1,333 Matching Results

Search Results

Advanced search parameters have been applied.

Investigation on Durability and Reactivity of Promising Metal Oxide Sorbents During Sulfidation and Regeneration

Description: Research activities and efforts of this research project were concentrated on formulating various metal oxide sorbents with various additives under various formulation conditions, conducting experiments on initial reactivity of formulated sorbents with hydrogen sulfide, and testing hardness of formulated sorbents. Experiments on reactivity of formulated metal oxide sorbents with wet hydrogen sulfide contained in a simulated coal gas mixture were carried out for 120 seconds at 550 o C (see Table 1) to evaluate reactivity of formulated sorbents with hydrogen sulfide. Hardness of formulated sorbents was evaluated in addition to testing their reactivity with hydrogen sulfide. A typical simulated coal gas mixture consists of 9107-ppm hydrogen sulfide (0.005 g; 1 wt %), 0.085-g water (15.84 wt %), 0.0029-g hydrogen (0.58 wt %), and 0.4046-g nitrogen (81.34 wt%).
Date: May 1, 1997
Creator: Kwon, K. C.
Partner: UNT Libraries Government Documents Department

Co-adsorption studies of hydrogen with nitrogen in zeolites

Description: The use of co-adsorption studies of N{sub 2} with H{sub 2} makes it possible to obtain information about adsorption of N{sub 2} by monitoring changes in the rotational spectrum of the co-adsorbed H{sub 2} molecules. The authors present such results on N{sub 2}/H{sub 2} in Na-13X. The authors have demonstrated that inelastic neutron scattering studies of H{sub 2} co-adsorbed with other molecules can be used as an effective probe of their adsorption sites and interactions with zeolite hosts. Simulation studies are clearly required for extracting the wealth of detail which is evident in these data.
Date: August 1998
Creator: Eckert, J.; Trouw, F. R. & McMenomy, M.
Partner: UNT Libraries Government Documents Department

Nitrogen Removal From Low Quality Natural Gas

Description: Natural gas provides more than one-fifth of all the primary energy used in the United States. It is especially important in the residential sector, where it supplies nearly half of all the energy consumed in U.S. homes. However, significant quantities of natural gas cannot be produced economically because its quality is too low to enter the pipeline transportation system without some type of processing, other than dehydration, to remove the undesired gas fraction. Such low-quality natural gas (LQNG) contains significant concentration or quantities of gas other than methane. These non- hydrocarbons are predominantly nitrogen, carbon dioxide, and hydrogen sulfide, but may also include other gaseous components. The nitrogen concentrations usually exceeds 4%. Nitrogen rejection is presently an expensive operation which can present uneconomic scenarios in the potential development of natural gas fields containing high nitrogen concentrations. The most reliable and widely used process for nitrogen rejection from natural gas consists of liquefying the feed stream using temperatures in the order of - 300{degrees}F and separating the nitrogen via fractionation. In order to reduce the gas temperature to this level, the gas is compressed, cooled by mullet-stream heat exchangers, and expanded to low pressure. Significant energy for compression and expensive materials of construction are required. Water and carbon dioxide concentrations must be reduced to levels required to prevent freezing. SRI`s proposed research involves screening new nitrogen selective absorbents and developing a more cost effective nitrogen removal process from natural gas using those compounds. The long-term objective of this project is to determine the technical and economical feasibility of a N{sub 2}2 removal concept based on complexation of molecular N{sub 2} with novel complexing agents. Successful development of a selective, reversible, and stable reagent with an appropriate combination of capacity and N{sub 2} absorption/desorption characteristics will allow selective separation of N{sub 2} ...
Date: October 1, 1997
Creator: Alvarado, D.B.; Asaro, M.F.; Bomben, J.L.; Damle, A.S. & Bhown, A.S.
Partner: UNT Libraries Government Documents Department

