【作者】 任慧；

【导师】 屈一新；

【作者基本信息】 北京化工大学 ， 应用化学， 2008， 博士

【摘要】 化学最初是建立在原子分子学说上的一种实验科学,研究分子的行为和分子间的反应,对分子的认识和改造是化学科学的首要任务。化学与理论化学在20世纪都取得了辉煌的成就,但未获得社会应有的认可,理论化学尤其未受到应有的重视。量子化学是应用物理学的量子力学原理和方法来研究化学体系的结构和化学反应性能的科学。随着量子理论的发展,量子化学目前正成为化学结构理论的基础,成为广大化学家所使用的工具。实验和理论能够共同协力探讨分子体系的性质,使整个化学领域发生了巨大的变革和进步。现代化学不再是纯实验科学了。论文针对现代化学中的几个课题,采用量子化学计算结合实验共同对相关体系进行了研究,对量子化学在现代化学中的应用进行了有益的尝试。卟啉化合物是一类特殊的大环共轭芳香体系,血红素、叶绿素为这类化合物的典型代表。这类化合物的应用十分广泛,尤其在仿生催化上具有重要的研究意义。卟吩环是卟啉类化合物的基本结构,对其电子结构和构型的正确描述是研究卟啉类物质的基础。采用传统的从头算HF方法和DFT方法在不同的基组水平上对卟吩结构进行几何优化和NMR计算,并对结果进行了比较。采用DFT的方法计算得到的构型参数与实验结构之间有更好的吻合性,说明考虑电子相关能在该类物质的结构计算中不可忽视。在DFT计算方法中,同样基组水平采用不同的泛函得到的优化构型也并不完全相同,同时考虑定域项和非定域项的B3LYP方法得到了更接近实验值的结果。采用STO-3G基组得到的优化构型是卟吩与其互变异构体之间相互转化反应历程中的二级鞍点结构。对NMR的计算,DFT方法显然也比传统HF方法更合适。白炭黑是一种超细具有活性的SiO₂粒子,是橡胶工业中一种重要的补强填料,但白炭黑的加工性能始终是制约其应用的瓶颈。为了改善其加工性能,必须对二氧化硅进行表面改性。采用KH-792,KH-590和KH-570等不同硅烷偶联剂对纳米SiO₂进行了改性处理并用于SSBR橡胶的补强,对改性后的SiO₂和补强后的橡胶的一些宏观性能进行了检测。采用量子化学的计算方法对改性SiO₂及其补强SSBR单元进行了结构优化和频率计算,并进一步进行了成键分析。结果表明:硅烷偶联剂对SiO₂粉体改性对改善加工性能作用明显,不同硅烷偶联剂的种类和结构对二氧化硅补强橡胶的机械物理性能有影响。偶联剂KH-792与二氧化硅接枝形成的Si—O键的键长最短,O的电负性最大,说明它与二氧化硅的键合最为紧密。KH-792中两个N原子的孤对电子有较大的离域化效应使补强橡胶具有更高的拉伸强度和延展性。偶联剂KH-590接枝二氧化硅后另一端的有机基团S显示较大的S—C键键长,有从偶联剂断裂的趋势,在反应过程容易释放出硫自由基（S·）,与橡胶分子发生交联反应,提高了胶料的交联密度,大大加强了其定伸应力和撕裂强度。不同硅烷偶联剂、二氧化硅和SBR之间所形成的化学键的有着明显差异,这些差异是导致补强橡胶宏观机械物理性能之间差异的根本原因。氮氧化物（NO_x）对生态环境、工农业生产和人体健康均有巨大的危害。因此对NOx化物的脱除越来越引起人们的重视,选择性催化还原技术及其催化剂的研究是其中重要的课题之一。制备了Ag/Al₂O₃及Ag/USY分子筛催化剂,测试了其比表面积和活性。采用原位红外技术对Ag/Al₂O₃催化剂上丙烯选择性催化还原NO_x的反应进行了研究。结果表明,Ag/Al₂O₃催化剂上丙烯还原NOx在350℃以上才能有较高的NO_x转化率,较为合适的反应温度区间是400～450℃。在Ag/Al₂O₃催化剂表面的SCR反应中,NCO和CN是反应的关键中间物种,对N₂+C₃H₆的活化能够极大丰富反应体系中的这些物种,给SCR反应活性带来明显的促进。采用密度泛函的方法对Ag/Al₂O₃催化剂上NO、O₂及不同的还原剂的吸附结构进行了全优化,并对全优化构型进行频率计算和NBO分析。根据热力学计算的结果,反应体系中NO、O₂能自发的吸附与催化剂的活性组分Ag上,该吸附有力地削弱了原来的分子之间的成键,有利于SCR反应的发生,这也是催化剂活性的体现。尽管常见的几种还原剂并不能自发吸附于活性组分表面,但是还原剂碳链的减少和不饱和度增加有利于其在催化剂上的吸附,对增强反应活性是有利的。对反应的重要中间物种NO₃^-在活性组分上Ag和Ag⁺上的三种吸附结构形式进行了计算。结果表明形成的三种吸附结构中,以单齿吸附的反应活性最强。同样的吸附,NO₃^-在Ag⁺上的吸附对与NO键的影响更为强烈。因此在进一步的实验中可以通过控制催化剂表面酸性以达到生成更多单齿活性中间物种的目的,同时可以调控Ag在载体上的负载量达到活性表面选择的目的。论文研究表明量子化学理论研究和实验研究的结合是现代化学的必经之路。更多还原

