Mechanism of photochemical reduction of chromium(VI) by alcohols and its environmental aspects

The idea of photochemical abatement of the Cr(VI) pollution has been verified by investigating the photoreduction mediated by aliphatic alcohols under conditions mimicking the environmental ones. Effects of the alcohol nature, pH and presence of oxygen are analysed. The time-resolved spectra are used to follow the generation of the transient chromium Cr(V), Cr(IV) and Cr(II) species and the R₁R₂CHOH√⁺ radicals. A direct interaction between chromate(VI) and an electron donor is a precondition of the photoreduction via the photoinduced electron transfer (PET). Two pathways of the PET are identified: one-electron transfer for intermolecular and two-electron transfer for the intramolecular systems. In the case of the alcohol mediators the option is pH-controlled.     

Synthesis and photochemical properties of porphyrie-quinone compounds

The results of studies on the synthesis of porphyrin-quinone compounds and investigation of their photochemical properties are summarized. Effects of various factors (the redox potential, the distance between donor and acceptor moieties, their spatial orientation, the free energy of the reaction, and solvents) on the photoinduced electron transfer in these model systems are discussed. The dyad and triad model systems have been compared. The possibility of using these systems for modeling the primary steps of photosynthesis is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1. pp. 9–24, January, 1996.     

Fundamental aspects of electrocatalysis

A theory for electrochemical electron transfer is proposed which explicitly accounts for the electronic structure of the electrode; it applies both to simple and to bond-breaking reactions. Interactions with narrow d-bands lead to changes in the local density of states of the reactant as its electronic level fluctuates due to solvent reorganization. More importantly, it can significantly reduce activation barriers, and in extreme cases induce dissociative adsorption. The model gives some justification to recent suggestions that the center of the d-band is a key factor for electrocatalysis, and it offers a route for calculating reaction rates using results from ab initio calculations as input.     

蜂窝催化剂上甲醇自热重整制氢的动力学研究

400 ℃～460 ℃,400 h－1～1 600 h－1,O2/CH3OH(mol ratio)=0.10～0.25,H2O/CH3OH (mol ratio) =1.0～1.8下,通过正交实验设计方法,用BSD-2A型内循环无梯度反应器研究了Zn-Cr/CeO2-ZrO2蜂窝催化剂上甲醇自热重整制氢反应的宏观动力学。以甲醇水蒸气重整反应、甲醇分解反应和甲醇完全氧化反应为独立反应进行了研究,得出了幂指数型反应速率表达式,并根据实验结果,利用最小二乘法求解了动力学参数值。F检验表明该动力学模型是高度显著的。该多重反应动力学方程的得出为蜂窝反应器的进一步模拟、优化和设计提供了数据。     

Ab initio calculation for inner reorganization energy of gas-phase electron transfer in organic molecule–ion systems

A series of electron transfer (ET) reactions between some organic molecules have been investigated through ab initio calculations. Biphenyl (Bp) and 9,9^′-dimethylfluorene anion radicals are chosen as the donor, whereas several organic molecules with different redox abilities are chosen as the acceptor. The inner reorganization energy and the endothermicity of the ET reactions in those molecule–ion systems have been estimated through the HFSCF and complete active space multiconfiguration SCF calculations. Double-well potentials for the gas-phase ET reactions have been constructed using the linear reaction coordinate, and the results show that the quinone-containing ET reactions are in Marcus' inverted region. It has been found that the inner reorganization energies are different for various donor-acceptor couples, unlike the experimentally fitted ones. The contribution from the inter-ring torsional motion in Bp to the inner reorganization energy has been evaluated from the energy difference of the biphenyl-acceptor and the dimethylfluorine-acceptor systems. Comparisons with the experimentally observed results have been made.     

