Rate Of Product Formation Research Articles

Promoting CO2 Electroreduction to Multi‐Carbon Products by Hydrophobicity‐Induced Electro‐Kinetic Retardation

AbstractAdvancing the performance of the Cu‐catalyzed electrochemical CO2 reduction reaction (CO2RR) is crucial for its practical applications. Still, the wettable pristine Cu surface often suffers from low exposure to CO2, reducing the Faradaic efficiencies (FEs) and current densities for multi‐carbon (C2+) products. Recent studies have proposed that increasing surface availability for CO2 by cation‐exchange ionomers can enhance the C2+ product formation rates. However, due to the rapid formation and consumption of *CO, such promotion in reaction kinetics can shorten the residence of *CO whose adsorption determines C2+ selectivity, and thus the resulting C2+ FEs remain low. Herein, we discover that the electro‐kinetic retardation caused by the strong hydrophobicity of quaternary ammonium group‐functionalized polynorbornene ionomers can greatly prolong the *CO residence on Cu. This unconventional electro‐kinetic effect is demonstrated by the increased Tafel slopes and the decreased sensitivity of *CO coverage change to potentials. As a result, the strongly hydrophobic Cu electrodes exhibit C2+ Faradaic efficiencies of ≈90 % at a partial current density of 223 mA cm−2, more than twice of bare or hydrophilic Cu surfaces.

Promoting CO2 Electroreduction to Multi-Carbon Products by Hydrophobicity-Induced Electro-Kinetic Retardation.

Advancing the performance of the Cu-catalyzed electrochemical CO2 reduction reaction (CO2 RR) is crucial for its practical applications. Still, the wettable pristine Cu surface often suffers from low exposure to CO2 , reducing the Faradaic efficiencies (FEs) and current densities for multi-carbon (C2+ ) products. Recent studies have proposed that increasing surface availability for CO2 by cation-exchange ionomers can enhance the C2+ product formation rates. However, due to the rapid formation and consumption of *CO, such promotion in reaction kinetics can shorten the residence of *CO whose adsorption determines C2+ selectivity, and thus the resulting C2+ FEs remain low. Herein, we discover that the electro-kinetic retardation caused by the strong hydrophobicity of quaternary ammonium group-functionalized polynorbornene ionomers can greatly prolong the *CO residence on Cu. This unconventional electro-kinetic effect is demonstrated by the increased Tafel slopes and the decreased sensitivity of *CO coverage change to potentials. As a result, the strongly hydrophobic Cu electrodes exhibit C2+ Faradaic efficiencies of ≈90 % at a partial current density of 223 mA cm-2 , more than twice of bare or hydrophilic Cu surfaces.

(Invited) Electroenzymatic Hydrogen Production: Mediated/Direct Electron Transfer Strategies and Continuous Product Analysis

Metalloenzymes such as hydrogenases and nitrogenases are of interest to electrochemists for mechanistic study as well as applied biotechnological hydrogen and ammonia production. In order to interface these enzymes with electrodes mediated and direct electron transfer methods have been reported, each having their strengths and weaknesses. In addition to establishing efficient electron transfer with enzymes, dynamic product analysis is also desirable since rates of product formation (and the distribution of products) can be determined during an experiment with varying electrode potential (and thermodynamic driving force for heterogeneous electron transfer).Our recent efforts concerning the design of electrode:enzyme interfaces are presented here, including (i) mediated vs. direct electron transfer strategies, (ii) rotating ring disk electrochemistry, and (iii) continuous mass spectrometry and gas chromatography [1-2]. In this work, an [FeFe]-hydrogenase is employed as a model enzyme for molecular hydrogen formation, with a view to expand these approaches towards enzymatic electrocatalytic studies of nitrogenases. Limitations and difficulties of the presented approaches will be discussed.