Materials and Component Development for Advanced Turbine Systems

Description: In order to meet the 2010-2020 DOE Fossil Energy goals for Advanced Power Systems, future oxy-fuel and hydrogen-fired turbines will need to be operated at higher temperatures for extended periods of time, in environments that contain substantially higher moisture concentrations in comparison to current commercial natural gas-fired turbines. Development of modified or advanced material systems, combined with aerothermal concepts are currently being addressed in order to achieve successful operation of these land-based engines. To support the advanced turbine technology development, the National Energy Technology Laboratory (NETL) has initiated a research program effort in collaboration with the University of Pittsburgh (UPitt), and West Virginia University (WVU), working in conjunction with commercial material and coating suppliers as Howmet International and Coatings for Industry (CFI), and test facilities as Westinghouse Plasma Corporation (WPC) and Praxair, to develop advanced material and aerothermal technologies for use in future oxy-fuel and hydrogen-fired turbine applications. Our program efforts and recent results are presented.
Date: October 1, 2008
Creator: Alvin, M.A.; Pettit, F.; Meier, G.; Yanar, N.; Chyu, M.; Mazzotta, D. et al.
Partner: UNT Libraries Government Documents Department

Literature study of metallic ternary and quanternary hydrides

Description: Metallic hydrides are being considered as an attractive solution to storage problems involved in using hydrogen as an alternative fuel. In this application, the unclassified literature was surveyed to find metallic ternary hydride systems of the type MM'H/sub x/; M is a transition element, a member of the rare earth element series, or a member of the actinide element series, and M' is a transition element. Reported quaternary hydrides of the same metallic element series were also reviewed. The hydride-forming systems found and some of their most interesting properties are summarized. Recent advances in the understanding of the absorption characteristics and the stability of these hydride materials are reviewed. (auth)
Date: September 19, 1975
Creator: Newkirk, H.W.
Partner: UNT Libraries Government Documents Department

A local view of bonding and diffusion at metal surfaces

Description: First-principles density functional calculations and corresponding experimental results underline the importance of basic chemical concepts, such as coordination, valence saturation and promotion-hybridization energetics, in understanding bonding and diffusion of atoms at and on metal surfaces. Several examples are reviewed, including outer-layer relaxations of clean hcp(0001) surfaces, liquid-metal-embrittlement energetics, separation energies of metal-adatom dimers, concerted substitutional self-diffusion on fcc(001) surfaces, and adsorption and diffusion barrier sites for adatoms near steps.
Date: September 1, 1996
Creator: Feibelman, P.J.
Partner: UNT Libraries Government Documents Department

Structure sensitive adsorption of hydrogen on ruthenium and ruthenium-silver catalysts supported on silica

Description: Supported metal catalysts typically consist of particles with sizes less than 10 nm, and because of the small crystallite size, low coordination number sites (edges and corners) represent a significant fraction of all surface sites. Furthermore, it has been demonstrated that adsorption rates can be much greater at these low coordination sites than on basal plane sites. What has not been generally appreciated, however, is that preferential adsorption at edge and corner sites may explain the mechanism by which a promoter, or the addition of a second metal to form a bimetallic, can alter the selectivity and rate of reaction. For example, the measurements of hydrogen adsorption onto supported Ru-Ag catalysts show marked decreases in the amount of hydrogen adsorbed relative to the amount adsorbed on Ru catalysts. Although it is known that Ag does not dissociatively adsorb hydrogen, this decrease cannot be explained by a simple one-to-one site blocking mechanism unless Ag preferentially populates edges and corners, thereby reducing the number of Ru edge sites. Indeed, Monte Carlo simulations of Ru-Group IB metal catalysts predict that Group IB metal atoms preferentially populate corner and edge sites of ruthenium crystals. This evidence, taken together, suggests that adsorption occurs preferentially at Ru corner and edge sites, which act as portals onto basal planes. A model based on this portal theory for hydrogen adsorption onto supported ruthenium bimetallic catalysts has been developed using a rate equation approach. Specifically, the model accounts for the following features: (1) preferential adsorption through portals, (2) basal plane site-energy multiplicity, and (3) hydrogen spillover onto the support. A comparison of model predictions with experiment is presented for different concentration of Ag in Ru-Ag catalysts. The portal model of hydrogen adsorption can explain the observed decreased in the amount of hydrogen adsorbed on Ru-Ag catalysts. The model can ...
Date: February 12, 1999
Creator: Kumar, N.
Partner: UNT Libraries Government Documents Department

