Quantum chemistry study on the mechanism of the reaction between ozone and 2,3,7,8‐TCDD

Despite of its fundamental importance, the mechanism of the reaction between ozone and dioxins are still lack detailed investigation so far. It is well-known that quantum chemical calculation is a well-established method for investigating chemical reactions. In this article, quantum chemical calculation was employed to investigate the mechanism of the reaction between ozone and dioxins, as exemplified by 2,3,7,8-TCDD. The theoretical study showed that, 2,3,7,8-TCDD was gradually destructed by ozone via six cleavages of the CC bonds. All the six cleavages of the CC bonds were calculated and discussed in detail based on the theoretical calculations by the UB3LYP/6-31G(d) method. At the same time, the energies of stationary points along the reaction process were calculated by the UMP2/6-311g(d,p)//UB3LYP/6-31G(d) method and the activation energy was obtained. The obtained activation energy was 12.25 kcal/mol, which was lower than that of the reaction between benzene and O₃(16.64 kcal/mol). This indicated that, by comparison with benzene, 2,3,7,8-TCDD could be more efficiently destructed by O₃. The reason for this result was also discussed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Reaction of C2HCl2＋O2： Combined TR-FTIR Spectroscopy and Electronic Structure

The product channels and mechanisms of the C2HC12＋O2 reaction are investigated by step-scan time-resolved Fourier transform infrared emission spectroscopy and the G3MP2// B3LYP/6-311G（d,p） level of electronic structure calculations. Vibrationally excited products of HCI, CO, and CO2 are observed in the IR emission spectra and the product vibrational state distribution are determined which shows that HCI and CO are vibrationally excited with the nascent average vibrational energy estimated to be 59.8 and 51.8 kJ/mol respectively. In combination with the G3MP2//B3LYP/6-311G（d,p） calculations, the reaction mechanisms have been characterized and the energetically favorable reaction pathways have been suggested.     

Theoretical study on reactions of cyclic-N3 with NO, NO2 and Cl2

In this article, we report our detailed mechanistic study on the reactions of cyclic-N₃ with NO, NO₂ at the G3B3//B3LYP/6-311+G(d) and CCSD(T)/aug-cc-pVTZ//QCISD/6-311+G(d)+ZPVE levels; the reactions of cyclic-N₃ with Cl₂ was studied at the G3B3//B3LYP/6-311+G(d) and CCSD(T)/aug-cc-pVTZ//QCISD/6-31+G(d)+ZPVE levels. Both of the singlet and triplet potential-energy surfaces (PESs) of cyclic-N₃ + NO, cyclic-N₃ + NO₂ and the PES of cyclic-N₃ + Cl₂ have been depicted. The results indicate that on singlet PESs cyclic-N₃ can undergo the barrierless addition–elimination mechanism with NO and NO₂ forming the respective dominant products N₂ + ¹cyclic-NON and ¹NNO(O) + N₂. Yet the two reactions on triplet PESs are much less likely to take place under room temperature due to the high barriers. For the cyclic-N₃ + Cl₂ reaction, a Cl-abstraction mechanism was revealed that results in the product cyclic-N₃Cl + Cl with an overall barrier as high as 14.7 kcal/mol at CCSD(T)/aug-cc-pVTZ//QCISD/6-31+G(d)+ZPVE level. So the cyclic-N₃ radical could be stable against Cl₂ at low temperatures in gas phase. The present results can be useful for future experimental investigation on the title reactions.     

Ab initio quantum chemical studies on the reactions of CF3O2 with OH

The potential energy surface for the CF₃O₂ + OH reaction has been theoretically investigated using the DFT (B3LYP/6-311G(d,p)) level of theory. Both singlet and triplet potential energy surfaces are investigated. The reaction mechanism on the triplet surface is simple. However, the reaction mechanism on the singlet surface is more complicated. It is revealed that the formation of CF₃O + HO₂ is the dominant channel on the triplet surface. The potential energy surface (PES) for this reaction has been given according to the relative energies calculated at the DFT/B3LYP/6-311G(d,p) level. Because this reaction involves both triplet and singlet states, triplet–singlet intersystem crossing (ISC) crossing also have been investigated in this paper.     

