柴油超深度加氢脱硫研究取得新进展 - 图文(5)

常低（<2%），这就使得表征分子筛中的杂原子变得极具挑战性。紫外拉曼光谱可以避开分子筛合成中中间物种产生荧光的干扰而增加灵敏度。更重要地是，利用紫外共振拉曼光谱，可以选择性的激发出杂原子分子筛中骨架杂原子的信息。这些优点为紫外共振拉曼光谱研究分子筛，特别是杂原子分子筛的合成机理提供了非常有利的条件。在本工作中，范峰滔等人利用原位共振拉曼技术结合非有机模板剂合成分子筛体系，研究了含铁分子筛的晶化机理。该工作不仅从分子水平上研究了分子筛从五、六元环碎片、四面体杂原子中心成核到最终形成骨架的过程，而且利用含铁分子筛样品对不同激发光源的吸收能力不同，选择性地研究了粒子内部以及表面不同的晶化过程，结合高分辨电镜技术明确地指出Fe-ZSM-5分子筛成核发生在凝胶粒子的中央，并且随着晶化时间的延长逐渐向外表面生长。

From molecular fragments to crystals: A UV Raman spectroscopic study on Fe-ZSM-5 synthesis mechanism

Fengtao Fan, Keju Sun, Zhaochi Feng, Haian Xia, Bo Han, Yuxiang Lian, Pinliang Ying, and Can Li*

Chem. Eur. J., Full paper. DOI: 10.1002/chem.200801916

Abstract：The entire sequence of crystallization events of Fe-ZSM-5 was monitored by UV Raman spectroscopy combined with HRTEM, UV-vis spectra, X-ray diffraction patterns and Periodic DFT calculations. Fe-ZSM-5 was synthesized using an organic-free method to avoid signal interference from the organic template in Raman spectra. The framework irons with the Resonance Raman bands at 516, 1115, and 1165 cm-1 and Raman band at 1016 cm-1 are detected for Fe-ZSM-5. In the early synthesis stage of Fe-ZSM-5, the precursor contains iron atoms in distorted tetrahedral coordination and five- and six-membered silicate rings. Nucleation via aggregation of the precursor species was monitored by UV Raman spectroscopy based on the Resonance Raman effect, and confirmed by Periodic DFT calculations. The unparalleled evolutions of the iron species on the surface and in the bulk phase are detected by UV Raman spectroscopy excited with 244 and 325 nm,

confirmed by HRTEM. It is found that the nucleation takes place first in the core of the amorphous particles, and the crystalline nuclei with Fe-ZSM-5 structure are formed in the core by consuming the amorphous shell. Finally the amorphous particles are completely transformed into Fe-ZSM-5 crystals.

Keywords：synthesis mechanism ? hydrothermal synthesis ? Fe-ZSM-5? zeolite ? UV Raman spectroscopy

最近，我组光催化分解硫化氢研究工作取得最新进展（Guijun Ma, Hongjian Yan, Jingying Shi, Xu Zong, Zhibing Lei, Can Li, 2008, Journal of Catalysis , Full paper, http://dx.doi.org/10.1016/j.jcat.2008.09.017 ）。

利用光催化技术分解H2S制氢不仅可以回收H2S中的氢，而且可以利用丰富、廉价、清洁的太阳能资源，实现将太阳能转化为氢能的目标。在以往的光催化分解H2S的研究中，大多采用间接的方法来制取氢气，即将H2S溶于NaOH等碱性水溶液中，生成的硫离子(S2-或HS-)作为牺牲试剂，在光催化剂及光照的作用下，

水溶液中的质子(H+)被还原产生氢气。由于水溶液中单一硫离子作为牺牲试剂时光催化产氢反应的稳定性比较低，往往加入另一种阴离子（如SO32-, H2PO2-, S2O32-）与硫离子共同作为牺牲试剂，以维持稳定的光催化产氢活性，在光催化产氢过程当中，硫离子最终被氧化为各种硫的含氧酸盐副产物，无法得到单质硫。该工作采用无水的二乙醇胺(DEA)为H2S的吸收剂及光催化反应溶液，以M/CdS作为光催化剂，实现了可见光及室温条件下即可将H2S完全分解为H2和S的目标，在波长为420 nm处的量子效率达到30％。

Abstract：The conversion of H2S into H2 and S (H2S → H2 + S) is beneficial for both environment and energy. Here we report that H2S can be splitted stoichiometrically into hydrogen and sulfur on CdS-based photocatalysts under visible light irradiation using ethanolamine as H2S solvent and reaction media at room temperature. Raman spectra show that the produced sulfur exists as S4 and S6 after photocatalytic reaction. The hydroxyls of the reaction media are found to be crucial for the hydrogen production and the rate determination step (RDS) of photocatalytic splitting H2S in diethanolamine is discussed. Electrochemical evaluation shows that the potential of H2S splitting in ethanolamine is greatly lowered and the photo-generated electrons could be fully used to reduce protons for hydrogen production. A free radical related one-electron electrochemical oxidation process on platinum electrode is suggested. This work demonstrates the possibility for the direct splitting H2S into S and H2 via photocatalysis.

