Formation Mechanism Of Co Research Articles

Formation Mechanism of CO2 and CH4 Hydrates in Bubbly Flow in a Horizontal Pipeline

Formation Mechanism of CO₂ and CH₄ Hydrates in Bubbly Flow in a Horizontal Pipeline

Magnetic field intensity dependent microstructure evolution and recrystallization behavior in a Co–B eutectic alloy

• Magnetic field-dependent microstructure evolution and recrystallization were studied. • Composition segregation resulting in the formation of FCC-Co/Co2B eutectic under 20 T. • The application of the magnetic field was found to promote recrystallization. Systematic understanding on the magnetic field intensity dependent microstructure evolution and recrystallization behavior in a Co-B eutectic alloy under a constant undercooling (∆ T ≈100 K) were carried out. Absent of the magnetic field, the comparable size of divorced FCC-Co and Co 3 B eutectic ellipsoidal grains coexist with a few regular lamellas. When the magnetic field is less than 15 T, the elongated primary FCC-Co dendrites parallel to the magnetic field with the dispersed FCC-Co nano-particles embedded within the Co 3 B matrix occupy the inter-dendrite regions. Once the magnetic field increases to 20 T, the FCC-Co/Co 2 B anomalous eutectic colonies dominate. The formation mechanism of Co 2 B phase is discussed from several aspects of the competitive nucleation, the chemical redistribution induced by the thermomagnetic-induced convection and magnetic dipole interaction, and the strain-induced transformation. Furthermore, the application of magnetic field is found to promote recrystallization, proved by the lower density of misorientation, the appearance of FCC-Co annealed twins and more Co 3 B sub-grains. This work could further enrich our knowledge about the magnetic-dependent microstructure evolution and recrystallization process in the undercooled Co-B system and provide guidance for controlling the microstructures and properties under extreme conditions.

Highly selective CO2 electrolysis in aqueous media by a water-soluble cobalt dimethyl-bipyridine complex.

A water-soluble Co complex with dimethyl-bipyridine ligands reduced CO2 to CO electrochemically with almost 100% selectivity at -0.80 V vs. NHE in an aqueous medium (pH 6.8) without an organic solvent. The reaction overpotential was 270 mV. A possible CO formation mechanism was discussed based on experiments and calculations.

Intrinsic kinetics of CO2 methanation on low-loaded Ni/Al2O3 catalyst: Mechanism, model discrimination and parameter estimation

The mechanism and kinetic of CO2 methanation reaction of 9.5 % Ni/Al2O3 catalyst is analysed under a wide range of operating conditions. Once the catalyst activity is stabilized, the influence of temperature, total pressure and space velocity is studied for kinetic characterisation. A data set comprising of 153 experimental runs has been used to develop a kinetic model capable to accurately predict the reaction rate. Ni/Al2O3 catalyst shows an apparent activation energy of 80.1 kJ mol−1 in CO2 hydrogenation. Data obtained under differential mode adjust quite precisely to a power-law model with H2O inhibition, with a water adsorption constant of 3.1 atm−1 and apparent orders of 0.24 and 0.27 for H2 and CO2, respectively. Based on DRIFTS results, we propose for the first time the H-assisted CO formation route, which is compared with the more conventionally reported carbonyl route, and describe the corresponding reaction rate LHHW equation, resulting in notable improvement for mean deviation (D) of 7.0 % in our model related to that based on the carbonyl route (D = 20.1 %) usually suggested for catalysts with higher Ni loads around 20 %. The H-assisted CO formation route considers the formate species decomposition into carbonyls via H-assisted CO formation mechanism and further carbonyls hydrogenation into CHO as the rate determining step. Thus, the LHHW mechanism, in which carbonyls as well as formate species participate in CO2 methanation, is capable to reflect the kinetics of lowly-loaded Ni/Al2O 3 catalyst with high accuracy under relevant process conditions (315−430 °C, 1−6 bar, H2 to CO2 molar ratios between 1–16 and, different reagents and products partial pressures).

