首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献,搜索用时 156 毫秒
1.
TiO2光催化反应机理及动力学研究进展   总被引:77,自引:0,他引:77  
唐玉朝  胡春  王怡中 《化学进展》2002,14(3):192-199
光催化处理环境污染物是基于催化反应过程中的一些自由基对污染物的氧化或还原作用,反应途径通常是HO*攻击或空穴直接攻击,对可见光敏感的化合物也可能通过激发态来分解.动力学的表述多数符合L-H模式,广泛研究了L-H模式下的吸附与催化活性的关系,对动力学的研究也是了解其反应机理的重要途径.  相似文献   

2.
运用程序电位阶跃方法,避免甲酸解离吸附的干扰,成功地研究了Pt(100)单晶电极上甲酸经活性中间体直接氧化至CO2的反应动力学.提出对电化学暂态实验数据进行积分变换求解动力学参数的方法,编制了相关的计算机软件,首次获得甲酸在Pt(100)单晶电极上直接氧化的反应动力学参数。结果给出在0.02V至0.15V电位区间,速率常数kf的对数随电极电位线性增长,kf从9.51×10-4上升到1.38×10-2cm·s-1.获得传递系数β=0.309,5×10-3mol·L-1HCOOH+0.5mol·L-1H2SO4溶液中甲酸的扩散系数D=1.80×10-5cm2.s-1.  相似文献   

3.
采用B3LYP和CCSD(T)方法对R-C≡P(R=-BH2, -CH3,-NH2, -OH)体系进行了理论研究.结果表明,含C≡P三键的异构体BH2-C≡P和CH3-C≡P在各自的体系中分别是热力学最稳定的结构.而在HO-C≡P和NH2-C≡P体系中,热力学最稳定的结构却是H-P=C=O和含C≡N三键的N≡C-PH2.动力学理论研究表明,没有相关实验研究的R-C≡P(R=-BH2, NH2)体系中共有5种异构体是动力学稳定的. 在HO-C≡P体系的2种动力学稳定的异构体中, H-P=C=O连接方式的异构体已被实验所证实,而另外一种HO-C≡P连接方式的异构体的动力学稳定性较高,实验中可以观察到.对于CH3C≡P体系,研究所预示的2种动力学稳定的异构体中CH3-C≡P已被实验证实,从理论上推测另一种动力学稳定性较高的异构体HC≡C-PH2在实验中也可以检测到.  相似文献   

4.
1-1PbCl2或任何有羟基的物种等。12PbCl2(s)+H2Y2→PbY2-+2H+2Cl或其他相似答案1-3pH的缓冲剂1-4金属指示剂15Pb2+H2Y2→PbY2-+2H+或其他类似答案,但因pH为6,EDTA必须写成H2Y2-Pb2+0(黄)→Pb02+(红)或者其他妻似答案。·16络合锡卜7SnY+nF-+ZH”卡SnF”a。+Hoyz-l-8HzY‘+PbllO‘”今PbY‘十二O(黄)+ZH”或类似答案19H-+F卡HF或其他类似答案1-10n(剩余量EDTA)二n(标准Ph‘“)=(24.05。L)(0.009970mol/L)/(1000。L/L)=2.398x10-‘molr;(原始EDTA),(25.…  相似文献   

5.
 采用TiCl4气固相同晶取代法制得的Ti-ZSM-5作催化剂,对H2O2氧化苯乙烯反应的宏观动力学进行了研究,考察了催化剂、苯乙烯和H2O2用量及反应温度对苯乙烯氧化反应速率的影响.结果表明,催化剂Ti-ZSM-5和底物苯乙烯对苯乙烯氧化反应速率的贡献均为一级,而H2O2为1/2级;苯乙烯氧化反应的表观活化能Ea=48.14kJ/mol.当以丙酮为溶剂,在n(PhCH∶CH2)/n(H2O2)=7.91,催化剂用量为20g/L,反应温度为343K的条件下,反应360min时,苯乙醛选择性和H2O2利用率分别可达91.9%和88.6%.  相似文献   

6.
用电化学质谱(EMS)和动力学模型分析等方法研究了次亚磷酸根在镍电极上的电化学氧化机理和动力学.研究表明,次亚磷酸根的电化学氧化是通过从P-H键脱离一个原子H,形成磷中心自由基(PHO2-•),而磷中心自由基(PHO2-•)进一步进行电化学反应形成最终产物亚磷酸。利用该模型,推导出相关动力学方程并通过与实验数据拟合获得动力学参数.结果表明,该模型能很好地模拟次亚磷酸根在镍电极上的电化学氧化过程.  相似文献   

