臭氧在烟气中氧化零价汞的量子化学研究

利用量子化学方法计算研究了臭氧在烟气中氧化零价汞的微观反应机理,采用MP2/SDD计算方法优化得到反应物、过渡态、中间体及产物的几何构型,并通过振动分析与IRC分析确定反应过渡态和中间体,在QCISD(T)/SDD水平上计算能量,同时进行零点能校正,计算了反应活化能,并采用经典过渡态理论(TST)计算反应的速率常数,拟算出反应的阿累尼乌斯表达式.结果表明,臭氧在烟气中产生的NO3、O3和NO2粒子对零价汞进行氧化的活化能分别为22.94 kJ/mol,53.34kJ/mol和168.23kJ/mol.通过活化能比较,得到3种粒子的氧化性强弱为:NO3＞O3＞NO2在298 K下,将计算获得的反应速率常数与文献数据进行比较,结果吻合较好.     

二氧化锰改性活性炭吸附汞的机理研究

为探究经MnO2改性后活性炭(C14H6)吸附汞的反应机理,应用量子化学从头计算的MP2方法,优化6-311+g(d,p)/SDD基组得到反应物、中间体、过渡态和产物的几何构型,计算反应的动力学参数.采用经典过渡态理论分别计算了在298~1 500K和0.000 1~3 MPa条件下各反应的反应速率常数,并比较分析各反应速率常数的变化趋势.结果表明:在同时含有Hg、C14H6和MnO2的情况下,MnO2和C14H6的反应要比Hg和C14H6的反应快,且MnO2(C14H6)要比C14H6更易与Hg反应;反应速率常数随温度和压力的升高呈现增大趋势;经MnO2改性后的活性炭比未改性的活性炭吸附Hg的效果要好.     

含铬废物焚烧中CrOCl2＋OH→CrO2Cl＋HCl基元反应研究

含铬废物焚烧过程中形成具有不同氧化价态的多种铬氧化物,其毒性有较大差异,尤其是六价铬化合物具有极强的致癌作用.利用量子化学的方法研究了铬/氢/空气/氯焚烧体系中CrOCl 2+OH→CrO 2Cl+HCl反应的反应机理.通过Gaussian 98 软件在B3LYP/6-311+G(3df,2p)理论水平上,优化出各驻点的几何结构并得到经过零点能校正后的各驻点能量,通过过渡态搜索和内禀反应坐标分析确定该反应为基元反应.分别计算了正、逆反应的活化能,并采用传统过渡态理论计算了该反应的正向反应速率常数.     

高浓度CO2气氛下煤焦异相还原NO的量子化学研究

氧燃烧技术是一种能综合控制燃煤污染排放的新型燃烧技术,循环烟气中NOx被碳氢化合物的均相、煤焦(碳)异相还原,使得NOx排放大为降低.高浓度CO2气氛是氧燃烧技术的最大特点之一,为了研究高浓度CO2气氛下煤焦(碳)异相还原NO相关反应,采用了密度泛函计算方法B3LYP/6-31G(d),计算煤焦(碳)异相还原NO反应以及CO和O2影响NO还原过程的相关反应,优化得到反应路径上稳定点的几何构型;采用QCISD(T)/6-311G(d,p)方法计算得到了反应过程中各稳定点的能量,并计算得到活化能;使用经典过渡态理论计算反应速率常数,得出每个反应的阿累尼乌斯表达式,研究了详细反应路径和机理.初步探讨了氧燃烧方式下煤焦异相还原NO机理,获得了重要相关反应的反应路径和动力学参数;并且为进一步研究煤焦与多种气体联合作用机理提供了理论基础.     

铬/氢/空气焚烧动力学模型机理分析及反应速率常数计算

建立完善的含铬固体废物焚烧动力学模型,获取模型中各反应的反应速率常数,是对含铬固体废物焚烧过程进行动力学研究的基础.应用量子化学理论,采用量子化学计算软件Gaussian03,在B3LYP/6-311++G(d,p)理论水平研究了铬/氢/空气焚烧动力学模型中各反应的微观机理,对该焚烧动力学模型进行修正,并根据传统过渡态...     

