The interaction of CO2 and CO with Fe‐doped SrTiO3(100) surfaces

The interaction of CO₂ and CO with 0.013 at.% Fe‐doped SrTiO₃(100) was investigated in situ with Metastable Induced Electron Spectroscopy (MIES) and XPS at room temperature. To clear up the influence of surface defects, cleaned and sputtered SrTiO₃ surfaces were investigated. Sputtering results in the breaking of Ti? O bonds in the surface and the formation of oxygen‐related defects as well as reduced titanium on the surface. Cleaned SrTiO₃ surfaces do neither interact with CO₂ nor with CO. Sputtered surfaces show a CO formation during CO₂ exposure and—to a lesser extent—during CO exposure. The CO groups can be detected very well with MIES because of its extreme surface sensitivity. With XPS, the characteristic carbonate peak shift of the C 1s orbitals can be detected. Copyright © 2011 John Wiley & Sons, Ltd.     

The interaction of H2O with Fe‐doped SrTiO3(100) surfaces

The interaction of H₂O with 0.013 at.% Fe‐doped SrTiO₃(100) was investigated in situ with Metastable Induced Electron Spectroscopy (MIES), Ultraviolet Photoelectron Spectroscopy (UPS) and XPS at room temperature. Low Energy Electron Diffraction (LEED) was applied to gather information about the surface termination. To clear up the influence of surface defects, untreated and weakly sputtered SrTiO₃ surfaces were investigated. The sputtering results in the formation of oxygen‐related defects in the top surface layer. The interaction of untreated SrTiO₃ surfaces with H₂O is only weak. Small amounts of OH groups can be identified only with MIES due to its extreme surface sensitivity. Sputtered surfaces show a larger OH formation. Nondissociative H₂O adsorption is not observed. We therefore conclude that the exposure of H₂O to SrTiO₃(100) results in the dissociation near surface defects only, resulting in the formation of surface hydroxyl groups. Copyright © 2010 John Wiley & Sons, Ltd.     

XPS,UPS, and STM studies of nanostructured CuO films

A Cu₁O_1.7 oxide film containing a large amout of superstoichiometric oxygen was obtained by low-temperature oxidation of metallic copper in the oxygen plasma. An STM study of the film structure showed that ～10 nm planar copper oxide nanocrystallites with particles packed parallel to the starting metal surface. In an XPS study, the spectral characteristics of the Cu2p and O1s lines indicated that particles with a CuO lattice formed (E _bnd(Cu2p _3/2) = 933.3 eV and a shake-up satellite, E _bnd(O1s) = 529.3 eV). The additional superstoichiometric oxygen is localized at the sites of contact of nanoparticles in the interunit space and is characterized by a state with the binding energy E _bnd(O1s) = 531.2 eV. Due to the formation of a nanostructure in the films during low-temperature plasma oxidation, the resulting copper oxide has a much lower thermal stability than crystalline oxide CuO.     

Interaction of cobalt with ceria thin films and its influence on supported Au nanoparticles

The interaction of Co with ceria thin films and its influence on the sintering behavior of Au were investigated by scanning tunneling microscopy(STM), synchrotron radiation photoemission spectroscopy(SRPES) and X-ray photoelectron spectroscopy(XPS). The strong interaction between Co and CeO_2(111) leads to oxidation of Co to Co~(2+) at 300 K, accompanied by partial reduction of ceria surface at low Co coverages. Subsequent Co deposition results in an increasing fraction of metallic Co. Annealing to high temperatures induces Co~(2+)ions diffuse into the CeO_2 film, while the small metallic Co islands agglomerate into larger ones. The bimetallic Co–Au particles were prepared by deposition of Au on the existing Co particles on ceria surfaces. The sintering behavior of Co–Au bimetallic surfaces is found to be highly determined by the stoichiometry of ceria supports. The addition of Co to the Au/CeO_2 surface suppresses the sintering of Au particles at high temperatures in comparison with that of pure Au particles. However, Au particles are less stable on the Co/CeO_(1.82) layer than on CeO_(1.82) surface.     

