Absence Of CO Research Articles

Pd/PVP‐ Catalyzed Formylation of Amines and Nitroarenes to N‐Formamides with CO2 and Dimethylamine Borane: The Influence of CO2 on the Formation of Azoxyarenes

AbstractThe reactivity of dimethylamine borane (DMAB) towards amines and nitroarenes was investigated in the presence of the CO2 and Pd/PVP (PVP=polyvinylpyrrolidone) nanocatalyst. The formation of borane formate, Me2NH.BH2(OCHO), by the insertion of CO2 into the B−H bond was evidenced by NMR. The reaction of DMAB with CO2 also produced a second product, DMF, formed via self‐formylation. In the presence of aromatic or aliphatic amines corresponding N‐formamides were formed efficiently. Under the same conditions nitroarenes were hydrogenated to anilines or to azoxyarenes in the absence of CO2. In both reactions very high TOF values, up to 30 min−1, were obtained. Applying a higher excess of DMAB enabled the transformation of nitroarenes to N‐formamides. The Pd/PVP catalyst was used in 7 consecutive cycles of N‐methylaniline formylation with excellent selectivity and a total TON equal to 4700.

CO2 delivery techniques in mini-sternotomy surgery and neurological events: a multicentric study

BackgroundThe impact of air bubbles into the cerebral circulation after open heart surgery has been a topic of discussion since the introduction of the heart-lung machine. The aim of the study was to evaluate whether the use of a dedicated commercial sponge diffuser is better than a custom-made narrow section cannula or the absence of CO2 in preventing neurological events after aortic valve replacement via J mini-sternotomy.MethodsThree cohorts of J-shaped mini-sternotomy performed at three different centers were prospectively compared: CO2 supplied via sponge diffuser, CO2 supplied via cannula, and no CO2 supply. Propensity matching was used to obtain comparable groups. The primary endpoints were postoperative stroke, transitory ischemic attack, convulsions, and dizziness. Secondary endpoints were 30-day mortality, duration of mechanical ventilation, and intensive care unit length of stay.Results275 patients were enrolled in the study. After propensity matching, the sponge diffuser cohort had a significantly lower duration of mechanical ventilation (P < 0.001) and 30-day mortality (P = 0.05) when compared to the cannula cohort and the no-CO2 cohort, a lower incidence of all neurological events (P = 0.03) and dizziness (P = 0.05) when compare to the no-CO2 cohort, and a lower intensive care unit length of stay when compared to the cannula cohort (P = 0.001).ConclusionsThe sponge diffuser used to deliver the CO2 into the surgical field during aortic valve replacement via J mini-sternotomy has been demonstrated to guarantee better neurological outcomes compared to a custom-made narrow section cannula or the absence of CO2.

Thermochemical analysis of premixed ammonia/biogas flames in a model gas turbine swirl combustion system

This study examined the premixed NH3/biogas combustion at near stoichiometric using an experimentally validated numerical method. Raising the NH3 wt.% in NH3/CH4 combustion at φ = 0.8 brought up the average reaction temperature (Tavg) due to heat retention. Intensified by CO2 addition, Tavg in NH3/biogas increased by a factor of 1.2 compared to NH3/CH4. At φ = 1.1, higher NH3 and CO2 wt.% reduced Tavg. The local Damköhler number (Da) was reduced marginally in the absence of CO2 as φ increased from 0.8 to 1.1. Conversely, local Da grew considerably in the presence of CO2 and was particularly sensitive to variations in the excess air ratio. Increased NH3 wt.% promoted NO emission, primarily via N + OH → NO + H and H + HCNO → CH2 + NO pathways. NH3/biogas produced more NO than NH3/CH4 from φ = 0.9 to 1.1, but as φ approached 1.1, NO is generally lowered. N2O is produced mainly by NH + NO → N2O + H. Fuel-lean operation generally results in a higher N2O than fuel-rich operation. The NH3/biogas combustion at φ = 0.8 is a potential clean fuel solution in lowering NO emissions, as compared to NH3/CH4 combustion.

