Perovskites-like composites for CO2 photoreduction into hydrocarbon fuels

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Instant conversion of air to a clathrate hydrate: CO(2) hydrates directly from moist air and moist CO(2)(g)

The rapid conversion of vapor mixtures containing the gases CO(2), H(2)S, and HCN to clathrate hydrates was reported recently. The novel method is based on the pulsing of warm vapor mixtures, including a carrier gas, into a cold condensation chamber. With cooling, the vapors, which also include ～1% water and either tetrahydrofuran or trimethylene oxide as a catalyst, nucleate aqueous solution nanodroplets that, on a millisecond time scale, crystallize as hydrate nanoparticles that consume 100% of the water. Humid air approximates the content of mixtures used successfully in the vapor-to-hydrate conversions. FTIR spectra are examined for gas hydrates formed directly from air and air enriched with CO(2), as well as hydrate particles for which CO(2)(g) serves as both guest and aerosol medium. In each instance all of the water in the condensed phase converts to a clathrate hydrate. The subsecond ether-catalyzed formation of the hydrates near 230 K requires only a few percent of the CO(2) pressure used in conventional processes that yield fractional amounts of gas hydrates on an hour time scale in the same temperature range.     

Synthesis of bunte salts from 1,2-benzisothiazol-3-ones and vice versa

1,2-Benzisothiazol-3-ones undergo ring-opening when treated with sodium hydrogen sulphite solution, giving Bunte salts, reconversion of which to benzisothiazol-3-ones can be effected with dilute alkali.     

Interaction of pharmaceutical hydrates with supercritical CO2

The aim of this work was to study the solubility in supercritical CO₂ of the hydrated phase of three model drugs, namely theophylline, carbamazepine, and diclofenac sodium, in comparison with the respective anhydrous form. Possible solid-state modifications, stemming from the interaction with supercritical CO₂, were investigated by differential scanning calorimetry, thermogravimetric analysis, hot stage microscopy, Fourier Transform infrared spectroscopy and Karl-Fischer titrimetry. It was found that all three pharmaceutical hydrates exhibited higher solubility in supercritical CO₂ than the relevant anhydrous phases. In the case of theophylline monohydrate, the instability of the crystal phase at the experimental temperature adopted has been evidenced. Diclofenac sodium tetrahydrate represents a peculiar case of chemical interaction with the acid supercritical fluid, mediated by crystal water. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamic and thermodynamic properties of clathrate hydrates

Vibrational spectra and thermodynamic properties of ices and the cubic structure I (CS-I) clathrate hydrate have been studied by the lattice dynamics method. The phonon density of states for the empty hydrate framework and for xenon hydrate have been determined; the vibrational frequencies of the guest molecules in large and small cavities have been found. The stability of the hydrate with respect to the external pressure at low temperatures and its thermodynamic stability at temperatures around 0°C have been studied. It has been found that the empty hydrate framework is unstable in certain temperature and pressure regions. A definite degree of occupation of the large cavities by the guest molecules is necessary for the hydrate to become stable. It has been found that there is a maximum of the critical temperature at which the hydrate exists, which is a function of the external pressure.Dedicated to Dr. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Conductometric determination of quaternary ammonium salts by sodium perchlorate and vice versa

A conductometric method is proposed for the determination of quaternary ammonium salts (chloride or bromide), based on the poor solubility of the relative perchlorates. A comparison between expected and found values shows that the method is suitable, rapid, and easy for quantities in the range from 0.2 to 5 g. The error depends on the solubility of the relative perchlorate. The apparent and tentative solubility product of the studied compounds were calculated. The obtained values allowed to propose benzyltributyl ammonium chloride (BTBA Cl) as precipitant for the conductometric titration of perchlorate. This easy, rapid and accurate determination can be used to analyze the perchlorate ion even in concentrated solutions and to determine stability constants for complex formation in aqueous solutions.     

Conductometric determination of quaternary ammonium salts by sodium perchlorate and vice versa

A conductometric method is proposed for the determination of quaternary ammonium salts (chloride or bromide), based on the poor solubility of the relative perchlorates. A comparison between expected and found values shows that the method is suitable, rapid, and easy for quantities in the range from 0.2 to 5 g. The error depends on the solubility of the relative perchlorate. The apparent and tentative solubility product of the studied compounds were calculated. The obtained values allowed to propose benzyltributyl ammonium chloride (BTBA Cl) as precipitant for the conductometric titration of perchlorate. This easy, rapid and accurate determination can be used to analyze the perchlorate ion even in concentrated solutions and to determine stability constants for complex formation in aqueous solutions. Received: 11 June 1997 / Revised: 8 October 1997 / Accepted: 11 October 1997     

Efficient conversion of CO2 and H2O into hydrocarbon fuel over ZnAl2O(4)-modified mesoporous ZnGaNO under visible light irradiation

Considering light absorption by narrowing the band gap and gas capture by the mesostructure and basicity of material, an efficient artificial photosynthesis system was constructed based on a mesoporous ZnAl(2)O(4)-modified ZnGaNO photocatalyst.     