(Invited) Al-Doped SrTiO3 Photocatalyst for Selective CO2 Reduction with Water as a Reductant

Among various strategies toward finding new energy sources to replace conventional fossil fuels, photocatalytic conversion of CO2 into useful chemicals using water as an electron donor and a proton source has been increasingly attracting attentions because it can convert light energy to chemical energy. The photocatalytic conversion of CO2 involves photoabsorption (light harvesting), charge separation, and H2O oxidation, as well as the consumption of the photogenerated electrons for reduction. The evolution of H2 rather than CO is preferred when H2O is used as the electron donor, since the redox potential of CO2/CO (−0.51 V vs NHE, at pH 7) is more negative than that of H+/H2 (−0.41 V vs NHE, at pH 7) in an aqueous solution. Therefore, “high selectivity toward CO2 reduction” is one of the most important requirements for the photocatalytic system to achieve the CO2 conversion in water. Various mixed oxides including tantalum-based NaTaO3, Ta2O5, Sr2KTa5O15, titanium-based BaLa4Ti4O15, CaTiO3, Na2Ti3O7, K2Ti6O13, La2Ti2O7, SrTiO3, gallium-based Ga2O3, and ZnGa2O4, and SrNb2O6 were found to be excellent photocatalysts for the conversion of CO2 into CO in the presence of Ag cocatalyst. However, these materials show significant activity for CO evolution only when irradiated with deep region UV-light (λ < 300 nm). Therefore, a series of photocatalysts which can drive under the photoirradiation with UV-light at λ > 300 nm is strongly desired in the research area of the photocatalytic conversion of CO2. Recently, Domen et al. reported that Al-doped SrTiO3 (Al-STO) with suitable cocatalysts such as MoOy/RhCrOx exhibited a promising photocatalytic activity for overall water splitting under photoirradiation at λ > 300 nm; the apparent quantum efficiency of the MoOy/RhCrOx/Al-STO reached close to 69% at 365 nm. Thus, we herein describe our investigation into the photocatalytic conversion of CO2 by H2O using the Al-STO photocatalyst with Ag and AgCo cocatalysts under photoirradiation with λ > 300 nm. Al-STO photocatalyst was fabricated by a flux method using anhydrous SrCl2 as a flux reagent. A mixture of SrTiO3, Al2O3, and anhydrous SrCl2 was ground for 10 min, and then transferred into an alumina crucible and calcined at 1423 K under air for 15 h. Ag cocatalyst was employed to modify the surface of the as-prepared Al-STO photocatalyst via a chemical reduction method. Al-STO was dispersed in deionized ultrapure water, and AgNO3 and NaH2PO2 were added to the suspension, then it was maintained at 353 K for 1.5 h. Photocatalytic activity of Ag/Al-STO photocatalyst was evaluated by using an inner-irradiation type reaction vessel in a quasi-flowing batch system. The photocatalyst powder was dispersed in 1.0 L of an aqueous NaHCO3 solution, and the dissolved air in this suspension was degassed by a flow of high-purity CO2 gas. CO2 was continuously bubbled into the reaction solution at a flow rate of 30 mL/min. The suspension was irradiated using a 400 W high-pressure Hg lamp with a Pyrex filter equipped with a cooling water system (irradiation wavelength: λ > 300 nm). The gaseous products in the outlet gas, e.g., CO, H2, and O2, were analyzed by gas chromatography (FID-GC with methanizer: CO, TCD-GC: H2 and O2). The attached figure shows a formation rate of CO (red), H2 (blue), and O2 (green) in the photocatalytic conversion of CO2 with H2O using undoped STO and Al-STO in the presence of Ag cocatalyst. It should be noted that the formation rate of CO is significantly increased by the doping of Al into STO. Moreover, the addition of Co species as a second cocatalyst to Ag/Al-STO drastically improved its activity for the photocatalytic conversion of CO2 by H2O as the electron donor, with extremely high selectivity toward CO evolution (99.8%), in which Ag and Co might enable CO2 reduction and H2O oxidation on the Al-STO surface, respectively. The formation rate of CO up to 52.7 μmol/h was observed over AgCo/Al-STO when irradiated with the UV light at wavelengths above 300 nm, which is ten-times higher than that over Ag/Al-STO (4.7 μmol/h). Furthermore, isotope-experiments using 13C-labeled CO2 gas revealed that 13C-labeled CO (m/z = 29) is selectively observed by GC-MS analysis, indicating that the CO evolved over the Ag/Al-STO and AgCo/Al-STO photocatalysts should be derived from the introduced CO2 gas. Figure caption Formation rates of products and selectivity toward CO evolution in the photocatalytic conversion of CO2 using bare Ag/STO (undoped STO), Ag/ and AgCo/Al-STO. Red: CO, green: O2, blue: H2, black circle: selectivity. Loading amount of Ag: 1wt%, Ag : Co = 2 : 1 (mol). Figure 1

