A review of the selective reduction of NOx, with hydrocarbons under lean-burn conditions with non-zeolitic oxide and platinum group metal catalysts

Research on the selective reduction of NOx with hydrocarbons under lean-burn conditions using non-zeolitic oxides and platinum group metal (PGM) catalysts has been critically reviewed. Alumina and silver-promoted alumina catalysts have been described in detail with particular emphasis on an analysis of the various reaction mechanisms that have been put forward in the literature. The influence of the nature of the reducing agent, and the preparation and structure of the catalysts have also been discussed and rationalised for several other oxide systems. It is concluded for non-zeolitic oxides that species that are strongly adsorbed on the surface, such as nitrates/nitrites and acetates, could be key intermediates in the formation of various reduced and oxidised species of nitrogen, the further reaction of which leads eventually to the formation of molecular nitrogen. For the platinum group metal catalysts, the different mechanisms that have been proposed in the literature have been critically assessed. It is concluded that although there is indirect, mainly spectroscopic, evidence for various reaction intermediates on the catalyst surface, it is difficult to confirm that any of these are involved in a critical mechanistic step because of a lack of a direct quantitative correlation between infrared and kinetic measurements. A simple mechanism which involves the dissociation of NO on a reduced metal surface to give N(ads) and O(ads), with subsequent desorption of N-2 and N2O and removal of O(ads) by the reductant can explain many of the results with the platinum group metal catalysts, although an additional contribution from organo-nitro-type species may contribute to the overall NOx reduction activity with these catalysts.

Enhancing the Efficiency of Slit-Coupling to Surface-Plasmon Polariton via Dispersion Engineering

We describe a simple method for enhancing the efficiency of coupling from a free-space transverse-magnetic (TM) plane-wave mode into a surface-plasmon-polariton (SPP) mode. The coupling structure consists a metal film with a dielectric-filled slit and a planar, dielectric layer on the slit-exit side of the metal film. By varying the dielectric layer thickness, the wavevector of the SPP mode on the metal surface can be tuned to match the wavevector magnitude of the modes emanating from the slit exit, enabling high-efficiency radiation coupling into the SPP mode at the slit exit. An optimal dielectric layer thickness of approximately 100 nm yields a visible-frequency SPP coupling efficiency approximately 4 times greater than the SPP coupling efficiency without the dielectric layer. Commensurate coupling enhancement is observed spanning the free-space wavelength range 400 nm < or = lambda(0) < or = 700 nm. We map the dependence of the SPP coupling efficiency on the slit width, the dielectric-layer thickness, and the incident wavelength to fully characterize this SPP coupling methodology

Density functional theory study of the interaction between CO and on a Pt surface:CO/Pt(111), O/Pt(111), and CO/O/Pt(111)

Ab initio total energy calculations within the Density Functional Theory framework were carried out for Pt(111), Pt(111)-p(2x2)-CO, Pt(111)-p(2x2)-O, and Pt(111)-p(2x2)-(CO+O) to provide an insight into the interaction between CO and O on metal surfaces, an important issue in CO oxidation, and also in promotion and poisoning effects of catalysis. The geometrical structures of these systems were optimized with respect to the total energy, the results of which agree with existing experimental values very well. It is found that (i) the local structures of Pt(111)-p(2x2)-(CO+O), such as the bond lengths of C-O, C-Pt, and O-Pt (chemisorbed O atom with Pt), are almost the same as that in Pt(111)-p(2x2)-CO and Pt(111)-p(2x2)-O, respectively, (ii) the total valence charge density distributions in Pt(111)-p(2x2)-(CO+O) are very similar to that in Pt(111)-p(2x2)-CO, except in the region of the chemisorbed oxygen atom, and also nearly identical to that in Pt(111)-p(2x2)-O, apart from in the region of the chemisorbed CO, and (iii) the chemisorption energy of CO on a precovered Pt(111)-p(2x2)-O and the chemisorption energy of O on a precovered Pt(111)-p(2x2)CO are almost equal to that in Pt(111)-p(2x2)-CO and Pt(111)-p(2x2)-O, respectively. These results indicate that the interaction between CO and chemisorbed oxygen on a metal surface is mainly shore range in nature. The discussions of Pt-CO and Pt-O bonding and the interaction between CO and the chemisorbed oxygen atom on Pt(111) are augmented by local densities of states and real space distributions of quantum states.

