CO Shift Research Articles

Application of Multipolar Charge Models and Molecular Dynamics Simulations to Study Stark Shifts in Inhomogeneous Electric Fields

Atomic multipole moments are used to investigate vibrational frequency shifts of CO and H(2) in uniform and inhomogeneous electric fields using ab initio calculations and Molecular Dynamics (MD) simulations. The importance of using atomic multipole moments that can accurately represent both molecular electrostatics and the vibrational response of the molecule to changes in the local electric field is highlighted. The vibrational response of CO to applied uniform and inhomogeneous electric fields is examined using Density Functional Theory calculations for a range of test fields, and the results are used to assess the performance of different atomic multipole models. In uniform fields, the calculated Stark tuning rates of Deltamu = 0.52 cm(-1)/(MV/cm) (DFT), Deltamu = 0.55 cm(-1)/(MV/cm) (fluctuating three-point charge model), and Deltamu = 0.64 cm(-1)/(MV/cm) (Multipole model up to octupole), compare favorably with the experimentally measured value of 0.67 cm(-1)/(MV/cm). For H(2), which has no permanent dipole moment, CCSD(T) calculations demonstrate the importance of bond-weakening effects in force fields in response to the applied inhomogeneous electric field. Finally, CO in hexagonal ice is considered as a test system to highlight the performance of selected multipolar models in MD simulations. The approach discussed here can be applied to calibrate a range of multipolar charge models for diatomic probes, with applications to interpret Stark spectroscopy measurements in protein active sites.

A simple empirical model for the collisional spectral shift of air-broadened CO 2 lines

A simple empirical model is proposed for the pressure-induced shifts of air-broadened CO 2 absorption lines. It is based on the introduction of components symmetric and antisymmetric with respect to the rotational quantum number m, and on a separation of vibrational and rotational contributions. These components are modelled though empirical analytical laws with parameters that are obtained from fits of the measured shifts in only two different bands. It is then shown that the model leads to satisfactory results for a number of other vibrational transitions in which the shifts take significantly different values. This provides a simple way to generate values for unmeasured transitions and this tool can thus be used to complement spectroscopic databases.

Collision energy dependence of the reactions of metastable Ne (2 p53 s3P2, 3P0) with small molecules

Crossed supersonic beams were employed to study the ionization reactions at various collision energies E (≈1–7 kcal/mol) of Ne ∗ (2 p 53 s 3 P 2, 3 P 0) with CO, N 2, NO, CO 2, C 2H 2, and O 2. Reasons for non-Franck–Condon behavior and possible mechanisms (Penning, excitation transfer, and ion-pair) are discussed. Complete fits, populations, and line shifts are given for CO, N 2, NO, and C 2H 2. With increasing E, CO and N 2 exhibited a blue shift that increased, whereas NO ( X and a) and C 2H 2 exhibited a blue shift that decreased. Line shifts for CO 2 and O 2 are given, as is a partial CO 2 fit.

Theoretical prediction on the wavelength–temperature shift in pulsed TE CO 2 lasers

The wavelength–temperature shift observed in pulsed TE CO 2 lasers is discussed theoretically by means of Six-temperature model rate equations for tunable TE CO 2 lasers. Numerical calculations of the temperature–wavelength shift in a pulsed TE CO 2 laser with a simple plano-concave stable resonator, whether excited by conventional low-inductance fast-discharge scheme or by a long-pulse Pulser/sustainer discharge scheme, show that the laser output wavelengths are within the 10P branch as the ambient temperature varies from 228 to 338 K, but will change as the ambient temperature varies. The laser output wavelengths will move to the transition lines with longer wavelengths in the 10P branch as the ambient temperature increases and vice versa. The calculated results also illustrate that near the ambient temperature of 310 K, the laser is more likely to operate on multi-transition lines. Considering this wavelength–temperature shift, the chilling device adopted in high-power high repetition rate TE CO 2 lasers is important in maintaining a stable laser output spectra as well as a stable laser output power. The numerical results also suggest that a frequency agile resonator is highly recommended if stable laser output spectra are required in TE CO 2 lasers.