Essential role of lattice oxygen in methanol electrochemical refinery toward formate.

Developing technologies based on the concept of methanol electrochemical refinery (e-refinery) is promising for carbon-neutral chemical manufacturing. However, a lack of mechanism understanding and material properties that control the methanol e-refinery catalytic performances hinders the discovery of efficient catalysts. Here, using 18O isotope-labeled catalysts, we find that the oxygen atoms in formate generated during the methanol e-refinery reaction can originate from the catalysts' lattice oxygen and the O-2p-band center levels can serve as an effective descriptor to predict the catalytic performance of the catalysts, namely, the formate production rates and Faradaic efficiencies. Moreover, the identified descriptor is consolidated by additional catalysts and theoretical mechanisms from density functional theory. This work provides direct experimental evidence of lattice oxygen participation and offers an efficient design principle for the methanol e-refinery reaction to formate, which may open up new research directions in understanding and designing electrified conversions of small molecules.

The Compressive Strength and Microstructure of Alkali-Activated Mortars Utilizing By-Product-Based Binary-Blended Precursors

Researchers have investigated the feasibility of using ultrafine palm oil fuel ash (u-POFA) as a cement replacement material because of its potential to reduce the environmental impact of concrete production. u-POFA, a by-product of palm oil fuel combustion, is a suitable replacement for Portland cement in concrete mixes because of its sustainability and cost-effectiveness. This study investigated the microstructural and compressive strengths of alkali-activated mortars (AAMs) based on fly ash (FA) and granulated blast-furnace slag (GBFS) being added with varying percentages of u-POFA. The mixture samples were prepared in eighteen mortars using sodium metasilicate (Na2SiO3) as the source material and sodium hydroxide (NaOH) as the alkaline activator. This study used field-emission scanning electron microscopy coupled with energy-dispersive X-ray spectrometry, X-ray diffraction, X-ray fluorescence, and Fourier-transform infrared spectroscopy to characterize the binary-blended mortars after 28 days of curing and determined the strength of the FA+GBFS (87.80 MPa), u-POFA+GBFS (88.87 MPa), and u-POFA+FA mortars (54.82 MPa). The mortars’ compressive strength was influenced by the CaO/SiO2 and SiO2/Al2O3 ratios in the mixture, which was directly due to the formation rate of geopolymer products of the calcium–alumina–silicate–hydrate (C–(A)–S–H), aluminosilicate (N–A–S–H), and calcium–silicate–hydrate (C–S–H) phases. Based on the contents of FA and GBFS, u-POFA significantly enhanced concrete strength; therefore, u-POFA used in a suitable proportion could enhance binary-blended AAMs’ microstructure.

Pyroglutamination-Induced Changes in the Physicochemical Features of a CXCR4 Chemokine Peptide: Kinetic and Structural Analysis.