H2-induced CO adsorption and dissociation over Co/Al2O3 catalyst

The activation of adsorbed CO is an important step in CO hydrogenation. The results from TPSR of pre-adsorbed CO with H2 and syngas suggested that the presence of H2 increased the amount of CO adsorption and accelerated CO dissocia-tion. The H2 was adsorbed first, and activated to form H* over metal sites, then reacted with carbonaceous species. The oxygen species for CO2 formation in the presence of hydrogen was mostly OH*, which reacted with adsorbed CO subsequently via CO*+OH* → CO2*+H*; however, the direct CO dissociation was not excluded in CO hydrogenation. The dissociation of C-O bond in the presence of H2 proceeded by a concerted mechanism, which assisted the Boudourd reaction of adsorbed CO onthe surface via CO*+2H* → CH*+OH*. The formation of the surface species (CH) from adsorbed CO proceeded as indicated with the participation of surface hydrogen, was favored in the initial step of the Fischer-Tropsch synthesis.     

Ultrathin Co3O4 Layers Realizing Optimized CO2 Electroreduction to Formate

Electroreduction of CO₂ into hydrocarbons could contribute to alleviating energy crisis and global warming. However, conventional electrocatalysts usually suffer from low energetic efficiency and poor durability. Herein, atomic layers for transition‐metal oxides are proposed to address these problems through offering an ultralarge fraction of active sites, high electronic conductivity, and superior structural stability. As a prototype, 1.72 and 3.51 nm thick Co₃O₄ layers were synthesized through a fast‐heating strategy. The atomic thickness endowed Co₃O₄ with abundant active sites, ensuring a large CO₂ adsorption amount. The increased and more dispersed charge density near Fermi level allowed for enhanced electronic conductivity. The 1.72 nm thick Co₃O₄ layers showed over 1.5 and 20 times higher electrocatalytic activity than 3.51 nm thick Co₃O₄ layers and bulk counterpart, respectively. Also, 1.72 nm thick Co₃O₄ layers showed formate Faradaic efficiency of over 60 % in 20 h.     

MIES and UPS(HeI) studies on reduced TiO2(110)

We have studied reduced TiO₂(110) surfaces by combining metastable impact electron spectroscopy (MIES) and UPS(HeI). The reduced Ti species were preparation‐induced: their number density was modified either by adsorption of K atoms or by a combined annealing/oxygen exposure procedure. The emission from the bandgap state (binding energy 0.9 eV), caused by reduced Ti³⁺ 3d species, was monitored. Bandgap emission is seen clearly with UPS(HeI) and thus can be used to monitor the number density of the near‐surface reduced species. A corresponding spectral structure cannot be seen with MIES. We propose that the excess charge density introduced either by preparation‐induced oxygen vacancies or by K adsorption is delocalized over several surface and subsurface Ti sites; this, together with the partial shielding of the reduced Ti species, prevents detection of the reduced Ti species with MIES. The re‐oxidation and restructuring of the reduced TiO₂(110) surface, caused by simultaneous oxygen exposure and annealing, was studied at temperatures between 400 and 770 K, again by recording the Ti³⁺ 3d emission (0.9 eV bandgap state) with UPS(HeI). The surface can be completely re‐oxidized by oxygen exposure at any selected annealing temperature in the range given above. Morphology changes, leading to a partially reduced surface, take place when the re‐oxidized surface is further annealed at T > 600 K under reducing conditions. The results give support to the assumption that the re‐oxidation is caused by the growth of additional titania whereby the Ti stems from the bulk and the oxygen originates from the gas. The restructuring of the re‐oxidized surface upon annealing under reducing conditions appears to be due to diffusion of Ti interstitials to the surface. Copyright © 2004 John Wiley & Sons, Ltd.     

