vibrational excitation of the CO2 molecule plays an important role in the process. The complexity of the present state-to-state (STS) models makes it difficult to find out the key parameters. In this paper we propose as an alternative a numerical method based on the diffusion formalism developed in the past for analytical studies. The non-linear Fokker-Planck equation is solved by the time-dependent diffusion Monte Carlo method. Transport quantities are calculated from STS rate coefficients. The asymmetric stretching mode of CO2 is used as a test case. We show that the method reproduces the STS results or a Treanor distribution depending on the choice of the boundary conditions. A positive drift, whose energy onset is determined by the vibrational to translational temperature ratio, brings molecules from mid-energy range to dissociation. The high-energy fall of the distribution is observed even neglecting VT processes which are normally believed to be its cause. Our study explains several puzzling features of previous studies, provides new insights into the control of the dissociation rate and a much sought compression of the required data for modeling.

Spin-orbit coupling and dissociation of CO2 molecules

Potential surfaces of the CO2 molecule for the ground and excited 3B2, 1B2 electronic states are calculated by quantum chemistry methods. The calculation of the spin-orbit coupling in the molecule shows a large the matrix element, which removes the prohibition for the dissociation-recombination process CO2(X1Σ) + M ↔ CO(X1Σ) + O(3P) + M. The barrier on the potential curve for 3B2, the energy of which exceeds the limit of dissociation into components in the ground states, explains the data on the dissociation and recombination energies measured in experiments with shock tubes. The absorption cross section of CO2 molecules in the UV spectral region measured at high temperatures allowed us to plot branches of potential curves near their minima for two upper singlet states assigned to the 1B2 and 1A2 symmetry.

CO2dissociation activated through electron attachment on the reduced rutile TiO2(110)-1×1 surface

Converting CO$_2$ to useful compounds through the solar photocatalytic reduction has been one of the most promising strategies for artificial carbon recycling. The highly relevant photocatalytic substrate for CO$_2$ conversion has been the popular TiO$_2$ surfaces. However, the lack of accurate fundamental parameters that determine the CO$_2$ reduction on TiO$_2$ has limited our ability to control these complicated photocatalysis processes. We have systematically studied the reduction of CO2 at specific sites of the rutile TiO$_2$(110)-1x1 surface using scanning tunneling microscopy at 80 K. The dissociation of CO2 molecules is found to be activated by one electron attachment process and its energy threshold, corresponding to the CO$_2^{\dot-}$/CO$_2$ redox potential, is unambiguously determined to be 2.3 eV higher than the onset of the TiO$_2$ conduction band. The dissociation rate as a function of electron injection energy is also provided. Such information can be used as practical guidelines for the design of effective catalysts for CO$_2$ photoreduction.

Martian corona: Nonthermal sources of hot heavy species

We have studied the production of hot O and C atoms, and hot CO2 and CO molecules in the Martian upper atmosphere and exosphere by dissociative recombination (DR) of O2+ and CO+ ions, and sputtering of the atmosphere by incident O+ pick‐up ions. Production and collisional thermalization of the hot particles in the upper atmosphere are described by using a unique Monte Carlo test particle approach to simulate both nonthermal processes. Velocity distributions, atmospheric loss rates, and density profiles are derived for suprathermal O, C, CO, and CO2 at low and high solar activity. At high solar activity the hot oxygen escape rate estimated from DR of O2+ is found to be less than two times the sputtering rate. Sputtering is found to efficiently populate the corona with molecular species such as CO and CO2 at high solar activity and also to produce a carbon escape rate that is comparable to that derived from the major photochemical sources. Dissociation of CO2 molecules by the impacting pick‐up ions flux are found to produce about 50% of the sputtered exospheric oxygen density at high solar activity. Collisions of the background atmospheric gas with hot O atoms produced by DR of O2+ produce densities of hot CO2 and CO molecules larger than 102 cm−3 for altitudes lower than 1000 km, at both high and low solar activity. Interestingly, the hot CO2 density scale height is observed to be process dependent. The hot oxygen energy distributions associated with sputtering and DR near the exobase are also found to follow distinct decreasing energy laws. We suggest that the effects of the solar zenithal angle (SZA), crustal magnetic fields, and atmospheric tides on the ionospheric structure may produce exospheric signatures.

Analysis of the dynamics of a mechanical Q-switched CO2 laser: Six-temperature model

A six-temperature kinetic model for a CO2-N2-He system is used to describe the dynamic processes of a mechanical Q-switched CO2 laser that is set up using a fast chopper. We put special emphasis on the effect of dynamical parameters on the laser intensity. It takes into account the effects of electrical excitation, energy transfer processes, thermal energy transport, as well as the dissociation of CO2 molecules and rotational relaxation of rotational levels. The results calculated are in satisfactory agreement with experimental data.