CO2 capture and electrochemical conversion

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Phase field modeling of CH4 hydrate conversion into CO2 hydrate in the presence of liquid CO2

We present phase field simulations to estimate the conversion rate of CH(4) hydrate to CO(2) hydrate in the presence of liquid CO(2) under conditions typical for underwater gas hydrate reservoirs. In the computations, all model parameters are evaluated from physical properties taken from experiment or molecular dynamics simulations. It has been found that hydrate conversion is a diffusion controlled process, as after a short transient, the displacement of the conversion front scales with t(1/2). Assuming a diffusion coefficient of D(s) = 1.1 x 10(-11) m(2) s(-1) in the hydrate phase, the predicted time dependent conversion rate is in reasonable agreement with results from magnetic resonance imaging experiments. This value of the diffusion coefficient is higher than expected for the bulk hydrate phase, probably due to liquid inclusions remaining in the porous sample used in the experiment.     

Viability of clathrate hydrates as CO2 capturing agents: a theoretical study

Capture and sequestration of green house gas CO(2) is a major challenge for scientists and identifying right materials for this purpose is a task of outstanding importance. Through reliable computational studies, we have demonstrated that the clathrate cages (5(12), 4(3)5(6)6(3), 5(12)6(2), 5(12)6(4), and 5(12)6(8)) have a great potential to store CO(2). All the considered clathrates and their CO(2) inclusion complexes are optimized at B3LYP/6-31G(d) level of theory. The impact of DFT-D, M05-2X, and MP2 functionals on interaction energy were tested using various basis sets. Although different functionals and basis sets show variation in absolute IE values, the trend is consistent and does not depend on the level of the calculations. Dispersion was found important for these complexes and DFT-D shows comparable IE values with MP2 functional. The optimum and maximum cage occupancy for all the considered cages were tested on the basis of quantum chemical calculations. The maximum cage occupancy for all five considered cages (5(12), 4(3)5(6)6(3), 5(12)6(2), 5(12)6(4), and 5(12)6(8)) is one, two, two, two, and seven CO(2) molecules, respectively, and the optimum cage occupancy is one, one, one, two, and five CO(2) molecules, respectively. Thus, 5(12)6(8) cages can host up to 7 CO(2) molecules, resulting in about 32 wt %, which makes them highly promising materials.     

仿生多孔 MgO-TiO2合成及其光催化 CO2还原性能

研究表明, MgO能够活化吸附在其表面的 CO2分子,促进 HCO3–的生成,而在 H原子存在的条件下, HCO3–为 CO2光催化还原为碳氢化合物和 CO的活性中间体. CO2为对称的直线型分子,在化学反应中表现出极高的稳定性,成为阻碍人工光合作用发展的重要因素.在设计新型光催化剂时,复合 MgO可能会有效提高催化剂的活性.绿色植物的叶片结构或茎中存在大量尺寸不一的多孔结构,以利于植物生命活动(包括光合作用和呼吸作用)过程中气体的有效扩散和水分、营养物质的运输. TiO2因其良好的化学稳定性、无毒且成本低廉,在人工光合成领域得到广泛的研究.因此,本文以空心菜杆为模板, TiO2为主体催化剂,应用溶胶-凝胶法,通过调节 MgO的含量合成了一系列仿生多孔结构的 MgO-TiO2复合物.
　　样品的 X射线衍射、X射线光电子能谱和高分辨透射镜表征结果证明,生物模板空心菜杆在550oC下煅烧5 h之后可被完全移除,且 MgNO3分解为 MgO,生成 TiO2-MgO复合物.从扫描电镜中可观察到,以空心菜杆为模板合成的 MgO-TiO2,模板的空心管状结构得以保持,在长度和宽度上有一定程度的皱缩.横截面和纵截面图说明样品很好地复制了空心菜杆的导管和筛管组成的多孔结构.同时N2吸附-脱附结果表明,样品中存在3–5 nm的介孔结构.同时我们发现,由于 MgO的加入,0.05% MgO-TiO2复合物的比表面积比 TiO2减少了18%,之后随着 MgO含量的增加, MgO-TiO2复合物的比表面积呈下降趋势.标准状况下,测试了样品对 CO2的吸附量.结果表明,随 MgO含量的升高,吸附量先增加后减小,且 MgO-TiO2复合物的吸附量为 TiO2的1.3–1.8倍.结合样品比表面积及原位红外光谱测试结果,说明样品的 CO2吸附量受 MgO的含量与样品的比表面积双重因素的影响. CO2吸附包括物理吸附和化学吸附,而且对于同种样品,吸附量与样品比表面积正相关.当 MgO-TiO2复合物的比表面积随着 MgO含量的增加而减小时, CO2吸附量却先增加后减小,表明 MgO的加入极大地促进了 CO2的化学吸附.以 MgO-TiO2复合物作为光催化剂将 CO2和 H2O还原为 CH4. CH4的总产量随着光照时间的增加而增加,10 h后的总产量随着 MgO含量的升高先增加后减少,与样品的 CO2吸附量的变化趋势相似但不完全相同.与 TiO2(6.5μmol/g)相比, MgO-TiO2复合物样品催化作用下的 CH4的最终产量均增大,活性最好的0.2% MgO-TiO2(18.7μmol/g)的产量达到了它的2.88倍,说明 MgO对 CO2具有活化作用,且活化后的 CO2更容易生成 CH4.综合结果表明, CO2在催化剂表面的吸附量、电子的表面迁移、反应活性位点等因素共同决定了催化剂的光催化活性.     