Chemical and Structural Evolution of Rb2-2xK2xTi2O5 Layered Titanates When Exposed to Ambient Air.

In this report, we combine thermogravimetric analysis, X-ray diffraction, and infrared spectroscopy to investigate the chemical and structural evolution upon exposure of alkali titanates Rb2Ti2O5 and K2Ti2O5 and mixed compound Rb2-2xK2xTi2O5, for which 0 ≤ x ≤ 1, to the ambient atmosphere. We show that a complete solid solution exists between the potassium and rubidium end-members and that mixed compounds exhibit an intermediate behavior. When exposed to the ambient atmosphere, all compounds degrade, with the progressive formation of first hydrates and then bicarbonates and a much quicker degradation of the rubidium titanate than of the potassium titanate. On the contrary, we show that upon hydration in the absence of CO2, the crystal structure of K2Ti2O5 is more quickly impacted than that of Rb2Ti2O5. These observations should be useful for understanding the evolution of the functional properties of M2Ti2O5 alkali titanates upon aging in the ambient atmosphere, as well as for the optimization of their hydration-dependent properties.

Carbon Dioxide Driven Methane Consumption in Soil Ecosystem

Soil is an important source and sink of greenhouse gas carbon dioxide (CO2) and methane (CH4). During CH4 consumption CO2 is produced as an end product. It is generally assumed that CO2 would inhibit CH4 consumption due to feedback inhibition. To test the effect of CO2 on methanotrophy, experiments were conducted in microcosms with different initial concentration of CO2 and CH4. Changes in CH4 consumption potential and abundance of pmoA gene copies in relation to CO2 concentration were estimated. In general, CH4 consumption ceased in the absence of CO2. In presence of CO2, rate of CH4 consumption (ng CH4 consumed g−1 soil d−1) varied from 0.283 to 0.481 at 1000 ppm of CH4 and 2.958 to 4.994 at 10,000 ppm of CH4. Abundance of methanotrophs (pmoA gene copies g−1 soil) ranged from 4.5 × 105 to 107 × 105 g−1 soil. A follow up experiment was carried out to evaluate CH4 consumption in the presence or absence of CO2, which proved that CO2 is essential for CH4 consumption. Study concludes that CO2 is a precursor molecule for CH4 consumption in soil ecosystem and methanotrophs are capable of mitigating both the greenhouse gases, CH4 and CO2.

The adsorption of U(VI) on chlorite: batch, modeling and XPS study

Abstract A mechanistic modelling of the adsorption processes onto individual minerals presenting in the near- and far-fields can greatly enhance the credibility of long-term safety assessments of granite-based geological repositories. In this study, the titration and U(VI) adsorption characteristics of chlorite, one of the major minerals of rock fractures, have been studied. Potentiometric titration curves at two ionic strengths (0.1 and 0.4 mol/L NaCl) are successfully interpreted by considering protonation/deprotonation reactions on generic edge sites (≡SOH) in the framework of a non-electrostatic surface complexation model (SCM). The adsorption of U(VI) on chlorite was reached after 24 h, the adsorption kinetics can be described by a pseudo-second-order model. A non-electrostatic SCM with three surface complexes (≡SOUO2 +, ≡SO(UO2)3(OH)5 and ≡SO(UO2)3(OH)7 2−) was set up based on pH edges of U(VI) at adsorption equilibrium in the absence of CO2. Additional, experimental data measured as a function of U(VI) concentration, solid-to-liquid ratio and carbonate concentration were well reproduced by the proposed model. Finally, parallel experiments were conducted using X-ray photoelectron spectroscopy (XPS) to analyze the variation of U(VI) surface species speciation at different pH values. The good agreement between SCM prediction and XPS analysis demonstrates the reliability of the model in predicting and quantifying the radionuclides retention by chlorite.