Study on the CO Formation Mechanism during Coal Ambient Temperature Oxidation

The CO formation rules of coal were analyzed by a self-developed testing device under ambient temperature. The changes of functional groups caused by oxidation were obtained using Fourier-transform infrared spectroscopy (FTIR). The experimental results showed that CO was generated during the ambient temperature oxidation. The highest concentration level of CO could be 389 ppm. The methylene and aldehyde groups on the side chains were involved in the reaction. For the quantum mechanical approach, we employed the density functional theory with the 6–31 G (d, p) basis set. Density functional theory–based computations interpreted the possible reaction sites on a coal molecule by electronic static potential analysis. The rationality of the predicted reactions was also evaluated by transition state analysis and energy analysis. This research theoretically proved that coal could be oxidized to carbon monoxide under ambient temperatures and gave the possible reaction paths.

Numerical study of methane combustion under moderate or intense low-oxygen dilution regime at elevated pressure conditions up to 8 atm

This paper investigates the effect of operating pressure (up to 8 atm) on the moderate or intense low-oxygen dilution (MILD) combustion of methane. Computational fluid dynamics (CFD) modeling was firstly conducted for a laboratory-scale combustor to obtain the distributions of temperature and minor species (CH2O and OH), and pollutants (CO and NO) emission under elevated operating pressures. To provide further insight into the heat release characteristics, flame structure, CO formation mechanism as well as extinction limit, a counterflow diffusion flame with hot oxidizer diluted oxidizer configuration was also modeled using detailed chemistry. The CFD modeling results show that increasing the operating pressure tends to increase both peak value and spatial gradient of the combustion temperature, and reduce the width of the reaction zone, indicating the departure of MILD combustion regime when using the identical burner. However, enhancing the internal flue gas recirculation by minimizing the air nozzle diameter can help sustain the MILD combustion regime. The kinetic modeling shows that MILD combustion features only positive heat release region, while traditional combustion exists both negative and positive heat release regions, where multiple peaks are observed. In addition, MILD combustion shows a dual oxygen consumption stage regardless of operating pressures. Simultaneously, MILD combustion exhibits a stretched S-curve of flame response without extinction and re-ignition processes, while traditional combustion presents obvious extinction and ignition points. These unique phenomena can be used for identifying MILD combustion regime in future work.

Highly Dispersed Ni0/NixMg1–xO Catalysts Derived from Solid Solutions: How Metal and Support Control the CO2 Hydrogenation

Among the Ni-based catalysts studied for CO2 activation reactions, NixMg1–xO solid solutions present advantageous characteristics, mainly linked with the homogeneous distribution of the Ni species inside the MgO structure, leading to highly dispersed Ni0 supported catalysts. In this work, we report on the preparation and characterization of NixMg1–xO precatalysts calcined at different temperatures. The resulting Ni0/NixMg1–xO catalysts were tested for the methanation of CO2. Following the structural, morphological, and chemical changes during both the calcination and the reduction, we were able to observe clear correlations between the reactivity of the catalysts and their physical properties, leading to a better understanding of the reaction mechanism and the respective contributions of the metal and the support. While no change was observed in the formation of CH4 over the range of temperature tested, the CO formation as byproduct clearly changed with the increasing temperatures. Our results are consistent with the hypothesis that two different CO formation mechanisms are occurring, but depending on the temperature, one dominates over the other. This study illustrates the importance of the complex interplay of metal particles and oxidic support (at the interface), both actively participating in the CO2 hydrogenation mechanism.