Oxidative reforming of methane for hydrogen and synthesis gas production:Thermodynamic equilibrium analysis

A thermodynamic analysis of methane oxidative reforming was carried out by Gibbs energy minimization (at constant pressure and temperature) and entropy maximization (at constant pressure and enthalpy) methods,to determine the equilibrium compositions and equilibrium temperatures,respectively.Both cases were treated as optimization problems (non-linear programming formulation).The GAMS 23.1 software and the CONOPT2 solver were used in the resolution of the proposed problems.The hydrogen and syngas production were favored at high temperatures and low pressures,and thus the oxygen to methane molar ratio (O 2 /CH 4) was the dominant factor to control the composition of the product formed.For O 2 /CH 4 molar ratios higher than 0.5,the oxidative reforming of methane presented autothermal behavior in the case of either utilizing O 2 or air as oxidant agent,but oxidation reaction with air possessed the advantage of avoiding peak temperatures in the system,due to change in the heat capacity of the system caused by the addition of nitrogen.The calculated results were compared with previously published experimental and simulated data with a good agreement between them.     

有机共轭体系电子转移反应的溶剂重组能

应用Marcus双球模型计算溶剂重组能λs时,在AM1法优化给受体几何构型基础上,提出了共轭体系电子云分布的扁球模型,并用统计的方法求出了rD/A.同时依照Miller等的处理办法,结合其他理论及实验证据将电子转移交叉反应中联苯分子的扭转能计入溶剂重组能λs中,从而用实验速率常数拟合出含扭转能的λs值.此实验拟合值与扁球法得到的λs计算值吻合得很好.通过比较理论值与实验值,发现了给受体间距的大小、受体分子的变化、溶剂的不同对λs计算值相对λs实验值的偏差的影响,直接证实了电子给受体的耦合作用,溶剂分子参与的超交换电子转移及溶质溶剂分子表面相互作用等量子因素造成的实际反应体系对溶剂经典连续介质模型的偏离.     

A unique trapping by crystal forces of a hydronium cation displaying a transition state structure

An hydronium cation has been discovered which is unique among all crystallographic such ions of the Cambridge Database. Of composition H₇O₃⁺ it has a structure that is totally different from those classically known with structures H₂O-H₂O-H₃O⁺ and H₂O-(H₃O⁺)-H₂O. Unlike the crystallographically classical ones, the cation discussed here has a bifurcated hydrogen bond. From a central H₃O⁺ moiety a single hydrogen bond donor extends to two adjacent water molecules. Quantum chemical calculations in absence of the crystal environment demonstrate that the bifurcated hydrogen bond structure is that of a transition state for the H₇O₃⁺ complex. Thus remarkably, it appears that crystal forces have captured the ion in what would otherwise be a short-lived and unstable transition state formation.     

乙酸自热重整制氢用类水滑石衍生Zn-Ni-Al-Fe-O催化剂研究

采用共沉淀法制备了Zn_(2.4)Ni_(0.6)Al_xFe_(1-x)O_(4.5±δ)(x=1/0.5/0)系列类水滑石型镍基催化剂,用于乙酸自热重整制氢,并利用XRD、H_2-TPR、BET、XPS等表征手段对催化剂进行了表征。结果表明,Zn_(2.4)Ni_(0.6)Al_(0.5)Fe_(0.5)O_(4.5±δ)催化剂在乙酸自热重整中乙酸转化率维持在100%,氢气产率为2.39 mol-H_2/mol-HAc。Zn-Al水滑石前驱体经焙烧后形成了ZnO为骨架的复合氧化物,铁的适量添加增大了催化剂的比表面积,经还原后形成Fe NiZn合金,Fe以及Zn的给电子作用提高了Ni的抗氧化能力,催化剂的抗氧化烧结和抗积炭能力得到提高。     

Theoretical study of the remote control of hydrogen bond strengths in donor-bridge-acceptor systems: principles for designing effective bridges with substituent tuning

Remote control of hydrogen bond strengths has been studied based on conjugated donor-bridge-acceptor (pyrrole-bridge-imine) systems. The neutral and protonated states of the imine can change the hydrogen bonding ability of the pyrrole because, in the protonated state, significant partial intramolecular charge transfer (ICT) is induced that causes partial delocalization of the positive charge onto the pyrrole moiety. An efficient bridge, regardless of its length, should help electrons to flow out of pyrrole. A previously developed design strategy for the bridge (low bridge HOMO/LUMO) leads to the study of cyano- and fluoro-substituted conjugated systems. Substitution positions are found to be of key importance for maximizing the protonation-induced response from the donor-bridge-acceptor systems. Our results not only help to identify useful bridge substitution patterns, but also highlight interesting issues regarding the bridge conformation and the fluorine lone-pair effect.     