Implementation of a novel EOR screening methodology to the oilfields in Türkiye

In response to growing energy demand of Türkiye, an enhanced oil recovery (EOR) applicability assessment was conducted through an improved screening methodology, calibrated with successful applications. The methodology incorporated some improvements in applicability ranges and a novel pointing system. 159 oilfields in Türkiye were characterized based on reservoir properties and categorized as heavy, weak and strong aquifer support. The characterization revealed how source rock type and regional paleo-tectonic events dictate primary recovery and need for EOR. The EOR assessment implemented promised 58 applicable cases out of 315. Carbon dioxide (CO2) injection is applicable for many fields, which could stimulate feasibility of carbon capture projects in the country. Immiscible nitrogen injection might be an alternative for many of the medium and light oil reservoirs in the absence of CO2. Polymer flooding is also promising mainly for fields having weak-aquifer support. However, our hands-on experience suggests that conformance control is required to control flow of EOR agent in densely fractured carbonates. Thermal methods do not seem applicable in heavy oil reservoirs due to depth limitations except in-situ combustion, which requires pilot test confirmation. Provided methodology in this study may be used as a guideline for other fields to assess EOR potential.

CO in situ directed highly efficient CrOx@silicalite-1 for propane oxidation dehydrogenation by CO2

The propane oxidation dehydrogenation assisted by CO2 (CO2-ODHP) is currently a hot research topic, not only to meet growing demand of propylene but also to favor the CO2 neutralization. In present work, a series of CrOx@S1-n-1.0 with different Cr contents (n= 2.2, 3.6 and 4.5 wt%) is synthesized based on a small gas molecule directing synthesis strategy, wherein the gaseous CO of 1.0 MPa was in situ introduced in the synthesis system to regulate the interaction and dispersion of CrOx over silicalite-1 (S1) support. The characterization results of XRD, XPS, H2-TPR, and Raman indicate that the CO can affect the oxidation state and dispersion of Cr species. As observed, the Cr species were highly dispersed over CrOx@S1–3.6 %-1.0 (in the form of Cr6+ valance state), which however would aggregate to generate Cr2O3 nanoparticles over the CrOx@S1–3.6 %-0a prepared by impregnation method in absence of CO. The activity measurement indicates that the CrOx@S1–3.6 %-1.0 possesses the highest activity by displaying an average propane conversion of 50.4 % and CO2 conversion of 23.6 % at 600 °C, which surpasses most of the literature reports. The CO2-ODHP reaction mechanism was further investigated by in situ DRIFTS, which indicates that dissociated H of propane can react with CO2 to form formate (-COOH), in turn further reacts with H to produce byproducts CO and H2O, and the formate species can also react with the CrO3 active site to form bicarbonate species (HCO-3). Generally, present work has proposed a small gas molecule directing strategy to adjust the dispersions and chemical states of the loaded guest meals over catalytic support. The study of present work would contribute to other highly efficient catalyst design.

Effective incorporation of cobalt near surface region for cobalt-free cathodes in lithium-ion batteries

Cobalt-free cathode materials, particularly Ni-rich layered oxide cathode materials, are ideal for electric vehicle Li-ion batteries, offering high energy density and cost-effectiveness. However, high Ni content in high-temperature synthesis leads to issues like increased Li/Ni cation mixing and reduced rate capability, mainly due to the absence of Co. Therefore, this study investigated the utilization of a small amount of Co instead of completely removing it to enhance electrochemical performance. A simple pre-calcination process was used to induce Co substitution beneath the Ni-rich layered oxide cathode materials surface. A coating process was also performed for comparison. The Li/Ni cation mixing in the Co-substituted sample during high-temperature calcination was 2.43%, demonstrating a superior value compared to the Co-coating process. Rate capability tests showed superior performance for Co-substituted sample (164.2 mAh g−1) at 2 C compared to coated sample (151.0 mAh g−1). Moreover, Co substitution improved not only the cycle stability but also the high-temperature stability at an elevated state of charge.This study focuses on the surface modification of cobalt-free cathode, providing direct insight into the effects of Co substitution and typical Co coating and suggests an optimal process that uses small amounts of Co.

Phototrophic Fe(II) oxidation by Rhodopseudomonas palustris TIE-1 in organic and Fe(II)-rich conditions.