Effects of Preheating and CO2 Dilution on Oxy-MILD Combustion of Natural Gas

Oxy-moderate or intense low-oxygen dilution (MILD) combustion, which is a novel combination of oxy-fuel technology and MILD regime, is numerically studied in the present work. The effects of external preheating and CO2 dilution level on the combustion field, emission, and CO formation mechanisms are investigated in a recuperative laboratory-scale furnace with a recirculating cross-flow. Reynolds-averaged Navier–Stokes (RANS) equations with eddy dissipation concept (EDC) model are employed to perform a 3-D simulation of the combustion field and the turbulence–chemistry interactions. In addition, a well-stirred reactor (WSR) analysis is conducted to further examine the chemical kinetics of this combination when varying the target parameters. The simulations used the skeletal USC-Mech II, which has been shown to perform well in the oxy-fuel combustion modeling. Results show that with more preheating, the uniformity of temperature distribution is noticeably enhanced at the cost of higher CO emission. Also as inlet temperature increases, the concentration of minor species rises and CO formation through the main path (CH4→CH3→CH2O→HCO→CO→CO2) is strengthened, while heavier hydrocarbons path (C2H2→CO) is suppressed. Meanwhile, greater CO2 addition notably closes the gap between maximum and exhaust temperatures. In a highly CO2-diluted mixture, chain-branching reactions releasing CH2O are strengthened, while chain-terminating reactions are weakened. CH2O production through CH3O is accelerated compared with the straight conversion of methyl to formaldehyde. When diluting the oxidant, methylene CH2(s) plays a more influential role in CO formation than when pure oxygen is used, contributing to higher CO emission.

Insights into the CO Formation Mechanism during Steam Reforming of Dimethyl Ether over NiO/Cu-Based Catalyst

Steam reforming of dimethyl ether on Cu-based catalyst was experimentally studied. It is found that formation of H2 and CO2 occurred over Cu/γ-Al2O3/Al, while methanol decomposition to CO and H2 was the main reaction over Cu/Ni/γ-Al2O3/Al in methanol steam reforming (MSR), which is similar to that on metallic Ni. However, XPS results show that nickel species existed as an oxidation state (NiO) over Cu/Ni/γ-Al2O3/Al. Therefore, reaction pathways of MSR over Cu(111) and NiO/Cu(111) were further explored using theoretical density functional theory calculations, and it was found that different reactivities of CH2O* resulted in the distinct product selectivity. On Cu(111), CH2O* reacting with OH* to CH2OOH* is favored, while CH2O* prefers to dehydrogenate to H* and CO* directly on NiO/Cu(111). This provided further evidence on the experimental results and fundamental understanding on the role of NiO species in affecting the MSR mechanism, which was helpful for rational design of selective Cu-based catalysts.

Chemical tracers in proto-brown dwarfs: CO, ortho-H2CO, para-H2CO, HCO+, CS observations

We present a study of the CO isotopologues and the high-density tracers H$_{2}$CO, HCO$^{+}$, and CS in Class 0/I proto-brown dwarfs (proto-BDs). We have used the IRAM 30m telescope to observe the $^{12}$CO (2-1), $^{13}$CO (2-1), C$^{18}$O (2-1), C$^{17}$O (2-1), H$_{2}$CO (3-2), HCO$^{+}$ (3-2), and CS (5-4) lines in 7 proto-BDs. The hydrogen column density for the proto-BDs derived from the CO gas emission is $\sim$2-15 times lower than that derived from the dust continuum emission, indicating CO depletion from the gas-phase. The mean H$_{2}$CO ortho-to-para ratio is $\sim$3 for the proto-BDs and indicates gas-phase formation for H$_{2}$CO. We have investigated the correlations in the molecular abundances between the proto-BDs and protostars. Proto-BDs on average show a factor of $\sim$2 higher ortho-to-para H$_{2}$CO ratio than the protostars. Possible explanations include a difference in the H$_{2}$CO formation mechanism, spin-selective photo-dissociation, self-shielding effects, or different emitting regions for the ortho and para species. There is a tentative trend of a decline in the HCO$^{+}$ and H$_{2}$CO abundances with decreasing bolometric luminosity, while the CS and CO abundances show no particular difference between the proto-BDs and protostars. These trends reflect the scaled-down physical structures for the proto-BDs compared to protostars and differences in the peak emitting regions for these species. The C$^{17}$O isotopologue is detected in all of the proto-BDs as well as the more evolved Class Flat/Class II BDs in our sample, and can probe the quiescent gas at both early and late evolutionary stages.

