Online NMR spectroscopic study of species distribution in MEA–H2O–CO2 and DEA–H2O–CO2

Quantitative online NMR spectroscopy was used for studying the species distribution in solutions of carbon dioxide in aqueous monoethanolamine (MEA) and diethanolamine (DEA). The mass fraction of the amine in the unloaded solution was 0.2 and 0.3 g/g, respectively, the carbon dioxide loading was up to 1.1 ??molCO₂/molamine$1.1\text{\hspace{0.17em}??}\text{mo}{\text{l}}_{\text{C}{\text{O}}_2}/\text{mo}{\text{l}}_{\text{amine}}$, temperatures were between 293 and 353 K. A special apparatus was designed that allows preparing the mixtures gravimetrically and applying pressures up to 25 bar to keep the carbon dioxide in solution. It was coupled to a 400 MHz NMR spectrometer by heated capillaries. By using both ¹H and ¹³C NMR spectroscopy quantitative information on the concentrations of the following species were obtained: amine, carbamate, bicarbonate, and carbon dioxide. Due to the fast proton transfer between molecular and protonated amine, only the sum of their concentrations can be determined. Furthermore, a byproduct, 2-oxazolidone, was observed and quantified. The experimental data were used for developing a thermodynamic model of the studied electrolyte solutions based on the extended Pitzer G^E-model. In the model development, also vapor–liquid equilibrium data from the literature were included. The model gives reliable results both for the species distribution and the vapor–liquid equilibrium of the studied mixtures.     

Ambient temperature sol–gel synthesis of CeO2–SiO2 and TiO2–CeO2–SiO2 films with high efficiency of UV absorption and without destructive oxidation on heat sensitive organic substrate

Highly efficient UV absorption films of CeO₂–SiO₂ and TiO₂–CeO₂–SiO₂ were synthesized through an epoxide assisted sol–gel strategy. As proven by their UV–vis transmittance spectra, the obtained films show very strong absorption in the UV region, at the same time, keeping the high transparency in the visible range. Due to the unique chemistry of this route and the delicate selection of Ce precursor salts, the ceria in the film can be crystallized at ambient temperature, resulting in the effective UV absorption and oxidation minimization of the films. These advantages guarantee their application in the protection of heat-sensitive organic materials.     

Oxidation of phenol on RuO2–TiO2/Ti anodes

The oxidation of phenol on the RuO₂–TiO₂/Ti electrode has been studied by cyclic voltammetry, polarization measurements, electrochemical impedance spectroscopy and potentiostatic transients in H₂SO₄ and NaCl aqueous solutions. A reaction path with polymerization as the main reaction and side reactions after the initial step, similar to the reaction path on other electrode materials, is suggested. The formation of a phenoxy radical in a diffusion-controlled irreversible process is the initial step. The polymerization of phenoxy radicals leads to the formation of porous polyoxyphenylene film, strongly adherent to the electrode surface. The cyclic voltammetry measurements indicate side products, which could be, according to the literature, of quinone-like structure. Polyoxyphenylene film inhibits further oxidation of phenol, although complete electrode passivation was not observed. The presence of polyoxyphenylene film does not influence the pseudocapacitive behaviour of the electrode to a great extent, since the polyoxyphenylene film covers dominantly the coating surface, while active sites placed within coating cracks remain uncovered. The film seems to be permeable for hydrogen ions and water molecules.     

Long-Chain Alkane Dehydrogenation over Hierarchically Porous Ti-Doped Pt–Sn–K/TiO2–Al2O3 Catalysts

Kinetics and Catalysis - Hierarchically porous γ-Al2O3, TiO2–Al2O3 composite supports, and Pt–Sn–K/Al2O3 and Pt–Sn–K/TiO2–Al2O3 catalysts were prepared...     