HO2自由基与NO2反应通道的理论研究

应用密度泛函理论DFT/B3LYP对HO₂＋NO₂反应进行了研究, 在B3LYP/6-311G^**和CCSD(T)/6-311G^**水平上计算了HO₂自由基与NO₂分子反应的单重态和三重态反应势能面, 计算结果表明, 单重态反应势能面中的直接氢抽提反应机理是此反应的主要反应通道, 即HO₂自由基的氢原子转移到NO₂分子的氮原子上形成产物P₁ (HNO₂＋³O₂), 另一个可能的反应通道是单重态反应势能面上HO₂中的端位氧原子进攻NO₂分子中的氮原子形成中间体1 (HOONO₂), 接着中间体1 (HOONO₂)经过氢转移形成产物P₂ (trans-HONO＋³O₂), 以上两个反应通道都是放热反应通道, 分别放热90.14和132.52 kJ•mol^－1.     

n‐Butane Monomolecular Cracking on Acidic Zeolites: A Density Functional Study

采用5T簇模型,利用密度泛函理论在B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d)水平下研究正丁烷在酸性分子筛上的单分子催化裂解反应。本文重点详细研究了正丁烷在分子筛表面不同C位的脱氢反应。在B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d)水平下计算所得第一和第二位C-C键裂解的活化能垒分别为 238、217 kJ/mol。而第一第二序位脱氢反应能垒分别为296、242 kJ/mol。正丁烷不同序位脱氢反应的活化能垒相差54 kJ/mol。从计算结果可以看出,正丁烷在分子筛上催化裂解脱氢反应优先发生在第二位C原子上。此外,本文还讨论了簇模型结构与酸性的关系,结果显示改变封端Si-H键的键长的方法可以用来模拟分子筛酸性变化。最后研究了分子筛酸性变化与正丁烷催化裂解反应能垒的关系。     

Synthesis of Cr2(MoO4)3

Studies on the kinetics and mechanism of the reaction leading to Cr₂(MoO₄)₃ have been made using X-ray diffraction and infrared spectroscopy. The apparent activation energy, E=285±22 kJ/mol has been calculated, based on the Ginstling-Brounstein diffusion controlled model.     

CH2＝CHCl与O(3P)反应的理论研究

用量子化学密度泛函理论和QCISD (Quadratic configuration interaction calculation)方法, 对O(³P)与CH₂CHCl的反应进行了理论研究. 在UB3LYP/6-311＋＋G(d,p), UB3LYP/6-31＋＋G(3df, 3pd)计算水平上, 优化了反应物、产物、中间体和过渡态的几何构型, 并在UQCISD(T)/6-311＋＋G(2df,2pd)水平上计算了单点能量. 为了确证过渡态的真实性, 在UB3LYP/6-311＋＋G(3df,3pd)水平上进行了内禀坐标(IRC)计算和频率分析, 并确定了反应机理. 研究结果表明, 反应主要产物为CH₂CHO和Cl.     

CH3S与HO2气相反应机理的理论研究

采用密度泛函理论的B3LYP方法, 在6-311＋＋G(d,p)基组水平上研究了CH3S自由基与HO2自由基的微观反应机理, 全参数优化了反应势能面上各驻点的几何构型, 振动分析和内禀反应坐标(IRC)分析结果证实了中间体和过渡态的真实性, 计算所得的键鞍点电荷密度的变化情况也确认了反应过程. 找到了五条可能的反应通道, 对结果的分析表明: 单线态反应通道(5) CH3S＋HO2→CH3SOOH (1P), 是所有通道中的主要反应通道. 该通道不需要克服过渡态能垒, 属于放热反应, 在动力学和热力学上都是最为有利的. 对于三线态反应通道来说, 通道(1)CH3S＋HO2→COM11→TS1→COM12→CH3SH＋O2 (3P)为主要反应通道, 控制步骤的活化能为53.5 kJ/mol, 能垒最低, 属于放热反应, 在动力学和热力学上都是有利的.     

First-principles study of O2 adsorption and dissociation on the CuCr2O4 (100) surface

The adsorption and dissociation of molecular oxygen on spinel CuCr₂O₄ (100) surface were carried out by first-principles calculations based on density functional theory (DFT). The calculated results indicate that the Cr site is most favorable for atomic oxygen adsorption, with an adsorption energy of 402.8 kJ/mol. For molecular oxygen adsorption, there are three types of favorable interaction modes: O₂ forms bonds with the Cu site or O₂ binds to two Cr sites or O₂ interacts with both Cu and Cr sites simultaneously. The lowest activation energy (E_a = 35.4 kJ/mol) was found through exploring possible reaction pathways for O₂ dissociation. The relationship between E_a and reaction enthalpy (ΔH) for O₂ dissociation adsorption reactions fits Brønsted-Evans-Polanyi (BEP) behavior.     

