CO2and CO Research Articles

In-situ DRIFTS steady-state study of CO2 and CO methanation over Ni-promoted catalysts

Promoting the performance of catalytic systems by incorporating small amount ofalkali has been proved effective for several reactions whilst controversial outcomes are reported for the synthetic natural gas production. This work studies a series of Ni catalystsfor CO2and CO methanation reactions.In-situDRIFTS spectroscopy evidenced similar reaction intermediates for all evaluated systems and it is proposed a reaction mechanism based on: i) formatedecompositionand ii) hydrogenation of lineal carbonyl species to methane. Compared to bare Ni, the enhanced CO2methanation rates attained by NiFe/Al and NiFeK/Al systems are associated to promotedformates decomposition into lineal carbonyl species. Also forCO methanation, the differences in the catalysts’ performances were associated to the relative concentration of lineal carbonyl species. Under CO methanation conditions and opposing the CO2methanation results where the incorporation of K delivered promoted catalytic behaviours, worsened CO methanation rates were discerned for the NiFeK/Al system.

The Facile Dissociation of Carbon–Oxygen Bonds in CO2and CO on the Surface of LaCoSiHxIntermetallic Compound

AbstractIn catalysis science, the electronic structure of the active site determines the structure–activity relationship of the catalyst to a large extent. Therefore, modulating the electronic structure has become a main route for the rational design of metal‐based catalyst materials. In this work, we prepared a LaCoSiHxmaterial that has more electronegativity and a lower workfunction than traditional supported Co‐based catalysts. Using CO2methanation as a model catalytic reaction, the facile dissociation of CO2and CO (a key reaction intermediate) on the surface of the LaCoSiHxcatalyst is observed by various experimental methods (e.g., in situ Raman and FTIR) at room temperature. Moreover, theoretical calculation results further show that LaCoSiHxhas a much stronger capacity for carbon–oxygen bond activation than the Co surface. The intrinsic mechanism is attributed to the marked electron transfer from catalysts into the antibonding orbital of CO2and CO.

CO+first-negative band emission: A tracer for CO in the Martian upper atmosphere

Context.Recently, the Imaging Ultraviolet Spectrograph (IUVS) on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite observed CO+first-negative band limb emission in the Martian upper atmosphere.Aims.We aim to explore the photochemical processes in the Martian upper atmosphere, which drive this band emission.Methods.A photochemical model was developed to study the excitation processes of CO+first-negative band emission (B2Σ+→ X2Σ+) in the upper atmosphere of Mars. The number density profiles of CO2and CO from two different models, namely, Mars Climate Database (MCD) and Mars Global Ionosphere-Thermosphere (MGIT), were used to determine the limb intensity of this band emission.Results.By increasing the CO density by a factor of 4 and 8 in MCD and MGIT models, respectively, the modelled CO+first-negative band limb intensity profile is found to be consistent with the IUVS/MAVEN observation. In this case, the intensity of this band emission is significantly determined by the ionisation of CO by solar photons and photoelectrons, and the role of dissociative ionisation of CO2is negligible.Conclusions.Since CO is the major source of the CO+(B2Σ+), we suggest that the observed CO+first-negative band emission intensity can be used to retrieve the CO density in the Martian upper atmosphere for the altitudes above 150 km.

Investigating the Rosetta/RTOF observations of comet 67P/Churyumov-Gerasimenko using a comet nucleus model: influence of dust mantle and trapped CO