We investigate the physicochemical effects of pyroglutamination on the QHALTSV-NH2 peptide, a segment of cytosolic helix 8 of the human C-X-C chemokine G-protein-coupled receptor type 4 (CXCR4). This modification, resulting from the spontaneous conversion of glutamine to pyroglutamic acid, has significant impacts on the physicochemical features of peptides. Using a static approach, we compared the transformation in different conditions and experimentally found that the rate of product formation increases with temperature, underscoring the need for caution during laboratory experiments to prevent glutamine cyclization. Circular dichroism experiments revealed that the QHALTSV-NH2 segment plays a minor role in the structuration of H8 CXCR4; however, its pyroglutaminated analogue interacts differently with its chemical environment, showing increased susceptibility to solvent variations compared to the native form. The pyroglutaminated analogue exhibits altered behavior when interacting with lipid models, suggesting a significant impact on its interaction with cell membranes. A unique combination of atomic force microscopy and infrared nanospectroscopy revealed that pyroglutamination affects supramolecular self-assembly, leading to highly packed molecular arrangements and a crystalline structure. Moreover, the presence of pyroglumatic acid has been found to favor the formation of amyloidogenic aggregates. Our findings emphasize the importance of considering pyroglutamination in peptide synthesis and proteomics and its potential significance in amyloidosis.

Influence of cholesterol on kinetic parameters for human aromatase (P450 19A1) in phospholipid nanodiscs

Cholesterol, a significant constituent of the endoplasmic reticulum membrane, exerts a substantial effect on the membrane's biophysical and mechanical properties. Cholesterol, however, is often neglected in model systems used to study membrane-bound proteins. For example, the influence of cholesterol on the enzymatic functions of type 2 cytochromes P450, which require a phospholipid bilayer and the redox partner P450-oxidoreductase (POR) for activity, are rarely investigated. Human aromatase (P450 19A1) catalyzes three sequential oxygenations of 19‑carbon steroids to estrogens and is widely expressed across various tissues, which are characterized by varying cholesterol compositions. Our study examined the impact of cholesterol on the functionality of the P450 19A1 complex with POR. Nanodiscs containing P450 19A1 with 20% cholesterol/80% phospholipid had similar rates and affinity of androstenedione binding as phospholipid-only P450 19A1 nanodiscs, and rates of product formation were indistinguishable among these conditions. In contrast, the rate of the first electron transfer from POR to P450 19A1 was 3-fold faster in cholesterol-containing nanodiscs than in phospholipid-only nanodiscs. These results suggest that cholesterol influences some aspects of POR interaction with P450 19A1 and might serve as an additional regulatory mechanism in this catalytic system.

Effects of fuel-hydrogen levels on combustion, operability, and emission parameters of CH4/H2/O2/CO2 stratified flames in a dual-swirl gas turbine burner

Towards the development of emission-free hydrogen gas turbines with wider operability limits, the combined effects of lean premixed combustion, dual combustion (combustion staging), hydrogen enrichment, and oxy-fuel combustion on the combustion and emission characteristics of CH4/H2/O2/CO2 flames are investigated in a dual annular counter-rotating swirl burner. The central stream is of a higher equivalence ratio (∅) of 0.9 for stable flame ignition, whereas the annular stream is of a lower ∅ of 0.65 to maintain the burner’s environmental performance. The stratified flame reactions are modelled using the partially premixed combustion model, which has been validated using the available experimental data. The inner recirculation zone becomes smaller as the hydrogen fraction (HF) becomes higher until it vanishes and there exists only an outer recirculation zone when the secondary hydrogen fraction approaches 100%. For 100% HF in both primary and secondary flow, the maximum combustion temperature within the combustor was observed to be as high as 2350 K. Increasing HF makes the flame more compact and anchored to the burner centre body with faster kinetics, less ignition delay time, and, accordingly, with increased potential for flashback. The product formation rate was found to increase in the inner shear layer at higher HF, implying a higher flame intensity and a more compact flame. The hydrogen fraction of the primary stream (maintained at higher equivalence ratio) is observed to be dominant in regulating CO mole fractions. Stable well-anchored flames are obtained over the considered fuel mixtures, indicating the role of stratified combustion in widening the operability of gas turbine combustors under stratified combustion conditions.

Interfacial Electronic Interaction in In2O3/Poly(3,4-ethylenedioxythiophene)-Modified Carbon Heterostructures for Enhanced Electroreduction of CO2 to Formate.