Rhodopseudomonas palustris TIE-1 grows photoautotrophically with Fe(II) as an electron donor and photoheterotrophically with a variety of organic substrates. However, it is unclear whether R. palustris TIE-1 conducts Fe(II) oxidation in conditions where organic substrates and Fe(II) are available simultaneously. In addition, the effect of organic co-substrates on Fe(II) oxidation rates or the identity of Fe(III) minerals formed is unknown. We incubated R. palustris TIE-1 with 2 mM Fe(II), amended with 0.6 mM organic co-substrate, and in the presence/absence of CO2 . We found that in the absence of CO2 , only the organic co-substrates acetate, lactate and pyruvate, but not Fe(II), were consumed. When CO2 was present, Fe(II) and all organic substrates were consumed. Acetate, butyrate and pyruvate were consumed before Fe(II) oxidation commenced, whereas lactate and glucose were consumed at the same time as Fe(II) oxidation proceeded. Lactate, pyruvate and glucose increased the Fe(II) oxidation rate significantly (by up to threefold in the case of lactate). 57 Fe Mössbauer spectroscopy revealed that short-range ordered Fe(III) oxyhydroxides were formed under all conditions. This study demonstrates phototrophic Fe(II) oxidation proceeds even in the presence of organic compounds, and that the simultaneous oxidation of organic substrates can stimulate Fe(II) oxidation.

Exploring dolomite as a promising support for Ni catalysts in CO2 methanation

Ni catalysts supported on Al-modified calcined dolomite were developed, using a natural mineral as the precursor. Treatment with 3% w/w Al improved thermal stability and increased the surface area. The variation in Ni loading (5–30% w/w) was studied to characterize the structural, morphological, and chemical properties. The CO2 capture capacity of the solids, evaluated by Thermogravimetric Analysis at 400 °C (100–800 μmol∙g−1), decreased with increasing Ni loading due to the reduction of basic sites. CO2-TPD analyses revealed the presence of captured CO2 in various basic sites, especially in the strong ones, with efficient formation of thermally stable carbonates. In catalytic tests at 400 °C, conversions exceeding 50% were achieved for higher Ni loadings and around 50% for lower loadings, with 100% selectivity towards CH4. The application of in situ and operando Diffuse reflectance infrared Fourier transform spectroscopy techniques provided insights into the formation of carbonates and their transformation into formate, methoxy, and formyl species, explaining the total selectivity towards CH4 and the absence of CO in the products. This comprehensive approach significantly contributes to the understanding of the reaction dynamics and opens new perspectives for the utilization of Ni catalysts supported on modified dolomite.

Supramolecular Interactions between Reduced Vitamin K1 and Dissolved CO2 and H2o in Aprotic Solvents

Vitamin K1 is a naphthoquinone (NQ) that can be electrochemically reduced at negative potentials in two one-electron steps in aprotic organic solvents. The first electron transfer at potential E 1 forms the anion radical (NQ• –) and the second electron transfer process at potential E 2 results in the formation of the dianion (NQ2–). If a hydrogen bond donor (H-D) such as water or an alcohol is progressively added to the aprotic organic solvent, both E 1 and E 2 shift towards more positive potentials. The shifts in potential are much greater for E 2 compared to E 1 as the hydrogen bond donor is added, so that a sufficiently high donor concentration, E 2 merges with E 1 and only one voltammetric wave is observed at potential E 3 due to the transfer of two-electrons. The shifts in potential with added hydrogen bond donors can be rationalized by supramolecular interactions between the strongly electronegative oxygen atoms in the quinone anions (especially the dianions) and the donor hydrogen atoms, and can be modelled according to an electrochemical square-scheme mechanism involving multiple electron transfer and chemical bonding steps. NQ + e– ⇌ NQ• – E 1 NQ• – + e– ⇌ NQ2– E 2 NQ + 2e– + nH-D ⇌ [NQ(H-D)n]2– E 3 NQ + 2e– + nCO2 ⇌ [NQ(CO2)n]2– E 4 In addition to H-bonding interactions, reduced forms of NQ also undergo supramolecular interactions with CO2(g) when it is purged into solution. Similar to the situation seen for H-bonding, when CO2 is purged into solution, the two one-electron processes merge into one two-electron process at less negative potentials (E 4). The mechanism can be considered analogous to the H-bonding case where the electronegative oxygen atoms in the reduced quinones interact with the electropositive carbon atoms in CO2. However, the supramolecular interactions appear to be stronger with CO2 than with water, since substantially less CO2 needs to be added to cause the two one-electron reduction processes of NQ to merge into one two-electron process. Controlled potential electrolysis experiments were conducted to determine the chemical reversibility of the supramolecular interactions. It was found that, (i) fully reducing NQ under a CO2 atmosphere and then applying an oxidizing potential resulted in the 100% conversion back to the starting material and, (ii) reducing NQ under a CO2 atmosphere and then purging the solution with argon resulted in the CO2 being released as CO2(g) or CO2 • – to leave NQ in its neutral form or as NQ2–. Figure 1. Cyclic voltammograms for 1,4-naphthoquinone in acetonitrile containing 0.2 M Bu4NPF6 at a scan rate of 0.1 V s–1 at a 1 mm diameter planar Pt electrode in the presence and absence of CO2. Figure 1