Context.Cometary outgassing is induced by the sublimation of ices and the ejection of dust originating from the nucleus. Therefore measuring the composition and dynamics of the cometary gas provides information concerning the interior composition of the body. Nevertheless, the bulk composition differs from the coma composition, and numerical models are required to simulate the main physical processes induced by the illumination of the icy body.Aims.The objectives of this study are to bring new constraints on the interior composition of the nucleus of comet 67P/Churyumov-Gerasimenko (hereafter 67P) by comparing the results of a thermophysical model applied to the nucleus of 67P and the coma measurements made by the Reflectron-type Time-Of-Flight (RTOF) mass spectrometer. This last is one of the three instruments of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), used during the Rosetta mission.Methods.Using a thermophysical model of the comet nucleus, we studied the evolution of the stratigraphy (position of the sublimation and crystallisation fronts), the temperature of the surface and subsurface, and the dynamics and spatial distribution of the volatiles (H2O, CO2and CO). We compared them with the in situ measurements from ROSINA/RTOF and an inverse coma model.Results.We observed the evolution of the surface and near surface temperature, and the deepening of sublimation fronts. The thickness of the dust layer covering the surface strongly influences the H2O outgassing but not the more volatiles species. The CO outgassing is highly sensitive to the initial CO/H2O ratio, as well as to the presence of trapped CO in the amorphous ice.Conclusions.The study of the influence of the initial parameters on the computed volatile fluxes and the comparison with ROSINA/RTOF measurements provide a range of values for an initial dust mantle thickness and a range of values for the volatile ratio. These imply the presence of trapped CO. Nevertheless, further studies are required to reproduce the strong change of behaviour observed in RTOF measurements between September 2014 and February 2015.

Uncertainty analysis of a European high-resolution emission inventory of CO<sub>2</sub> and CO to support inverse modelling and network design

Abstract. Quantification of greenhouse gas emissions is receiving a lot of attention because of its relevance for climate mitigation. Complementary to official reported bottom-up emission inventories, quantification can be done with an inverse modelling framework, combining atmospheric transport models, prior gridded emission inventories and a network of atmospheric observations to optimize the emission inventories. An important aspect of such a method is a correct quantification of the uncertainties in all aspects of the modelling framework. The uncertainties in gridded emission inventories are, however, not systematically analysed. In this work, a statistically coherent method is used to quantify the uncertainties in a high-resolution gridded emission inventory of CO2 and CO for Europe. We perform a range of Monte Carlo simulations to determine the effect of uncertainties in different inventory components, including the spatial and temporal distribution, on the uncertainty in total emissions and the resulting atmospheric mixing ratios. We find that the uncertainties in the total emissions for the selected domain are 1 % for CO2 and 6 % for CO. Introducing spatial disaggregation causes a significant increase in the uncertainty of up to 40 % for CO2 and 70 % for CO for specific grid cells. Using gridded uncertainties, specific regions can be defined that have the largest uncertainty in emissions and are thus an interesting target for inverse modellers. However, the largest sectors are usually the best-constrained ones (low relative uncertainty), so the absolute uncertainty is the best indicator for this. With this knowledge, areas can be identified that are most sensitive to the largest emission uncertainties, which supports network design.

Electronegativity Measurements and Analysis for CO2 and CO in DC Plasma Discharge

Electronegativity of CO 2 and CO in dc plasma discharge was investigated employing the Allan-Boyd-Reynolds (ABR), the current balance (CB), the orbital motion limited (OML), and the floating potential (FP) methods by taking advantage of the positive ion number density using the recorded I-V curves. Electron energy distribution functions were evaluated, and electron number density and temperature were obtained. Electron temperature and number density were also obtained for both gases, employing the exponentially rising electron current. Results obtained for positive and negative ions were found to be compatible for ABR, CB, and OML for each gas with the FP method to be more than one order of magnitude higher for both gases. Electronegativity of the CO 2 and CO was deduced using the measured data for electron and negative ion number densities, with the FP method at about one order of magnitude higher than those for the remaining methods.

