Interaction of Ag and O on W(1 1 0) studied by scanning tunneling microscopy

The structural changes of Ag films on W(1 1 0) upon coadsorption of oxygen have been studied by scanning tunneling microscopy. The exposure of one monolayer Ag to oxygen leads to a phase separation into an Ag bilayer and patches of O-covered W(1 1 0). The effective Ag island thickness increases linearly with oxygen exposure. For Ag submonolayer-islands the onset of the bilayer formation is delayed, the induction period increases with the available free W area. We conclude that the steps of the transport process are (1) dissociation of oxygen on W and on the Ag islands, (2) site exchange of atomic oxygen with Ag atoms predominantly at the island edges - while on W(1 1 0) the oxygen is immobile, (3) diffusion of the displaced Ag atoms to the island edges where they are incorporated into the monolayer and (4) initiation of Ag bilayer formation, once the W(1 1 0) is saturated with O. This indicates an unexpected activity of the Ag monolayer on W(1 1 0) towards oxygen dissociation. In case of a reversed deposition sequence, where submonolayer quantities of Ag are adsorbed on an oxygen-precovered W(1 1 0) surface, growth of Ag clusters is observed. The distribution of cluster size and cluster height depends critically on the spatial order within the predeposited oxygen overlayer - it is obvious that the oxygen overlayer on the W surface acts as a structured template for preferential Ag nucleation.     

Direct reaction of adsorbed molecular oxygen with hydrazine on a clean Pt(111) surface

The oxidation of hydrazine on the clean Pt(111) surface has been investigated by temperature-programmed reaction spectroscopy (TPRS) in the temperature range 130–800 K. Direct reaction of molecular oxygen is observed on the Pt(111) surface for the first time, as indicated by the desorption of nitrogen beginning at 130 K with a maximum rate at 145 K, below the molecular oxygen dissociation temperature. Direct reaction of hydrazine with adsorbed molecular oxygen results in the formation of water and nitrogen. With excess hydrazine, all surface oxygen is reacted, forming water. When only adsorbed atomic oxygen is present, the low-temperature nitrogen yield decreases by a factor of 3 and the peak nitrogen desorption temperature increases to 170 K. No high-temperature (450–650 K) nitrogen desorption characteristic of nitrogen atom recombination is seen, indicating that during oxidation the nitrogen-nitrogen bond in hydrazine remains intact, as observed previously for hydrazine decomposition on the Pt(111) surface and hydrazine oxidation on rhodium. Two water desorption peaks are observed, characteristic of desorption-limited (175 K) and reaction-limited (200 K) water evolution from the Pt(111) surface. For low coverages of hydrazine, only the reaction-limited water desorption is observed, previously attributed to water formed from adsorbed hydroxyl groups. When excess hydrazine is adsorbed, the usual hydrazine decomposition products, H₂, N₂ and NH₃, are also observed. No nitrogen oxide species (NO, NO₂ and N₂O) were observed in these experiments, even when excess oxygen was available on the surface.     

硫脲在HNO3介质中共吸附行为的喇曼光谱研究

用常规Raman谱、电化学现场表面增强喇曼散射光谱(SERS)和时间分辨SERS光谱(TRSERS)研究了硫脲(TU)在HNO₃介质中与NO-3的共吸附行为.实验结果表明,NO₃^-离子能被TU诱导共吸附在其质子化氨基上;TU以S端按σ配位键方式化学吸附在银电极表面.在较正电位区间(≥-0.6V),TU垂直吸附,电位负移(≤-0.8V),TU由垂直逐渐转变为倾斜甚至平躺吸附;在较负的电位下(≤-0.8V),TU在HNO₃介质中比在HClO₄中更稳定,甚至在-2.0V的电位下亦能检测到TU的SERS信号.     