Mechanistic insights into heterogeneous zinc dicarboxylates and theoretical considerations for CO2-epoxide copolymerization

Copolymerization of epoxides and CO(2) with heterogeneous zinc dicarboxylates is prominent since the early days of this area of chemistry. However, in over 30 years of research, the efficiency of this catalyst system could not be improved significantly. Furthermore, a huge activity difference between zinc glutarate and its lower homologue zinc succinate exists, which could not be explained so far. A detailed investigation of the underlying copolymerization mechanisms on heterogeneous catalysts is therefore necessary. Such investigations are so far lacking, which renders logical improvements of the catalysts difficult. We therefore decided to conduct a detailed investigation on the different zinc-dicarboxylic catalysts, their copolymerization efficiency, solid state structure and supplemented the results with theoretical calculations. The results imply that the widely discussed bimetallic mechanism (for homogeneous catalysts) is in place for heterogeneous zinc dicarboxylates as well. Theoretical calculations conducted to identify an "ideal" Zn-Zn distance suggest an optimal separation of Zn atoms in the range of 4.3-5.0 ?. The combined copolymerization experiments and calculated models give a consistent explanation for the difference in activity of the different zinc-dicarboxylate catalysts and give a hint why the activity of the heterogeneous zinc-dicarboxylate system is limited.     

Formation conditions and thermodynamic model predictions of carbon monoxide hydrates

With a fine accuracy and conciseness, Chen-Guo hydrate model has been widely applied to predict the hydrates formation conditions of different systems, including inhibitor containing systems and salt containing systems. However, the model could not predict the formation condition of carbon monoxide (CO) hydrates as the parameter values of CO required in the calculation are not available. In this work, CO hydrate formation pressures were measured at different temperatures in tetrahydrofuran (THF) solution first, then the parameter values of CO required in Chen-Guo model were fitted completely for the first time. On that basis, the hydrates formation conditions of different systems including CO were predicted by the model to verify the accuracy of the fitted values. The comparison between the predicted results and our experimental data (or literature data) shows that the absolute average deviation percentage (AADP) of structure I hydrates is no more than 1.481%, and the AADP of structure II hydrates is less than 6.796%. It is proved that the fitted parameter values of CO are credible, and Chen-Guo model is capable of predicting the formation conditions of CO hydrates. The experimental results and model modifications extend the applied range of Chen-Guo model and promote the development of CO hydrates thermodynamics research.     

Structures of hydrocarbon hydrates during formation with and without inhibitors

The formation of hydrates from a methane-ethane-propane mixture is more complex than with single gases. Using nuclear magnetic resonance (NMR) and high-pressure powder X-ray diffraction (PXRD), we have investigated the structural properties of natural gas hydrates crystallized in the presence of kinetic hydrate inhibitors (KHIs), two commercial inhibitors and two biological ice inhibitors, or antifreeze proteins (AFPs). NMR analyses indicated that hydrate cage occupancy was at near saturation for controls and most inhibitor types. Some exceptions were found in systems containing a new commercial KHI (HIW85281) and a recombinant plant AFP, suggesting that these two inhibitors could impact the kinetics of cavity formation. NMR analysis confirmed that the hydrate composition varies during crystal growth by kinetic effects. Strikingly, the coexistence of both structures I (sI) and II (sII) were observed in NMR spectra and PXRD profiles. It is suggested that sI phases may form more readily from liquid water. Real time PXRD monitoring showed that sI hydrates were less stable than sII crystals, and there was a conversion to the stable phase over time. Both commercial KHIs and AFPs had an impact on hydrate metastability, but transient sI PXRD intensity profiles indicated significantly different modes of interaction with the various inhibitors and the natural gas hydrate system.     

On the thermodynamic stability and structural transition of clathrate hydrates

Gas mixtures of methane and ethane form structure II clathrate hydrates despite the fact that each of pure methane and pure ethane gases forms the structure I hydrate. Optimization of the interaction potential parameters for methane and ethane is attempted so as to reproduce the dissociation pressures of each simple hydrate containing either methane or ethane alone. An account for the structural transitions between type I and type II hydrates upon changing the mole fraction of the gas mixture is given on the basis of the van der Waals and Platteeuw theory with these optimized potentials. Cage occupancies of the two kinds of hydrates are also calculated as functions of the mole fraction at the dissociation pressure and at a fixed pressure well above the dissociation pressure.     

A new method for the calculation of molecular formulae from accurate mass data and vice versa

A calculator is described for the rapid manual conversion of accurate mass data into molecular formulae. The method uses any information available about the ion to simplify the process. Calculation of accurate masses from a molecular formula is even more rapidly determined.