活性炭纤维吸附汞的量子化学研究

构建四碳环模型结构作为活性炭纤维的基本模型框架,采用量子化学密度泛函理论B3LYP方法在lanl2dz基组水平上研究了活性炭纤维表面对汞的微观吸附机理,讨论了该簇模型在羰基、内酯、羧基和酚羟基官能团下对汞的吸附作用.结果表明:与单纯的活性炭纤维相比,羰基、内酯、羧基官能团的存在能够促进对单质汞的吸附,使其更倾向于化学吸附;而酚羟基对汞的吸附起不到促进作用.试验结果与理论计算结果一致,表明量子化学的理论计算是研究汞吸附机理的一种有效方法.     

煤焦催化CO还原N2O的反应机理

为了研究燃烧过程中氮氧化物的转化特性,采用M06-2X/6-311G(d)密度泛函理论研究了CO还原N_2O的均相和异相反应过程,并通过计算热力学与动力学参数分析其反应机理。结果表明:CO均相还原N_2O的活化能为216.93 kJ/mol,煤焦异相催化CO还原N_2O反应的活化能为133.06 kJ/mol;CO还原N_2O的均相和异相反应过程差异较大,CO与N_2O的均相还原反应速率决定反应步是R→TS1,而异相还原反应速率决定反应步是IM→TS,在298.15～1 800 K内,异相还原的反应速率始终大于均相反应速率;煤焦表面可以为N_2O的还原提供反应位点,对气体之间的反应具有催化作用。     

丁烯/丁醇异构体低温氧化Waddington反应机制理论研究

Waddington机理是烯烃和醇类异构体低温氧化机理建模的重要组成部分．针对丁烯/丁醇异构体,系统研究了低温氧化过程的Waddington动力学机制．基于量子化学原理,对该反应机制下的反应速率常数和物种热力学性质进行计算．基于过渡态理论,结合RRKM/ME方法,获得目标体系温度-/压力依赖的速率系数．在统计热力学的基础上,计算了所有关键物种温度相关的内能、生成焓、熵和热容等热力学量．与文献结果比较发现,异丁烯(R4和R5体系)的动力学与热力学参数均与文献值吻合较好．该理论计算结果可直接用于丁烯和丁醇异构体低温氧化动力学模型构建．     

铝锂/镁合金与H_2O反应的热力学分析

根据吉布斯能最小原理,利用FactSage计算研究了Al-Li-H2O体系和Al-Mg-H2O反应体系的热力参数,研究了温度、合金组成和H2O量的影响。结果表明:Al-Li-H2O体系氧化反应可以自发进行,随着温度的升高反应放出的热量减少;合金组成中Al含量越高,生成的H2越少;随着Li含量增大,固态产物由Al2O3向LiAlO2、Li2O转变。Al-Mg-H2O体系氧化反应可以自发进行,随着温度的升高反应放出的热量减少;合金组成中Al含量越高生成的H2越多;随着Mg含量增大,最终固态产物由Al2O3向MgAl2O4、MgO转变。Al中添加Li或Mg因产物发生转变而对制氢反应有促进作用;H2O量增加有助于反应最终温度的降低,温差为1800~2000 K,对金属制氢的实施应用有指导意义。     

不同价态五氧化二钒吸附水和氨的机理研究

为研究不同价态的V_2O_5(V_6O_(15)及V_6O_(15)~+)吸附H_2O和NH_3的反应机理,应用量子化学得到反应物、中间体、过渡态和产物的几何构型,对比分析反应过程中优化结构的势能、反应能垒、键长和吸附能等数据.结果表明:V_6O_(15)和V_6O_(15)~+均可吸附H_2O生成V—OH,但是对于后者整个反应表现为放热,而且反应能垒更低,说明V_6O_(15)~+更容易与H2O反应生成BrФnsted酸位;NH_3在V_6O_(15)~+上的吸附能更大,更容易形成可与NO反应的—NH4~+;在SCR脱硝反应中阳离子团簇V_6O_(15)~+比中性团簇V_6O_(15)活性更大.     