Modifications of Surface Properties of Beta Ti by Laser Gas Diffusion Nitriding

Beta-type Ti-alloy is a promising biomedical implant material as it has a low Young’s modulus and is also known to have inferior surface hardness. Various surface treatments can be applied to enhance the surface hardness. Physical vapor deposition and chemical vapor deposition are two examples of this but these techniques have limitations such as poor interfacial adhesion and high distortion. Laser surface treatment is a relatively new surface modification method to enhance the surface hardness but its application is still not accepted by the industry. The major problem of this process involves surface melting which results in higher surface roughness after the laser surface treatment. This paper will report the results achieved by a 100 W continuous wave (CW) fiber laser for laser surface treatment without the surface being melted. Laser processing parameters were carefully selected so that the surface could be treated without surface melting and thus the surface finish of the component could be maintained. The surface and microstructural characteristics of the treated samples were examined using x-ray diffractometry, optical microscopy, three-dimensional surface profile and contact angle measurements, and nanoindentation test.

Propriétés optiques et analytiques des nanotrous : vers la conception de biocapteurs en résonance des plasmons de surface localisés

Les biocapteurs sont utilisés quotidiennement pour déterminer la présence de molécules biologiques dans une matrice complexe, comme l’urine pour les tests de grossesses ou le sang pour les glucomètres. Les techniques courantes pour la détection des autres maladies nécessitent fréquemment le marquage de l’analyte avec une autre molécule, ce qui est à éviter pour fin de simplicité d’analyse. Ces travaux ont pour but la maximisation de la sensibilité d’une surface d’or ou d’argent nanotrouée, afin de permettre la détection de la liaison de molécules biologiques par résonance des plasmons de surface localisés (LSPR), en utilisant la spectroscopie de transmission. Un biocapteur portable, rapide et sans marquage pour quantifier des analytes d’intérêt médical ou environnemental pourrait être construit à partir de ces travaux. Dans l’objectif d’étudier de nombreuses configurations pour maximiser la sensibilité, le temps et le coût des méthodes de fabrication de nanostructures habituelles auraient limité le nombre de surfaces nanotrouées pouvant être étudiées. Un autre objectif du projet consiste donc au développement d’une technique de fabrication rapide de réseaux de nanotrous, et à moindres coûts, basée sur la lithographie de nanosphères (NSL) et sur la gravure au plasma à l’oxygène (RIE). La sensibilité à la variation d’indice de réfraction associée aux liaisons de molécules sur la surface du métal noble et la longueur d’onde d’excitation du plasmon de surface sont influencées par les caractéristiques des réseaux de nanotrous. Dans les travaux rapportés ici, la nature du métal utilisé, le diamètre ainsi que la périodicité des trous sont variés pour étudier leur influence sur les bandes LSPR du spectre en transmission pour maximiser cette sensibilité, visant la fabrication d’un biocapteur. Les surfaces d’argent, ayant un diamètre de nanotrous inférieur à 200 nm pour une périodicité de 450 nm et les nanotrous d’une périodicité de 650 nm démontre un potentiel de sensibilité supérieur.