【Abstract】 Chemistry is originally an experimental science built on atomic and molecular theory.The primary task of chemistry is to study the behavior of molecules,the reactions between them,and based on these understandings to rebuild molecules.Although brilliant achievements in the 20th century were made,chemistry and theoretical chemistry did not gain enough attention as they deserved,especially for theoretical chemistry.Quantum chemistry is a science that studies the structures and reactions of chemical system using quantum mechanics theories and methods.With the development of quantum theory,nowadays quantum chemistry has formed the fundamentals of chemical structure theory and is widely applied in all branches of chemistry and molecular physics.The combination of theory and experimentation today makes it possible for chemical sciences to probe the nature of molecular system and brings remarkable innovations and achievements for the whole chemical field. The modern chemistry is not an experimental science anymore.In this paper,three selected typical issues in the modern chemistry are studied using the combination of quantum chemistry and experimental investigations with the hope that this attempt could make contributions for the application of quantum chemistry in modern chemistry.Porphyrins are special kind of compounds with conjugated aromatic rings.Hemoglobin,Chlorophyll are typical compounds belong to those materials.These compounds find extensive applications,particularly as bionic catalyts.The porphin is the basic structure of this kind of compounds.Therefore,correct description of its electronic structure is the foundation for the research concerning the porphyrin materials.The molecular structure of Free-Base Porphyrin（H₂P） has been fully optimized using the Density Functional Theory（DFT） methods,as well as ab initio Hartree-Fock method at various basis sets levels.The results obtained at various levels are discussed and compared with each other and with the available experimental data.Nuclear Magnetic Resonance （NMR） have also been calculations.It is found that DFT method has better performance in geometry caculating.That indicating electronic correlation must be included in the calculations concerning the structure of this kind of materials.There are still some differences in the optimized structures obtained using different basis in DFT method. Results obtained using B3LYP approach are closer to the experimental data.The optimized structure obtained using STO-3G basis sets is only a saddle point structure in tautomerism.For NMR calculation,DFT is also more appropriate method than HF. Silica is an active and superfine material.It finds wide applications as a reinforcement fill in the rubber industry.But the poor processing properties of silica is a obstacle that restricts its application.As a consequence,surface modification of silica is necessary to improve its processing performance.In this study,the effect of the modification on the silica and its influence on the reinforced SSBR are studied using the combination of quantum chemistry and experimental investigations. The surface of the nano-silica was modified by different silane coupling agents,such as KH-792,KH-590 and KH-570.Then the modified silica was filled into the styrene-butadiene rubber（SSBR）.Different instruments were employed to characterize the properties of modified silica and reinforced SSBR.The optimized geometries of molecular modified silica reinforced SBR were obtained by using B3LYP calculation of density functional theory（DFT）.The natural bond orbital analyses were carried out.The experimental results showed that:silica surface modification with silane couplings significantly improves the processing properties of silica.The mechanical properties of reinforced rubber were dependent on the type and structure of the silane coupling used.The results of quantum chemistry calculations indicated that the Si-O bond length of the silica modified by with KH-792 is the shortest one with the oxygen atom bearing more negative charge on it.This implies that the silica and KH-792 is reinforced.SSBR reinforced with KH-792 shows a higher tensile strength and a higher elongation.This can be attributed to the effect of intensified delocalization of the lone electron pairs of the two N atoms in KH-792.Modification with KH-590 results in a change in the length of the S-C bond located at the other end of KH-590 molecule.The length of the S-C bond becomes longer as compared to that of the original one.This makes the scission of the S-C bond easy and more sulfur free radical（·S_y·） can be produced.Consequently,the degree of crosslink of the rubber reinforced with the silica modified by KH-590 was increased, resulting in an increase in the stress and tear strength of reinforced SSBR. The differences in the mechanical properties of the reinforced rubber were resulted from the differences in the properties of the bonds formed between silica,silane coupling agents and SSBR.Nitrogen oxides（NO_X） are pollutants that are harm to the ecological environment,industrial and agricultural production as well as human health.The main technology used for the removal of NO_X is selective catalytic reduction（SCR） method.In this study,Ag/Al₂O₃ and Ag/USY catalysts for the SCR of NO_X.were prepared,tested and characterized.It was found that to obtain a higher conversion of NO_X SCR with propane over Ag/Al₂O₃ needs a temperature higher then 350℃.The more appropriate reaction temperature range is 400～450℃.NCO and CN play crucial roles in the SCR reaction over Ag/Al₂O₃.So SCR activity can be greatly promoted with the N₂ and C₃H₆ being activated.The adsorption of NO,O₂ and reducing agents on Ag/Al₂O3.has been studied using DFT. The frequencies of the.optimized geometries of the adsorbed species and NBO were calculated,According to the results of thermodynamic calculations,the adsorption of NO and O₂ on the catalysts containing Ag is an spontaneous process.The bonds of NO and O₂ are observably weakened by the absorption.Adsorption of hydrocarbons with longer and saturated carbon chains is not spontaneous.However,decreasing the length of the carbon chain or saturation of the reducing molecules can enhance their absorption and subsequently increase their reactivity.The geometries of NO₃^-,the important intermediate species, adsorbed on Ag and Ag⁺ were calculated.The results indicate that the unidentated adsorbed nitrate has the highest activity among the three absorption geometries.The adsorption of NO₃^- on Ag⁺ shows stronger impact no the N-O bond.Therefore,catalyst surface acidity can be adjusted to generate more unidentated nitrate,and the load of Ag can be controlled to obtain a more active surface in the future catalyst design.From the study,we can draw a conclusion that the combination of quantum chemistry research and experimental study is the best way of modern chemistry research.更多还原