NOx-Sorbing Metal Oxides, MnOx–CeO2. Oxidative NO Adsorption and NOx–H2 Reaction

(n)MnO_x–(1–n)CeO₂ binary oxides have been studied for the sorptive NO removal and subsequent reduction of NO_x sorbed to N₂ at low temperatures (150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO^– ₃) and/or nitrite (NO^– ₂) species on the surface depending on temperature, O₂ concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NO_x toward H₂ was examined for MnO_x–CeO₂ impregnated with Pd, which is known as a nonselective catalyst toward NO–H₂ reaction in the presence of excess oxygen. The Pd/MnO_x–CeO₂ catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H₂ at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnO_x–CeO₂ surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H₂–O₂ combustion, H₂–NO reaction was suppressed to a certain extent in the presence of O₂. Nevertheless, Pd/MnO_x–CeO₂ attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H₂, and 6% O₂ in He at as low as 150 °C, compared to ca. 30% conversion for Pd/–Al₂O₃ at the same temperature. The combination of NO_x-sorbing materials and H₂-activation catalysts is expected to pave the way to development of novel NO_x-sorbing catalysts for selective deNO_x at very low temperatures.     

TG/DSC studies of modified 1–vinyl-2-pyrrolidone–divinylbenzene copolymers

In this paper, the synthesis and characterization of porous copolymers of 1-vinyl-2-pyrrolidone with divinylbenzene are presented. They were obtained by suspension polymerization as pure polymers or composite materials with different inorganic fillers. The influence of the type of filler on the textural and thermal properties was investigated in detail. It was found that the value of the porous surface area and the degree of double bonds’ conversion of composites are much lower than in the case of pure copolymers. Thermal properties of the obtained materials were investigated by the means of thermogravimetry and differential scanning calorimetry.     

HBr/H2O2-mediated formation of C–S bond with thiosulfates

A novel, efficient, and green protocol to construct C–S bond has been developed via HBr/H₂O₂-mediated sulfenylation of styrenes and 4-hydroxycoumarins leading to unsymmetrical sulfides. Various unsymmetrical sulfides were prepared in one step with moderate to good yields using environmentally-friendly H₂O₂ as oxidant and HBr as catalyst. Based on the preliminary experimental results, a plausible reaction mechanism was proposed for HBr/H₂O₂-mediated formation of C–S bond with thiosulfates.     

Li ion dynamics in Li3xLa2/3–x□1/3–2xTiO3 studied by NMR

⁷Li nuclear magnetic resonance relaxation times, T₁ and T_1ρ, versus temperature are reported in the 150–900 K temperature range on the lithium lanthanum titanates, Li_3xLa_2/3–x□_1/3–2xTiO₃, which are fast ionic conductors. Two characteristic frequencies of Li⁺ motions are evidenced in these compounds: the first is in the range of the Larmor frequency when the second one is in the range of the radio-frequency field. These frequencies are respectively attributed to motion of the Li⁺ ion inside the cage formed by the oxygen ions and to jumps between the cages. The T₁ and T_1ρ studies on ⁶Li nuclei confirm the above results and show that the relaxation is not due to quadrupolar interaction at a variance, which is generally accepted.     

Solid–liquid phase equilibria in the system K2SO4–MgSO4–H2O at 318 K

The polythermal solubility diagram of the system K₂SO₄–MgSO₄–H₂O presents the formation of three double salts, picromerite, leonite, langbeinite appearing in this order with increasing temperature. In the temperature range between 314.15 K and 320.65 K, picromerite and leonite ought to coexist. The search in the literature revealed a lack of isothermal phase equilibrium data within this temperature range. Therefore, the solubility in the system K₂SO₄–MgSO₄–H₂O was determined in the whole concentration range at 318 K. The solid phases, epsomite, leonite, picromerite and arcanite occur with increasing potassium sulfate concentration. A two-salt point of leonite and picromerite is established at 0.618 molal K₂SO₄ and 3.030 molal MgSO₄ at the temperature of investigation.     