含铬废物焚烧过程中气态较低价铬的氯化物、氯氧化物热力学性质的量子化学研究

含铬废物焚烧过程中,会产生不同价态的气态铬化合物,高价态铬毒性高,低价态铬毒性低;需对该过程的反应机理进行深入研究。热力学参数是对含铬废物焚烧体系理论研究的基础。应用量子化学理论的不同方法和基组,研究了含铬废物焚烧过程中Cr/H/O/Cl体系下较低价态铬的氯化物、氯氧化物的几何结构、振动频率及生成焓等热力学参数,与其他文献数据对比,验证了量子化学计算方法的有效性,为进一步探索反应机理奠定了基础。     

Mechanism of transition metal cluster catalysts for hydrogen evolution reaction

Studying the hydrogen evolution reaction (HER) catalyst is important for the global energy crisis. Clusters have many special characteristics due to quantum size effect and super high specific surface area, including optical performance, catalytic performance, etc. In this work, the structures of transition metal cluster TM_n (TM = Co, Ni, Cu, Pd, Pt, n = 4–10) were searched and optimized by quantum chemistry methods. To search for non-precious metal catalysts, we calculated the Gibbs free energies for HER process on different clusters. Furthermore, the electronic structures of clusters before and after the reaction with H were analyzed, including the molecular surface electron distribution, the frontier molecular orbital, and the charge transfer properties, which dominated the HER processes. The results show that the Cu clusters have excellent HER catalytic properties due to its suitable surface electron distribution and HOMO/LUMO levels, especially Cu₄, Cu₇ and Cu₉, which even comparable to Pt catalysts. These results can help us better understand the mechanism of clusters catalyze HER process.     

Theoretical study on the reaction of magnesium with water in the gas-phase

The reaction of magnesium with water is of interest for propulsion and hydrogen generation. Reaction mechanism of Mg with water was investigated by ab initio quantum chemical methods. The geometries and frequencies of all reactants, products, intermediates and transition states were calculated at the B3LYP/6-311G++(3df, 2p) level. Energies at a higher level of accuracy were obtained at G2M (CC2) level using the B3LYP-optimized geometries. The Mg and water firstly formed an atom-molecule adduct Mg⋅₂OH, and then either formed MgOH + H by a H-dissociation process or formed HMgOH by the process of H-migration from one to the other side of the adduct molecule. The barrier heights of two processes are 48.28 kcal/mol and 32.51 kcal/mol. The rate constants were calculated by using the variational transition state theory with the zero-curvature tunneling correction in a temperature range of 1000-5000 K. The results showed that H-migration process was dominant in the studied temperature range and the branch ratio of H-dissociation process appeared bigger at higher temperature.     

Advances in modeling hydrocarbon cracking kinetic predictions by quantum chemical theory: A review

In the modeling of hydrocarbon thermal cracking processes, complicated reaction networks of multicomponent reactants make kinetic parameter predictions very challenging. To solve this problem, the additivity method and Evans‐Polanyi equation were proposed for the prediction of kinetic factors. As the calculation of kinetic parameters using quantum chemical theory was used for higher accuracy, new additivity methods at the quantum theory level were developed for the prediction of thermodynamic kinetic parameters. At the same time, a reaction class transition state theory RC‐TST, analogous to the Evans‐Polanyi equation, was proposed by considering quantum factors for kinetic constant evaluation. Quantum calculation methods promoted mechanistic studies of electronic effects to accurately reveal the kinetic constant rules with different structural factors. Under these circumstances, kinetic parameter predictions by different quantum chemical computation methods were firstly introduced and reviewed. Meanwhile, development of the new additivity method and RC‐TST theory at the quantum chemistry level were summarized, and the new outlook on electronic effects with an appropriate quantum chemical computational method into the new additivity method was conducted to develop more perspicuous and accuracy in a simplified method for the calculation of complicated thermal cracking reaction.     

