异核氧化物团簇与小分子的反应研究

研究气态条件下异核氧化物团簇与小分子的反应,可从分子水平揭示多组分氧化物催化剂中的各组分在化学转化中的作用,为理性设计和氧化物催化剂改进提供理论基础.本文综述了异核氧化物团簇活化和转化小分子的研究新进展,讨论了异核掺杂引起的氧化物团簇局部电荷环境、局部自旋环境以及成键结构的变化对一些重要活性氧物种的反应性的调控,展示了氧化物团簇掺杂贵金属原子所带来的奇特化学反应以及新的反应机理.     

镍钴双原子团簇催化甲烷干重整反应机理及其动力学研究

本研究采用密度泛函理论方法对NiCo双原子团簇催化甲烷干法重整反应的体系进行了计算研究。通过计算结果得出甲烷脱氢、二氧化碳活化、C*和CH*的氧化、H₂和H₂O的生成四个反应过程可能的反应路径。最后,运用能量跨度模型分析循环反应的动力学信息,发现298K时甲烷脱氢过程中不易生成C*。913 K时甲烷脱氢过程决速中间体由IM1-1变成了IM6-1、决速过渡态由TS78-1变成了TS56-1;虽然可以生成C*,但能量跨度的减小加快了C*和CH*的消去。本工作可以了解NiCo双原子团簇催化甲烷干法重整的作用机理,为实验研究提供理论基础。     

单个金或银原子掺杂的氧化钒团簇上的甲烷活化反应

运用密度泛函理论系统研究了甲烷在MV_3O_y~q (M=Au/Ag,y=6–8,q=0或±1)团簇上的吸附和活化。研究得到了吸附体系的微观几何构型、吸附能、电荷分布等性质,找到了5个可以明显活化甲烷分子的含Au团簇。在这些体系中,Au均吸附在基底团簇V_3O_y~q的O位置,而CH_4均在Au原子上被活化。团簇电荷对活化能力有明显影响,阳离子团簇的活化能力最强,中性体系次之,阴离子团簇的活化能力很弱。测试计算表明引入D3色散矫正对于体系结构和能量的计算结果影响不大。本文作为单原子催化剂上甲烷吸附和活化反应的团簇模型研究,为进一步研究单原子催化剂上甲烷的活化机理提供了基础,也为合理设计低温下甲烷转化的单原子催化剂提供了有益的线索。     

担载型贵金属催化剂上甲烷直接羰基化反应

利用程序升温脉冲反应、恒温脉冲反应及探针分子表面反应技术较系统地考察了担载型贵金属催化剂上甲烷直接羰基化制乙醛的反应，研究发现通过采用总反应分解法操作后，能够克服甲烷直接羰基化反应的热力学限制，将总反应转化为两个可在较温和条件发生的反应，首次实现了CH4＋CO→CH3CHO的反应即首先进行甲烷的分解，然后引入CO与甲烷分解所产生的表面物种直接反应生成乙醛．本文还探讨了甲烷吸附条件，CO与甲烷分解所产生的表丙碳物种间的作用等反应的影响因素、探针分子CH3I的表面反应结果显示甲烷分解产生的CHx（ad）（x≤3）物种可能是该反应的活性中间体     

Ag/Se二元团簇的形成以及Ag与Se团簇反应的研究

用飞行时间质谱仪研究了激光直接溅射Ag/Se混合样品产生的二元团簇以及团簇正离子的光解行为;并用串级溅射反应装置研究了Ag和Se正负离子产物.在直接溅射产生的Ag/Se二元团簇中,正离子主要系列是:[(Ag₂Se)_nAg⁺],[(Ag₂Se)_nAg₃⁺];负离子主要系列是:[(Ag₂Se)_nAgSe^-],[(Ag₂Se)_nAgSe₂^-],[(Ag₂Se)_nSe^-].团簇正离子的光解结果表明,同样条件下Ag/Se二元团簇正离子光解比率比Ag/S大.在Ag和Se样品串级溅射实验中,主要得到AgSe_n⁺(n=4～9)和AgSe_nSe^-(n=4～7)系列的产物,在AgSe_n⁺系列中,n=4,6时丰度较大.这表明串级溅射反应和直接溅射二元混合样品两种过程中成簇机理是不同的.     