CO2-adsorbent spongy electrode for non-aqueous Li–O2 batteries

Regulation of the Li₂CO₃ byproduct is the most critical challenge in the field of non-aqueous Li–O₂ batteries.Although considerable efforts have been devoted to preventing Li₂CO₃ formation,no approaches have suggested the ultimate solution of utilizing the clean Li₂O₂ reaction instead of that of Li₂CO₃.Even if extremely pure O₂ is used in a Li–O₂ cell,its complete elimination is impossible,eventually generating CO₂ gas during charge.In this paper,we present the new concept of a CO₂-adsorbent spongy electrode(CASE),which is designed to trap the evolved CO₂ using adsorption materials.Various candidates composed of amine functional groups(–NH2)for capturing CO₂ were screened,with quadrapurebenzylamine(QPBZA)exhibiting superior CO₂-adsorbing ability among the proposed candidates.Accordingly,we fabricated the CASE by sandwiching QPBZA between porous carbon layers,which facilitated the transport of gaseous products.The new electrode was demonstrated to effectively capture the evolved CO₂ during charge,therefore altering the reaction pathways to the ideal case.It is highly advantageous to mitigate the undesirable CO₂ incorporation in the next discharge,resulting in improved cyclability.This novel concept of a CO₂-sponging electrode provides an alternative route to the realization of practically meaningful Li–O₂ batteries.     

Effect of hydrothermal aging on NOx reduction performance for Sb–V–CeO2/TiO2 catalyst

Research on Chemical Intermediates - Herein, we investigated the NOx reduction performance of Sb–V–CeO2/TiO2 (SbVCT) catalyst subjected to hydrothermal aging, where 6 vol% of H2O was...     

Molecular structures and electronic properties of helical thiophene carbon–sulfur oligomers, H2(C2S)nC2H2 (n?=?1–20)

Structure optimizations of the thiophene carbon–sulfur H₂(C₂S) _n C₂H₂ (n = 1–20) were carried out using density functional theory calculations at the B3LYP/6-31G(d) level. The B3LYP/6-31G(d) geometrical data for heptamer H₂(C₂S)₇C₂H₂ and undecamer H₂(C₂S)₁₁C₂H₂ are in good agreement with the X-ray crystallographic data for the helical (C₂S)_n β-heptathiophene and β-undecathiophene, respectively. Structural and electronic properties of helical oligothiophenes obtained at the B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level are reported. The strain energy formula of n oligothiophenes as a linear function of their molecular length was obtained.     

An efficient and stable Mn–K/CeO2–Al2O3 catalyst for hydrogenation of benzoic acid to benzaldehyde

A Mn–K/CeO₂–Al₂O₃ catalyst for the hydrogenation of benzoic acid (BAC) to benzaldehyde (BAD) has been developed. The catalyst exhibits efficient activity in the reaction and is still stable after 102 h of testing.     

Solid–liquid–gas equilibrium of the naphthalene–biphenyl–CO2 system: Measurement and modeling

The first and last melting points (FLMP) method was employed to measure the melting temperature–composition (T–w$T–w$) data at solid–liquid–gas (SLG) equilibrium for the naphthalene–biphenyl–CO₂ system. Results show that the system's phase diagram is simple eutectic under all investigated pressures (0.1, 3.0, 6.0 and 8.0 MPa), and the system's eutectic composition is almost constant. The (T–w$T–w$) data measured with a high-pressure differential scanning calorimetry are in good agreement with these from FLMP. The semi-predictive model using solubility data (SMS) and the calculation model combining with G^E models (CMG) for binary systems were extended to this ternary system. For the SMS model, the Peng–Robinson equation of state (PR-EoS) with the van der Waals one-fluid mixing rule was used to correlate the solubility data of the two solutes in CO₂ to obtain the two interaction parameters k₁₂ and k₁₃ and calculate the fugacity coefficients of the solutes in the liquid and vapor phases; the UNIFAC method was also applied to the activity coefficient of the solutes in the liquid phase. For the CMG model, the PR-EoS combining respectively the MHV1, LCVM, and modified LCVM (mLCVM) mixing rules was applied to the fugacity coefficients of the solutes. Results show that the CMG model with MHV1 gives the best prediction of the system's SLG equilibrium, while the SMS model and the CMG model with mLCVM provide comparable and acceptable results.     

