Formation Of CO Research Articles

An Overview of H2 and CH4 as Environmentally Sustainable Alternative Reductants to C for Chromite Smelting

The application of hydrogen (H2) and methane (CH4) as gaseous reductants for pure chromite (FeCr2O4) is reviewed in four theoretical approaches. These approaches are evaluated against the conventional process, where the sole reductant is a solid carbon (C) source. The sustainability is measured by gaseous carbon monoxide (CO(g)) formation, determined by the reaction stoichiometry of each theoretical approach. Decreased CO(g) formation is critical for alleviating the adverse environmental impact of ferroalloy production. The prereduction of FeCr2O4 by H2, followed by reduction by CH4 shows the largest decrease in CO(g) formation, i.e., a 75% decrease, compared to the conventional process. Furthermore, the H2‐based prereduction and CH4‐based primary reduction occur at lower temperatures than C‐based reduction, due to kinetic advantages, and thus decrease energy consumption. The overview discusses the environmental impact of substituting C with H2 and CH4 and briefly discusses how it can be implemented in industry.

Palladium-catalyzed difluorocarbene transfer enables access to enantioenriched chiral spirooxindoles

AbstractWe disclose herein an unprecedented Pd-catalyzed difluorocarbene transfer reaction, which assembles a series of structurally interesting chiral spiro ketones with generally over 90% ee. Commercially available BrCF2CO2K serves as the difluorocarbene precursor, which is harnessed as a user-friendly and safe carbonyl source in this transformation. Preliminary mechanistic studies exclude the formation of free CO in the reaction process, and importantly, we also find that BrCF2CO2K outcompete gaseous CO and several common CO surrogates in this asymmetric process. The reaction mechanism, including the in-situ progressive release of the difluorocarbene, the rapid migratory insertion of ArPd(II) = CF2 species, and subsequent defluorination hydrolysis by water to introduce the carbonyl group, accounts for the overall high efficiency and uniqueness. This work clearly showcases the advantage and potential of the difluorocarbene in synthesis and supplies a mechanistically distinct route for asymmetric carbonylative cyclization reactions.

Dual electric field effects boost bifunctional oxygen electrocatalysis

Regulation of the surface microenvironment is crucial for the development of highly active and durable OER/ORR bifunctional catalysts. In this study, a bifunctional m-CoSx@NSC electrocatalyst with dual electric field effects was designed and fabricated by synchronous pyrolysis of organic sulfur-rich cobalt compounds (Co-DC) and melem. The introduction of nitrogen-rich melem effectively induced the conversion of Co-DC and the growth of tentacles to form a hierarchical carbon skeleton. The interfacial micro-electric field between the carbon layer and CoSx active species improves the intrinsic activity and stability of m-CoSx@NSC. Finite element method simulation and in-situ measurements proved that the tentacle-induced external local electric field promotes the formation of Co(OH)2/CoOOH intermediates and mass transfer, thus accelerating the catalytic reaction kinetics. Through the synergistic effect of dual electric fields, the m-CoSx@NSC catalyst demonstrated a low overpotential of 340 mV for OER and a high half-wave potential of 0.85 V for ORR. Furthermore, the m-CoSx@NSC-based ZAB exhibited an open-circuit voltage of 1.42 V, a maximum power density of 87.38 mW cm−2, a specific capacity of 876.17 mAh gZn−1, and a cycling performance of 700 cycles. The synergistic regulation of the internal and external microenvironments provides a novel insight to improve the catalytic reaction kinetics of OER/ORR.

Techno-economic-environmental study of CO2 and aqueous formate solution injection for geologic carbon storage and enhanced oil recovery

As carbon capture, utilization, and storage (CCUS), carbon-dioxide enhanced oil recovery (CO2 EOR) has inherent shortcomings, such as inefficient oil recovery and carbon storage, and low storage security with mobile CO2. This paper presents a techno-economic-environmental analysis of using formate species, a product of CO2 electrochemical reduction, as an alternative carbon carrier for sequestration and EOR in a carbonate oil reservoir in the Gulf of Mexico Basin. CO2 injection, water-alternating-CO2 injection, and aqueous formate solution injection were compared using a compositional reservoir simulation model and an economic calculator. Formate solution injection yielded greater levels of oil recovery and net carbon storage, where the carbon-bearing species resided in the dense aqueous phase without having to rely on petrophysical trapping mechanisms (structural and capillary). The enhanced oil production, net carbon storage, and storage security can be promoted by providing formate-based CCUS with more incentives (e.g., greater tax credit) in comparison to CO2-based CCUS for EOR and the manufacture of chemicals and products. In establishing carbon storage incentive policies and regulations, policymakers should include alternative carbon carriers.

