CHARACTERIZATION OF A POTASSIUM-PROMOTED COBALT MOLYBDENUM ALUMINA WATER-GAS SHIFT CATALYST

A series of potassium-promoted CoMo/Al2O3 has been investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). CoMoO4 was found in the CoMo/Al2O3 catalyst by XRD and is destroyed by the presence of potassium. The reducibility of molybdenum is enhanced by potassium in the CoMoK/Al2O3 catalyst and is easier to reduce to Mo(IV) during sulfidation. In the oxidic state catalyst cobalt is increased on the surface by the addition of potassium. After sulfidation this phenomena disappeared, the distribution of cobalt remains at a constant level and is unaffected by the potassium content. The addition of potassium leads to a monotonical decrease of the molybdenum dispersion with the impregnating amount of potassium in the oxidic state catalyst but is more complicated after sulfidation. Potassium is well dispersed on the surface in both the oxidic and sulfided state. The activity in the water-gas shift reaction was correlated with the potassium content of CoMoK/Al2O3.

ROLE OF H2S IN THE REDUCTION OF MOO3/AL2O3

MoO3/Al2O3 is reduced at least partly by sulfur which is formed from H2S in sulfidation with H2S/N2 mixture. SO2 formation during TPD of MoO3/Al2O3 with presorbed H2S provides evidence for the explanation.

WATER-SOLUBLE AND AMPHIPHILIC POLYMERS .6. A STUDY ON THE SURFACE-COMPOSITION OF CAST FILMS OF PST/PMAA AND PEO-PST-PEO BLOCK POLYMERS BY XPS

Thin films of PSt/PMAA and PEO-PSt-PEO block polymers were deposited on a polystyrene substrate by solution adsorption (with or without solvent treatment), and the film surfaces were characterized by means of XPS. Direct solvent - casting of PEO-PSt-PEO from benzene solutions resulted in PSt-rich surfaces, whereas PMAA richer surfaces were obtained for PSt/PMAA films cast from DMF solutions. Moreover, solvent treatment after casting had profound effect on the film surface composition. Treatment with water markedly increased the surface concentration of polar PEO segments. In the case of PSt-PMAA block polymers, the PSt content on the surface increased in the order of water < ethanol < cyclohexane < petroleum ether, the last-named giving films with almost pure PSt surface. It is well worth noticing that the bulk composition had little to do with the surface composition for both PSt/PMAA and PEO-PSt-PEO block polymers within the composition range investigated when subsequent solvent treatment was applied.

STUDIES ON RADIATION EFFECTS OF PTFE .2. RADIATION-INDUCED STRUCTURAL-CHANGES AND THE TEMPERATURE EFFECT

In this work PTFE sheets irradiated with gamma-rays at 150-degrees-C and 200-degrees-C were studied using x-ray photoelectron spectroscopy (XPS). The main structural changes in PTFE due to radiation are the formation of CF3 and CF groups. An irradiation temperature dependence of the relative content of the three kinds of groups in irradiated PTFE was observed. The CF3 groups, especially when irradiation is carried out a lower temperatures, can defluorinate in the same manner as previosly reported for CF2 groups. The CF groups, on the other hand, are observed to increase with increasing irradiation dose and irradiation temperature; the latter was explained as due to an increase in branching structures.

XPS STUDY OF CORROSION BEHAVIOUR OF TITANIUM IN H2C2O4 SOLUTION

The corrosion behaviour of titanium substance and the XPS characterization of Ti surface in the H2C2O4 solution have been first studied by X-ray photoelectron spectroscopy, The experimental results show that there am mile Ti-2 and Ti2+ on sample surface in 10% H2C2O4 solution for two boars corrosion at 80 degrees C, but if corrosion is extended to 4 hones, the surface composition is mainly TiO2 with a small amount of Ti2+. This result corresponds to the structure of TiH1.642 composion in sample surface found by XRD analysis. Since bath TiO2 and the surface coating RuO2 are of Gald-Redstone structure, therefore electrode materials of Ti-Ru are stable in chemical industry.