Combustion and pyrolysis of iso-butanol: Experimental and chemical kinetic modeling study

The first reaction mechanism for iso-butanol (372 species and 8723 reversible elementary reactions) pyrolysis and combustion that includes pressure dependent kinetics and proposes reaction pathways to soot precursors has been automatically generated using the open-source software package RMG. High-pressure reaction rate coefficients for important hydrogen abstraction reactions from iso-butanol by hydrogen, methyl and HO₂ were calculated using quantum chemistry at the CBS-QB3 level. The mechanism was validated with recently published iso-butanol combustion experiments as well as new pyrolysis speciation data under diluted and undiluted conditions from 900 to 1100 K at 1.72 atm representative of fuel rich combustion conditions. Sensitivity and rate of production analysis revealed that the overall good agreement for the pyrolysis species, and in particular for the soot precursors like benzene, toluene and 1,3-cyclopentadiene, depends strongly on pressure dependent reactions involving the resonantly stabilized iso-butenyl radical. Laminar flame speed, opposed flow diffusion flame speciation profiles, and autoignition are also well-captured by the model. The agreement with speciation profiles for the jet-stirred reactor could be improved, in particular for temperatures lower than 850 K. Flux and sensitivity analysis for iso-butanol consumption revealed that this is primarily caused by uncertainty in iso-butanol + OH, iso-butanol + HO₂ and the low temperature peroxy chemistry rates. Further theoretical and quantum chemical studies are needed in understanding these rates to completely predict the combustion behavior of iso-butanol using detailed chemistry.     

Reaction mechanism for the free-edge oxidation of soot by O2

The reaction pathways for the oxidation by O₂ of polycyclic aromatic hydrocarbons present in soot particles are investigated using density functional theory at B3LYP/6-311++G(d,p) level of theory. For this, pyrene radical (4-pyrenyl) is chosen as the model molecule, as most soot models present in the literature employ the reactions involving the conversion of 4-pyrenyl to 4-phenanthryl by O₂ and OH to account for soot oxidation. Several routes for the formation of CO and CO₂ are proposed. The addition of O₂ on a radical site to form a peroxyl radical is found to be barrierless and exothermic with reaction energy of 188 kJ/mol. For the oxidation reaction to proceed further, three pathways are suggested, each of which involve the activation energies of 104, 167 and 115 kJ/mol relative to the peroxyl radical. The effect of the presence of H atom on a carbon atom neighboring the radical site on the energetics of carbon oxidation is assessed. Those intermediate species formed during oxidation with seven-membered rings or with a phenolic group are found to be highly stable. The rate constants evaluated using transition state theory in the temperature range of 300–3000 K for the reactions involved in the mechanism are provided.     

Comprehensive reaction mechanism for n-butanol pyrolysis and combustion

A detailed reaction mechanism for n-butanol, consisting of 263 species and 3381 reactions, has been generated using the open-source software package, Reaction Mechanism Generator (RMG). The mechanism is tested against recently published data – jet-stirred reactor mole fraction profiles, opposed-flow diffusion flame mole fraction profiles, autoignition delay times, and doped methane diffusion flame mole fraction profiles – and newly acquired n-butanol pyrolysis experiments with very encouraging results. The chemistry of butanal is also validated against autoignition delay times obtained in shock tube experiments. A flux and sensitivity analysis for each simulated dataset is discussed and reveals important reactions where more accurate rate constant estimates were required. New rate constant expressions were computed using quantum chemistry and transition state theory calculations. Furthermore, in addition to comparing the proposed model with the eight datasets, the model is also compared with recently published n-butanol models for three of the datasets. Key differences between the proposed model and the published models are discussed.     

铬/氢/空气体系焚烧动力学模型修正

建立完善的含铬废物焚烧动力学模型,有利于对含铬废物焚烧体系进行动力学研究,便于进一步分析剧毒六价铬生成的影响因素,尽而提出减少六价铬排放措施.应用量子化学理论和过渡态理论分析了铬/氢/空气体系焚烧动力学模型中反应的微观机理,并对该动力学模型进行修正.研究表明,该焚烧动力学模型中有4个总包反应,每个总包反应都由两个基元反应组成.修正后的铬/氢/空气体系焚烧动力学模型删除了4个总包反应,增加了6个基元反应.最后,还计算出新增加的6个基元反应的反应速率常数