Elucidating Singlet Oxygen Production in Li-Ion and Metal-Air Batteries

At high voltages, Li-ion and Li-air batteries undergo unwanted electrochemical reactions that can permanently decrease the performance of the battery. Recent experiments studying off-gassing from NMC cathodes have yielded different results for the trends of O2, CO2, and CO gas production with varying Ni composition. Studies also disagree on the origin of the elements in the gas. Very recently, it was suggested that not only is Li2CO3 on NMC cathodes responsible for the majority of CO2 production [1] but that singlet oxygen is produced when Li2CO3 is bias above 3.82 V [2]. This and other studies suggest singlet oxygen production as a common degradation pathway in Li-ion, Li-air [3,4], and Na-air [5]. With the use of first principles methods, we attempt to reconcile these experimental works and propose a universal mechanism of singlet oxygen production. We will also discuss a way to experimentally verify our mechanism by varying the electrolyte, which we claim will change the onset potential of singlet oxygen production in a predictable way. [1] 1. Renfrew, S. E. & McCloskey, B. D. Residual Lithium Carbonate Predominantly Accounts for First Cycle CO2and CO Outgassing of Li-Stoichiometric and Li-Rich Layered Transition-Metal Oxides. J. Am. Chem. Soc. (2017). doi:10.1021/jacs.7b08461 [2] 1. Mahne, N., Renfrew, S. E., McCloskey, B. D. & Freunberger, S. A. Electrochemical Oxidation of Lithium Carbonate Generates Singlet Oxygen. Angew. Chemie Int. Ed. (2018). doi:10.1002/anie.201802277 [3] 1. Mahne, N. et al. Singlet oxygen generation as a major cause for parasitic reactions during cycling of aprotic lithium-oxygen batteries. Nat. Energy (2017). doi:10.1038/nenergy.2017.36 [4] 1. Wandt, J., Jakes, P., Granwehr, J., Gasteiger, H. A. & Eichel, R.-A. Lithium–Air Batteries Singlet Oxygen Formationduring the Charging Process of an Aprotic Lithium–Oxygen Battery. [5] 1. Schafzahl, L. et al. Singlet Oxygen during Cycling of the Aprotic Na-O2 Battery. Angew. Chemie Int. Ed. (2017). doi:10.1002/anie.201709351

Comparison of CK model and line by line method using old and updated parameters/databases

Thermal radiation transfer in a 2D enclosure filled with non-gray gases, namely H2O, CO2, or their mixture, is calculated using the line-by-line approach and the correlated-k (CK) model. This study shows the effect of spectral databases on the accuracy of LBL and CK model calculations. Line-by-line calculations were carried out using two databases for high temperature, i.e. the HITEMP1995 and the HITEMP2010 high-resolution databases. Calculations of the CK model were conducted using two sets of parameters, i.e. the old (earlier) parameters {A. Soufiani, J. Taine, High temperature gas radiative property parameters of statistical narrow-band model for H2O, CO2and CO and correlated-k (CK) model for H2O and CO2, Int. J. Heat Mass Transfer 40 (1997) (987–991)} and the new (updated) parameters {(Rivière, P. and A. Soufiani, Updated band model parameters for H2O, CO2, CH4and CO radiation at high temperature, International Journal of Heat and Mass Transfer, 2012. 55(13), 3349–3358)}. The angular and spatial discretization of the radiative transfer equation is performed using the discrete ordinates method and finite volume method, respectively. Seven test cases with different medium temperature (both isothermal and non-isothermal) and homogeneous or non-homogeneous concentrations of participating gases are considered. This study intends to provide a comprehensive evaluation of the CK model with two sets of parameters and LBL method using the HITEMP95 database in a wide range of medium temperatures (from 1000 to 2500 K) and concentration of participating gases (from 10% to 100% mole fraction). The line-by-line results based on the HITEMP2010 high-resolution spectral database are used as benchmarks to evaluate the accuracy of other approximate models. Very good agreement for both the wall heat flux and the radiative source term was observed between the LBL results using the HITEMP2010 database and the results of the CK model in all the test cases. It is concluded that for all considered test cases, the CK method with the new parameters provides better accuracy than with the old ones.