7.
研究了N-(O,O-二异丙基)磷酰化-L-(或D-)丝氨酸和L-(或D-)组氨酸在水溶液中的反应及其与L-(或D-)组氨酸甲酯在DMSO中的反应,用SDS作对离子试剂,采用离子对反相高效液相色谱方法及反应产物进行分析。结果表明,所有反应体系中均有丝组二肽生成,而L-L和D-D型丝组二肽的生成量约是L-D和D-L型产物的4倍。  相似文献   

8.
Cth和NO都具有未配对电子,它们之间的反应属于自由基之间的反应.该反应可能经历的通道很多,因此研究这个反应,具有重要的学术价值.另一方面,烃类在燃烧过程中可热解成CH、CW、C:H或CIn等自由基碎片’‘’,亚甲基CW与NO的反应是重要的基元反应之一.除此之外NO是重要的环境污染物,在大气中低浓度NO能够存在较长时间”’,可继续与CHZ自由基发生反应.因此就环境保护方面来说,CIn自由基与NO反应的研究也有较大的现实意义.虽然以前很多人都通过实验测出过CW与NO总反应的速车常数’‘,’-’‘,但关于反应动力学方面的…  相似文献   

9.
溴酸钾氧化偶氮砷Ⅲ动力学光度法测定钯   总被引:2,自引:0,他引:2  
根据在稀H2SO4介质中,痕量钯(Ⅱ)对溴酸钾氧化偶氮胂Ⅲ褪色反应的显著的催化作用,建立了测定痕量钯的催化动力学光度法。方法检出限为0.13μg/L,测定范围为0-8.0μg/L。可用于矿石中痕量钯的测定。  相似文献   

10.
茂金属催化乙烯聚合反应动力学   总被引:1,自引:1,他引:0  
以茂金属化合物[(CH3)2C(η-C5H3)(η-C9H6)]ZrCl2为主催化剂,甲基铝氧烷MAO为助催化剂催化乙烯聚合,对不同的反应条件下(如温度,铝锆摩尔比)聚合反应的动力学进行了研究,并根据此聚合反应体系的动力学特点及考虑到活性中心的再活化,在分析和研究以往的动力学模型的基础上,对烯烃均相聚合动力学反应作了一些假定,建立了动力学模型,用模型对实验数据进行了拟合,结果表明与实验数据相吻合,可以认为,在该聚合反应体系中,确实存在铝氧烷的再活化作用,根据模拟拟合得到了聚合反应的动力学参数。  相似文献   

11.
The in situ open‐circuit voltages (Voc) and the in situ photoconductivities have been measured to study electron behavior in photocatalysis and its effect on the photocatalytic oxidation of methanol. It was observed that electron injection to the conduction band (CB) of TiO2 under light illumination during photocatalysis includes two sources: from the valence band (VB) of TiO2 and from the methanol molecule. The electron injection from methanol to TiO2 is slower than that directly from the VB, which indicates that the adsorption mode of methanol on the TiO2 surface can change between dark and illuminated states. The electron injection from methanol to the CB of TiO2 leads to the upshift of the Fermi level of electrons in TiO2, which is the thermodynamic driving force of photocatalytic oxidation. It was also found that the charge state of nano‐TiO2 is continuously changing during photocatalysis as electrons are injected from methanol to TiO2. Combined with the apparent Langmuir–Hinshelwood kinetic model, the relation between photocatalytic kinetics and electrons in the TiO2 CB was developed and verified experimentally. The photocatalytic rate constant is the variation of the Fermi level with time, based on which a new method was developed to calculate the photocatalytic kinetic rate constant by monitoring the change of Voc with time during photocatalysis.  相似文献   

12.
Visible‐light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross‐coupling reactions, α‐amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible‐light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible‐light‐absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo‐ or metal catalysis.  相似文献   

13.
Semiconductor photocatalysis is a trustworthy approach to harvest clean solar light for energy conversions, while state‐of‐the‐art catalytic efficiencies are unsatisfactory because of the finite light response and/or recombination of robust charge carriers. Along with the development of modern material characterization techniques and electronic‐structure computations, oxygen vacancies (OVs) on the surface of real photocatalysts, even in infinitesimal concentration, are found to play a more decisive role in determining the kinetics, energetics, and mechanisms of photocatalytic reactions. This Review endeavors to clarify the inherent functionality of OVs in photocatalysis at the surface molecular level using 2D BiOCl as the platform. Structure sensitivity of OVs on reactivity and selectivity of photocatalytic reactions is intensely discussed via confining OVs onto prototypical BiOCl surfaces of different structures. The critical understanding of OVs chemistry can help consolidate and advance the fundamental theories of photocatalysis, and also offer new perspectives and guidelines for the rational design of catalysts with satisfactory performance.  相似文献   