Effect of conversion of NO2 into no on the catalytic reduction of NO2 with C3H6 in excess O2

During the reduction of NO₂ by C₃H₆ in O₂ over alumina-supported Au, Rh and Pt it was found that three parallel reactions take place,i.e., reduction of NO₂ to N₂ and N₂O, partial decomposition of NO₂ to NO and oxidation of C₃H₆ to CO and CO₂. In the absence of C₃H₆, the NO₂→NO+O₂ reaction reaches a fast equilibrium on Rh and Pt but not on Au and γ-Al₂O₃. Addition of C₃H₆ to the NO₂+O₂ mixture leads to the formation of NO above equilibrium conversion levels.     

Structures and stabilities of HPS2 isomers

The potential energy surface of HPS² system containing nine isomers and fifteen transition states is obtained at MP2/6-311++G(d, p) and QCISD(t)/6-311++G(3df, 2p)(single-point) levels. On the potential energy surface, the lowest-lying trans-HSPS(E1) is found to be thermodynamically the most stable isomer followed by cis-HSPS(E2) and HP(S)S(C_2v, E3) at 3.43 and 14.17 kJ/mol higher, respectively. The computed results show that species E1, E2, E3, stereo HP(S)S(C_s, E4) with PSS three-membered ring, isomers trans-HPSS(E5) and cis-HPSS(E6) which coexist with E4 are kinetically stable isomers. The products E6 and E5 in the reaction of HP with S² can be isomerized into higher kinetic stable isomer E4 with 65.75 and 71.73 kJ/mol reaction barrier height, respectively. The predicated results may correct the possible inaccurate conclusion in that the product was experimentally assigned as isomer cis-HPSS(E6).     

CH3S自由基H迁移异构化及脱H2反应的直接动力学研究

采用密度泛函方法(MPW1PW91)在6-311G(d,p)基组水平上研究了CH₃S自由基H迁移反应CH₃S→CH₂SH (R1), 脱H₂反应CH₃S→HCS＋H₂ (R2)以及脱H₂产物HCS异构化反应HCS→CSH (R3)的微观动力学机理. 在QCISD(t)/6- 311＋＋G(d,p)//MPW1PW91/6-311G(d,p)＋ZPE水平上进行了单点能校正. 利用经典过渡态理论(TST)与变分过渡态理论(CVT)分别计算了各反应在200～2000 K温度区间内的速率常数k^TST和k^CVT, 同时获得了经小曲率隧道效应模型(SCT)校正后的速率常数k^CVT/SCT. 结果表明, 反应 R1, R2 和R3的势垒△E^≠分别为160.69, 266.61和241.63 kJ/mol, R1为反应的主通道. 低温下CH₃S比CH₂SH稳定, 高温时CH₂SH比CH₃S更稳定. 另外, 速率常数计算结果显示, 量子力学隧道效应在低温段对速率常数的计算有显著影响, 而变分效应在计算温度段内对速率常数的影响可以忽略.     

Kinetics and mechanism of the reaction of Ba(No3)2 with TiO2(anatase) in the solid-solid state and the liquid-solid state

The reaction of Ba(NO₃)₂ with TiO₂(anatase) was studied by TG and DTA. According to simultaneous TG and DTA, the reaction occurred sharply around the melting temperature of Ba(NO₃)₂, ～577°C, at low heating rates, and the reaction followed after melting of Ba(NO₃)₂ as the rate was raised. For the isothermal reactions the conversion α vs time relationship was given by the equation: kt = 1 - (1-α)^1/3. The relationship was shown by one straight line below 577°C, and by two lines with a bend above 577°C. The reaction rates at the earlier period above 577°C were about $\text{1}\text{5}$ smaller than those at the later period, which were nearly on the extrapolated log k vs 1/T line obtained below 577°C. The activation energy was 212 kJ mol^?1 for the solid-solid reaction and 231 kJ mol^?1 for the earlier period in the liquid-solid reaction.     