Inhibition Effect of 2,3,5-Triphenyl-2H-tetrazolium Chloride and 2,4,6-Tri(2-pyridyl)-s-triazine on the Corrosion of Mild Steel in 1 mol/L HCl and Mechanism Study (II)

The inhibitory effect of 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and 2,4,6-tri(2-pyridyl)-s-triazine (TPT) molecules on the corrosion of mild steel in 1 mol/L HCl and microcosmic inhibitory mechanism were investigated by X-ray photoelectron spectroscopy and ellipsometry. XPS results showed that C Is and N Is peaks of TTC, C Is and N Is peaks of TPT and their integral areas were obtained, which suggested the layer of the inhibitors (TTC or TPT) should have effectively protected the mild steel surface from the corrosion; and the depression from the inhibitors for the corrosion of mild steel surface was studied using ellipsometry combined with potentiodynamic polarization and the phasic difference was gained, which displayed the inhibitory coverage of the inhibitors formed.

Characteristics of sulfide corrosion products on 316L stainless steel surfaces in the presence of sulfate-reducing bacteria

It has been found that microbial communities play a significant role in the corrosion process of steels exposed in aquatic and soil environments. Biomineralization influenced by microorganisms is believed to be responsible for the formation of corrosion products via complicated pathways of electron transfer between microbial cells and the metal. In this study, sulfide corrosion products were investigated for 316L stainless steel exposed to media with sulfate-reducing bacteria media for 7 weeks. The species of inorganic and organic sulfides in the passive film on the stainless steel were observed by epifluorescence microscope, environmental scanning electron microscope combined with energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The transformation from metal oxides to metal sulfides influenced by sulfate-reducing bacteria is emphasized in this paper. (c) 2005 Elsevier B.V. All rights reserved.

Effect of nano-TiO(2)on MP-25 resin

MP-25 resin is a chlorine-containing polymer widely used in coatings. The effects of two types of nano-TiO2 (P-25 and RM301 LP) on MP-25 were studied with saline immersion, UV irradiation, and electrochemical impedance spectroscopy. UV irradiation was evaluated in terms of gloss change and X-ray photoelectron spectroscopy (XPS). The results indicate that, compared to pigment R-930 TiO2, P-25 reduced the immersion resistance and accelerated UV aging of the MP-25 coating, whereas RM301 LP showed the opposite effects. XPS analysis showed that MP-25 resin degraded under UV irradiation via dechlorination and C-C bond breakage, similarly to poly(vinyl chloride), but RM301 LP could inhibit the aging of MP-25 to a certain extent. A skin effect of oxygen and chlorine was identified in MP-25 resin by XPS. RM301 LP could improve the impedance of the MP-25 coating because of its excellent fill capacity. Hence, rutile nano-TiO2 RM301 LP represents an excellent additive for MP-25 resin. (c) 2007 Wiley Periodicals, Inc.

Epoxidation of propylene on NaCl-modified silver catalysts with air as the oxidant

Propylene epoxidation by air was carried out on NaCl-modified silver (NaCl/Ag) catalysts, and the catalysts were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The effects of NaCl loadings, propylene to oxygen ratio, and the reaction time on the catalytic performance were investigated. It was found that the addition of NaCl to silver significantly increases the propylene oxide (PO) selectivity. The PO yield has a maximum when the NaCl loading is about 10 wt.%. Also 12.4% conversion of propylene and 31.6% selectivity to PO are obtained on the NaCl/Ag (10 wt.%) catalyst at 350 degreesC, space velocity 1.8 x 10(4) h(-1) and C3H6:O-2 = 1:2. XPS and XRD characterizations show that AgCl formed on the silver catalyst was favorable to propylene epoxidation. A compound with highly oxidized Ag ion was also found, which may be effective for the reaction. (C) 2002 Elsevier Science B.V. All rights reserved.