Temperature and pressure effects on the decomposition mechanisms of 2,6-diamino-3,5-dinitropyrazine-1-oxide crystal: ab initio molecular dynamics study.

The decomposition process of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) crystal at high temperatures (2500 and 3390K) and detonation pressure of 33.4 GPa coupled with temperatures were studied by ab initio molecular dynamics simulations. The results show that the initial decomposition mechanism of LLM-105 is the same under different conditions. The product analysis indicates that high temperature is conducive to the formation of N2 and CO2, but inhibited the formation of H2O. It is found that the formation mechanism of H2O is the same under different conditions, which involves the reaction between OH radical and H radical. Although the detailed processes of the formation of N2 are different, they all involve the reaction between nitrogen-containing fragments, and its core is the formation of intermediates with R1-NN-R2 structure. The core of the formation of CO2 under different conditions is to form the intermediate R1-CO-R2 with carbonyl structure, and then generate the fragment with -OCO- structure, and finally generate CO2. This research may provide new insights into the initiation and subsequent decomposition mechanisms of energetic materials under extreme conditions. The LLM-105 supercell was constructed using the Materials Studio 7.0 package. AIMD simulations were performed in the CASTEP package. AIMD simulations adopted NVT and NPT ensemble, and the temperature was controlled by Nosé thermostat, while the pressure was controlled by Andersen barostat. Besides, DFT calculations were carried out at the B3LYP/6-311 + G(d,p) level using the Gaussian 09 package.

Manganese Doped‐Nitrogenated Carbon as an Efficient Catalyst for Acidic Electrocatalytic Reduction of CO2

AbstractRenewable electricity‐driven CO2 electroreduction to value‐added chemicals is a feasible approach to alleviate both environmental and energy issues. However, CO2 reduction reaction (CO2RR) systems in alkaline electrolytes are constrained by intrinsic limitations such as salt accumulation that impede further industrialization. Herein, an atomically dispersed Mn doped‐nitrogen carbon (AD MnNC) catalyst is developed to electrochemically reduce CO2 to CO in both neutral and acidic media. Benefiting from well‐dispersed MnNx sites, the maximum CO Faradaic efficiency (FECO) reaches ≈100% at −0.73 V versus reversible hydrogen electrode (RHE) with CO current density (JCO) of 20.4 mA cm−2 in neutral 0.5 m KHCO3. Due to diminished *H adsorption, AD MnNC achieves a FECO of 85.3% at pH 2.0, effectively suppressing the hydrogen evolution reaction (HER) in an acidic electrolyte. The mechanistic study reveals that AD MnNC accelerates the production of *COOH intermediates through a proton‐coupled electron transfer (PCET) pathway and thus promotes CO formation.

CO2 hydrogenation to methanol over Pt functionalized Hf-UiO-67 versus Zr-UiO-67.

Sustainable methanol formation from CO2/H2 is potentially a key process in the post-fossil chemical industry. In this study, Hf- and Zr-based metal-organic framework (MOF) materials with UiO-67 topology, functionalized with Pt nanoparticles, have been tested for CO2 hydrogenation at 30 bar and 170-240°C. The highest methanol formation rate, 14 molmethanol molPt-1 h-1, was obtained over a Hf-based catalyst, compared with the maximum of 6.2 molmethanol molPt-1 h-1 for the best Zr-based analogue. However, changing the node metal did not significantly affect product distribution or apparent activation energy for methanol formation (44-52 kJ mol-1), strongly indicating that the higher activity of the Hf-based analogues is associated with a higher number of active sites. Both catalysts showed stable catalytic performance during testing under kinetic conditions, but the addition of 2 vol% water to the feed induced catalyst deactivation, in particular the Hf-MOFs. Interestingly, mainly methanol and methane formation rates decreased, while CO formation rates were less affected by deactivation. No direct correlation was found between catalytic stability and framework stability (crystallinity, specific surface area). Experimental and computational studies suggest that water adsorption strength to the MOF node may affect the relative catalytic stability of Hf-UiO-67-Pt versus Zr-UiO-67-Pt methanol catalysts.This article is part of the discussion meeting issue 'Green carbon for the chemical industry of the future'.