HNO自由基与O2反应机理的理论研究

采用密度泛函理论(DFT)和从头算方法,在B3LYP/6-311++G(d,p)水平上对反应HNO+O_2做了理论计算研究。优化得到了反应物、中间体、过渡态和产物的几何构型以及相应的能量值、振动频率。通过分析反应路径的能量差异,以及异构化难易程度,发现HNO+O_2反应有2种产物通道:HOONO和HNO_3。其中过氧亚硝酸HOONO是主要产物,有3种稳定的构象。     

Kinetics of low temperature CO oxidation over Pt/SnO2 catalyst

In a CO−O₂ stoichiometric mixture, the kinetic parameters, reaction order, rate constant and activation energy of CO oxidation over a Pt/SnO₂ catalyst have been measured using a fixed bed flow reactor near 0°C. The results show that it is a first-order reaction. The activation energy of CO oxidation over Pt/SnO₂ prepared with SnO₂ calcined at 300°C was approximately 21 kJ/mol. The activation energy of CO oxidation over Pt/SnO₂ changed slowly with SnO₂ calcination temperature above 400°C, and reached approximately 45 kJ/mol.     

Reactions of CH3O2 radicals on solid surface

The reaction probability of CH₃O₂ radicals with NO₂, CH₄, C₃H₆, and CH₃CHO on the solid surface of KCl in flow at low pressure and temperature range of 297–353 K has been studied. The chosen conditions allowed excluding homogeneous interaction of radicals. The heterogeneous radical decay of peracetic acid served as a source of CH₃O₂ radicals. On the basis of ESR measurements of CH₃O₂ radicals with the above‐mentioned compounds, a heterogeneous reaction mechanism has been identified. The reactivity of NO₂ was greatest for the compounds studied. The effective activation energy was evaluated to be 10.4 ± 0.8 kJ/mol for the reaction of RO₂ radicals with NO₂ and ?21.3 ± 2.8 kJ/mol for methane. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 591–595, 2004     

Hydrogenation of nitrate in water over bimetallic Pd-Ag/Al2O3 catalysts

Hydrogenation of nitrate (NO₃ ⁻) in water was studied with 0.8 ×10⁻³–3.2 ×10⁻³ mol/dm³ of reactant in the temperature range of 293–313 K over palladium promoted Ag catalysts. Pd-Ag catalysts with a low ratio of Ag/Pd were characterized by high efficiency in the reduction of nitrates. The degradation of nitrates followed approximately first order decay and the estimated apparent activation energy was about 4 kJ/mol.     

Pd(Cu)在MgO(100)表面吸附CO和O2的理论研究

采用固体镶嵌势能模型和DFT/B3LYP方法研究了在Pd/MgO和Cu/MgO表面吸附CO和O₂分子的电子性质. 计算结果表明, 在完美MgO(100)表面Pd原子对CO和O₂的吸附能分别为206.5和84.8 kJ/mol, 因此可知Pd原子更容易吸附CO分子; 而当Pd原子附着于有氧缺陷的MgO表面时, 它对两种分子的吸附都非常弱. 相反, 附着于MgO表面的Cu原子对O₂分子的吸附更为有利, 其吸附能在140～155 kJ/mol之间. 研究结果还表明, 对于双分子吸附体系, 即CO＋CO, CO＋O₂, O₂＋O₂体系, 双分子之间的结合力可减小完美MgO表面上Pd原子与被吸附分子的相互作用, 使吸附能减少了46～96 kJ/mol. 而对于在MgO表面上的Cu原子, 只有O₂＋O₂ 体系使吸附能减少了大约50～71 kJ/mol.     

苯并氧化呋咱稳定性和异构化的DFT和ab initio研究

运用B3LYP/6-31G(d)密度泛函理论（DFT）方法对苯并氧化呋咱、邻二亚硝基苯及其间的异构化反应进行了计算研究。结果表明,苯并氧化呋咱的分子总能量比邻二亚硝基苯的低;由苯并氧化呋咱异构为邻二亚硝基苯的正向反应活化能（Ea+=51.0kJ/mol）,与文献实测值（58.6kJ/mol）较接近,而其逆向反应活化能（Ea-=4.6kJ/mol）很小,从而揭示了苯并氧化呋咱比邻二亚硝基苯更稳定·此外,进行了HF/3-21G、HF/6-31G(d)和MP2/6-31G(d)//6-31G(d)水平下相应的计算,发现B3LYP-DFT的结果较abinitio为优。谐振动频率的B3LYP/6-31G(d)计算还支持了邻二亚硝基苯为苯并氧化呋咱“自-自”互变重排反应的中间体。