铝硫二元团簇的组分及其光解规律

硫与金属元素所形成的二元团簇具有很多重要的特性,已受到人们的普遍重视.用激光-串级飞行时间质谱仪,我们曾研究了硫与过渡金属钽、铁等的二元团簇.最近我们选取主族金属元素铝,研究了铝硫团簇的形成及其光解,实验结果表明,与钽硫或铁硫团簇相比,铝硫团簇无论在其组份构成还是在其光解方面,都表现出鲜明的特有规律性.实验的主要参数如下:溅射用激光为Nd:YAG 二倍频,其输出强度控制在约10~7W·cm~(-2),激光的重复频率10Hz 样品位于激光束的焦点附近,由焦距f=50cm 的透镜调整其聚焦状     

贵金属纳米团簇的制备及在生物检测中的应用

介绍了贵金属纳米团簇(noble metallic nanoclusters, NMNCs)的研究现状及其作为一种新型荧光标记纳米材料在生物检测中的重要作用。重点总结了贵金属纳米团簇的优异性质、三种常用的制备方法(模板法、单分子层保护法和蚀刻法)及其近年来在生物传感器、生物探针、细胞标记及成像等领域的应用进展。简要评述和展望了贵金属纳米团簇的发展方向和应用前景。     

贵金属甲烷燃烧催化剂*

贵金属催化剂具有较高的甲烷燃烧活性,但是其弱的稳定性抑制了其在VOC脱除以及低浓瓦斯治理等领域的应用,因此提高贵金属甲烷燃烧催化剂的稳定性是目前研究的热点。本文综述了活性组分、载体、助剂和前驱体对贵金属甲烷燃烧催化剂性能的影响;重点介绍了具有较高甲烷燃烧活性的Pd基催化剂受这些因素的影响;结合甲烷燃烧动力学分析了反应组分对催化剂性能的影响;讨论了催化剂失活的机理以及导致研究结论存在较大分歧的原因,提出了避免这些分歧的措施。     

甲烷催化燃烧反应机理及催化剂研究进展

在煤矿开采及燃气轮机等工业应用或移动源领域存在甲烷大体量排放,且传统高温焚烧法会导致二次污染,因此,在低温下实现甲烷高效转化成为亟待解决的问题.从能源利用和环境保护角度,催化燃烧技术是实现甲烷废气高效净化的有效措施.本文综述了近年来催化机理和催化剂的研究进展.首先,在实验和理论基础上,总结概括了甲烷氧化机理,其中,重点...     

铝原子Bernal多面体团簇的理论研究

将遗传算法用于铝原子团簇的构型计算.运用这种方法,从任意构型开始,较好地计算了6、8、9、10个铝原子组成的原子团簇的能量最低时的构型,发现这四种铝原子团簇的能量最低构型分别取四种Bernal多面体排列.并对得到的四种构型用密度泛函方法（DFT）进行量子化学计算,结果表明，这类构型是势能面上的极小值点,可以稳定存在.     

TPSR Studies of the Activation of Methane on Supported Noble Metal Catalysts

Methane decomposition on silica-supported noble metal catalysts was deeply investigated by means of the temperature programmed surface reaction (TPSR).The results obtained show that methane can be effectively decomposed into different surface carbons, which show different reactivities and features to form higherhydrocarbons.     

Structural, Electronic, and Optical Properties of Noble Metal Clusters from First Principles

We examine low-energy isomeric forms, static polarizabilities, and optical absorption spectra of Ag _n , n = 2–8, and Au _n , n = 2–3, clusters using first principles computations within the static and time-dependent versions of the density functional theory. The noticeable decrease in the static polarizabilities of Ag₇ and Ag₈ compared to the values characteristic of Ag _n , n = 2–6, is correlated with the transition from two-dimensional to three-dimensional structures at n = 7. The optical spectra computed within the time-dependent local density approximation for the most stable structures are in good agreement with the available experimental data and the results of earlier theoretical studies. Optical spectra of higher-energy isomers typically present features that are not observed in the experimental spectra. The d electrons affect the spectra of noble metal clusters by quenching the oscillator strengths through screening of the s electrons and by getting directly involved in the excitations. Due to the larger s–d hybridization in Au compared to Ag, these effects are more pronounced in Au _n clusters.     

