Application of Density Functional Theory for evaluation of standard two-electron reduction potentials in some quinone derivatives

In this research, two-electron reduction potentials are calculated for a set of eight quinones using Density Functional Theory (DFT) at B1B95/6-31G^** and B1B95/6-311++G^** levels in aqueous solution. Two different mechanisms, direct and indirect, which have been presented before, are employed for these calculations. DPCM and CPCM models of solvation are carried out to include solution phase contribution. The results show that CPCM is properly matched with DFT method at the B1B95 level in both direct and indirect mechanisms. It is found that direct mechanism gives more accurate two-electron reduction potentials in comparison to indirect mechanism. Mean Absolute Deviation (MAD) obtained through indirect mechanism and CPCM model of solvation are about 0.041 and 0.022 V for 6-31G^** and 6-311++G^**, respectively. The MAD values of direct mechanism are about 0.024 and 0.018 V for 6-31G^** and 6-311++G^** basis sets, respectively. The calculated MAD for both direct and indirect mechanisms is comparable with MAD previously reported at MP3 level for this set of molecules.     

Application of thermal analysis to study smelting reduction kinetics

A thermal analysis study on the reduction of iron oxide rich slags under different conditions is presented in this paper. The effects of important process variables such as time, temperature, lime-silica ratio, FeO level in slag etc. are discussed. It is shown that the mechanism of reduction by externally added graphite is different from that by a carbon saturated bath although the activation energy values are similar.     

Syntheses and Properties of Lanthanide Hydroxy-meso-tetra(p-chlorophenyl)porphyrin Complexes

Introduction The syntheses and characterization of porphyrins and metalloporphyrins have been studied extensively[1]. Hemoglobin, myoglobin or cytochrome P450, has been applied as a model compound[2]. Wong C. P. et al.[3] synthesized the first lanthanide porphyrin, acetylacetonate tetraphenylporphyrin europium, in 1974.     

甲烷在金属铁及氧化铁表面还原NO的研究

在程序控温电加热水平陶瓷管反应器、N₂气氛和模拟烟气气氛及300~1 100℃时,对甲烷在金属铁及其氧化铁表面还原NO的特性进行了实验研究。为使甲烷在脱硝反应后完全燃尽以及脱硝反应过程生成的CO等中间产物完全燃尽,在第一段加热炉后串联了第二段加热炉,补充氧气,实现燃尽。结果表明,甲烷在金属铁及氧化铁表面能够高效地还原NO。在N₂气氛中,在900℃以上温度范围内甲烷在金属铁表面的脱硝效率超过95%,与甲烷在氧化铁表面的脱硝效率差别很小。在模拟烟气条件下,当过量空气系数小于1.0时,在900℃以上时,甲烷在金属铁和氧化铁表面的脱硝效率都能超过90%,且未燃尽和燃尽两种条件下NO的还原率相差不大。NO同时通过金属铁的直接还原和甲烷的再燃还原两种反应机理脱除。而甲烷则通过还原氧化铁为金属铁,从而使金属铁直接还原NO可持续进行。同时,甲烷再燃反应的中间产物HCN/NH₃等被氧化铁还原,从而使燃尽后的脱硝效率不下降。研究结果表明,甲烷和金属铁或氧化铁在富燃料条件下可有效地还原NO。     

Synthesis and Characterization of Liquid Crystal of meso-Tetra(4-n-octanoyloxyphenyl)porphyrin

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Transition metal coordinated framework porphyrin for electrocatalytic oxygen reduction

A series of transition metal coordinated framework porphyrin was evaluated regarding the electrocatalytic oxygen reduction reactivity for an optimized selection of the coordinated metal ion.     

Thermal studies of cobalt,iron and tin metalloporphyrins

A free-base tetraphenyl porphyrin (TPP) and its corresponding metalloporphyrins (MTPP) where M = Co, Fe and Sn were synthesized and characterized by UV–visible spectroscopy, FTIR and ¹Hnmr spectroscopy. Thermal studies of these porphyrins were carried out in synthetic air from room temperature to 800 °C using thermal analyser. The residues of MTPP after thermal treatment were qualitatively analysed, which showed the presence of corresponding metal oxides. Further, the above MTPP were subjected to thermogravimetry–evolved gas and mass spectrometry (TG–EGA–MS) analysis for the detailed information about evolved gases at their corresponding decomposition temperatures. This information may be used to predict the probable mechanism for ring opening of the macromolecular porphyrins.     