Belt‐Like Cobalt Phosphate Tetrahydrate as the Non‐Noble Metal Catalyst with Enhanced Catalytic Reduction Activity

AbstractIn this work, the belt‐like cobalt phosphate tetrahydrate (Co−P‐HT) was successfully synthesized by the hydrothermal method without adopting template and complicated manipulation. To the best of our knowledge, the as‐prepared Co−P based materials were used as heterogeneous catalysts to catalytic reduction of organic molecules (e. g., 4‐nitrophenol) at room temperature for the first time. Especially, the Co−P‐HT exhibited enhanced catalytic reduction activity by about 3.59 times higher than that of the plate‐like cobalt phosphate octahydrate (Co−P‐RT). Moreover, Co−P‐HT also exhibited excellent catalytic activity than some noble metal‐containing materials. In addition, the Co−P‐HT could maintain its enhanced catalytic activity after the four successive catalytic test, further confirming the stability of this material. The characterization results demonstrated that the as‐prepared Co−P based materials presented distinguishable physicochemical properties, such as different chemical compositions, morphologies, coordination environments and the ability of electrons transfer and distribution. Besides, a formation mechanism of Co−P‐HT was purposed in which this material could be obtained from Co−P‐RT. The Co−P‐HT could be considered as the potential catalyst to substitute some cobalt‐based and noble metal‐containing materials in mild conditions.

Comparison of the characteristics and mechanism of CO formation in O2/N2, O2/CO2 and O2/H2O atmospheres

Abstract The characteristics and mechanisms of CO formation in O2/CO2 and O2/H2O atmospheres were investigated both experimentally and numerically. Comparison experiments in O2/N2, O2/CO2 and O2/H2O atmospheres were performed in a flow reactor at atmospheric pressure covering fuel-rich to fuel-lean equivalence ratios and temperatures from 973 K to 1773 K. Experimental results demonstrated that CO formation in an O2/CO2 atmosphere is the highest and that CO formation is the lowest under all fuel-rich, stoichiometric and fuel-lean conditions. The updated chemical kinetic mechanism satisfactorily reproduced the experimental results. For O2/CO2 atmospheres, the presence of a high CO2 concentration enhances CO2 + H = CO + OH and CH2(S) + CO2 = CH2O + CO dramatically, strengthens HCO + M = H + CO + M by the chaperone effect of CO2, and contributes exclusively to CH3OCO = CH3O + CO. The contribution of the pathway CO2 → CO is significant, and CH3 → CH3OCO → CH2O and CH3 → CH3OCO → CO are exclusive channels in O2/CO2 atmospheres. For O2/H2O atmospheres, although the high chaperone effect of H2O facilitates HCO + M = H + CO + M, CO + OH = CO2 + H is enhanced due to the abundant OH radicals and HCCO + H = CH2(S) + CO is suppressed due to the lack of H radicals. The pathway CO→CO2 is enhanced due to sufficient OH radicals, and CH3 → (CH2(S)) → CH3OH → CH3O → CH2O and CH3 → (CH2(S)) → CH3OH → CH2OH are exclusive channels. Moreover, the pathway CH2O → HCO → CO is amplified in both O2/CO2 and O2/H2O atmospheres.

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.

Porous Co–Mo phosphide nanotubes: an efficient electrocatalyst for hydrogen evolution

The construction of efficient and low-cost bimetallic phosphide catalysts for hydrogen evolution is still in challenge. In this work, a series of porous Co–Mo phosphide nanotubes which are synthesized via in situ phosphidation process of CoMoO4 nanorods precursor at different phosphatization temperature have been used for hydrogen evolution reaction (HER). X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, X-ray photoelectron spectroscopy and N2 adsorption–desorption experiments were used to characterize the as-synthesized Co–Mo phosphide nanotubes. Results indicate that the phosphatization temperature is the key factor in the formation process of tube-like structure. The possible formation mechanism of Co–Mo phosphide nanotubes was further proposed. Additionally, the as-synthesized CoMoP-600 nanotubes displayed the highest HER catalytic performance and long-time durability in 0.5 M H2SO4 solution. The high catalytic performance of CoMoP-600 catalyst may be attributed to the favorable composition and the large surface area. This study shines a light in the application of bimetallic catalysts for the HER and provides us a new way to design and synthesize porous hollow tube-like structure materials.