Recent Advances on Confining Noble Metal Nanoparticles Inside Metal-Organic Frameworks for Hydrogenation Reactions

Hydrogenation reaction is one of the pillars of the chemical industry for the synthesis of drugs and fine chemicals. To achieve high catalytic performance, it is still highly desirable for constructing novel supported metal catalysts. Different from conventional supports like metal oxides, zeolites and carbon materials, metal-organic frameworks(MOFs) as the emerging porous materials have Hexhibited great potential to host metal nanoparticles (NPs) for achieving hydrogenation reactions with high catalytic efficiency, due to their unique porous structures. Recently, many progresses have been made, and thus, it is necessary to summarize the recent progresses on confining metal NPs inside MOFs for hydrogenation reactions. In this review, we first introduced the general synthesis methods for confining noble metal NPs inside MOFs. Then, the applications of noble metal NPs/MOFs catalysts in hydrogenation reactions were summarized, and the synergistic catalytic performances among noble metal NPs, metal nodes, functional groups, and pore channels in MOFs were illustrated. Subsequently, the hydrogen spillover effect involved in the hydrogenation reactions was discussed. Finally, we provide an outlook on the future research directions and challenges of confining noble metal NPs inside MOFs for hydrogenation reactions.     

Beyond Reduction Cocatalysts: Critical Role of Metal Cocatalysts in Photocatalytic Oxidation of Methane with Water**

Environmentally sustainable and selective conversion of methane to valuable chemicals under ambient conditions is pivotal for the development of next-generation photocatalytic technology. However, due to the lack of microscopic knowledge about non-thermal methane conversion, controlling and modulating photocatalytic oxidation processes driven by photogenerated holes remain a challenge. Here, we report novel function of metal cocatalysts to accept photogenerated holes and dominate selectivity of methane oxidation, which is clearly beyond the conventional concept in photocatalysis that the metal cocatalysts loaded on the surfaces of semiconductor photocatalysts mostly capture photogenerated electrons and dominate reduction reactions exclusively. The novel photocatalytic role of metal cocatalysts was verified by operando molecular spectroscopy combined with real-time mass spectrometry for metal-loaded Ga₂O₃ model photocatalysts under methane and water vapor at ambient temperature and pressure. Our concept of metal cocatalysts that work as active sites for both photocatalytic oxidation and reduction provides a new understanding of photocatalysis and a solid basis for controlling non-thermal redox reactions by metal-cocatalyst engineering.     

细菌吸附还原贵金属离子特性及表征

提炼、富集贵金属是细菌固定金属的重要用途．部分细菌还可还原金属离子,如海藻、枯草杆菌等均有较强的吸附、还原AU3+等金属离子的能力[1~3]．本文研究了从生态环境中筛选的几种细菌及其吸附、还原Pd2+、Pt4+、Au3+、Ag+、Rh3+等贵金属离子的特性,以期了解细菌固定金属的作用机制,提高细菌的还原能力,并将所得结果用于回收贵金属和制备高分散度贵金属催化剂．1实验部分D01细菌从生态环境中筛选、培养,并按常规微生物法制备大量菌体．所用仪器为SCR20BC高速冷冻离心机,BairdPS－4电感耦合等离子原子发射光谱仪,740SXFTIR光…     

Mechanisms of Reactions in the Solid State

The reaction of two solid phases X and Y to give a solid compound XY_v is taken as an example for the discussion of transport mechanisms and reaction steps. The following methods of investigation are discussed: determination of the rate law, marker experiments, and calculation of the reaction rate. It is pointed out that the investigation of powder reactions leads to problematic conclusions.     

The Theory of Pericyclic Reactions

Pericyclic reactions include thermal and photochemical cycloadditions and cycloreversions, electrocyclic reactions and sigmatropic shifts. Configuration interaction analysis can be used for making predictions about preferred reaction pathways, about reaction rates, about the nature of possible intermediate steps, and above all about the stereochemistry of such reactions.     

聚合物负载贵金属催化剂的合成及其在氢化反应中的应用进展

聚合物负载贵金属催化剂大多具有良好的光学催化活性,并且反应后容易从反应物中分离,重复实用性高,成为近年来人们研究的热点。常见的聚合物载体主要为有机聚合物及多种无机-有机杂化材料。本文主要按聚合物载体种类的不同,综述了聚合物负载Pt、Pd、Rh等贵金属催化剂的制备方法及其在烯烃、二烯烃、炔烃和硝基芳香化合物等物质的催化氢化中的应用情况。同时,对以树形分子为载体的催化剂、负载多元金属催化剂以及负载金型催化剂的研究及应用情况也进行了总结和评述。