Excessive Ethanol Oxidation Versus Efficient Chain Elongation Processes

PurposeChain elongation is a metabolic feature that consists of the elongation of short-chain fatty acids to longer and more valuable acids when ethanol is available. To lower the operational costs, the process can also be performed using mixed microbial cultures. However, certain microorganisms in the mixed cultures can use the ethanol provided in competing reactions, which is usually termed excessive ethanol oxidation (EEO). Although minimizing ethanol use is essential, there is a lack of studies analyzing the extent, causes, and solutions to excessive ethanol oxidation processes.MethodsTo address this knowledge gap, ethanol, and acetic acid mixtures, at a molar ratio of 5 to 2, were fermented, and the following were analyzed: the fermentation profile at different (1) pH and (2) headspace gas compositions, (3) a 16S analysis of the headspace gas composition fermentations, and (4) a thermodynamic analysis of the reactions involved.Results and Conclusions: All fermentations, except the ones at the lowest pH (5.3), exhibited a significant EEO activity that reduced the yield of chain-elongated products. It was demonstrated that neither the inhibition of methanogenic activity nor the increased H2 partial pressure is an efficient method to inhibit EEO. It was also shown that CO2 can act as an electron acceptor for EEO, promoting the growth of acetogenic bacteria. In the absence of CO2, sulfate was used as an electron acceptor by sulfate-reducing bacteria to facilitate EEO. Methods such as low pH operation with in-line extraction, and the use of alternative sulfur salts, are proposed to increase the ethanol use efficiency in chain elongation processes.Graphical

Decolouration of azo dyes by radicals generated from K2S2O8 automatically in homogeneous aqueous solutions

In this work, at 15 °C and 25 °C, authors study the decolouration reactions (or degradation reactions or oxidation reactions) of 0.10 mM azo dyes (methyl orange and congo red) by (1) K2S2O8 and (2) Co2+/K2S2O8, expounding the roles of K2S2O8 and Co2+: K2S2O8 can oxidize azo dyes automatically in water by radicals; Co2+ has catalysis for oxidation of K2S2O8, whether Co2+ is from CoSO4 or Co(NO3)2, CoCl2, CoAc2. The decolouration degree of azo dyes in all systems quickens with the increase of the initial concentration of K2S2O8 and the reaction temperature. In the presence and absence of Co2+, comparative experiments are done between the oxidation of K2S2O8 and oxone, K2S2O8 shows weaker oxidation than oxone. The decolouration reaction of methyl orange (MO) in the system of (0.10 mM MO + 2.00 mM K2S2O8) accords with the second order reaction, the reaction rate constants are 4.789 M−1 min−1 at 15 °C and 5.894 M−1 min−1 at 25 °C respectively, the activation energy Ea is 14813 J/mol, and Arrhenius equation is k = 2.328 exp[-14813/(RT)].