Insights into CO 2 Fixation Pathway of Clostridium autoethanogenum by Targeted Mutagenesis

ABSTRACTThe future sustainable production of chemicals and fuels from nonpetrochemical resources and reduction of greenhouse gas emissions are two of the greatest societal challenges. Gas fermentation, which utilizes the ability of acetogenic bacteria such as Clostridium autoethanogenum to grow and convert CO2 and CO into low-carbon fuels and chemicals, could potentially provide solutions to both. Acetogens fix these single-carbon gases via the Wood-Ljungdahl pathway. Two enzyme activities are predicted to be essential to the pathway: carbon monoxide dehydrogenase (CODH), which catalyzes the reversible oxidation of CO to CO2, and acetyl coenzyme A (acetyl-CoA) synthase (ACS), which combines with CODH to form a CODH/ACS complex for acetyl-CoA fixation. Despite their pivotal role in carbon fixation, their functions have not been confirmed in vivo. By genetically manipulating all three CODH isogenes (acsA, cooS1, and cooS2) of C. autoethanogenum, we highlighted the functional redundancies of CODH by demonstrating that cooS1 and cooS2 are dispensable for autotrophy. Unexpectedly, the cooS1 inactivation strain showed a significantly reduced lag phase and a higher growth rate than the wild type on H2 and CO2. During heterotrophic growth on fructose, the acsA inactivation strain exhibited 61% reduced biomass and the abolishment of acetate production (a hallmark of acetogens), in favor of ethanol, lactate, and 2,3-butanediol production. A translational readthrough event was discovered in the uniquely truncated (compared to those of other acetogens) C. autoethanogenum acsA gene. Insights gained from studying the function of CODH enhance the overall understanding of autotrophy and can be used for optimization of biotechnological production of ethanol and other commodities via gas fermentation.

Kinetic and Mechanisms of the Homogeneous, Unimolecular Elimination of Phenyl Chloroformate andp‐Tolyl Chloroformate in the Gas Phase

ABSTRACTThe gas‐phase elimination of phenyl chloroformate gives chlorobenzene, 2‐chlorophenol, CO2, and CO, whereasp‐tolyl chloroformate producesp‐chlorotoluene and 2‐chloro‐4‐methylphenol CO2and CO. The kinetic determination of phenyl chloroformate (440–480oC, 60–110 Torr) andp‐tolyl chloroformate (430–480°C, 60–137 Torr) carried out in a deactivated static vessel, with the free radical inhibitor toluene always present, is homogeneous, unimolecular and follows a first‐order rate law. The rate coefficient is expressed by the following Arrhenius equations:Phenyl chloroformate:Formation of chlorobenzene, logkI= (14.85 ± 0.38)–(260.4 ± 5.4) kJ mol−1(2.303RT)−1;r= 0.9993Formation of 2‐chlorophenol, logkII= (12.76 ± 0.40) – (237.4 ± 5.6) kJ mol−1(2.303RT)−1;r= 0.9993p‐Tolyl chloroformate:Formation ofp‐chlorotoluene: logkI= (14.35 ± 0.28) – (252.0 ± 1.5) kJ mol–1(2.303RT)−1;r= 0.9993Formation of 2‐chloro‐4‐methylphenol, logkII= (12.81 ± 0.16) – (222.2 ± 0.9) kJ mol−1(2.303RT)–1;r= 0.9995The estimation of thekIvalues, which is the decarboxylation process in both substrates, suggests a mechanism involving an intramolecular nucleophilic displacement of the chlorine atom through a semipolar, concerted four‐membered cyclic transition state structure; whereas thekIIvalues, the decarbonylation in both substrates, imply an unusual migration of the chlorine atom to the aromatic ring through a semipolar, concerted five‐membered cyclic transition state type of mechanism. The bond polarization of the C–Cl, in the sense Cδ+…Clδ−, appears to be the rate‐determining step of these elimination reactions.

Effects of Ambient Temperature Condition on Biodiesel Properties Derived from Palm Oil

Crude palm oil (CPO) is currently the most preferable feedstock to be converting into biodiesel via transesterification process in this region. Though the commercial projections for biodiesel have grown, there remains some concerns with respect to its resistance to degradation during storage that possibly will compromise the fuel quality. The purpose of this study is to investigate the influences of ambient temperature condition on properties of biodiesel characteristics and emission. The biodiesel samples were stored and monitored in glass container at the temperature 6°C, 25°C and 30°C, and blending of biodiesel was varied from 5vol% (B5) - 45vol% (B45). The changes of density, kinematic viscosity, flash point, water content, acid value, and as well as emission of CO2and CO were observed. The result show storage under ambient temperatures properties of CPO biodiesel were found to have higher value compare to the other temperature storage and also have significant effect on the CO emission.

