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通过快速扫描FT-IR光谱仪在氧化物纳米集群催化剂中可见光驱动水氧化时直接观察氧化物表面中间体
Narayanappa Sivasankar1, Walter W Weare, Heinz Frei
1Physical Biosciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA.
Journal of the American Chemical Society
|July 21, 2011
概括
研究人员使用氧化催化剂和可见光在水氧化过程中检测到表面氧化物中间体. 这一发现为分子层面的氧气进化机制提供了关键的见解.
科学领域:
- 催化剂是一种催化剂.
- 摄影化学的使用.
- 表面科学是一门学科.
背景情况:
- 水的氧化是人工光合作用和可再生能源生产的关键过程.
- 了解催化中间体对于设计高效的氧化水催化剂至关重要.
- 氧化纳米集群是氧化物进化反应的有希望的催化剂.
研究的目的:
- 在由氧化纳米集群催化的氧化水过程中检测和描述表面中间体.
- 通过使用先进的光谱技术,阐明分子水平上氧气进化的机制.
主要方法:
- 使用了一种[Ru(bpy) ((3))) ((2+) 可见光敏感器的脉冲激发.
- 采用快速扫描里埃变换红外光谱 (FT-IR) 在减弱总反射模式.
- 分析了表面中间体的振动模式,使用H(2) O,D(2) O和D(2)(18) O同位素.
主要成果:
- 通过在830厘米的OO振动模式观察,成功检测出表面氧化物中间体 (IrOOH).
- 通过同位素转移确认的光谱分配: (D) 的30厘米 (-1) 和氧-18 ((18) O) 的24-46厘米 (-1).
- 通过其激光脉冲响应证明了中间体的动力相关性.
结论:
- 本研究介绍了在氧化物演变中的表面中间体在氧化物多电子催化剂中的第一次直接观察.
- 这些发现为水氧化途径提供了关键的机械洞察力.
- 这项工作为合理设计更高效的电催化剂为水分裂铺平了道路.
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02:44Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide
Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.
02:50Catalysis
The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
02:04Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
01:46Oxidative Cleavage of Alkenes: Ozonolysis
In ozonolysis, ozone is used to cleave a carbon–carbon double bond to form aldehydes and ketones, or carboxylic acids, depending on the work-up.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
02:21Oxidation of Alkenes: Syn Dihydroxylation with Potassium Permanganate
Alkenes can be dihydroxylated using potassium permanganate. The method encompasses the reaction of an alkene with a cold, dilute solution of potassium permanganate under basic conditions to form a cis-diol along with a brown precipitate of manganese dioxide.
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.