Coadsorption of nitric oxide and oxygen on the Ag(110) surface

The coadsorption of NO and O-2 on Ag(110) surface has been studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and in situ Raman spectroscopy. The existence of oxygen enhances the adsorption of NO by forming the NOx species, that is, NO2 and NO3, and the NO in turn as a promotor facilitates the cleavage of the dioxygen bond, forming the surface atomic oxygen species having the same spectral characteristics as those produced using oxygen at high pressure. The oxygen species generated by the interaction is composed of two parts. One is produced directly by the decomposition of surface NO-O-2 complex at ca 625 K, which raised an O 1s feature at 530.5 eV and is absent at ca 800 K, while the another with an O 1s binding energy of 529.2 eV emerges at higher temperatures and shows similar properties as the reported gamma-state oxygen which bound tightly on restructured silver surface. The exposure to NO and O-2 causes noticeable changes in the morphology of the Ag(110) surface and the flat terraces superseded by small (ca 0.1 mu m) pits, and particles with typical diameters of a few micrometres were formed at elevated temperatures. (C) 1999 Elsevier Science B.V. All rights reserved.

Structure and properties of samarium overlayer and Sm/Rh surface alloy on Rh(100)

The structure and properties of Sm overlayer and Sm/Rh surface alloy have been investigated with Auger electron spectroscopy (AES), low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption spectroscopy (TDS). The growth of Sm on Rh(100) at room temperature (RT) appears following the Stranski-Krastanov growth mode and only the trivalent state Sm is observed from XPS results. Thermal treatment of the Sm film at 900 K leads to the formation of ordered surface alloy which shows the c(5 root2 x root2)R45 degrees and c(2 x 2) LEED patterns. Annealing the Sm film at temperature above 400 K makes the binding energy (B.E.) of Sm 3d(5/2) shift to higher energy by 0.7 eV, which indicates charge transfer from Sm to Rh(100) substrate, causing the increase of CO desorption temperature.

Reversible regeneration of molybdenum carbonyl species on an alumina thin film

The thin alumina film-supported metallic molybdenum model catalyst was prepared by thermal decomposition of MO(CO)6, and CO chemisorption on the catalyst was investigated in-situ by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). The results showed that a molybdenum-carbonyl-like species was formed on the alumina surface at low temperature by high coordination of CO with the surface metallic molybdenum nanoparticles, indicating a reversible regeneration of molybdenum carbonyl on the alumina surface. CO chemisorption on the model catalyst surface caused the Mo 3d XPS peak to shift toward higher binding energy. The formed molybdenum carbonyl species appeared at about 240 K in the TDS. The supported metallic molybdenum nanoparticles were quite different from the bulk molybdenum in chemical properties, which indicated a prominent particle-size effect of the clusters.

Copper phthalocyanine on InSb(111)A?interface bonding, growth mode and energy band alignment

Copper phthalocyanine on InSb(111)A?interface bonding, growth mode and energy band alignment, D.A. Evans, H.J. Steiner, S. Evans, R. Middleton, T.S. Jones, S. Park, T.U. Kampen, D.R.T. Zahn, G. Cabailh and I.T. McGovern, J. Phys.: Condens. Matter, 15, S2729?S2740, (2003)