CO2 Hydrogenation on Ru Single-Atom Catalyst Encapsulated in Silicalite: a DFT and Microkinetic Modeling Study.

The critical levels of CO2 emissions reached in the past decade have encouraged researchers into finding techniques to reduce the amount of anthropogenic CO2 expelled to the atmosphere. One possibility is to capture the produced CO2 from the source of emission or even from air (i.e., direct air capture) by porous materials (e.g., zeolites and MOFs). Among the different usages of captured CO2, its conversion into light fuels such as methane, methanol, and formic acid is essential for ensuring the long-awaited circular economy. In the last years, single-atom catalysts encapsulated in zeolites have been considered to this purpose since they exhibit a high selectivity and activity with the minimum expression of catalytic species. In this study, a detailed mechanism composed by 47 elementary reactions, 42 of them in both forward and reverse directions and 5 of them that correspond to the desorption of gas products just forwardly studied), has been proposed for catalytic CO2 hydrogenation over Ru SAC encapsulated in silicate (Ru1@S-1). Periodic density functional theory (DFT) calculations along with microkinetic modeling simulations at different temperatures and pressures were performed to evaluate the evolution of species over time. The analysis of the results shows that carbon monoxide is the main gas produced, followed by formic acid and formaldehyde. The rate analysis shows that CO(g) is formed mainly through direct dissociation of CO2 (i.e., redox mechanism), whereas COOH formation is assisted by OH. Moreover, the Campbell's degree of rate control analysis suggests that the determining steps for the formation of CO(g) and CH2O(g) gas species are their own desorption processes. The results obtained are in line with recent experimental and theoretical results showing that Ru1 SACs are highly selective to CO(g), whereas few atom clusters as Ru4 increase selectivity toward methane formation.

Molecular insights into the synergistic inhibition mechanisms of antifreeze protein and methanol on carbon dioxide hydrate growth

The formation of CO2 hydrates during CO2 transportation and deep-sea injection poses a significant risk of pipeline blockage. Combining kinetic (KHIs) and thermodynamic hydrate inhibitors (THIs) serves as a promising efficient and economical strategy to mitigate this issue, whose performance and microscopic mechanisms yet are still poorly understood. This study employs molecular dynamics simulations to explore the effects of the combination of winter flounder antifreeze protein (wf-AFP) as a KHI and methanol as a THI on CO2 hydrate growth. We find that methanol and wf-AFP exhibit an intriguing synergistic inhibition performance on hydrate growth. In the AFP-only system, AFP serves as a spatial hindrance near the hydrate growth interface. However, in the AFP + methanol system, AFP changes its position due to the attractive force of methanol. Part of the AFP fragment remains on the hydrate interface, while the rest surrounds the CO2 droplet. Methanol, in addition to disrupting the water structure, combines with AFP to act as a double barrier to CO2 dissolution into the aqueous solution, thereby significantly reducing the gas source for hydrate growth. These findings provide molecular-level insights into hydrate inhibition mechanisms and guide the design of efficient inhibitors for safe CO2 transportation and injection.

Molecular insights into the formation of carbon dioxide hydrates on the external surface of sodium montmorillonite in the presence of various types of organic matters