The mechanism of reduction of iron oxide by hydrogen

Precipitated iron oxide samples were characterized using temperature-programmed reduction. H₂ was used as the reduction agents. The two-stage reduction was observed: Fe₂O₃ was reduced to Fe₃O₄ and then reduced to metallic Fe. The activation energy for the two reduction steps of iron oxide are 89.13 and 70.412 (kJ mol⁻¹), respectively. The simulation by reduction models of the TPR patterns presents well fitting of unimolecular model for Fe₂O₃→Fe₃O₄ reduction and two-dimensional nucleation according to Avarmi–Erofeev model for Fe₃O₄→Fe.     

Electrodes modified with iron porphyrin and carbon nanotubes: application to CO2 reduction and mechanism of synergistic electrocatalysis

Electrodes modified with iron porphyrin and carbon nanotubes (FeP–CNTs) were prepared and used for CO₂ electroreduction. The adsorption of iron porphyrin onto the multiwalled carbon nanotubes was characterized by scanning electron microscopy and ultraviolet and visible spectroscopy. The electrochemical properties of the modified electrodes for CO₂ reduction were investigated by cyclic voltammetry and CO₂ electrolysis. The FeP–CNT electrodes exhibited less negative cathode potential and higher reaction rate than the electrodes modified only with iron porphyrin or carbon nanotubes. A mechanism of the synergistic catalysis was proposed and studied by electrochemical impedance spectroscopy and electron paramagnetic resonance. The direct electron transfer between iron porphyrin and carbon nanotubes was examined. The current study shed light on the mechanism of synergistic catalysis between CNTs and metalloporphyrin, and the iron porphyrin–CNT-modified electrodes showed great potential in the efficient CO₂ electroreduction.     

Application of flow chemistry to the reduction of nitriles to aldehydes

Reduction of nitriles to aldehydes with diisobutylaluminium hydride (DIBAL-H) is an important transformation in organic chemistry. But the use of this reaction is limited for the lack of reproducibility due to the instability of the intermediates formed. In the current article we disclose the improvement of the reaction applying continuous flow technology.     

甲烷在氧化铁表面还原NO的特性与反应机理研究

在程序控温电加热水平陶瓷管反应器中,在300~1 050 ℃,对N₂气氛中甲烷在氧化铁(充分氧化后的铁丝网卷)表面还原NO的特性进行了实验研究,测试了NO脱除效率、CO生成量以及反应后铁样品表面组分和微观状态的变化特点,分析了甲烷在氧化铁表面还原NO的反应机理。在此基础上,在1 000 ℃时,对模拟烟气条件下甲烷在氧化铁表面还原NO的持久性进行了实验研究。结果表明,甲烷在氧化铁表面能够高效地还原NO。在N₂气氛下,在850 ℃以上达到100%的NO脱除效率。在模拟烟气中,甲烷在氧化铁表面脱除NO的能力具有很好的持久性。实验结果表明,在1 000 ℃时,采用由体积分数为2.0%的O₂、16.8%的 CO₂和524×10^-6的 NO,N₂配平的模拟烟气,1.17% CH₄能够在连续100 h内保持100%的NO脱除效率,而未出现下降的趋势。对反应机理的研究结果表明,甲烷在氧化铁表面还原NO的机理包括甲烷通过再燃机理还原NO以及甲烷通过在氧化铁表面还原氧化铁为金属铁、金属铁进而直接还原NO两种主要反应机理。其中,后者为主要反应机理。     

Electrocatalytic Nitrite Reduction to Nitrogen Oxide by a Synthetic Analogue of the Active Site of Cu‐Containing Nitrite Reductase Incorporated in Nafion Film