Carbonylation of dimethyl ether in mordenite using Inelastic Neutron Scattering

Zeolite mordenite (MOR, Si/Al = 10) was used as catalyst for the reaction between CO and dimethyl ether (DME) to give methyl acetate. Since the reaction is catalysed by Brønsted acid sites, Inelastic Neutron Scattering (INS) is an appropriate technique to identify the intermediates. Although the accepted mechanism goes through an adsorbed methoxy, its characteristic peak at 963 cm−1 was only detected in the reaction MOR + DME, in the absence of CO. When CO is present, the peak at 963 cm−1 is substituted by other peaks that give valuable information of the reaction intermediates, indicating that either methoxy intermediates are not formed or are quickly replaced by the acetyl intermediate, [SiO(COCH3)Al], strongly stabilised in the micropore pockets of mordenite. Upon reaction of MOR + CO + DME, a characteristic peak at 1050 cm−1, although being present in liquid methyl acetate, could not be assigned to adsorbed methyl acetate since it loses intensity as the reaction proceeds (upon heating), and was assigned to a strong interaction between CO and DME adsorbed in one or two Brønsted sites, leading to some intermediate that shares this vibrational feature with methyl acetate in liquid phase. Finally, a peak at 1275 cm−1 in the spectrum of MOR + CO + DME upon heating is assigned to the formation of methyl acetate when the sample is heated, corresponding to C–O stretching of methyl acetate. This is further confirmed by the absence of this peak before heating. Overall, INS technique has allowed an accurate determination and interpretation of peaks involved in the carbonylation of DME in mordenite.

Role of active oxygen species in Fe-doped ZrO2 catalyst during CO2 assisted ethane dehydrogenation reaction

CO2 assisted ethane dehydrogenation provides a promising route for the utilization of shale gas and greenhouse gas. This study investigates the role and evolution of active oxygen species over Fe-doped ZrO2 catalysts in distinct dehydrogenation reactions via Mars-van Krevelen mechanism. Fe doping led to an increase in active oxygen species (from 12.9% to 23.4%) benefitted from the phase transformation of ZrO2. This enhancement significantly boosted ethane dehydrogenation activity from 5.0 to 16.1 mmolEthene/gCat/h. In the absence of CO2, the ethane conversions rapidly decreased with a deactivation rate constant (kd) of 0.930 h−1 due to the irreversible oxygen species loss and coke deposition. Although the catalytic stability of the optimal catalyst was greatly improved (kd = 0.006 h−1) after CO2 introduction, a decrease in ethane conversion occurred when CO2 could not supplement oxygen species due to the formation of coke layers. A simple O2 oxidation can effectively restore stable activity during 5 reaction-regeneration cycles for 3600 mins.

Acetate Production by Moorella thermoacetica via Syngas Fermentation: Effect of Yeast Extract and Syngas Composition

Gasifiers produce a gaseous mixture of CO/CO2/H2, also known as synthesis gas (syngas), containing varying compositions and ratios depending on the lignocellulose material types, gasifier design, and gasification conditions. Different physicochemical and thermodynamic properties of each gas type in the various syngas blends can influence syngas fermentation performance for the production of chemicals such as acetate. This study examined the effect of syngas composition (CO, CO/H2, CO/CO2/H2, and CO/H2) and its corresponding ratio on acetate production using Moorella thermoacetica, a thermophilic homoacetogen as the biocatalyst. We also investigated the effect of yeast extract addition for enhancing acetate production. A syngas fermentation study performed at a total pressure of 19 psig (2.29 atm) demonstrated that syngas fermentation in the absence of CO (30%CO2/70%H2) or at low CO proportions (21%CO/24%CO2/55%H2) resulted in the highest volumetric productivity of acetate (0.046 ± 0.001 and 0.037 ± 0.001 g/L/h, respectively). Interestingly, syngas fermentation without CO reached the highest YP/X of 22.461 ± 0.574 g-acetate/g-biomass, indicating that more acetate was produced compared to cell biomass. Higher biomass production was obtained when the CO proportion was increased up to 75% in CO/H2 fermentation. However, the cell growth and acetate production dramatically decreased with increasing CO proportion up to 99.5% CO as the sole constituent of the syngas. Even so, acetate production using 99.5% CO could be improved by adding 2 g/L yeast extract.