To address the urgent challenge of global climate change due to the greenhouse effect resulting from increasing carbon dioxide (CO2) emissions, viable technologies for geological CO2 storage must be developed. Of such technologies, CO2 hydrates holds significant promise for CO2 storage in seabed sediments, which typically contain clay minerals and organic matter (OM). Thus, investigating the structure of clay mineral interfaces and their interactions with OM is crucial for understanding the nucleation and growth of CO2 hydrate in seabed sediments. In this study, molecular dynamics simulations were used to investigate CO2 hydrate formation on the external surface of sodium montmorillonite (Na-Mnt) in the presence of various types of OM. The results show that the Na-Mnt surface adsorbed certain numbers of sodium ions (Na+) and OM molecules. The hydration of Na + disrupted of the hydrogen bond structure of CO2 hydrates, while hydrogen bonds that formed between OM and H2O molecules hindered CO2 hydrate formation. Consequently, CO2 hydrates predominantly formed in the bulk-like solution away from the Na-Mnt. However, the electrostatic interaction between the carboxyl groups of OM and Na+ mitigated the inhibitory effect of Na+ on CO2 hydrate formation. Over all, these findings can serve as a fundamental theoretical basis for understanding the formation and occurrence characteristics of CO2 hydrates in seabed sediments with a rich Mnt content. Such understanding will help to advance the development of CO2 storage technologies utilizing CO2 hydrates in seabed sediments.

Optimized strategies for efficient CO2 trapping using hydrate technology by pressure adjustment

The hydrate-based method enhances oceanic CO2 storage capacity and is deemed beneficial for controlling greenhouse gas emissions. However, the non-uniform CO2 hydrate crystal interface in the sub-seabed storage layer acts as a barrier, slowing down mass transfer kinetics. This work employed in-situ nuclear magnetic resonance (NMR) technology to compare three different pressure adjustment strategies and observe CO2 bubble dispersion after hydrate dissociation, secondary nucleation, and crystal growth mechanism, along with pore water changes. The presence of micro/nano CO2 bubbles with high internal pressure and high specific surface area in the dissociation liquid significantly accelerated secondary micro-structural phase transition rates. The optimal hydrate-based CO2 storage efficiency reached up to 81.7 %. Moreover, the secondary formation of CO2 hydrates distributed more uniformly within the large, medium, and small pores and led to a significantly increased residual water conversion rate (reaching up to 88 %) in medium pores. The post-secondary formation of high-density hydrates resulted in low fluid mobility (T1/T2 mostly distributed in the range of 0 ∼ 10) and exhibited a mixed wettability state between pore fluids. Utilizing the “memory effects” of CO2 hydrate effectively overcame late-stage mass transfer barriers of solid hydrates films. Our findings extend the understanding of CO2 hydrate formation kinetics under pressure adjustment strategies.

Enhanced synergies for product distributions and interactions during co-pyrolysis between corn stover and tyres

Co-pyrolysis has been studied for its potential to recycle energy from biomass and waste tyres, as well as enhance the quality of the bio-oil. In this paper, the TG-FTIR-GC/MS technique and a fast-infrared heated reactor were used to investigate the co-pyrolysis behaviors and mechanism of waste tyres (WT) and corn stover (CS). Based on the TG-FTIR-GC/MS analysis, co-pyrolysis synergy promoted the production of methane and aromatics while inhibiting the formation of CO2. Co-pyrolysis products distribution shows that the best synergy occurred at a ratio of 30 % WT with the highest oil yield deviation of 19.67 % and the lowest water yield deviation of −13.30 %. Response surface method (RSM) was utilized to optimize the oil production and the highest oil yield of 30.25 wt% was acquired at a heating rate of 25 °C/s and a ratio of 40 % WT. According to the oil analysis, the light fraction of oil (gasoline and diesel) was more than 50 % in all conditions and there was a large number of aromatics (more than 30 %) presented in oil. The char characteristics indicated that several metals combined with -S radicals during co-pyrolysis which formed much metal sulfide and sulfate in chars.

Operando spectroscopic studies on redox mechanism for CO2 hydrogenation to CO on In2O3 catalysts

The catalytic activities of In2O3 catalysts with different surface area for both cyclic unsteady-state (transient) and steady-state reverse water–gas shift (RWGS) reactions were systemically investigated. The initial CO formation rates during CO2-oxidation of the H2-reduced In2O3 catalysts were close to the CO formation rates in steady-state RWGS conditions at 325 °C, suggesting a redox mechanism for the steady-state RWGS reaction over the In2O3 catalysts. Transient kinetics for the In3+/In+ redox and products (H2O, CO) formation during the cyclic H2-reduction and CO2-oxidation of In2O3 under periodic feeding of H2 ↔ CO2 were studied by time-resolved operando UV–vis and In K-edge X-ray absorption experiments at 325 °C. During the H2-reduction, the surface In3+-O species was reduced to produce H2O and In+-□ (□: oxygen vacancy). Subsequent re-oxidation of the In+-□ by CO2 gave CO and the In3+-O species. The transient CO formation rates were close to the consumption rates of In+-□ under CO2, providing a quantitative evidence on the redox mechanism for unsteady-state RWGS reaction over In2O3. These results indicate that the unsteady-state and steady-state RWGS reactions are primary driven by the In3+/In+ redox mechanism. Kinetic results show that the reoxidation step is the rate-limiting step in the steady-state RWGS reaction.