Applications of SXPS for studying surface structure, reaction mechanisms and kinetics

Description: Soft x-ray photoelectron spectroscopy (SXPS) from the S 2p core level has been used to study adsorbate induced reconstruction, identify reaction intermediates and study reaction kinetics on the Ni(111) surface. The S 2p binding energy is affected by the nature of the surface adsorption site. It has been determined from the number of S 2p states and their relative binding energies that adsorbed S induces a reconstruction of the Ni(111) surface and that the S adsorbs in fourfold sites on terraces and in troughs. S 2p SXPS has also been used to identify adsorbed species during the thermal decomposition of methanethiol on Ni(111). CH{sub 3}SH adsorbs as CH{sub 3}S{minus} at low temperatures. Above 200 K, the CH{sub 3}S{minus} changes adsorption site and the C-S bond begins to cleave. The relative concentrations of CH{sub 3}S{minus} in the two different sites and of atomic S have been monitored as a function of temperature and initial coverage. As a result of the sensitivity and resolution available in SXPS, reaction rates and kinetic parameters have been obtained for the decomposition of benzenethiol on Ni(111) by monitoring the changes in the surface composition continuously as a function of temperature and time.
Date: December 31, 1994
Creator: Mullins, D. R.; Huntley, D. R. & Overbury, S. H.
Partner: UNT Libraries Government Documents Department

Cesium/oxide interactions for ultrathin films on {alpha}-Al{sub 2}O{sub 3}(0001) and {alpha}-Al{sub 2}O{sub 3}(1{bar 1}02)

Description: The interaction of cesium at the (0001) and (1{bar 1}02) surfaces of sapphire has been investigated using a variety of surface analytical techniques. Reflection mass spectrometric measurements yield initial Cs adsorption probabilities of 0.9 and 0.85 for the unreconstructed (0001) and (1{bar 1}02) surfaces, respectively. The adsorption probability decreases dramatically for these surfaces at critical Cs coverages of 2.O {times} 10{sup 14} and 3.4 {times} 10{sup 14} atoms/cm{sup 2}, respectively. Thermally induced reconstruction of the (0001) surface to form an oxygen deficient surface results in a decrease in the initial probability and capacity for Cs adsorption. Low energy electron diffraction (LEED) demonstrates that an intermediate, mixed domain surface yields an initial adsorption probability of 0.5 while a ({radical}31 {times} {radical}31) R {plus_minus} 9{degree} reconstructed surface yields a value of 0.27. Thermal desorption mass spectrometry (TDMS) shows that surface reconstruction eliminates the high binding energy states of Cs (2.7 eV/atom), consistent with the observed changes in adsorption probability. In contrast, reconstruction of the (1{bar 1}02) surface produces only minor changes in Cs adsorption. X-ray photoelectron spectroscopy (XPS) indicates that no formal reductive/oxidative chemistry takes place at the interface. We interpret the facile adsorption and strong binding of Cs on sapphire to result from Cs interacting with coordinatively unsaturated oxygen.
Date: March 1, 1995
Creator: Zavadil, K.R. & Ing, J.L.
Partner: UNT Libraries Government Documents Department

Lateral interaction energy derived from Frumkin isotherm for c(2 x 2) Br/Ag(100)

Description: The structure of the bromide adlayer on Ag(100) and the adsorption isotherm have been determined by using in situ surface x-ray scattering techniques and chronocoulometry. Bromide adsorbed on Ag(100) forms a fourfold-hollow-site lattice gas and the adsorption saturates at 1/2 monolayer in a c(2 x 2) structure. The Frumkin isotherm has been employed to fit the experimentally obtained isotherm. Using the experimentally determined electrosorption valency, the lateral interaction energy of 220 meV/atom at full coverage is obtained.
Date: October 1997
Creator: Wang, J. X.; Ocko, B. M. & Wandlowski, T.
Partner: UNT Libraries Government Documents Department

Development and application of thin-layer spectroelectrochemical techniques for the study of organosulfur monolayers adsorbed at gold