Formate, as an important chemical raw material, is considered to be one of the most promising products for industrialization among CO2 electroreduction reaction (CO2RR) products, but it still suffers from poor selectivity and a low formation rate at a high current density on account of the competitory hydrogen evolution reaction. Herein, the heterogeneous nanostructure was constructed by anchoring In2O3 nanoparticles on poly(3,4-ethylenedioxythiophene) (PEDOT)-modified carbon black (In2O3/PC), in which the PEDOT polymer interface layer could immobilize In2O3 nanoparticles and obtain a notable reduction in electron transfer resistance among the In2O3 particles, showing a 27% increase in the total electron transfer rate. The optimized In2O3/PC with rich heterogeneous interfaces selectively reduced CO2 to formate with a high FE of 95.4% and a current density of 251.4 mA cm-2 under -1.18 V vs RHE. Also, the formate production rate for In2O3/PC was up to 7025.1 μmol h-1 cm-2, surpassing most previously reported CO2RR catalysts. The in situ XRD results revealed that In2O3 particles were reduced to metallic indium (In) as catalytic active sites during CO2RR. DFT calculations verified that a strong interface interaction between In sites and PC induced electron transfer from In sites to PC, which could optimize the charge distribution of active sites, accelerate electron transfer, and elevate the p-band center of In sites toward the Fermi level, thereby lowering the adsorption energy of *OCHO intermediates for CO2 conversion to formate.

Self-supported ultrathin NiCo layered double hydroxides nanosheets electrode for efficient electrosynthesis of formate

Electrochemical CO2 reduction into energy-carrying compounds, such as formate, is of great importance for carbon neutrality, which however suffers from high electrical energy input and liquid products crossover. Herein, we fabricated self-supported ultrathin NiCo layered double hydroxides (LDHs) electrodes as anode for methanol electrooxidation to achieve a high formate production rate (5.89 mmol h−1 cm−2) coupled with CO2 electro-reduction at the cathode. A total formate faradic efficiency of both anode for methanol oxidation and cathode for CO2 reduction can reach up to 188% driven by a low cell potential of only 2.06 V at 100 mA cm−2 in membrane-electrode assembly (MEA). Physical characterizations demonstrated that Ni3+ species, formed on the electrochemical oxidation of Ni-containing hydroxide, acted as catalytically active species for the oxidation of methanol to formate. Furthermore, DFT calculations revealed that ultrathin LDHs were beneficial for the formation of Ni3+ in hydroxides and introducing oxygen vacancy in NiCo-LDH could decrease the energy barrier of the rate-determining step for methanol oxidation. This work presents a promising approach for fabricating advanced electrodes towards electrocatalytic reactions.

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Selective formate production from H2 and CO2 using encapsulated whole-cells under mild reaction conditions

Biocatalytic CO2 reduction into formate is a crucial strategy for developing clean energy because formate is considered as one of the promising hydrogen storage materials for achieving net-zero carbon emissions. Here, we developed an efficient biocatalytic system to produce formate selectively by coupling two enzymatic activities of H2 oxidation and CO2 reduction using encapsulated bacterial cells of Citrobacter sp. S-77. The encapsulated whole-cell catalyst was made by living cells depositing into polyvinyl alcohol and gellan gum cross-linked by calcium ions to form hydrogel beads. Formate production using encapsulated cells was carried out under the resting state conditions in the gas mixture of H2/CO2 (70:30, v/v%). The whole-cell biocatalyst showed highly efficient and selective catalytic production of formate, reaching the specific rate of formate production of 110mmolL-1· gprotein-1·h-1 at 30°C, pH 7.0, and 0.1MPa. The encapsulated cells can be reused at least 8 times while keeping their high catalytic activities for formate production under mild reaction conditions.

