在绿色植物的放氧光合作用过程中,每个反应周期(即S态循环)都有两个底物水分子被氧化,释放出四个质子和四个电子,并最终释放一个氧气分子,这种化学反应机制维持着地球上的各种需氧生命活动。目前,人们已经清楚地知道,这个生物催化过程...在绿色植物的放氧光合作用过程中,每个反应周期(即S态循环)都有两个底物水分子被氧化,释放出四个质子和四个电子,并最终释放一个氧气分子,这种化学反应机制维持着地球上的各种需氧生命活动。目前,人们已经清楚地知道,这个生物催化过程是由光系统Ⅱ(photosystemⅡ,PSⅡ)中一个无机簇状结构(即锰簇Mn4O5Ca)催化完成的。然而,这两个底物水分子是在此反应同期的什么时候、什么地方、以什么方式结合到锰簇上的,目前仍旧是一个谜团。在探讨此问题的很多实验研究中,人们常用脉冲电子顺磁共振(electron paramagnetic resonance,EPR)波谱学方法,探测底物水分子在反应中间氧化态S2态锰簇中的结合方式和结合位点,即依据超精细耦合常数的大小来判断未成对电子与磁性核的距离。基于此前的实验数据和文献报道,EPR理论模拟的结果显示,中间S2态锰簇上仅仅可容纳一个可发生置换的底物水,并且已经发生完全去质子化。这个结合水可能就是研究人员使用时间分辨薄膜进样质谱(membrane-inlet mass spectrometry,MIMS)检测到的强磁性耦合氧。此结果排除了源自强磁性耦合14N信号的干扰。因此,理论和实验结果均说明,另一个底物水是在锰簇由S2态氧化到更高中间态S3态的过程中结合到锰簇上的,并最终参与了O2分子的形成。展开更多
Mixed Ga–Zn oxynitrides were synthesized using coprecipitation, wet-precipitation, and sol-id-solution methods. The oxynitrides were used as supports for Rh nanoparticle catalysts in photo-catalytic water splitting, ...Mixed Ga–Zn oxynitrides were synthesized using coprecipitation, wet-precipitation, and sol-id-solution methods. The oxynitrides were used as supports for Rh nanoparticle catalysts in photo-catalytic water splitting, CO oxidation, and H2 oxidation. Mixed Ga–Zn oxynitrides produced by wet precipitation and nitridation had good visible-light-absorption properties and high surface areas, so they were used to support uniformly sized poly(vinylpyrrolidone)-stabilized Rh nanoparticles. The nanoparticle size range was 2–9 nm. These catalysts had negligible activity in photocatalytic H2 production by water splitting with methanol as a sacrificial agent. Other mixed Ga–Zn oxynitrides were also inactive. A reference sample provided by Domen also showed very low activity. The in-fluence of particle size on Rh-catalyzed oxidation of CO and H2 was investigated. For CO oxidation, the activities of small particles were higher for particles with higher Rh oxidation degrees. The op-posite holds for H2 oxidation.展开更多
文摘在绿色植物的放氧光合作用过程中,每个反应周期(即S态循环)都有两个底物水分子被氧化,释放出四个质子和四个电子,并最终释放一个氧气分子,这种化学反应机制维持着地球上的各种需氧生命活动。目前,人们已经清楚地知道,这个生物催化过程是由光系统Ⅱ(photosystemⅡ,PSⅡ)中一个无机簇状结构(即锰簇Mn4O5Ca)催化完成的。然而,这两个底物水分子是在此反应同期的什么时候、什么地方、以什么方式结合到锰簇上的,目前仍旧是一个谜团。在探讨此问题的很多实验研究中,人们常用脉冲电子顺磁共振(electron paramagnetic resonance,EPR)波谱学方法,探测底物水分子在反应中间氧化态S2态锰簇中的结合方式和结合位点,即依据超精细耦合常数的大小来判断未成对电子与磁性核的距离。基于此前的实验数据和文献报道,EPR理论模拟的结果显示,中间S2态锰簇上仅仅可容纳一个可发生置换的底物水,并且已经发生完全去质子化。这个结合水可能就是研究人员使用时间分辨薄膜进样质谱(membrane-inlet mass spectrometry,MIMS)检测到的强磁性耦合氧。此结果排除了源自强磁性耦合14N信号的干扰。因此,理论和实验结果均说明,另一个底物水是在锰簇由S2态氧化到更高中间态S3态的过程中结合到锰簇上的,并最终参与了O2分子的形成。
基金supported by the National Basic Research Program of China (973 Program,2009CB220009)the National Natural Science Foundation of China (21106015,21120102036,and 20923006)+1 种基金the Research Fund for the Doctoral Program of Higher Education of China (20110041120005)the Swedish Energy Agency and K&A Wallenberg Foundation~~
基金the financial support by the Royal Netherlands Academy of Sciences and Arts and the Chinese Ministry of Science and Technology as part of the Program Strategic Scientific Alliances (PSA)supported by ESRF
文摘Mixed Ga–Zn oxynitrides were synthesized using coprecipitation, wet-precipitation, and sol-id-solution methods. The oxynitrides were used as supports for Rh nanoparticle catalysts in photo-catalytic water splitting, CO oxidation, and H2 oxidation. Mixed Ga–Zn oxynitrides produced by wet precipitation and nitridation had good visible-light-absorption properties and high surface areas, so they were used to support uniformly sized poly(vinylpyrrolidone)-stabilized Rh nanoparticles. The nanoparticle size range was 2–9 nm. These catalysts had negligible activity in photocatalytic H2 production by water splitting with methanol as a sacrificial agent. Other mixed Ga–Zn oxynitrides were also inactive. A reference sample provided by Domen also showed very low activity. The in-fluence of particle size on Rh-catalyzed oxidation of CO and H2 was investigated. For CO oxidation, the activities of small particles were higher for particles with higher Rh oxidation degrees. The op-posite holds for H2 oxidation.