Description: A main research interest is the characterization of monolayers formed by the spontaneous adsorption of organosulfur compounds at gold. This dissertation describes the development and application of long optical pathlength thin-layer spectroelectrochemistry in an attempt to address key issues regarding the reactivity of surface-immobilized molecules. The first section of this introductory chapter briefly describes the general approach to the preparation and characterization of these films. The last section provides an overview of the main principles and advantages of thin-layer spectroelectrochemistry for studying surface-adsorbed species. The body of this dissertation is divided into four chapters. Chapter 2 consists of a paper describing the design, construction, and characterization of a cuvette-based LOPTLC. Chapter 3 is a paper which examines the reductive desorption process using thin-layer spectroelectrochemistry to monitor and identify the desorption product. Chapter 4 is a paper describing the characterization of monolayers functionalized with a catechol terminal group which serves as a redox transformable coordination site for metal ion binding. Chapter 5 discusses the application of thin-layer spectroelectrochemistry to acid-base reactivity studies of surface-immobilized molecules. The final section provides some general conclusions and a prospectus for future studies. These chapters have been processed separately for inclusion on the data base. This report contains the introduction, references, and general conclusions. 78 refs.
Date: October 8, 1997
Creator: Simmons, N.
Partner: UNT Libraries Government Documents Department

Spectroscopy at metal cluster surfaces. Final report, September 15, 1993--September 14, 1996

Description: The focus of this research program is the study of gas phase metal clusters to evaluate their potential as models for the fundamental interactions present in catalysis. To do this, the authors characterize the chemical bonding present between the component atoms in metal clusters as well as the bonding exhibited by {open_quotes}physisorption{close_quotes} on metal atom or metal cluster surfaces. Electronic spectra, vibrational frequencies and bond dissociation energies are measured for both neutral and ionized clusters with a variety of laser/mass spectrometry techniques. The authors are particularly interested in bimetallic cluster systems, and how their properties compare to those of corresponding pure metal clusters.
Date: June 1, 1998
Creator: Duncan, M.A.
Partner: UNT Libraries Government Documents Department

Nature, strength, and consequences of indirect adsorbate interactions on metals

Description: Atoms and molecules adsorbed on metals affect each other even over considerable distances. In a tour-de-force of density-functional methods, the authors establish the nature and strength of such indirect interactions, and explain for what adsorbate systems they can critically affect important materials properties. These perceptions are verified in kinetic Monte Carlo simulations of epitaxial growth, and help rationalize a cascade of recent experimental reports on anomalously low diffusion prefactors. The authors focus their study on two metal systems: Al/Al(111) and Cu/Cu(111).
Date: February 14, 2000
Partner: UNT Libraries Government Documents Department

Electrochemical and scanning probe microscopic characterization of spontaneously adsorbed organothiolate monolayers at gold

Description: This dissertation presented several results which add to the general knowledge base regarding organothiolates monolayer spontaneously adsorbed at gold films. Common to the body of this work is the use of voltammetric reductive resorption and variants of scanning probe microscopy to gain insight into the nature of the monolayer formation process as well as the resulting interface. The most significant result from this work is the success of using friction force microscopy to discriminate the end group orientation of monolayer chemisorbed at smooth gold surfaces with micrometer resolution (Chapter 4). The ability to detect the differences in the orientational disposition is demonstrated by the use PDMS polymer stamp to microcontact print an adlayer of n-alkanethiolate of length n in a predefine pattern onto a gold surface, followed by the solution deposition of a n-alkanethiol of n {+-} 1 to fill in the areas on the gold surface intentionally not coated by the stamping process. These two-component monolayers can be discriminated by using friction force microscopy which detects differences in friction contributed by the differences in the orientation of the terminal groups at surfaces. This success has recently led to the detection of the orientation differences at nanometer scale. Although the substrates examined in this work consisted entirely of smooth gold films, the same test can be performed on other smooth substrates and monolayer materials.
Date: December 10, 1999
Creator: Wong, Sze-Shun Season
Partner: UNT Libraries Government Documents Department