Heterogeneously catalyzed asymmetric hydrogenation of C = C bonds directed by surface-tethered chiral modifiers

Asymmetric hydrogenation of C=C bonds is of the highest importance in organic synthesis, and such reactions are currently carried out with organometallic homogeneous catalysts. Achieving heterogeneous metal-catalyzed hydrogenation, a highly desirable goal, necessitates forcing the crucial enantiodifferentiating step to take place at the metal surface. By synthesis and application of six chiral sulfide ligands that anchor robustly to Pd nanoparticles and resist displacement, we have for the first time accomplished heterogeneous enantioselective catalytic hydrogenation of isophorone. High resolution XPS data established that ligand adsorption from solution occurred exclusively on the Pd nanoparticles and not on the carbon support. All ligands contained a pyrrolidine nitrogen to enable their interaction with the isophorone substrate while the sulfide functionality provided the required interaction with the Pd surface. Enantioselective turnover numbers of up to similar to 100 product molecules per ligand molecule were found with a very large variation in asymmetric induction between ligands: observed enantiomeric excesses increased with increasing size of the alkyl group in the sulfide. This likely reflects varying degrees of ligand dispersion on the surface: bulky substituent groups hinder close approach of ligand molecules to each other, inhibiting close-packed island formation, favoring dispersion as separate molecules, and leading to effective asymmetric induction. Conversely, small substituents favor island formation leading to very low asymmetric induction. Enantioselective reaction most likely involves initial formation of an enamine or iminium species, confirmed by use of an analogous tertiary amine, which leads to racemic product. Ligand rigidity and resistance to self-assembled monolayer formation are important attributes that should be designed into improved chiral modifiers.

Enantiospecific adsorption of alanine on the chiral Cu{531} surface

We have studied enantiospecific differences in the adsorption of (S)- and (R)-alanine on Cu{531}R using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. At saturation coverage, alanine adsorbs as alaninate forming a p(1 4) superstructure. LEED shows a significantly higher degree of long-range order for the S than for the R enantiomer. Also carbon K-edge NEXAFS spectra show differences between (S)- and (R)-alanine in the variations of the ð resonance when the linear polarization vector is rotated within the surface plane. This indicates differences in the local adsorption geometries of the molecules, most likely caused by the interaction between the methyl group and the metal surface and/or intermolecular hydrogen bonds. Comparison with model calculations and additional information from LEED and photoelectron spectroscopy suggest that both enantiomers of alaninate adsorb in two different orientations associated with triangular adsorption sites on {110} and {311} microfacets of the Cu{531} surface. The experimental data are ambiguous as to the exact difference between the local geometries of the two enantiomers. In one of two models that fit the data equally well, significantly more (R)-alaninate molecules are adsorbed on {110} sites than on {311} sites whereas for (S)-alaninate the numbers are equal. The enantiospecific differences found in these experiments are much more pronounced than those reported from other ultrahigh vacuum techniques applied to similar systems.

Surface-enhanced Raman scattering study of alizarin red S

This paper presents the application of surface-enhanced resonance Raman spectroscopy (SERRS) for the structural study of alizarin red S (ARS) and the nature of its interaction with silver nanoparticles. SERRS data for ARS over nanostructured silver electrodes suggest a surface-induced reaction of the adsorbed dye and the formation of an ion stabilized by the dye and alkali ions adsorbed at the metal surface. We found that precoating the SERS active substrate with 1-propanethiol inhibits the surface-induced modification of ARS. In addition to preventing structural modifications of ARS, the coating also concentrates the hydrophobic dye close enough to the SERS active interface enabling the observation of excellent Raman spectra of ARS in aqueous environment at ppm levels. The influence of resonance Raman effect and of the pH on the SERS spectra of ARS was also investigated. (C) 2010 Elsevier B.V. All rights reserved.

Effect of metal conditioners on the adhesive bonding of resin cements to cast titanium