Lithium adsorption on TiO2: studies with electron spectroscopies (MIES and UPS)

The adsorption of lithium atoms on rutile TiO₂(110) single crystals was studied with metastable‐induced electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS(HeI)) between 130 K and room temperature. Some auxiliary measurements on W(110) required for data interpretation are also reported. At 130 K ionic adsorption at titania prevails up to 0.3 monolayer equivalents (MLE) as judged from the weak Li(2s) emission in MIES for these exposures. The reduction of the Ti⁴⁺ cation is manifested by the growth of an occupied bandgap state in UPS: the alkali s‐electron is transferred to a near‐surface cation, thereby reducing it to Ti³⁺ 3d. The transfer of the s‐electron is responsible for the observed work function decrease up to ～0.5 MLE coverage. From the analysis of the UPS Ti³⁺ 3d signal, as well as from the Li(2s) emission, it is concluded that the degree of ionicity of the adsorbed Li decreases from 100% at 0.3 MLE to 40% at 0.7 MLE. Above 0.5 MLE the MIES spectra are dominated by an Li(2s)‐induced peak indicating the presence of Li with an at least partially filled 2s orbital. At temperatures above 160 K this peak is almost absent. Excluding Li desorption at these temperatures, we suggest that Li moves into or below the rutile TiO₂(110) surface above 160 K. Lithium insertion into the surface and intercalation are discussed. Copyright © 2004 John Wiley & Sons, Ltd.     

Reactions of CoS1.023 and Co3O4 with air and air/SO2 mixtures

It was reported in literature, that CoS_1+y oxidizes to CoO only, although it appears from Co-S-O predominance phase diagrams, that CoSO₄ is stable phase at partial pressures of SO₂ typical for sulfides oxidation. The experiments with CoS_1.023 oxidation with the air and the air/SO₂ gas mixture described in this paper, reveal that CoSO₄ phase is a product of such oxidation. However, the quantity of CoSO₄ is only of 1.4% of total cobalt content in the sample oxidized with the air and of 5.6-10.8% for oxidation with the air/SO₂ gas mixture. It is probably due to CoO layer, formed on CoS_1.023 grain's core, which results in hindering of oxidation after several minutes during the process. This revised version was published online in July 2006 with corrections to the Cover Date.     

铝表面自组装端羟基聚酯胺膜的XPS和STM表征

制备了端羟基聚酯胺(HTP)在铝基片上的自组装膜并进行了XPS和STM表征,确认了HTP在铝基片上的吸附组装;由XPS的吸附时间扫描,自组装单分子膜(SAMs)随浸泡时间的延长而增厚,在2 h后达到平衡。由HTP在铝基片的STM三维图可以看到HTP自组装膜以团块形式组成,其间包含孔洞缺陷。提出了铝基片上HTP–SAMs的多羟基结构与膜上孔洞的共同作用是提高环氧类涂层附着力的主要原因。     

Study of the electronic and atomic structure of thermally treated SrTiO3(110) surfaces

The electronic structure of heated SrTiO₃(110) surfaces was investigated with metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy (He(I)). Scanning tunnelling microscopy and atomic force microscopy (AFM) were used to study the topology of the surface. The crystals were heated up to 1000°C under reducing conditions in ultrahigh vacuum or under oxidizing conditions in synthetic air for 1 h, respectively. Under both conditions microfacetting of the surface is observed. The experimental results are compared with ab initio Hartree–Fock calculations, also presented here, carried out for both ideal and reconstructed SrTiO₃(110) surfaces. The results give direct evidence for Ti termination of the faceted TiO₂ rows. Copyright © 2003 John Wiley & Sons, Ltd.     