Formation mechanism and luminescence properties of silicon carbide nanowires with core-shell structure

For the preparation of SiC nanowires (SiC NWs) by carbothermal reduction, it is of great significance to study the formation mechanism of sic nanowires for process optimization and the controllable preparation. Although first-principles molecular dynamics (FPMD) can simulate systems of hundreds of atoms on a picosecond time scale, the results of FPMD are still insufficient to elucidate the formation mechanism of core-shell SiC nanowires. To make up this deficiency, this article has conducted Deep Potential Molecular Dynamics (DPMD) simulation on nanoseconds timescales with near FPMD accuracy for systems containing thousands of atoms, the results more concretively show the formation process of core-shell SiC nanowires. DPMD simulation results show when CO molecules react with SiO molecules, CO molecules are wrapped by SiO molecules to form agglomerates, SiO molecules in the agglomerates that can come into contact with the wrapped CO molecules will react with wrapped CO molecules to form the SiC core, and SiO molecules that in the outer layer of the agglomerates will disproportionate into the amorphous SiO2 shell. Furthermore, the formation mechanism of SiC nanowires was validated in combination with thermodynamics and experimental methods. Thermodynamic results show that vacuum conditions are favorable for the formation of SiO and CO and lower the temperature of SiC preparation. Finally, the core-shell structure of SiC NWs with good luminescence properties were successfully prepared by carbothermal reduction method using carbon black and silicon dioxide as raw materials under the pressure of less than 5 kPa.

An investigation of CO generation path upon loading coal from perspective of macromolecular simulation.

CO is a hazardous and pollutant gas that can be produced in many scenarios of coal-related operations. The study mainly investigated CO production process and mechanism when coal is subject to external forces. The effects of coal type, particle size, temperature, and inlet atmosphere on CO production from coal body fragmentation were investigated through coal loading experiments. Materials Studio software was used to carry out coal macromolecular mechanics simulation and molecular dynamics simulation, and the gas production mechanism of coal under loading was explored at the molecular level. It was found that under air atmosphere, the low degree of deterioration, small particle size, and elevated temperature are all more likely to cause coal samples to fragment and decompose to produce CO. The carbonyl group in the molecular structure of coal is shed or broken free radical fragments react with oxygen which may lead to CO formation.

Development of microbial formulation to enhance the removal of high explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) from contaminated soil

Excessive use of High Melting Explosive (HMX; Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) in various industrial activities, construction, mining, military exercises, and conflicts has resulted in severe contamination of soil and water. In the present study, a water-dispersible granule (WDG) was developed using microbial strains capable of degrading HMX. The developed microbial formulation was further investigated and characterized using soil microcosms study and the degradation pathway of HMX by these microbes were elucidated. Out of 6 bacterial strains initially selected for the study, Pelomonas aquatica and Kinneretia asaccharophila were found to be the most efficient HMX degraders in soil capable of removing 65 % and 61 % HMX respectively, within 30 days. These microbial strains formulated as WDGs has shelf-life of up to 6 months at 30˚C with only 16 % loss in viability. Enhancement of 19.64 % and 19.25 % HMX degradation in soil was observed with the use of WDGs from P. aquatica and K. asaccharophila, respectively. LC-MS (Liquid chromatography-mass spectrometry) analysis revealed the presence of nitroso derivate of HMX (1-NO-HMX) at 325 m/z as an intermediate metabolite indicating the single nitrite elimination pathway for HMX degradation leading to the formation of nitrite, nitrate, and CO2 as end products during degradation. The current study provides the base for the development of efficient microbial formulations for enhanced remediation of HMX contaminated soils.