Objective: To assess the effect of metal conditioners on the bond strength between resin cements and cast titanium. Method and Materials: Commercially pure titanium (99.56%) was cast using an arc casting machine. Surfaces were finished with 400-grit silicon carbide paper followed by air abrasion with 50-mu m aluminum oxide. A piece of double-coated tape with a 4-mm circular hole was then positioned on the metal surface to control the area of the bond. The prepared surfaces were then divided into 4 groups (n=10): G1, unprimed Panavia F; G2, Alloy Primer-Panavia F; G3, unprimed Bistite DC; G4, Metaltite-Bistite DC. Forty minutes after insertion of the resin cements, the specimens were detached from the mold and stored in water at 37 C for 24 hours. Shear bond strength was performed in a testing machine (MTS 810) at a crosshead speed of 0.5 mm/min. Data were analyzed using ANOVA and Tukey's test with a .05 significance level. The fractured surfaces were observed through an optical microscope at 10x magnification. Results: the G1 group demonstrated significantly higher shear bond strength (17.95 MPa) than the other groups. G3 (13.79 MPa) and G4 (12.98 MPa) showed similar mean values to each other and were statistically superior to G2 (9.31 MPa). Debonded surfaces generally presented adhesive failure between metal surfaces and resin cements. Conclusion: While the Metaltite conditioner did not influence the bond strength of the Bistite DC cement, the Alloy Primer conditioner significantly decreased the mean bond strength of the Panavia F cement.

Dental implants: Surface modification of cp-Ti using plasma spraying and the deposition of hydroxyapatite

The commercial pure titanium (cp-Ti) is currently being used with great success in dental implants. In this work we investigate how the cp-Ti implants can be improved by modifying the metal surface morphology, on which a synthetic material with properties similar to that of the inorganic part of the bone, is deposited to facilitate the bone/implant bonding. This synthetic material is the hydroxyapatite, HA, a calcium-phosphate ceramic. The surface modification consists in the application of a titanium oxide (TiO2) layer, using the thermal aspersion - plasma spray technique, with posterior deposition of HA, using the biomimetic method. The X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) and Diffuse Reflectance Infrared Fourier Transform (DRIFT) techniques have been used for characterizing phases, microstructures and morphologies of the coatings. The TiO2 deposit shows a mixture of anatase, rutilo and TiO2-x phases, and a porous and laminar morphology, which facilitate the HA deposition. After the thermal treatment, the previously amorphous structured HA coating, shows a porous homogeneous morphology with particle size of about 2-2.5 μm, with crystallinity and composition similar to that of the biological HA.

Functionalization of gold and silver nanoparticles with diphenyl dichalcogenides probed by surface enhanced Raman scattering

This paper describes a surface-enhanced Raman scattering (SERS) systematic investigation regarding the functionalization of gold (Au) and silver (Ag) nanoparticles with diphenyl dichalcogenides, i.e. diphenyl disulfide, diphenyl diselenide, and diphenyl ditelluride. Our results showed that, in all cases, functionalization took place with the cleavage of the chalcogenchalcogen bond on the surface of the metal. According to our density functional theory calculations, the molecules assumed a tilted orientation with respect to the metal surface for both Au and Ag, in which the angle of the phenyl ring relative to the metallic surface decreased as the mass of the chalcogen atom increased. The detected differences in the ordinary Raman and SERS spectra were assigned to the distinct stretching frequencies of the carbonchalcogen bond and its relative contribution to the ring vibrational modes. In addition, the SERS spectra showed that there was no significant interaction between the phenyl ring and the surface, in agreement with the tilted orientation observed from our density functional theory calculations. The results described herein indicate that diphenyl dichalcogenides can be successfully employed as starting materials for the functionalization of Au nanoparticles with organosulfur, organoselenium, and organotellurium compounds. On the other hand, diphenyl disulfide and diphenyl diselenide could be employed for the functionalization of Ag nanoparticles, while the partial oxidation of the organotellurium unit could be detected on the Ag surface. Copyright (C) 2011 John Wiley & Sons, Ltd.

Strategies for detecting DNA hybridisation using surface plasmon fluorescence spectroscopy