制备方法及焙烧温度对Co3O4/CeO2催化剂上CO低温氧化反应的影响

 分别采用沉淀氧化法、均匀沉淀法及络合燃烧法制备了Co3O4/CeO2复合氧化物催化剂,并在干燥及湿气条件下进行了CO氧化反应. 结果表明,采用沉淀氧化法经538 K焙烧制得的Co3O4/CeO2催化剂具有优异的CO低温氧化活性和较高的抗湿性能. 在196 K条件下,该催化剂上CO氧化的转化率为99%, 并且可连续保持400 min以上; 当温度上升到298 K时,经过 2400 min反应后, CO的转化率仍可达到94%; 当反应气中含3.1%湿气,温度为383 K时,经过2400 min反应后, CO的转化率仍保持在79%. 实验表明, Co3O4/CeO2催化剂的制备方法及焙烧温度对Co3O4与CeO2之间的相互作用有显著的影响,进而影响催化剂催化CO低温氧化的活性.     

H2-induced CO adsorption and dissociation over Co/Al2O3 catalyst

The activation of adsorbed CO is an important step in CO hydrogenation. The results from TPSR of pre-adsorbed CO with H2 and syngas suggested that the presence of H2 increased the amount of CO adsorption and accelerated CO dissociation. The H2 was adsorbed first, and activated to form H＊ over metal sites, then reacted with carbonaceous species. The oxygen species for CO2 formation in the presence of hydrogen was mostly OH^＊, which reacted with adsorbed CO subsequently via CO^＊＋OH^＊ → CO2^＊＋H^＊; however, the direct CO dissociation was not excluded in CO hydrogenation. The dissociation of C-O bond in the presence of H2 proceeded by a concerted mechanism, which assisted the Boudourd reaction of adsorbed CO on the surface via CO^＊＋2H^＊ → CH^＊＋OH^＊. The formation of the surface species （CH） from adsorbed CO proceeded as indicated with the participation of surface hydrogen, was favored in the initial step of the Fischer-Tropsch synthesis.     

O_2和CO在Co_2B_2/TiO_2和Co_2B_2Pt/TiO_2表面吸附的密度泛函研究

 采用密度泛函理论探讨了 TiO2 表面负载 Co2B2 和 Co2B2Pt 合金簇可能的负载构型. 结果表明, Co2B2 和 Co2B2Pt 合金簇倾向于以两个 Co 的形式负载在两个氧上. 态密度分析发现, 负载后, Co2B2 合金簇中部分 Co 原子和 B 原子成键加强, Co2B2Pt 合金簇中 Pt 原子和 B 原子成键也加强, 形成新的轨道. CO 和 O2 在 Co2B2/TiO2 和 Co2B2Pt/TiO2 表面吸附的结果表明, Co2B2Pt/TiO2 催化氧化 CO 性能的提高是由于 Pt 原子提高了 Co2B2 合金簇吸附 CO 和 O2 的能力.     

镨掺杂Bi2Sr3Co2O9+δ电子结构的XPS研究

研究了Pr掺杂Bi2Sr3Co2O9+δ体系的X射线光电子能谱,发现随着体系中Pr掺杂量的增大,内层电子结合能有缓慢增大的趋势,但掺杂量达到0.6时,测得的电子结合能减少0.4 eV左右,与分析材料中费米能级变化引起的结合能变化趋势相反.考虑到掺杂量达到0.6时,材料发生金属-绝缘体转变,所得到的表观结合能减少可能是绝缘体样品相对于样品底座存在正的电势差所引起的.     

Effects of pretreatment and reduction on the Co/Al2O3 catalyst for CO hydrogenation

The purpose of this study was to investigate the effect of preadsorbed CO at different temperatures, calcination temperatures, the combined influence of reduction temperature and time, and pretreatment using hydrogen or syngas as reduction agents on the F-T synthesis （FTS） activity and selectivity of Co/Al2O3 catalyst. The reactivity of the carbon species at higher preadsorption temperature with H2 in TPSR decreased, whereas the carbon-containing species showed higher reactivity over Co/Al2O3 catalyst with low calcination temperature. This agreed well with the order of catalytic activity for F-T synthesis on this catalyst. The catalytic activity of the catalyst varied with reduction temperature and time remarkably. CODEX optimization gave an optimum reduction temperature of 756 K and reduction time of 6.2 h and estimated C5＋ yield perfectly. The pretreatment of Co/Al2O3 catalyst with different reduction agents （hydrogen or syngas） showed important influences on the catalytic performance. A high CO conversion and C5＋ yield were obtained on the catalyst reduced by hydrogen, whereas methane selectivity on the catalyst reduced by syngas was much higher than that on the catalyst reduced by hydrogen.     