On the stability of electrochemical CO2 reduction reaction to formate at indium electrodes at biocompatible conditions

In a circular economy, carbon dioxide (CO2) has to serve as feedstock that can be utilized by electrochemical CO2 reduction reaction (eCO2RR). Using eCO2RR to C1-compounds such as formate (HCOO−) allows producing feed for microbial syntheses that generates value-added compounds. However, eCO2RR at biocompatible conditions is currently limited to short-term operation facing a gradual performance deterioration. Here, we evaluate the possible parameters affecting the stability of performance in terms of formate production rate (rHCOO−) and coulombic efficiency (CE) of eCO2RR at indium during 72 h batch mode operation. Formate accumulated over time affected catholyte conductivity, but statistical analysis showed this did not have an immediate influence on the performance. However, both are key factors altering the actual cathode potential over time that in turn is leading to changes in rHCOO− (maximum deviation of ± 0.03 mmol h−1 cm−2 at the stable performance at each condition) and CE (maximum deviation ± 40% at stable performance at each condition). These effects were more significant after reaching certain formate concentration and catholyte conductivity (ca. 70 mM and 21 mS cm−1, respectively). These results highlight the potential obstacles needed to be considered and tackled in order to achieve stable rHCOO− and CE over a long-term eCO2RR operation. This study discusses how to overcome these obstacles from different operational perspectives.

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Regulating the Electronic Structure of Bismuth Nanosheets by Titanium Doping to Boost CO2 Electroreduction and Zn-CO2 Batteries.

The electrochemical carbon dioxide reduction reaction (E-CO2 RR) to formate is a promising strategy for mitigating greenhouse gas emissions and addressing the global energy crisis. Developing low-cost and environmentally friendly electrocatalysts with high selectivity and industrial current densities for formate production is an ideal but challenging goal in the field of electrocatalysis. Herein, novel titanium-doped bismuth nanosheets (TiBi NSs) with enhanced E-CO2 RR performance are synthesized through one-step electrochemical reduction of bismuth titanate (Bi4 Ti3 O12 ).We comprehensively evaluated TiBi NSs using in situ Raman spectra, finite element method, and density functional theory. The results indicate that the ultrathin nanosheet structure of TiBi NSs can accelerate mass transfer, while the electron-rich properties can accelerate the production of *CO2 - and enhance the adsorption strength of *OCHO intermediate. The TiBi NSs deliver a high formate Faradaic efficiency (FEformate ) of 96.3% and a formate production rate of 4032µmolh-1 cm-2 at -1.01V versus RHE. An ultra-high current density of -338.3mA cm-2 is achieved at -1.25versus RHE, and simultaneously FEformate still reaches more than 90%. Furthermore, the rechargeable Zn-CO2 battery using TiBi NSs as a cathode catalyst achieves a maximum power density of 1.05mW cm-2 and excellent charging/discharging stability of 27 h.

A Versatile and Easy Method to Calibrate a Two-Compartment Flow Cell for Differential Electrochemical Mass Spectrometry Measurements.

Online techniques for the quantitative analysis of reaction products have many advantages over offline methods. However, owing to the low product formation rates in electrochemical reactions, few of these techniques can be coupled to electrochemistry. An exception is differential electrochemical mass spectrometry (DEMS), which gains increasing popularity not least because of its high time resolution in the sub-second regime. DEMS is often combined with a dual thin-layer cell (a two-compartment flow cell), which helps to mitigate a number of problems that arise due to the existence of a vacuum|electrolyte interface. However, the efficiency with which this cell transfers volatile reaction products into the vacuum of the mass spectrometer is far below 100%. Therefore, a calibration constant that considers not only the sensitivity of the DEMS setup but also the transfer efficiency of the dual thin-layer cell is needed to translate the signals observed in the mass spectrometer into electrochemical product formation rates. However, it can be challenging or impossible to design an experiment that yields such a calibration constant. Here, we show that the transfer efficiency of the dual thin-layer cell depends on the diffusion coefficient of the analyte. Based on this observation, we suggest a two-point calibration method. That is, a plot of the logarithm of the transfer efficiencies determined for H2 and O2 versus the logarithm of their diffusion coefficients defines a straight line. Extrapolation of this line to the diffusion coefficient of another analyte yields a good estimate of its transfer efficiency. This is a versatile and easy calibration method, because the transfer efficiencies of H2 and O2 are readily accessible for a large range of electrode-electrolyte combinations.