The electrocatalytic reduction of nitrite to NO by [CuMe₂bpa(H₂O)(ClO₄)]⁺ ( 1 ), which is a model for the active site of copper‐containing nitrite reductase, incorporated in Nafion film was investigated. The Cu complex in the Nafion matrix exhibits an intense band at 267 nm and a broad band around 680 nm, assigned to d–d and ligand field transitions, respectively. The 77‐K EPR spectrum of 1 in the Nafion matrix reveals the typical axial signals (g_//=2.28, g =2.08, A_//=13.3 mT) of a tetragonal Cu²⁺ chromophore. The redox potential, which is related to the Cu⁺/Cu²⁺ couple, was ?146 mV (ΔE=72 mV) at pH 5.5. The redox reaction of 1 in Nafion was not dependent on pH and was a diffusion‐controlled process. The electronic structure and redox properties of 1 in the negatively charged polymer matrix were almost the same as those in aqueous solution. In the presence of nitrite, an increase in the cathodic current was observed in the cyclic voltammogram of 1 in the Nafion matrix. The current increase was dependent on the nitrite concentration and pH in solution. Upon reaching ?400 mV, a linear generation of NO was observed for the 1 /Nafion film coated electrode. The relationship between the rate of NO generation and the nitrite concentration in solution was analyzed with the Michaelis–Menten equation, where V_max=45.1 nM s^?1 and K_m=15.8 mM at pH 5.5. The Cu complex serves the function of both the catalyst and electron transport in the Nafion matrix. The sensitivity of the electrode was estimated to be 3.23 μA mM^?1 in the range of 0.1–0.4 mM nitrite.     

Thermal investigations of direct iron ore reduction with coal

In this paper, fundamental mechanisms for iron ore reduction in coal–ore mixtures have been investigated using several advanced experimental techniques. Firstly, the thermal properties of coal–ore mixtures were studied and apparent specific heat of coal–ore mixtures against temperature was obtained at a heating rate of 10 °C/min. Several exothermic and endothermic peaks were observed which were related to the decomposition reactions and reduction. The flue gases from the mixture were analysed using a mass spectrometer. Secondly, the X-ray diffraction (XRD) and the iron phase analytical techniques were applied to identify the iron phase changes with the temperature. It has been found that coal devolatilisation and iron oxides reduction occur simultaneously during the heating of the mixture. H₂ and CO gases produced from coal devolatilisation and char gasification were responsible for the reduction of iron oxides at these temperatures. Iron oxides undergo step-wise reduction over the whole process. The results in this work provide a fundamental understanding for the direct reduced ironmaking processes.     

氮掺杂碳包埋钴纳米粒子电催化合成过氧化氢

电催化还原氧是一种新兴的可持续生产过氧化氢(H2O2)的合成技术,寻找低成本、高活性和高选择性的电催化剂是该技术实际应用的关键.钴氮掺杂的碳材料因含有钴氮(Co-Nx)催化活性位,成为一类新兴的可促进H2O2电化学合成的材料.本文采用低能耗干式球磨外加控制热解的方法来制备包含许多Co-Nx结构的钴氮掺杂碳材料.该方法使用材料廉价,即将醋酸钴、2-甲基咪唑和Ketjenblack EC-600JD高纯度且导电的碳黑分别作为金属、氮和碳的前体.在酸性介质中的电化学测试结果表明,该材料的氧还原反应电流密度明显增加,同时起始电位向正方向移动.该催化剂在较大电位范围内对H2O2的选择性约为90％.H2O2整体电解实验表明,H2O2产率达到100mmol gcat?1 h?1,H2O2法拉第效率达到85％(0.3Vvs.RHE条件下2h).耐久性测试(在0.3Vvs.RHE条件下6h)表明,催化剂表现出相对稳定的性能,且在整个测试循环中,法拉第效率达到约85％,表明催化剂在实际应用中具有良好的耐久性.催化剂表现出较高的电催化合成H2O2活性和选择性可能是由于形成了Co-Nx活性位,以及酸性环境和应用电位等其它因素的影响.     