Die Anregung und Emission von Fluorophoren nahe planaren Metalloberflächen und schiefen Gittern wurde mittels Oberflächenplasmonen Fluoreszenz Spektroskopie (SPFS) untersucht. Die Fluorophore konnten durch das evaneszente Plasmonenfeld angeregt und die einzelnen Abregungskanäle identifiziert werden.Die Sensorarchitektur für den Nachweis der Hybridisierung bestand aus auf einer Streptavidin-Matrix immobilisierten unmarkierten Sondensträngen. Cy5 markierte Zielsequenzen wurden aus der Lösung hybridisiert und die Adsorptionskinetiken konnten oberflächensensitiv detektiert werden.Ein neues Detektionsschema für unmarkierte Zielstränge wurde mittels fluoreszenzmarkirten Sondensträngen realisiert. Die Hybridisierung führte zu der Bildung von steifen helikalen Bereichen in der Probe und separierte den Farbstoff von der Metalloberfläche. Reduzierte Fluorezenzlöschung zeigte daher das Hybridisierungsereignis an.Die Verwendung eines potentiellen Förster-Paares zur Detektion von DNA Hybridisierung wurde untersucht. Donor und Akzeptor wurden an Ziel- und Sondenstrang immobilisiert und das Hybridisierungsereignis konnte anhand der Auslöschung der Donor-Fluorezenz nachgewiesen werden.Schließlich wurde der Einsatz von einzelstrangbindenden Proteinen (SSB) zur Steigerung der Sensitivität bezüglich Basenfehlpaarungen betrachtet. Verdrängungsreaktionen zwischen Proteinen und markierten Zielsträngen wurden anhand von SPS und Fluorezenzkinetiken studiert.

Investigation of the electric field enhanced PNA-DNA hybridization on Au surface by using surface plasmon field-enhanced fluorescence spectroscopy (SPFS)

Recently, the surface plasmon field-enhanced fluorescence spectroscopy (SPFS) was developed as a kinetic analysis and a detection method with dual- monitoring of the change of reflectivity and fluorescence signal for the interfacial phenomenon. A fundamental study of PNA and DNA interaction at the surface using surface plasmon fluorescence spectroscopy (SPFS) will be investigated in studies. Furthermore, several specific conditions to influence on PNA/DNA hybridization and affinity efficiency by monitoring reflective index changes and fluorescence variation at the same time will be considered. In order to identify the affinity degree of PNA/DNA hybridizaiton at the surface, the association constant (kon) and the dissociation constant (koff) will be obtained by titration experiment of various concentration of target DNA and kinetic investigation. In addition, for more enhancing the hybridization efficiency of PNA/DNA, a study of polarized electric field enhancement system will be introduced and performed in detail. DNA is well-known polyelectrolytes with naturally negative charged molecules in its structure. With polarized electrical treatment, applying DC field to the metal surface, which PNA probe would be immobilized at, negatively charged DNA molecules can be attracted by electromagnetic attraction force and manipulated to the close the surface area, and have more possibility to hybridize with probe PNA molecules by hydrogen bonding each corresponding base sequence. There are several major factors can be influenced on the hybridization efficiency.

Direct electron transfer to cytochrome c oxidase investigated by electrochemistry and time-resolved surface-enhanced infrared absorption spectroscopy