Experimental and numerical study on the CO formation mechanism in methane MILD combustion without preheated air

Moderate or intense low-oxygen dilution (MILD) combustion has increasingly attracted the attention of scholars because of its high efficiency and low-pollutant emission, particularly its emission of CO and NOX. MILD combustion without preheated air was achieved in this study. Numerical results obtained by a computational fluid dynamics model with GRI-Mech 3.0 conform well to those from the experiments. Three zones, namely, central zone, high CO concentration zone, and recirculation zone, were found in the furnace. The CO formation mechanisms were analyzed in the three zones by examining the rate of production. Analysis results showed that the reason for the appearance of high CO concentration zone was local high O2 concentration. High O2 concentration enhanced the reaction O+CH3⇔H+CH2O, which resulted in an amount of CH2O. High O2 concentration also enhanced the radical pool reaction H+O2⇔OH+O, which produced an amount of O radicals. Thus, reaction O+CH4⇔OH+CH3 was enhanced, and it had the largest production rate of OH and CH3. The OH radical led to an amount of HCO through the reaction OH+CH2O⇔HCO+H2O, and CH3 radical favored the production of CH2O. An amount of HCO was converted to CO by HCO+O2⇔HO2+CO, HCO+H2O⇔H+CO+H2O, and HCO+M⇔H+CO+M. The main CO formation path was CH4→CH3→CH3O→CH2O→HCO→CO in the central zone. The majority of CO in the recirculation zone came from the central or high CO concentration zones by convection or diffusion, and it was consumed by OH+CO⇔H+CO2.

TiO2 mediated photocatalytic oxidation of volatile organic compounds: Formation of CO as a harmful by-product

Photocatalytic oxidation (PCO) of volatile organic compounds (VOCs) including acetone, alcohols and hydrocarbons was investigated in a static reactor using an FTIR in situ method. Three commercially available TiO2 powders and one TiO2 sample synthesized via thermal hydrolysis of titanyl sulfate were employed in the kinetic experiments. PCO reactions were conducted under different UV light intensities, initial concentrations of substrates, humidities, and temperatures. The formation of the final oxidation products and the kinetics of their accumulation were investigated.Analysis of the FTIR spectra revealed the formation of CO along with CO2 and H2O as final products in the oxidation of VOCs over all the TiO2 samples. No other final products were detected. The method of spectral subtraction by minimizing the IR spectrum length was applied to accurately calculate the CO concentration. The conversion of organic substrates to CO did not exceed 5%. The differential selectivity of CO2 formation towards CO formation, which was defined as the initial CO2 rate divided by the sum of the initial CO2 and CO rates, was used to investigate the effect of the experimental parameters and the photocatalyst on the product distribution. The experimental conditions including light intensity, initial concentration and humidity as well as the photocatalyst and its pretreatment method did not exhibit a significant effect on the differential CO2 selectivity during acetone oxidation but an increase in the reaction temperature resulted in a decrease in the CO2 selectivity. A stronger influence was observed for the type of oxidizing substrate. The increase in the number of carbon atoms in the homologous series of C2–C4 alcohols and C6–C10 alkanes slightly decreased the CO2 selectivity. The most substantial effect was related to the extent of unsaturation in the C6 hydrocarbons. The CO2 selectivity decreased from 98.9% for hexane to 93.3% for benzene. Benzene exhibited the highest conversion to CO (approximately 5%) among all the studied substrates.Only the deposition of Pt (1wt.%) completely prevented the formation of CO during the photocatalytic oxidation of VOCs both at low and high UV intensity.Finally, the mechanism of CO formation is discussed.

Asymmetrical Supercapacitor Composed of Thin Co(OH)2 Nanoflakes on Three-Dimensional Ni/Si Microchannel Plates with Superior Electrochemical Performance