14.
Plasmon‐mediated carrier transfer (PMCT) at metal–semiconductor heterojunctions has been extensively exploited to drive photochemical reactions, offering intriguing opportunities for solar photocatalysis. However, to date, most studies have been conducted using noble metals. Inexpensive materials capable of generating and transferring hot carriers for photocatalysis via PMCT have been rarely explored. Here, we demonstrate that the plasmon excitation of nickel induces the transfer of both hot electrons and holes from Ni to TiO2 in a rationally designed Ni–TiO2 heterostructure. Furthermore, it is discovered that the transferred hot electrons either occupy oxygen vacancies (VO) or produce Ti3+ on TiO2, while the transferred hot holes are located on surface oxygens at TiO2. Moreover, the transferred hot electrons are identified to play a primary role in driving the degradation of methylene blue (MB). Taken together, our results validate Ni as a promising low‐cost plasmonic material for prompting visible‐light photochemical reactions.  相似文献   

15.
Green and efficient procedures are essential for the chemoselective hydrogenation of functionalized nitroarenes to form industrially important anilines. Herein, it is shown that visible‐light‐driven, chemoselective hydrogenation of functionalized nitroarenes with groups sensitive to forming anilines can be achieved in good to excellent yields (82–100 %) in water under relatively mild conditions and catalyzed by low‐cost and recyclable graphitic carbon nitride. The process is also applicable to gram‐scale reaction, with a yield of aniline of 86 %. A study of the mechanism reveals that visible‐light‐induced electrons are responsible for the hydrogenation reactions, and thermal energy can also promote the photocatalytic activity. A study of the kinetics shows that this reaction possibly occurs through one‐step hydrogenation or stepwise condensation routes. A wide range of applications can be expected for this green, efficient, and highly selective photocatalysis system in reduction reactions for the synthesis of fine chemicals.  相似文献   

16.
Visible light-driven photocatalysis of Au25-modified TiO2 was investigated. It induces oxidation of phenol derivates and ferrocyanide and reduction of Ag+, Cu2+ and dissolved oxygen. Thermodynamically uphill reactions such as oxidation of phenol accompanied by reduction of Cu2+ are also driven. The photocatalysis, which is based on the excitation of Au25, is observed even under 860 nm light.  相似文献   

17.
Epoxidation of olefins with H2O2 is one of the most important reactions in organic synthesis. We found that anatase TiO2 can be a good catalyst for the epoxidation of cyclooctene with H2O2 at room temperature. However, the catalyst deactivated quickly in the presence of excess amount of H2O2 because of the formation of inactive side‐on Ti‐η2‐peroxide species on the surface of TiO2, the presence of which was confirmed by isotope‐labelled resonance UV Raman spectroscopy and kinetics studies. Interestingly, the epoxidation reaction could be dramatically accelerated under irradiation of UV light with λ≥350 nm. This phenomenon is attributed to the photo‐assisted removal of the inactive peroxide species, through which the active sites on the surface of anatase TiO2 are regenerated and the catalytic epoxidation of cyclooctene with H2O2 is resumed. This finding provides an alternative for sustained epoxidation reactions on TiO2 at room temperature. Moreover, it also has significant implications on the deactivation pathway and possible solutions in Ti‐based heterogeneous catalysis or photocatalysis.  相似文献   

18.
Recently, the process by which energy is transferred from photoexcited semiconductor nanocrystals, called quantum dots (QDs), to other semiconductors has attracted much attention and has potential application in solar energy conversion (i.e., QD‐sensitized solar cells). Sensitization of wide band gap polyoxometalates (POMs) to visible light by using CuInS2 QDs dispersed in an organic solution is demonstrated herein. Photoluminescence quenching and lifetime studies revealed efficient electron transfer from the CuInS2 QDs to POMs, such as SiW12O40 and W10O32, that were hybridized with a cationic surfactant. CuInS2 QDs function as an antenna that absorbs visible light and supplies electrons to the POMs to enable certain photocatalytic reactions, including noble‐metal‐ion reduction. The photoenergy storage capabilities of the QD‐POM system, in which electrons photogenerated in QDs by visible‐light excitation are trapped and accommodated by POMs to form reduced POM, are also demonstrated. Electrons stored in the POM can be later discharged through reductive reactions, such as oxygen reduction, in the dark.  相似文献   

19.
Recent advances in direct‐use plasmonic‐metal nanoparticles (NPs) as photocatalysts to drive organic synthesis reactions under visible‐light irradiation have attracted great interest. Plasmonic‐metal NPs are characterized by their strong interaction with visible light through excitation of the localized surface plasmon resonance (LSPR). Herein, we review recent developments in direct photocatalysis using plasmonic‐metal NPs and their applications. We focus on the role played by the LSPR of the metal NPs in catalyzing organic transformations and, more broadly, the role that light irradiation plays in catalyzing the reactions. Through this, the reaction mechanisms that these light‐excited energetic electrons promote will be highlighted. This review will be of particular interest to researchers who are designing and fabricating new plasmonic‐metal NP photocatalysts by identifying important reaction mechanisms that occur through light irradiation.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号