New mechanism for the influence of Xe on the concentration of CO2 molecules in self-sustained CO-laser discharges

The dependence of the CO2 concentration on the discharge conditions and the mixture composition in a CO laser is studied experimentally. The experimental data are compared with the calculated results. A scheme of the reactions that govern the concentration of CO2 molecules under the experimental conditions in question is constructed. It is shown that, in a gas-discharge plasma, an admixture of Xe in a mixture containing CO molecules gives rise to a new mechanism for the dissociation of CO2 molecules by metastable xenon atoms. Under conditions close to the operating conditions of sealed-off CO lasers, the dissociation of CO2 molecules in collisions with metastable. Xe(3P2) atoms becomes the dominant dissociation mechanism in a He: CO mixture because it proceeds at a fast rate. This explains the observed decrease in the CO2 concentration in a xenon-containing He: CO mixture.

Kinetic modelling of electrooptically Q-switched CO2 laser

In this paper, a six-temperature model for CO2 lasers is used to describe the process of the dynamic emission in the electrooptically Q-switched laser. The dissociation of CO2 molecules, the electron excitation and the energy-transfer of vibrational levels and the rotational relaxation of rotational levels are involved. The calculated pulse waveforms are in good agreement with the experiment.

Dissociation of CO2 molecules in a wide temperature range

Expressions are derived for the dissociation rate constants of molecules of carbon dioxide in the temperature range from 300 to 40000 K under both thermally equilibrium and nonequilibrium conditions. Under nonequilibrium conditions, the rate constants are represented as a two-temperature dependence (on the gas temperatureT and on the unified temperature Tvof all vibrational modes of CO2) and as a one-temperature dependence in which averaged vibrational nonequilibrium is included

Limitation of the output power of cw electric-discharge CO2 lasers

The output power of a sealed-off tunable cw CO2 laser was optimised. The dependences of the small-signal gain for the 10P(20) line and of the output powers for different transmittances of the cavity on the discharge current were determined. The distributed loss coefficient and the saturation parameter were measured. The saturation parameter increased continuously with increase in the discharge current, leading to a mismatch between the output power and gain maxima. It was established that the principal factor limiting the output power of cw electric-discharge CO2 lasers is not an increase in the temperature of the active medium but the dissociation of CO2 molecules. When the latter is minimised in order to achieve the maximum laser power, low gas temperatures are not required.

Transient gain phenomena and their improvement in a fast-axial flow CO2 laser amplifier.

The present paper reviews our recent work on transient gain phenomena caused by both thermo & gas dynamic cooling mechanism and dissociation of CO2 molecules in a fast-axial flow (FAF) CO2 laser amplifier. Taking into account a time-dependent gas temperature T and an inverted population n2/n1, we theoretically formulate a transient gain as functions of the gas-flow velocity ν and the discharge current Idis including their spatial distributions along the radial direction from the plasma-tube axis to explain the transient power-decrease ΔP and the transient time tst required to be a stable value with respect to a plasma length l and an input probe power Pin Theoretical calculations are in good agreements with, corresponding experimental results. Possibilities for improving the above transient behavior are also demonstrated by cooling a plasma-tube wall and by use of an Au catalyst.

Degradation of the active mixture and the feasibility of regenerating it in an Iglan-3 multibeam 5-kW gas-discharge CO2laser

Experimental data are presented on the dissociation of CO2 molecules in the active medium of a multibeam gas-discharge laser as a function of the circulation velocity of the active mixture and of the discharge current. An analysis is given of the physical processes responsible for degradation of the active mixture, and its results are in agreement with data from other studies on both the value of the dissociation rate constant and the dependence of the degree of dissociation on the discharge current. A closed-cycle laser operating procedure is proposed in which the active mixture is regenerated in a high-temperature reactor at atmospheric pressure. Tests of this system showed that the regenerator provides for stable laser operation in the closed-cycle regime and enables the gas flow rate to be reduced by almost a factor of 30. Record values of the specific flow rate for high-power industrial gas discharge CO2 lasers, of the order of 6 liters kW−1 h−1, are reported.

Vertical distribution of neutral gases on venus

Abstract The vertical distribution of neutral CO2, O2, CO and O gases on Venus has been calculated, photochemical equilibrium being assumed. Kaplan's model of the atmospheric structure is adopted; and the solar ultraviolet radiation in the wavelengths from 1250 to 1950 A is assumed to be that of a 5000°K black body. It is found that the radiation is absorbed mainly by O2 molecules produced by three body recombination between O atoms. In consequence the altitude of the dissociation layer on Venus is higher than was derived earlier by taking into account the dissociation of CO2 molecules only. The calculated amounts of CO, O and O2 on Venus are 4, 4, 0.1 cm STP respectively.