氮掺杂碳包埋钴纳米粒子电催化合成过氧化氢

电催化还原氧是一种新兴的可持续生产过氧化氢(H2O2)的合成技术,寻找低成本、高活性和高选择性的电催化剂是该技术实际应用的关键.钴氮掺杂的碳材料因含有钴氮(Co-Nx)催化活性位,成为一类新兴的可促进H2O2电化学合成的材料.本文采用低能耗干式球磨外加控制热解的方法来制备包含许多Co-Nx结构的钴氮掺杂碳材料.该方法使用材料廉价,即将醋酸钴、2-甲基咪唑和Ketjenblack EC-600JD高纯度且导电的碳黑分别作为金属、氮和碳的前体.在酸性介质中的电化学测试结果表明,该材料的氧还原反应电流密度明显增加,同时起始电位向正方向移动.该催化剂在较大电位范围内对H2O2的选择性约为90％.H2O2整体电解实验表明,H2O2产率达到100mmol gcat?1 h?1,H2O2法拉第效率达到85％(0.3Vvs.RHE条件下2h).耐久性测试(在0.3Vvs.RHE条件下6h)表明,催化剂表现出相对稳定的性能,且在整个测试循环中,法拉第效率达到约85％,表明催化剂在实际应用中具有良好的耐久性.催化剂表现出较高的电催化合成H2O2活性和选择性可能是由于形成了Co-Nx活性位,以及酸性环境和应用电位等其它因素的影响.     

化学修饰电极的研究 V:铁卟啉修饰电极对氧的催化还原

By surface organio synthesis a Fe (III) tetra-o-aminophenyl porphyrin modified electrode was successfully prepared on glassy carbon electrode surface through amidization. The preparation considitions were invesigated in detail. Using cyclie voltametry and cyclie semidifferential polarography in an acidic aqueous solution the behavior of the catalytic reduction of oxygen on iron porphyrin modified electrode was studied. Based on experimental results it was shown that the irreversible process of 2- electronreduction to hydrogen peroxide belongs to EC parallel catalytic process.     

Selective four electron reduction of O2 by an iron porphyrin electrocatalyst under fast and slow electron fluxes

An iron porphyrin catalyst with four electron donor groups is reported. The porphyrin ligand bears a distal hydrogen bonding pocket which inverts the normal axial ligand binding selectivity exhibited by porphyrins bearing sterically crowded distal structures. This catalyst specifically reduces O(2) by four electrons under both fast and slow electron fluxes at pH 7.     

水蒸气对甲烷在金属铁表面还原NO行为的影响

采用程序控温电加热水平陶瓷管反应器,在N2气氛和模拟烟气气氛中、300~1100℃下,研究了水蒸气对甲烷在金属铁表面还原NO行为的影响,并对反应前、后铁样品进行了X光衍射(XRD)、扫描电子显微镜(SEM)及X光电子能谱(XPS)等表征。结果表明,水蒸气对甲烷在金属铁表面还原NO行为的影响较小。在N2气氛中,水蒸气参与了金属铁的氧化;与无水蒸气时相比,水蒸气存在时NO还原效率有所下降。当水蒸气含量从2.5%增加到7%时,由于水蒸气对金属铁的氧化导致其表面形成疏松的微观孔隙,使得NO的还原效率随水蒸气含量的增加而提高。甲烷则参与了铁氧化物的还原,使铁样品表面形成相对致密的Fe3O4和FeO氧化层,不利于NO与金属铁的接触,使得NO的还原效率低于无甲烷时的结果。在模拟烟气条件下,水蒸气使得甲烷在金属铁表面还原NO的效率增加;在1050℃下,反应段过量空气系数SR1=0.7和燃尽段过量空气系数SR2=1.2时,含7%的H2O和无H2O条件下脱硝效率分别为96.7%和90.6%。而在湿烟气中SO2使NO还原效率略有下降。持久性脱硝实验结果表明,当反应温度为1050℃时,在含7%的H2O、0.02%的SO2的模拟烟气中,1.14%的甲烷在金属铁表面持续50h都能保持90%以上的脱硝效率。