Multi-scale modelling of atomic layer deposition

High-permittivity ("high-k") dielectric materials are used in the transistor gate stack in integrated circuits. As the thickness of silicon oxide dielectric reduces below 2 nm with continued downscaling, the leakage current because of tunnelling increases, leading to high power consumption and reduced device reliability. Hence, research concentrates on finding materials with high dielectric constant that can be easily integrated into a manufacturing process and show the desired properties as a thin film. Atomic layer deposition (ALD) is used practically to deposit high-k materials like HfO2, ZrO2, and Al2O3 as gate oxides. ALD is a technique for producing conformal layers of material with nanometer-scale thickness, used commercially in non-planar electronics and increasingly in other areas of science and technology. ALD is a type of chemical vapor deposition that depends on self-limiting surface chemistry. In ALD, gaseous precursors are allowed individually into the reactor chamber in alternating pulses. Between each pulse, inert gas is admitted to prevent gas phase reactions. This thesis provides a profound understanding of the ALD of oxides such as HfO2, showing how the chemistry affects the properties of the deposited film. Using multi-scale modelling of ALD, the kinetics of reactions at the growing surface is connected to experimental data. In this thesis, we use density functional theory (DFT) method to simulate more realistic models for the growth of HfO2 from Hf(N(CH3)2)4/H2O and HfCl4/H2O and for Al2O3 from Al(CH3)3/H2O.Three major breakthroughs are discovered. First, a new reaction pathway, ’multiple proton diffusion’, is proposed for the growth of HfO2 from Hf(N(CH3)2)4/H2O.1 As a second major breakthrough, a ’cooperative’ action between adsorbed precursors is shown to play an important role in ALD. By this we mean that previously-inert fragments can become reactive once sufficient molecules adsorb in their neighbourhood during either precursor pulse. As a third breakthrough, the ALD of HfO2 from Hf(N(CH3)2)4 and H2O is implemented for the first time into 3D on-lattice kinetic Monte-Carlo (KMC).2 In this integrated approach (DFT+KMC), retaining the accuracy of the atomistic model in the higher-scale model leads to remarkable breakthroughs in our understanding. The resulting atomistic model allows direct comparison with experimental techniques such as X-ray photoelectron spectroscopy and quartz crystal microbalance.

Synthesis and characterization of oxide materials

Nanostructured materials are central to the evolution of future electronics and biomedical applications amongst other applications. This thesis is focused on developing novel methods to prepare a number of nanostructured metal oxide particles and films by a number of different routes. Part of the aim was to see how techniques used in nanoparticle science could be applied to thin film methods to develop functional surfaces. Wet-chemical methods were employed to synthesize and modify the metal oxide nanostructures (CeO2 and SiO2) and their structural properties were characterized through advanced X-ray diffraction, electron microscopy, photoelectron spectroscopy and other techniques. Whilst particulates have uses in many applications, their attachment to surfaces is of importance and this is frequently challenging. We examined the use of block copolymer methods to form very well defined metal oxide particulate-like structures on the surface of a number of substrates. Chapter 2 describes a robust method to synthesize various sized silica nanoparticles. As-synthesized silica nanoparticles were further functionalized with IR-820 and FITC dyes. The ability to create size controlled nanoparticles with associated (optical) functionality may have significant importance in bio-medical imaging. Thesis further describes how non-organic modified fluorescent particles might be prepared using inorganic oxides. A study of the concentrations and distributions of europium dopants within the CeO2 nanoparticles was undertaken and investigated by different microscopic and spectroscopic techniques. The luminescent properties were enhanced by doping and detailed explanations are reported. Additionally, the morphological and structural evolution and optical properties were correlated as a function of concentrations of europium doping as well as with further annealing. Further work using positron annihilation spectroscopy allowed the study of vacancy type defects formed due to europium doping in CeO2 crystallites and this was supported by complimentary UV-Vis spectra and XRD work. During the last few years the interest in mesoporous silica materials has increased due to their typical characteristics such as potential ultra-low dielectric constant materials, large surface area and pore volume, well-ordered and uniform pores with adjustable pores between 2 and 50 nm. A simple, generic and cost-effective route was used to demonstrate the synthesis of 2D mesoporous silica thin films over wafer scale dimensions in chapter 5. Lithographic resist and in situ hard mask block copolymer followed by ICP dry etching were used to fabricate mesoporous silica nanostructures. The width of mesoporous silica channels can be varied by using a variety of commercially available lithographic resists whereas depth of the mesoporous silica channels can be varied by altering the etch time. The crystal structure, morphology, pore arrangement, pore diameters, thickness of films and channels were determined by XRD, SEM, ellipsometry and the results reported. This project also extended work towards the study of the antimicrobial study of nanopatterned silver nanodot arrays formed using the block copolymer approach defined above. Silver nanodot arrays were successfully tested for antimicrobial activity over S. aureus and P. aeruginosa biofilms and results shows silver nanodots has good antimicrobial activity for both S. aureus and P. aeruginosa biofilms. Thus, these silver nanodot arrays shows a potential to be used as a substitute for the resolution of infection complications in many areas.