Keywords：Cadmium sulfide; Ethanolamine; Polysulfide; Hydrogen production; Hydrogen sulfide conversion; Photocatalysis; Electrochemistry

2-2-

我组继在光催化剂表面异相结及其光催化性能的研究工作Angew. Chem. Int. Ed.（张静、李

灿等，2008，DOI: 0.1002/anie.200704788）取得重要进展的基础上，最近又在表面异质结光催化剂制备及其光催化制氢研究中取得重要进展，研究结果发表在J. Am. Chem. Soc.（宗旭、李灿等，2008，DOI: 10.1021/ja8007825），美国C&E NEWS就这一研究进展在Science & Technology Concentrates栏目中给予Highlight 。

光催化剂的设计合成是发展太阳能催化制氢的关键，而发展高而效廉价的实用光催化剂面临巨大的挑战。这项工作借鉴半导体异质结概念在纳米CdS表面上组装纳米MoS2，使CdS和MoS2在原子层次上形成异质结，使光生电子和空穴的分离效率大幅度提高，从而获得高活性光催化剂。在这项研究中发现MoS2/CdS的光催化产氢活性比单独的CdS催化剂高30倍以上，在相同的实验条件下MoS2/CdS比担载贵金属助剂Pt、Ru、Rh、Pd、Au的CdS的光催化产氢活性还要高。该工作不仅表明表面异质结的形成可促进光生电子－空穴的分离，显著提高光催化活性，而且还发现在光催化剂中用相对廉价的MoS2代替贵金属助催化剂的可能性。这项工作对发展太阳能高效光催化剂及其光催化制氢过程具有重要指导意义和潜在的应用价值。

Abstract: This communication presents our recent results that the activity of photocatalytic H2 production can be significantly enhanced when small amount of MoS2 is loaded on CdS as co-catalyst. The MoS2/CdS catalysts show high rate of H2 evolution from photocatalytic reforming of lactic acid under visible light irradiation. The rate of H2 evolution on CdS is increased by up to 36 times when loaded with only 0.2 wt% of MoS2, and the activity of MoS2/CdS is even higher than those of the CdS photocatalysts loaded with different noble metals, such as Pt, Ru, Rh, Pd and Au. The junction formed between MoS2 and CdS and the excellent H2 activation property of MoS2 are supposed to be responsible for the enhanced photocatalytic activity of MoS2/CdS. Keywords：photocatalyst ? hydrogen ? MoS2 ? heterogeneous junction

我组范峰滔等人关于“原位紫外拉曼光谱研究X型分子筛合成机理”的工作发表在 Chemistry - A European Journal （Published Online: Apr

21 2008）上。分子筛作为催化、吸附和离子交换材料已经在石油加工、石油化工、煤化工、精细化工和环境等领域中得到重要的应用。近些年来，分子筛材料的应用范围又扩展到了新型组装材料，生物芯片、生物传感器等各个方面。但目前许多分子筛的合成更多地是依据经验，因而分子筛生成过程与晶化机理的研究对分子筛的合成研究具有重要的科学意义。本研究利用紫外拉曼光谱结合专门为高温高压水热体系设计的原位拉曼光谱池首次实现了水热条件下分子筛结构的原位监测，通过跟踪X型分子筛的合成过程，考察了合成过程当中液相和固相组分的变化。在合成过程中，液相中存在大量的单态硅物种，这些单态硅物种在反应中富集到固相表面，与固相物种结合并参与了分子筛的合成。初始凝胶的固相含有大量的硅铝四员环物种，通过拉曼谱峰的演变结合DFT理论计算认为：这些四员环以及含有支链的四员环物种之间相互连接形成四六员环的结构单元从而搭建出X型分子筛骨架结构。

Abstract：The hydrothermal synthesis of Zeolite X was studied by in situ UV Raman spectroscopy for the first time. An in situ Raman cell was specially fabricated for investigating the species derived in both solid and liquid phase under high pressure at temperatures up to 250 ℃. Under hydrothermal synthesis condition, it was observed that the liquid phase is dominated by monomer silicate species, which are loosely bonded to the gel phase and involve in zeolite framework formation, and amorphous aluminosilicate species composed of predominately four-membered rings are formed in the solid phase in the early stage of nucleation. The characteristic Raman bands of four-membered rings species were also calculated with DFT. It is proposed that four-membered rings formed at

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