Dynamics of intermediate-length alkane films absorbed on graphite

Description: The dynamics of flexible chain molecules near a solid interface is of fundamental interest in polymer science. This paper makes a preliminary report on a quasielastic neutron scattering study of the dynamics of monolayer films of C{sub 24}H{sub 66} adsorbed on graphite. Quasielastic scattering was observed at temperatures as low as {approximately}180 K, well below the monolayer melting temperature of 340 K. Preliminary analysis of the data indicates that at 230 K the entire molecule executes a rolling motion about its long axis while the terminal methyl groups exhibit relatively rapid reorientation.
Date: January 28, 2000
Creator: Herwig, K. W.; Fuhrmann, D.; Criswell, L.; Taub, H.; Hansen, F. Y.; Dimeo, R. et al.
Partner: UNT Libraries Government Documents Department

Probing the electrical double-layer structure at the rutile-water interface with x-ray standing waves.

Description: We demonstrate that the X-ray standing wave (XSW) technique is a powerful probe of the electrical double-layer (EDL) structure. Measurements were made of Sr adsorption at the rutile (110)-water interface from aqueous solutions. Our results show that Bragg XSW, using small-period standing waves generated by Bragg diffraction from the substrate, precisely probes the location of ions within the condensed layer, and the in situ partitioning of ions between the condensed and diffuse layers. Such measurements can provide important constraints for the development and verification of theoretical models that describe ion adsorption at the solid-water interface.
Date: November 28, 2000
Creator: Fenter, P.; Cheng, L.; Rihs, S.; Machesky, M.; Bedzyk, M. J. & Sturchio, N. C.
Partner: UNT Libraries Government Documents Department

Equilibrium binding studies of mono, di and triisocyanide ligands on Au powder surfaces

Description: The author`s group has previously shown that isocyanides are readily adsorbed from solutions to Au powder and bind to the Au surface in an end-on fashion through the terminal carbon. Later work demonstrated that the equilibrium constants for the reversible adsorption of electronically inequivalent isocyanides could be obtained using the Langmuir isotherm technique. This dissertation describes two projects completed which complement the initial findings of this group. Initially, several alkylisocyanides were synthesized to examine the effect of tail length on Au powder adsorption. It was observed that the length of the alkyl chain affected not only the Au surface binding affinity, but also the rate of surface saturation and saturation coverage values. Direct competition studies were also studied using a {sup 13}C-labeled isocyanide. These studies demonstrated the stabilization afforded by substrate-substrate packing forces in SAM`s formed by the longer chain isocyanides. In a second study, di and triisocyanides were synthesized to determine the effect that the length of the connecting link and the number of isocyanide groups (as points of attachment) have on Au adsorption stability. The work in this area describes the binding modes, relative binding affinities and surface coverage values for a series of flexible alkyl and xylyldiisocyanides on Au powder surfaces. This report contains only the introductory material, and general summary. Two chapters have been processed separately. 56 refs.
Date: October 8, 1997
Creator: Ontko, A.
Partner: UNT Libraries Government Documents Department

Cu interactions with {alpha}-Al{sub 2}O{sub 3}(0001): Effects of surface hydroxyl groups vs. dehydroxylation by Ar ion sputtering

Description: XPS studies and first principles calculations compare Cu adsorption on heavily hydroxylated sapphire (0001) with a dehydroxylated surface produced by Ar{sup +} sputtering followed by annealing in O{sub 2}. Annealing a cleaned sapphire sample with an O{sub 2} partial pressure of {approximately}5 x 10{sup {minus}6} Torr removes most contaminants, but leaves a surface with {approximately}0.4ML carbon and {approximately}0.4ML OH. Subsequent light (6 min.) Ar ion sputtering at 1 KeV reduces the carbon to undetectable levels but does not dehydroxylate the surface. Further sputtering at higher Ar ion excitation energies (>2 KeV) partially dehydroxylates the surface, while 5 KeV Ar ion sputtering creates oxygen vacancies in the surface region. Further annealing in O{sub 2} repairs the oxygen vacancies in the top layers but those beneath the surface remain. Deposition of Cu on the hydroxylated surface at 300 K results in a maximum Cu(I) coverage of {approximately}0.35 ML, in agreement with theoretical predictions.
Date: February 8, 2000
Partner: UNT Libraries Government Documents Department