Oxidation Kinetics of Neat Methyl Oleate and as a Blend with Solketal

The complexity of biodiesel aging has shown that the mechanism needs further research. The rate of aging product formation and associated interactions can help improve fuel quality. Since biodiesel is a multicomponent system and constant changes occur in the chemical environment, which interactions yield which products must be shown in more detail. Particularly under observation was the correlation between peroxides and epoxides. In addition, it is critical that the influence and interactions of new drop-in fuel candidates be investigated. In this work, the kinetics of the formation of aging products of methyl oleate (C18:1) are studied. The aim was to reduce the complexity in order to be able to make more precise and detailed statements about the mechanism. Ketones, acids, peroxide, and epoxide values were recorded. A distinction is made between pure methyl oleate and mixtures with 3 wt% isopropylidene glycerine (solketal). After solketal decomposed in the blends, the aging process showed changes. The influence of solketal resulted in a higher number of acids and epoxides over time. It implied that peroxides are not necessarily the precursor of epoxides. In summary, correlation and solketal’s influence showed that a sequence of aging products could be detected.

Effects of Adiabatic Flame Temperature and Oxygen Concentration in CH4/N2/O2 Nonswirl Jet Flames: Experimental and Numerical Study

AbstractThe combustion characteristics of oxygen-enriched air–methane (i.e., O2/N2/CH4) flames in a premixed mode are investigated using both experimentally and numerically under atmospheric conditions for emissions reduction purposes. The investigation is carried out using a gas turbine model combustor equipped with a multihole burner that mimics gas turbine micromixer burners. The resulting flame is of jet type, and the velocity of the jet is kept at 5.2 m/s for all the considered flames. Models used in the numerical study include large eddy simulation, discrete ordinate, and partially premixed combustion for turbulence, radiation, and species models, respectively. The numerical results are validated, and a suitable agreement is achieved with experimental data. The results indicated that the temperature distribution, shape, and size of O2/N2/CH4 flames are predominantly controlled by adiabatic flame temperature (Tad). However, the oxygen fraction, rather than Tad, is responsible for the reaction progress. The emission of NO, CO, and CO2 increases with an increase in oxygen fraction, and the product formation in O2/N2/CH4 flames is less compared to their oxy-fuel (i.e., O2/CO2/CH4) counterparts, because N2 is mostly inert, compared to CO2. The latter participates significantly in flame reactions, which increases the rate of product formation in O2/CO2/CH4 flames.

Electrochemical CO2 conversion to formic acid using engineered enzymatic catalysts in a batch reactor

Formic acid is one of the most valuable fuel products for the capture and conversion of CO2 due to its unique usage in fuel cells and hydrogen storage. Electrochemically mediated conversion of CO2 to FA has its advantages over the traditional Kemira process, in that high temperatures and pressures are not required, cutting on manufacturing and operating costs. However, selectivity of the metal catalysts used in CO2 conversion to certain products remains limited. Here, an engineered enzymatic catalyst is employed to convert CO2 into formic acid (in the form of formate) in a batch reactor. This work seeks to maximize both formate production and Coulombic efficiency, which is achieved primarily through: (1) adjustment of the operating voltage, (2) implementation of an O2 scavenger to mitigate competition with dissolved O2, and (3) control of system pH to maintain a stable operating range for the catalyst. Peak formate production and peak efficiency achieved in long-term experiments (> 40 h) were 225 mM and 91 %, respectively, both of which show promise of strong metrics for CO2 conversion to formate. The optimal operating cathode voltage was shown to be below the baseline voltage of − 0.75 V vs. Ag/AgCl. In short-term experiments (≈ 1 h), operating below this range, at approximately − 0.85 V, could achieve efficiencies of 100 %. By implementing sodium thiosulfate as an O2 scavenger, the rate of formate production improved by over 4 ×. Long-term retention of the efficiency, however, remains an issue to be addressed due to the enzyme sensitivity to pH and increased current at higher values of acid used on the anode.