A density functional theory-time-dependent density functional theory investigation of photo-induced hydrogen bond and proton transfer for 2-(3,5-dichloro-2,6-dihydroxy-phenyl)-benzoxazole-6-carboxylicacid

Given the paramount importance of excited-state relaxation in the photochemical process, excited-state hydrogen bonding interactions and excited-state intramolecular proton transfer (ESIPT) are always hot topics. In this work, we theoretically explore the excited-state dynamical behaviors for a novel 2-(3,5-dichloro-2,6-dihydroxy-phenyl)-benzoxazole-6-carboxylicacid (DDPBC) system. As two intramolecular hydrogen bonds (O1 H2⋯N3 and O4 H5⋯O6) exist in the DDPBC structure, we first check if the double proton transfer form cannot be formed in the S1 state. Then, we explore the changes of geometrical parameters involved in hydrogen bonds, based on which we confirm that the dual intramolecular hydrogen bonds are strengthened on photo-excitation. The O1 H2⋯N3 hydrogen bond particularly plays a more important role in excited state. When it comes to the photo-induced excitation, we find charge transfer and electronic density redistribution around O1 H2 and N3 atom moieties. We verify the ESIPT tendency arising from the O1 H2⋯N3 hydrogen bond. In the analysis of the potential energy curves, along with O1 H2⋯N3 and O4 H5⋯O6, we demonstrate that the ESIPT reaction should occur along with O1 H2⋯N3 rather than O4 H5⋯O6. This work not only clarifies the specific ESIPT mechanism for DDPBC system but also paves the way for further novel applications based on DDPBC structure in the future.     

铈源对甲醇水蒸气重整制氢CuO/CeO2催化剂的影响

采用沉淀法合成了CeO_2载体,再经浸渍法负载活性组分得到CuO/CeO_2催化材料,探究了铈源(Ce(NO_3)_3·6H_2O、Ce Cl_3·6H_2O、Ce(NH_4)_2(NO_3)_6、Ce(SO_4)_2·4H_2O)对CuO/CeO_2催化性能的影响。通过采用XRD、SEM、N_2O滴定、BET和H_2-TPR等表征手段对催化材料的结构和性质研究发现,四种铈源合成的CuO/CeO_2催化材料在Cu比表面积、还原性能以及活性组分和载体间的相互作用方面存在着明显差别。其中,由Ce(NO_3)_3·6H_2O合成的CuO/CeO_2催化材料的Cu比表面积较大,CuO还原温度较低,CeO_2载体与CuO之间相互作用较强,在甲醇水蒸气重整反应过程中,表现出较佳的催化活性,在反应温度为553 K,水醇比n(H_2O)/n(MeOH)为1.2,甲醇水蒸气气体空速(GHSV)为1760 h~(-1)时,甲醇的转化率为100%,重整气中CO摩尔含量为0.84%。     

Symmetry properties of adiabatic free energy surfaces and a diagram of kinetic modes in the case of electrochemical tunneling microscopy of redox systems

The symmetry properties of adiabatic free energy surfaces, which describe redox and dissociative electron transfer reactions in systems of the type in situ STM, are investigated. A notion of an effective overvoltage, which is a generalization of a traditional overvoltage to the case where the bias voltage is other than zero, is introduced. Diagrams of kinetic modes, which describe processes that can occur in systems of the type in situ STM under consideration, are constructed in the space of model parameters. It is shown that, in some cases, with the bias voltage other than zero, there may emerge DKR of a sufficiently complicated structure with several critical regions.__________Translated from Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 419–432.Original Russian Text Copyright © 2005 by Medvedev.     