Cytochrom c Oxidase (CcO), der Komplex IV der Atmungskette, ist eine der Häm-Kupfer enthaltenden Oxidasen und hat eine wichtige Funktion im Zellmetabolismus. Das Enzym enthält vier prosthetische Gruppen und befindet sich in der inneren Membran von Mitochondrien und in der Zellmembran einiger aerober Bakterien. Die CcO katalysiert den Elektronentransfer (ET) von Cytochrom c zu O2, wobei die eigentliche Reaktion am binuklearen Zentrum (CuB-Häm a3) erfolgt. Bei der Reduktion von O2 zu zwei H2O werden vier Protonen verbraucht. Zudem werden vier Protonen über die Membran transportiert, wodurch eine elektrochemische Potentialdifferenz dieser Ionen zwischen Matrix und Intermembranphase entsteht. Trotz ihrer Wichtigkeit sind Membranproteine wie die CcO noch wenig untersucht, weshalb auch der Mechanismus der Atmungskette noch nicht vollständig aufgeklärt ist. Das Ziel dieser Arbeit ist, einen Beitrag zum Verständnis der Funktion der CcO zu leisten. Hierzu wurde die CcO aus Rhodobacter sphaeroides über einen His-Anker, der am C-Terminus der Untereinheit II angebracht wurde, an eine funktionalisierte Metallelektrode in definierter Orientierung gebunden. Der erste Elektronenakzeptor, das CuA, liegt dabei am nächsten zur Metalloberfläche. Dann wurde eine Doppelschicht aus Lipiden insitu zwischen die gebundenen Proteine eingefügt, was zur sog. proteingebundenen Lipid-Doppelschicht Membran (ptBLM) führt. Dabei musste die optimale Oberflächenkonzentration der gebundenen Proteine herausgefunden werden. Elektrochemische Impedanzspektroskopie(EIS), Oberflächenplasmonenresonanzspektroskopie (SPR) und zyklische Voltammetrie (CV) wurden angewandt um die Aktivität der CcO als Funktion der Packungsdichte zu charakterisieren. Der Hauptteil der Arbeit betrifft die Untersuchung des direkten ET zur CcO unter anaeroben Bedingungen. Die Kombination aus zeitaufgelöster oberflächenverstärkter Infrarot-Absorptionsspektroskopie (tr-SEIRAS) und Elektrochemie hat sich dafür als besonders geeignet erwiesen. In einer ersten Studie wurde der ET mit Hilfe von fast scan CV untersucht, wobei CVs von nicht-aktivierter sowie aktivierter CcO mit verschiedenen Vorschubgeschwindigkeiten gemessen wurden. Die aktivierte Form wurde nach dem katalytischen Umsatz des Proteins in Anwesenheit von O2 erhalten. Ein vier-ET-modell wurde entwickelt um die CVs zu analysieren. Die Methode erlaubt zwischen dem Mechanismus des sequentiellen und des unabhängigen ET zu den vier Zentren CuA, Häm a, Häm a3 und CuB zu unterscheiden. Zudem lassen sich die Standardredoxpotentiale und die kinetischen Koeffizienten des ET bestimmen. In einer zweiten Studie wurde tr-SEIRAS im step scan Modus angewandt. Dafür wurden Rechteckpulse an die CcO angelegt und SEIRAS im ART-Modus verwendet um Spektren bei definierten Zeitscheiben aufzunehmen. Aus diesen Spektren wurden einzelne Banden isoliert, die Veränderungen von Vibrationsmoden der Aminosäuren und Peptidgruppen in Abhängigkeit des Redoxzustands der Zentren zeigen. Aufgrund von Zuordnungen aus der Literatur, die durch potentiometrische Titration der CcO ermittelt wurden, konnten die Banden versuchsweise den Redoxzentren zugeordnet werden. Die Bandenflächen gegen die Zeit aufgetragen geben dann die Redox-Kinetik der Zentren wieder und wurden wiederum mit dem vier-ET-Modell ausgewertet. Die Ergebnisse beider Studien erlauben die Schlussfolgerung, dass der ET zur CcO in einer ptBLM mit größter Wahrscheinlichkeit dem sequentiellen Mechanismus folgt, was dem natürlichen ET von Cytochrom c zur CcO entspricht.

Surface studies in ultra high vacuum

An ultra high vacuum system capable of attaining pressures of 10-12 mm Hg was used for thermal desorption experiments. The metal chosen for these experiments was tantalum because of its suitability for thermal desorption experiments and because relatively little work has been done using this metal. The gases investigated were carbon monoxide, hydrogen and ethylene. The kinetic and thermodynamic parameters relating to the desorption reaction were calculated and the values obtained related to the reaction on the surface. The thermal desorption reaction was not capable of supplying all the information necessary to form a complete picture of the desorption reaction. Further information was obtained by using a quadrupole mass spectrometer to analyse the desorbed species. The identification of the desorbed species combined with the value of the desorption parameters meant that possible adatom structures could be postulated. A combination of these two techniques proved to be a very powerful tool when investigating gas-metal surface reactions and gave realistic values for the measured parameters such as the surface coverage, order of reaction, the activation energy and pre-exponential function for desorption. Electron microscopy and X-ray diffraction were also used to investigate the effect of the gases on the metal surface.