Effect of Hydrogen Partial Pressure on Hydrocarbon Production from Deoxygenation of Stearic Acid

The catalytic deoxygenation experiments of stearic acid and hydrogen were performed for 6 hours in the presence of a solvent, dodecane, in a temperature range of 295-305°C and the rotational speed of 100rpm, under a certain hydrogen partial pressure (in argon), using palladium supported on active and mesoporous carbon as a catalyst. The results showed, the main liquid-phase product was n-heptadecane, while the main gaseous products were CO2and CO. When the partial pressure of hydrogen is 3.0MPa, the acid value of primary product is the lowest and the reaction tends to be gentle, conversion rate of stearic acid and selectivity to n-heptadecane is the highest.

A Study on CO<sub>2</sub>/CO Dual Sensor Module by NDIR Method

This research deals with the CO2/CO Dual Sensor Module measuring CO2 and CO, that is the representative environmental harmful material, simultaneously. In the measurement of the CO2and CO generally, the Non-Dispersive InfraRed method(NDIR method) is used for the precise measurement and durability. This method is to measure the concentration of the gas by using the Lambert-beer rule. When measuring the gas density with the NDIR method, the important factor is the apparatus for being called an optical chamber consisting of the emitter sensor and detector sensor are used for measuring concentration of the gas. Thus, this paper introduces an optical chamber of the new way of using the NDIR method and through this, shows an experimental result of the CO2gas concentration measurement and it presents possibility for measurement of the concentration of the CO.

Comparative study of core-excitation processes of C(1s) in CO, CO2, OCS andCS2molecules by electron impact

In the present work, the distorted-wave approximation is appliedto study the excitation of core-level electrons in OCS, CO2, CO andCS2molecules by electron impact. More specifically, we report calculated differentialand integral cross sections for the X1 Σ+ →1,3 Πtransitions in an incident energy range of 300–800 eV. We also report the ratios ofthese cross sections for the corresponding transitions leading to the tripletand singlet core-excited states as a function of incident energy. Theseratios are compared with the available experimental results for CO2and CO molecules obtained by both conventional energy-lossspectroscopy and the ejected-electron detection technique. Theresults confirm the existence of a broad resonance for CO2and CO molecules. Moreover, the good qualitative agreement between thecalculated and experimental ratios shows that the decays of the autoionizingstates are impact-energy independent. Quantitative agreement between theoryand experiment is also satisfactory.

Surface Properties of Carbided Molybdena–Alumina and Its Activity for CO2Hydrogenation

The surface properties of carbided molybdena–alumina were investigated through O2-TPD and TPSR along with the catalytic activities of the supported catalysts for CO2hydrogenation. The 1173 K-carbided catalyst exhibited the highest activity for the reaction on the CO adsorption basis. H2pretreatment of the passivated 973 K-carbided catalyst at 773 K did not affect the activity for CO2hydrogenation but a change was visible for the unpassivated catalyst. Through O2-TPD, it was found that the adsorbed oxygen oxidizes the surface carbon of the molybdenum carbide to form CO2and CO. A possible reaction scheme for the hydrogenation of CO2is given, along with an explanation for the lowered activity of the passivated catalysts. η-Mo3C2serves as an active site for CO2hydrogenation. TPSR results were correlated with the activity to reveal that the number of Mo carbides depends on the activity for CO2hydrogenation.

Alkene and Arene Combustion on Pd(111)

Oxidation reactions of ethene, propene, 1-butene, 1,3-butadiene, benzene, and toluene were studied on oxygen-precovered Pd(111) (0.25 ML–1.2 ML) using temperature-programmed reaction spectroscopy (TPRS). Combustion is the sole reaction pathway; no partial oxidation products are formed. Comparison of these results with those from Pd(100) demonstrates that the structure of the metal surface does not significantly affect the mechanism of catalytic oxidation of most of the olefins or aromatic hydrocarbons studied, although, in general, combustion occurs at higher temperatures on Pd(111). Only for benzene combustion is there an appreciable structure sensitivity. For all the hydrocarbons studied the CO2and CO yields are maximized for an oxygen precoverage of 0.34 oxygen atoms per surface palladium atom. Abrupt increases in carbon oxide production at specific oxygen coverages indicate that oxygen-induced surface reconstructions may play a role in the combustion activity.