Effects of structures of lower aliphatic alcohols and concentrations on CO2 chemical absorption and desorption reactions in various alcohol solutions of 1,8-diazabicyclo[5.4.0]undec-7-ene

Alcohol solutions of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) have received considerable interest as chemical absorbers of CO2 and switchable solvents because of their reversible reaction with CO2 and the polarity change triggered by CO2 absorption/desorption. However, there have been only a few systematic studies on the CO2 absorption and desorption behaviors of DBU–alcohol solutions. In this study, we determined the solubility of CO2 in binary solutions of DBU and various lower aliphatic alcohols at different temperatures. Except for the 2-methyl-2-propanol solution, which showed very low reactivity with CO2, all the DBU–alcohol solutions exhibited almost the same solubilities of CO2 at 298.2 K, independent of the alkyl groups present on the alcohols. However, their solubilities varied with DBU concentration. Moreover, we examined the amounts of CO2 recovery from the CO2-saturated solutions at high temperatures up to 393.2 K or the boiling points. The amount of CO2 per mole of DBU desorbed by heating was markedly influenced by both the alkyl group on the alcohols and the DBU concentration, indicating that at the studied concentrations, the temperature dependence of CO2 solubilities is strongly affected by the type of alcohol. To clarify this unique desorption behavior, we measured the 1H, 13C, and 15N nuclear magnetic resonance spectra of the DBU–alcohol solutions with and without CO2 at 298.2 K. In the absence of CO2, the nitrogen atoms at the 8-position of the DBU molecules strongly interact with the hydroxyl hydrogen atoms of the alcohol molecules via hydrogen bonding. As the DBU–alcohol solutions were saturated with CO2, the formation of protonated DBU ([DBUH]+) and alcohol-CO2 adduct (alkyl carbonate, [ROCO2]–) was confirmed. [DBUH]+ is stabilized by the solvation of free alcohol molecules, and the reverse reaction of [DBUH]+ with [ROCO2]– for CO2 release is hindered. Our findings are beneficial for designing and tuning DBU–alcohol systems for CO2 separation.

Utilizing Redox Transformations of Quinones to Modulate Weak Donor and Acceptor Bonding Interactions with H2o and CO2 in Organic Solvents