介孔CeO2负载的Co3O4催化剂催化富氢气体中的CO优先氧化反应

采用溶胶-凝胶法制备出介孔氧化铈(meso-CeO2)及其负载的氧化钴(Co3O4/meso-CeO2)催化剂,并将其应用于富氢气体中CO的优先氧化反应.通过N2物理吸附及X射线衍射表征考察了meso-CeO2和Co3O4/meso-CeO2的结构性质.活性评价结果表明,在高空速下,Co3O4/meso-CeO2催化剂上的CO优先氧化性能很好,但水和CO2对CO的氧化有一定的负作用.Co3O4/meso-CeO2催化剂的CO完全氧化温度窗口远大于沉淀法制备CeO2负载的氧化钴催化剂.     

桥联双核配合物[(DPC)2Co2(H2O)5]·2H2O的合成与晶体结构

The new complex formulated [(DPC)₂Co₂(H₂O)₅]·2H₂O (HDPC^- is pyridine-2,6-dicarboxylate) has been synthesized and the crystal structure was determined by X-ray diffraction. The crystal structure of the complex belongs to monoclinic system with space group P2₁/c, a=0.83850(10) nm, b=2.7386(4) nm, c=0.9610(2) nm, β=98.280 (10) °, V=2.1838(6) nm³, Z=4, D_c=1.746 g·cm^-3, μ=1.597 mm^-1. In the crystal the two Co²⁺ are in distorted octahedrons. The part of [Co(DPC)₂] possess an approximate D_2d symmetry, while the part of [OCo₍₂₎(OH₂)₅] has an approximate C₂ symmetry.     

Low-temperature formation and characterization of Cu2O nanoparticles in the binary gold alloys

Thermal analyses, using differential scanning calorimetry (DSC) and dilatometry, reveal an important anomaly at low temperature for Au-25 wt.% Cu composition after homogenization at 700°C during 2 hours under vacuum followed by heating up to 160°C before water quenching. This anomaly has been already observed and not explained. Surface characterization, using scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning tunneling microscopy (STM), exhibits a specific topography, consisting of a nanostructured surface. The precipitates of nanostructured particles are homogeneously scattered all over the surface for this 18-carat gold alloy. Moreover, X-ray photoelectron spectroscopy (XPS) shows that the composition of the observed particles corresponds to cuprous oxide phase (Cu₂O). The formation of such material can be explained by the diffusion of copper atoms from the lattice to the surface at 160°C. Pulsed radio-frequency glow discharge optical emission spectroscopy (RF GD-OES) further proves the proposed Cu₂O formation through a diffusion process. The appearance of such cuprous oxide nanoparticles on the Au-Cu alloy surface explains the low-temperature DSC and dilatometry anomaly and affects directly the surface electrical resistance at low temperature. These results might open a large gate for new ideas to investigate in catalytic, electronic, and antimicrobial activities.     

A Novel 3D Extended Network Cobalt Paradodecatungstate:Synthesis,Characterization and Crystal Structure of [Co(H2O)5]2[Co(H2O)4]3[H2W12O42]·11H2O

A cobalt paradodecatungstate [Co(H2O)5]2[Co(H2O)4]3[H2W12O42]·11H2O has been successfully synthesized and structurally characterized by X-ray crystallography. Structure analysis indicates that the title compound is of monoclinic, space group P21/n, with a = 13.449(3), b =19.585(4), c = 13.990(3) (A),β = 113.79(3)°, V = 3371.8(12) (A)3, Z= 2, R= 0.0519 and wR= 0.1242.The title compound exhibits a novel 3D extended network structure constructed by interconnecting the paradodecatungstate polyanion [H2W12O42]10- clusters and cobalt11 coordination ions.