Nanoscale cobalt hydroxide (Co(OH)2) particles are fabricated by electrodeposition on three-dimensional nickel/silicon microchannel plates (Ni/Si-MCPs) as the active electrode materials on the surface and sidewall of the Ni/Si-MCPs for miniature supercapacitors. The relationship among the electrodeposition time, morphology, formation mechanism of Co(OH)2 nanostructure, and capacitor performance is studied. Using an optimal electrodeposition time of 6min, the Co(OH)2 supercapacitor has a capacitance of 697.56Fg−1 (5.72Fcm−2) at 2mAcm−2 and the retention ratio is 91.20% after 2500 cycles. The large areal capacitance and excellent rate capability can be attributed to the unique 3D ordered porous architecture which facilitates electron and ion transport, enlarges the liquid-solid interfacial area, and enhances the utilization efficiency of the active materials. Meanwhile, the weight and size of the device are reduced. By using the Co(OH)2/Ni/Si-MCPs electrode as the positive electrode and CNTs/nickel foam (CNTs/NF) as the negative electrode, the device assembled with CR2025 batteries exhibits high energy density (38.39Whkg−1), high power density (5400Wkg−1 at 9.67Whkg−1), and stable power characteristic (2000 times with 80.63% retention). After charging each supercapacitor for 10s, the device can power a 5mm diameter light-emitting diode (LED) with different colors efficiently, for example, a blue LED for 20min.

Pyrolysis of superfine pulverized coal. Part 2. Mechanisms of carbon monoxide formation

The oxygen-containing gases released during coal pyrolysis comprise more than a half of the devolatilization products, especially the noncondensible species. The mechanisms of CO formation reactions remain problematic, particularly the identity of the functional group precursors for low-temperature CO. In this paper, pyrolysis experiments of superfine pulverized coal were carried out in the N2 and CO2 atmosphere under non-isothermal conditions, applying a fixed-bed reactor. The CO formation mechanisms were investigated from a functional-group standpoint. The deconvolution method via numerical analysis was adopted to resolve the multi-component envelop profiles of CO evolution. Five constituent reaction complexes induced by different oxygenated groups and reactions are recognized, combining the X-ray photoelectron spectroscopy (XPS) analysis. In addition, the effects of coal type, particle size, pyrolysis atmosphere and heating rate on the CO evolution were analyzed. Finally, different CO formation mechanisms initiated from the primary decomposition of distinctive oxygenated functionalities, secondary pyrolysis reactions of tars, and gasification reactions of chars are summarized.

A density functional theory study on formation mechanism of CO, CO2 and CH4 in pyrolysis of lignin

In order to understand formation mechanisms of CO, CO2 and CH4 in lignin pyrolysis, the decarbonylation, decarboxylation and demethylation reactions of various phenylic lignin model compounds were theoretically investigated by using density functional theory methods at B3LYP/6-31G++(d,p) level. Eight decarbonylation reaction pathways (1)–(8), eight decarboxylation reaction pathways (9)–(16) and a demethylation reaction pathways (17) were designed. The standard kinetic and thermodynamic parameters of every reaction pathway at different temperatures were calculated. The calculation results show that energy barriers of decarbonylation reaction pathways (1)–(4) are apparently higher than those of decarbonylation reaction pathways (5)–(8), and then CO is formed more easily through decarbonylation of phenyl (p-hydroxyphenyl, guaiacyl and syringyl) acetaldehyde; energy barriers of decarboxylation reaction pathways (9)–(12) are lower than those of decarboxylation reaction pathways (13)–(16), and then CO2 is formed more easily through decarboxylation of phenyl (p-hydroxyphenyl, guaiacyl and syringyl) formic acid. Compared with step-by-step radical reaction, the energy barrier of concerted reaction is lower, and CH4 is formed more easily through concerted reaction.

On the carbon monoxide formation in oxy-fuel combustion—Contribution by homogenous and heterogeneous reactions

This work investigates CO formation mechanisms under oxy-fuel combustion conditions. The importance of the possible explanations for increased inflame CO concentrations in oxy-fuel flames compared to air-firing are discussed. A model based on a detailed gas-phase reaction mechanism is combined with a lignite char combustion model, including apparent surface kinetics for oxidation as well as carbon dioxide and steam gasification and implication of diffusion limitation.In agreement with other authors work, it is concluded that in gas-fired oxy-fuel flames the CO formation is promoted by a homogenous reaction between hydrogen radicals and CO2. Additionally, this work concludes that in lignite-fired oxy-fuel combustion, this gaseous reaction route is of less importance. In oxy-lignite flames, CO2 gasification is the largest contributor to the increased CO formation compared to air firing. The substitution of CO2 with steam in the oxidizer during wet oxy-fuel combustion has moderate influence on the CO2 gasification, whereas the homogenous CO formation is strongly reduced.