Redox chemical transformations can be used to modulate supramolecular interactions between reduced quinones and acceptor molecules, with the application of an electric potential enabling the interactions to be switched on and off. The supramolecular interactions targeted include weak solution phase processes involving H-bonding with water molecules, and interactions between dissolved molecular gases such as CO2 and solution phase electroactive species. The advantage of this approach is that it enables the supramolecular complexing abilities of one molecule to be improved and tuned simply by changing its redox state. For instance, in one redox state the compound may undergo no supramolecular interactions, but once it is oxidized or reduced it undergoes very strong interactions. This enables the development of potential sensing devices as well as the ability to gain fundamental information regarding interactions that are difficult to quantify, including H-bonding.In aprotic organic solvents, neutral quinones (Q) undergo an EE reduction mechanism (E signifies an electron transfer) to first give a radical anion or semiquinone (Q•–) at potential E Q1, followed by an aromatic dianion (Q2–) at a more negative potential, E Q2. When water is progressively added to the solvent, the second reduction wave (E Q2) progressively moves towards more positive potentials until it eventually merges with the first reduction wave (E Q1), so the two electrons transfer at close to one potential. The reason for the shift in potential is because the quinone anions, especially the dianions, undergo very strong H-bonding interactions through the highly electronegative oxygen atoms in the reduced quinones with the hydrogen atoms from the water molecules. In order to be able to quantitatively study the reactions with water, it is essential that the exact water content of the solvent is known, and the water content can be precisely controlled. By performing careful calibration experiments using Karl Fischer coulometric titrations, it was possible to establish working curves of water content versus E Q2 – E Q1 (= ΔE) that enabled the accurate calculation of the water content of an organic solvent simply by recording one voltammogram in the presence of a quinone. Therefore, using this procedure, a voltammetric method for quickly estimating water contents of organic solvents down to the low ppm levels was established.In addition to H-bonding interactions, recent experiments have demonstrated that reduced quinones undergo interactions with CO2 and this has been proposed as a method for removing CO2 from industrial gas streams.The technique involves purging the gas through an ionic liquid containing a quinone and applying a reducing potential to produce the quinone dianion which interacts strongly with CO2 in a similar supramolecular mechanism as for H2O [Figure 1(a)]. Once the CO2 is “trapped”, the [quinone–(CO2)2]2– molecules can be separated, and an oxidizing potential applied which results in the [quinone–(CO2)2]2– complex being oxidized back to the starting material and the CO2 being released.Figure 1(b) shows the results from cyclic voltammetry and electrolysis experiments for the reduction of a quinone in the presence and absence of CO2. Under an argon atmosphere, two one-electron reduction processes are evident due to the reduction to the anion radical then at more negative potentials the dianion. However, when the solution is purged with CO2 gas, the voltametric waves immediately merge into one two-electron process due to the formation of the [quinone–(CO2)2]2– supramolecular complex This species is stable under electrolysis conditions and can exist in the bulk solution for long periods (hours). The mechanism can be varied by purging the solution containing the [quinone–(CO2)2]2– complex with an inert gas such as Ar or N2, resulting in two major pathways.In one pathway, the [quinone–(CO2)2]2– complex can be made to release the CO2 •– and leave the neutral quinone, and in the other pathway the charge remains on the quinone and the neutral CO2 is released as shown in Figure 1(c). Figure 1. (a) Reduction mechanism of 1,4-napthoquinone in the presence of CO2. The counterion for the anionic species is the electrolyte cation, n-Bu4N+. (b) Cyclic voltammograms for 1,4-napthoquinone in the presence and absence of CO2. (c) Proposed pathways for the reaction of NQ(CO2)2 2 – with excess argon gas. Figure 1

Introduction to the Principles of Electrochemistry through an Affordable Hands-on Electrochemical CO2 Reduction Experiment

We are grateful for the invitation to this session by Prof. Alice H. Suroviec. Electrochemical conversion of CO2 to useful chemicals and synthetic electrochemistry in general are rapidly developing and expanding areas of research and industrial application, which necessitates developing undergraduate curricula that will help students build and retain a strong foundational knowledge in this area of chemistry. Currently, there is a limited set of electrochemistry experiments that undergraduate students are typically exposed to in the laboratory, and synthetic electrochemistry is generally limited to water electroreduction to generate hydrogen gas. As a result, students develop limited knowledge, interest and appreciation of synthetic electrochemistry. At the same time, students today are more inclined to learn about methods and concepts that are important for climate action and sustainable development. With this motivation in mind, we developed a laboratory experiment designed to actively engage students in the learning process and help them understand synthetic electrochemistry through a hands-on experience involving CO2 electroreduction. In general, CO2 electroreduction can yield many different chemicals and requires complex and expensive electrochemical workstation and analytical instrumentation to identify and quantify the products, making it prohibitive for wide adaptation in undergraduate laboratories. Here, we propose a simple and affordable setup that still allows students to directly experience all the necessary steps of the process. The proposed laboratory experiment involves testing the performance of different cathodic electrocatalysts in CO2 reduction reaction conducted in a DIY divided electrochemical cell by measuring the produced CO gas with a CO meter using affordable and broadly available supplies. The students learn the importance of the electrocatalyst composition by changing the material of the cathode and observing different amounts of CO produced or the absence of CO when using the electrode selective for only water reduction. They learn about the influence of the applied potential on the reaction rate by changing the battery voltage and observing the quantitative difference in the produced gas. The experiment is designed to be safe when conducted on a standard laboratory bench (i.e., carbon monoxide concentrations outside of the cell are below the threshold of a standard CO detector).