用于电化学界面研究的共焦显微拉曼光谱技术(英文)

系统地介绍了将共焦显微拉曼光谱系统用于电化学界面研究的方法 ,包括铂电极的粗糙和电化学拉曼电解池的设计 .进行了铂上氢、氧和氯共吸附的拉曼光谱研究 .通过对甲醇氧化过程的现场跟踪 ,提出检测界面区溶液浓度变化和计算溶液 pH值的方法 .实验表明拉曼光谱技术可作为研究实际应用体系的重要工具 .     

Site-blocking effects of preadsorbed H on Pt(1 1 1) probed by 1,3-butadiene adsorption and reaction

The influence of hydrogen coadsorption on hydrocarbon chemistry on transition metal surfaces is a key aspect to an improved understanding of catalytic selective hydrogenation. We have investigated the effects of H preadsorption on adsorption and reaction of 1,3-butadiene (H₂CCHCHCH₂, C₄H₆) on Pt(1 1 1) surfaces by using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). Preadsorbed hydrogen adatoms decrease the amount of 1,3-butadiene chemisorbed on the surface and chemisorption is completely blocked by the hydrogen monolayer (saturation) coverage (θ_H = 0.92 ML). No hydrogenation products of reactions between coadsorbed H adatoms and 1,3-butadiene were observed to desorb in TPD experiments over the range of θ_H investigated (θ_H = 0.6-0.9 ML). This is in strong contrast to the copious evolution of ethane (CH₃CH₃, C₂H₆) from coadsorbed hydrogen and ethylene (CH₂CH₂, C₂H₄) on Pt(1 1 1). Hydrogen adatoms effectively (in a 1:1 stoichiometry) remove sites from interaction with chemisorbed 1,3-butadiene, but do not affect adjacent sites. The adsorption energy of coadsorbed 1,3-butadiene is not affected by the presence of hydrogen on Pt(1 1 1). The chemisorbed 1,3-butadiene on hydrogen preadsorbed Pt(1 1 1) completely dehydrogenates to H₂ and surface carbon upon heating without any molecular desorption detected, which is identical to that observed on clean Pt(1 1 1). In addition to revealing aspects of site blocking that should have broad implications for hydrogen coadsorption with hydrocarbon molecules on transition metal surfaces in general, these results also provide additional basic information on the surface science of selective catalytic hydrogenation of butadiene in butadiene-butene mixtures.     

Coadsorption of Cs with O and CO on Ru(0001): relation between structural and electronic properties

We have studied structural, electronic and energetical aspects of ordered overlayers which were prepared by depositing Cs and CO on the (2×2)−O-precovered Ru(0001) surface. This ternary system may serve as a model system to study the Cs promoted CO oxidation reaction over Ru(0001). The electronic properties of the Cs subsystem, in particular the delocalized character of the Cs–6 s state, are only little affected by the (2×2)−O overlayer, while the addition of CO leads to a demetallization of the Cs overlayer. The ternary system reveals two metastable configurations (besides a stable one) which are produced at low sample temperatures. In the first one, Cs and CO have changed their adsorption sites if compared to the stable ternary (2×2)−O+Cs+CO phase, i.e. Cs sits in hcp and CO in on-top position. Our studies emphasize the importance of the threefold hollow position of CO to strengthen the back bonding of CO. The surface structure of the second metastable (ternary) arrangement is still elusive.     

Rh2CO2/Al2O3上H2吸附及CO和H2共吸附

CO加氢反应机理一直是许多化学工作者感兴趣的课题．Rh催化剂因其优良的性能而被用于 CO加氢机理研     

Synergistic co-removal of zinc(II) and cefazolin by a Fe/amine-modified chitosan composite

A novel Fe/amine modified chitosan composite (Fe/N-CS) was facilely synthesized and showed great potential in the efficient co-removal of heavy metal ions and antibiotics from wastewater.     

SERS谱峰对电极电位阶跃的不同响应速率的证据

八十年代以来,人们除继续研究表面增强拉曼散射(SERS)效应的复杂机理和发现有关新体系外,逐渐将注意力集中在将SERS 技术应用于生物、分析和电化学研究,以获得固/液体系的界面结构和吸