Kinetics of photoreduction of 9,10-phenanthrenequinone in the presence of amines and polymethylbenzenes

A study of the kinetics of photoreduction of 9,10-phenanthrenequinone in the presence of hydrogen donors (para-substituted N,N-dimethylanilines and polymethylbenzenes) showed that plots of the quantum yield of photoreduction (_H) and apparent reaction rate constant (k _H) vs. oxidation potential of hydrogen donors are extreme. In the presence of amines, k _H and _H increase, as a whole, whereas they decrease in the presence of polymethylbenzenes. In coordinates _H-G _e (G _e is the change in the free energy of electron transfer) for pairs quinone-H donor, _H increases with G _e approaching to zero. For the amine series, this effect is mainly in the exothermic region of G _e (G _e < 0). For the series of polymethylbenzenes, this increase is observed in the endothermic region (G _e > 0).__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2381–2385, November, 2004.     

A supported gold catalyst for the elimination of hydrogen from CO2 feed gas in the production of urea

Supported gold catalyst for eliminating hydrogen from CO₂ feed gas in the production of urea is found to be superior to other industrial catalysts (e.g. Pt/Al₂O₃ and PdPt/Al₂O₃) in catalytic activity and resistance to sulfur poisoning.     

Computational studies on optoelectronic and charge transfer properties of some perylene‐based donor‐π‐acceptor systems for dye sensitized solar cell applications

We report DFT studies on some perylene‐based dyes for their electron transfer properties in solar cell applications. The study involves modeling of different donor‐π‐acceptor type sensitizers, with perylene as the donor, furan/pyrrole/thiophene as the π‐bridge and cyanoacrylic group as the acceptor. The effect of different π‐bridges and various substituents on the perylene donor was evaluated in terms of opto‐electronic and photovoltaic parameters such as HOMO‐LUMO energy gap, λ_max, light harvesting efficiency(LHE), electron injection efficiency (Ø_inject), excited state dye potential (E^dye*), reorganization energy(λ), and free energy of dye regeneration (). The effect of various substituents on the dye–I₂ interaction and hence recombination process was also evaluated. We found that the furan‐based dimethylamine derivative exhibits a better balance of the various optical and photovoltaic properties. Finally, we evaluated the overall opto‐electronic and transport parameters of the TiO₂‐dye assembly after anchoring the dyes on the model TiO₂ cluster assembly.     

Design,synthesis, and characterization of a novel c‐donor‐nc‐bridge‐c‐acceptor type block copolymer for optoelectronic applications

A novel conjugated block copolymer system containing a donor‐type conjugated block (c‐D) covalently connected to an acceptor type conjugated block (c‐A) via a nonconjugated and flexible bridge chain (nc‐B), also called a DBA type block copolymer, has been designed, synthesized, and characterized for potential cost‐effective and high‐efficiency optoelectronic applications such as solar cells. Specifically, D is a regio‐regular para‐2‐ethylhexyloxy‐substituted polyphenylenevinylene (or EH‐RO‐PPV), A is a regio‐regular polyphenylenevinylene with sulfone (SO₂) acceptor moiety and a linear oxydecane (‐OC₁₀H₂₁) group substituted on every phenylene unit, and B contains an aliphatic chain with two or four methylene units. The size of each block can be controlled via synthetic feed ratio of the monomer and the terminator. The measured average molecular weights of D, A, and DBA based on gel permission chromatography are in good agreements with the molecular weights calculated using the monomer:terminator synthetic feed ratios. Preliminary optoelectronic device studies revealed an order of magnitude better improvement in photoelectric power conversion efficiency of DBA over the corresponding D/A blend under identical fabrication and testing conditions. Such improvements could be attributed to more efficient photo induced charge separation and charge transport in DBA versus in D/A blends. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1149–1160