Tandem intramolecular Diels–Alder/retro-Diels–Alder cycloaddition of 2H-chromen-2-one as dienes with the expulsion of CO_2

To study the intramolecular Diels-Alder cycloadditon of 2H-chromen-2-one as a diene, a series of chiral N-allyl-N-benzylamides that contain a 2H-chromen-2-one moiety were designed for the synthesis of benzo[f]isoindol-1-ones via an intramolecular Diels-Alder and a subsequent retro-Diels-Alder cycloaddition with the expulsion of CO₂. Both the yield (80%-89%) and absolute stereocontrol of the tandem reaction were high when an electron-withdrawing group was attached to the dienophile. The double bond in the styrene substructure remained in the products could be further derivatized by dihydroxylation.     

Activity-determining factors for catalytic CO and CH4 oxidation on Pt/CeO2–ZrO2–Al2O3 cryogels

Research on Chemical Intermediates - Homogeneous 1 wt% Pt/CeO2–ZrO2–Al2O3 cryogels with Ce/Zr?=?1 and Ce/Al?=?0–1/2 were synthesized by one-pot...     

The Stabilization Effect of CO2 in Lithium–Oxygen/CO2 Batteries

The lithium (Li)–air battery has an ultrahigh theoretical specific energy, however, even in pure oxygen (O₂), the vulnerability of conventional organic electrolytes and carbon cathodes towards reaction intermediates, especially O₂⁻, and corrosive oxidation and crack/pulverization of Li metal anode lead to poor cycling stability of the Li-air battery. Even worse, the water and/or CO₂ in air bring parasitic reactions and safety issues. Therefore, applying such systems in open-air environment is challenging. Herein, contrary to previous assertions, we have found that CO₂ can improve the stability of both anode and electrolyte, and a high-performance rechargeable Li–O₂/CO₂ battery is developed. The CO₂ not only facilitates the in situ formation of a passivated protective Li₂CO₃ film on the Li anode, but also restrains side reactions involving electrolyte and cathode by capturing O₂⁻. Moreover, the Pd/CNT catalyst in the cathode can extend the battery lifespan by effectively tuning the product morphology and catalyzing the decomposition of Li₂CO₃. The Li–O₂/CO₂ battery achieves a full discharge capacity of 6628 mAh g⁻¹ and a long life of 715 cycles, which is even better than those of pure Li–O₂ batteries.     

Synthesis of bicyclic lactones via I2-mediated intramolecular tandem C–C/C–O bond formation

The iodine/DMAP-mediated intramolecular tandem C–C/C–O bond forming reaction of malonate bearing alkene moiety proceeded to give bicyclic lactones with good diastereoselectivity in good yield. The mechanistic investigation was also discussed on the basis of various control experimental results.     

Synthesis and structural characterization of copper–molybdenum–sulfur and copper–tungsten–sulfur cluster complexes (n-Bu4N)[OMS3Cu3Br2L2] with heterocyclic thiones as ligands

Reaction of (NH₄)₂[WOS₃] or (NH₄)₂[MoO₂S₂], n-Bu₄NBr, CuCl and Imt in acetone solvent afforded air- and moisture-stable clusters (n-Bu₄N)[MOS₃Cu₃(Imt)₂Br₂] (M = W or Mo, Imt = imidazolidine-2-thione). These compounds have been characterized by IR, UV–Vis, ¹H and ¹³C NMR spectra and single-crystal X-ray diffraction. They are crystallographically isostructural, with Imt and [MOS₃]²⁻ acting as monodentate and bidentate S-donor ligands, respectively. In the anions, the three Cu atoms have different coordination environments, one being distorted tetrahedral with Imt and Br as terminal ligands, the other two being approximately trigonal planar with Imt as a terminal ligand for one and Br as a terminal ligand for the other. W and Mo have approximately tetrahedral coordination geometry, with a terminal O and three triply-bridging S atoms. The NH groups of the Imt ligands serve as donors in intramolecular N–H?Br and in intermolecular N–H?Br and N–H?O hydrogen bonds, linking the anions to form layers with the cations in cavities.