Fabrication of porous Au/Cu alloy catalyst for CO2 electro-reduction to CO in three-chamber electrolyzer: With Cl2 and NaOH produced as byproducts

A three-compartment electrolyzer has been developed for the electro-reduction of CO2 to CO in an organic electrolyte, with NaOH and Cl2 produced as byproducts. In order to improve the performance of the electrolyzer, we have prepared an Au/Cu alloy electrode using a novel non-cyanide electroplating method with high porosity. By expanding the specific surface area of the cathode, and providing a large number of active sites for CO2 electro-reduction, the cathodic current density reaches to 92.7 mA·cm−2, and the Faradaic efficiency of CO formation remains stable at 94.0 %. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations analysis identified that alloying tune the electronic structure of the Au and Cu surface, resulting in promoting the activation of CO2.

Study of NO and CO Formation Pathways in Jet Flames with CH4/H2 Fuel Blends

The existing natural gas transportation pipelines can withstand a hydrogen content of 0 to 50%, but further research is still needed on the pathways of NO and CO production under moderate or intense low oxygen dilution (MILD) combustion within this range of hydrogen blending. In this paper, we present a computational fluid dynamics (CFD) simulation of hydrogen-doped jet flame combustion in a jet in a hot coflow (JHC) burner. We conducted an in-depth study of the mechanisms by which NO and CO are produced at different locations within hydrogen-doped flames. Additionally, we established a chemical reaction network (CRN) model specifically for the JHC burner and calculated the detailed influence of hydrogen content on the mechanisms of NO and CO formation. The findings indicate that an increase in hydrogen content leads to an expansion of the main NO production region and a contraction of the main NO consumption region within the jet flame. This phenomenon is accompanied by a decline in the sub-reaction rates associated with both the prompt route and NO-reburning pathway via CHi=0–3 radicals, alongside an increase in N2O and thermal NO production rates. Consequently, this results in an overall enhancement of NO production and a reduction in NO consumption. In the context of MILD combustion, CO production primarily arises from the reduction of CO2 through the reaction CH2(S) + CO2 ⇔ CO + CH2O, the introduction of hydrogen into the system exerts an inhibitory effect on this reduction reaction while simultaneously enhancing the CO oxidation reaction, OH + CO ⇔ H + CO2, this dual influence ultimately results in a reduction of CO production.

Hydrogen blending with natural gas for combustion efficiency improvement toward decarbonisation of power plants

Abstract The 12th Malaysia Plan highlighted Malaysia’s commitment to reduce Greenhouse Gas (GHG) emissions by 45% based on Gross Domestic Product (GDP) in 2030 and reach net zero by 2050. To achieve this target, Malaysia has to decarbonise the energy sector as it is the primary emission source, contributing up to 75% of GHG emissions in Malaysia. Hydrogen fuel is getting much attention globally, and it has been said that it can be a new renewable energy source to replace fossil fuels. Hydrogen combustion is clean and only produces water and energy. However, several studies have identified that hydrogen combustion could produce NOx, which is more harmful to the environment than CO2. Studies on hydrogen application in the energy sector in Malaysia are limited, and the implementation of total hydrogen fuel in power plants may not happen shortly. Hence, a fundamental study was proposed on co-firing hydrogen and natural gas fuel. This study aimed to examine co-firing characteristics such as temperature, pressure, and air-to-fuel ratio on GHG emission and energy release to find the optimum natural gas-to-hydrogen ratio. The model was developed using Aspen Plus, and hydrogen-natural gas blend percentages varied from 0% to 30%. The findings showed that increased operating temperature led to higher NOx formation, while varying pressures did not impact the CO2 and NOx formation. The pure natural gas combustion system was more sensitive towards air-to-fuel ratio changes, and an increase in air-to-fuel ratio to 1.5 led to 160% higher NOx formation due to an increase in nitrogen content. The combustion of the hydrogen blend led to lower CO2 formation but higher NOx formation. Lastly, the energy released by the hydrogen blending system was lower due to the formation of water that absorbed the heat released by the combustion.

Hydrate Formation and Dissociation of Liquid CO2 with Seawater Containing Organic Matters in Sand

Hydrate Formation and Dissociation of Liquid CO₂ with Seawater Containing Organic Matters in Sand