Temperature Measurement in Flames through CO2and CO Emission: New Highly Excited Levels of CO2

Spectra of CH4+ O2low-pressure flames have been recorded at a resolution of 0.020 cm−1with an infrared Fourier transform spectrometer in the spectral range 1790 to 5029 cm−1. Through the use of CO2and CO emission lines, the flame temperature has been determined with a precision of the order of 1%. Results (wavenumbers, band centers, and spectroscopic constants) concerning six new vibrational transitions Δv3= 1 with (2v1+v2) = 5 which have not been observed earlier and which occur between highly excited vibrational states are reported.

Methane Reforming Reaction with Carbon Dioxide over Ni/SiO2Catalyst: II. A Mechanistic Study

The mechanism of the carbon dioxide reforming of methane was investigated over a nickel-on-silica catalyst. Non-steady-state and steady-state isotopic transient experiments combined within situDRIFT spectroscopy investigations were used to quantify the amount of the various adspecies present on the working catalyst surface. It was found that as soon as the catalyst is contacted with the reacting mixture, dehydrogenated carbon adspecies originating from the initial adsorption of methane and carbon dioxide are deposited on the nickel particles. Under steady-state reaction conditions, a permanent pool of adspecies equivalent to one monolayer of carbide-like species is continuously fed by the dissociative activation of gaseous methane. This initial activation step of methane is shown to be reversible, since it allows a fast CH4/CD4exchange characterised by a marked isotopic effect. This pool of adspecies constitutes a reservoir of active carbon able to be oxidised into CO by oxygen atoms arising from the simultaneous carbon dioxide dissociation. This oxidation step which does not involve any C–H bond activation is assumed to be rate limiting since no kinetic isotopic effect is found for the formation of CO under the stoichiometric reforming conditions. Gaseous CO is also directly produced from the latter CO2dissociation. Adsorption/desorption equilibria ensure a fast interconversion between gaseous CO2and CO, as attested by their isotopic scrambling. A similar adsorption/desorption equilibrium is proposed for H2O which, combined with the reversible activation of CO2and CO, leads to the achieved water–gas-shift equilibrium. Besides the rapid steps which constitute the catalytic cycle, slow side reactions involving the migration of the carbide-like species through the nickel particle and their transformation into structured coke or graphite growing as hollow whiskers are proposed to account for the ageing phenomena described in Part I of this work. A particular configuration of active sites is proposed on the basis of the main mechanistic statements.

Surface Oxide Structures on Nonporous Carbon

Base uptake from aqueous solution, thermal desorption of CO2and CO, enthalpy of neutralization, and mass titration measurements have been carried out on the furnace black Black Pearls 570, both before and after oxidation in aqueous nitric acid. Taken together, the data indicate that unsaturated lactonic structures form an important part of the surface oxide layer.

Application of a counter-current gaseous diffusion model to the oxidation of hafnium carbide at 1200 to 1530�C

A counter-current gaseous diffusion model is presented to describe the oxidation of hafnium carbide between 1200 and 1530°C. The model separates the porous hafnia scale into two gas diffusion regions separated by a flame front, where O 2 and CO react to form CO 2.In the outer region, O 2 and CO 2 counter-diffuse; in the inner region, CO 2 and CO counter-diffuse. The concentration gradients of each gaseous specie in the pores of the hafnia are determined and the rate of oxidation is calculated. A porosity of 2% and a pore radius of 0.01 μm are representative of the values observed in hafnia during the early stages of HfC oxidation. These values lead to predictions of parabolic rate constants that are close to those measured by thermogravimetric analysis. In addition, the predicted and measured parabolic rate constants are shown to have the same dependence upon temperature and oxygen partial pressure.