Dynamics of CO Oxidation on a Polycrystalline Platinum Electrode: A Time-Resolved Infrared Study

Electro-oxidation of CO adsorbed on a polycrystalline Pt electrode in the potential region of hydrogen absorption is examined by fast time-resolved surface-enhanced infrared absorption spectroscopy coupled to voltammetry or chronoamperometry. Oxidation dynamics at a weak preoxidation peak around 0.5 V (vs RHE) and the main oxidation peak around 0.7 V observed in stripping voltammetry are focused. IR spectra show that the shift of bridge-bonded CO to atop sites triggers the partial oxidation of CO adsorbed at atop sites to yield the preoxidation peak. It is also shown that CO on terraces becomes very mobile in the main oxidation region after some amount of CO being oxidized via a nucleation-and-growth mechanism and that terrace CO is oxidized faster than CO adsorbed at step edges. The result is interpreted in terms of a Langmuir−Hinshelwood type mechanism involving adsorbed CO and an oxygen-containing species (most likely OH) adsorbed at steps. The oxidation mechanism is essentially identical to that proposed in some earlier studies, but more convincing spectroscopic evidence of the mechanism is presented.

Development of Advanced Reforming System for H2 Station Using CO Converter Equipped with CO2 Selective Membrane II

We developed a novel membrane reactor consisted of a CO shift catalyst and a membrane for selective CO2 separation. First, we successfully developed novel facilitated transport membranes with excellent performances exceeding our target values, i.e. CO2 permeance of 1x10-4 mol/(m2skPa) and CO2/H2 selectivity of 100 at 160 oC. The developed membrane maintained high performances for more than 400 hours. Second, we developed CO shift catalysts, which had high activity for the CO shift reaction at 160 oC. Among the catalysts developed in this study, precious metal-based catalysts had quite high activities. By combining the developed membrane and catalyst, a membrane reactor-type CO converter was fabricated. By using the CO converter, CO and CO2 concentrations in feed gas (14.8 and 7.4 %, respectively) were drastically reduced. Observed CO and CO2 concentrations at the feed-side exit of the CO converter were 5 ppm and 0.3 %, respectively.

Path-integral Monte Carlo simulation of ν3 vibrational shifts for CO2 in (He)n clusters critically tests the He–CO2 potential energy surface

Path-integral Monte Carlo simulations of the nu(3) vibrational band origin frequency shifts of CO(2) in (He)(n) clusters for n=1-40 show that although only the asymmetric-stretch mode of CO(2) is being excited, the effect of the associated change in the average value of Q(1) cannot be ignored. When this fourth degree of freedom is taken into account, the resulting predicted vibrational frequency shifts are in excellent agreement with experiment across this whole range of cluster size. It is also shown that the quality of predictions obtained from simulations on a given potential energy surface can depend significantly on the choice of the analytic function used to represent it.

The influence of solution pH on rates of an electrocatalytic reaction: Formic acid electrooxidation on platinum and palladium

We found for the first time that solution pH makes a significant difference in the rate of a prototypical electrocatalytic reaction, formic acid electrooxidation, under conditions where H + and OH − do not adsorb strongly on the surface, and we demonstrate that the results can be explained using the Marcus model. We changed the pH of formic acid solutions and found enhanced oxidation on Pd and Pt black catalysts with increased pH. The interpolated current density for the oxidation of 1 M HCOOH in 0.1 M perchlorate electrolyte after 2 min at 0.22 V vs. SHE on Pt increased 30-fold from 0.005 to 0.17 mA cm −2 as the pH was increased from 1 to 5, while for Pd there was a 4-fold increase from 0.12 to 0.53 mA cm −2. The data was also interpolated at a current density of 0.1 mA cm −2, and the potential required to reach this current shifted negative 62 mV per pH on palladium and 56 mV per pH on platinum. A 24 h experiment compared two solution pH, in which the higher pH demonstrated remarkably stronger performance. In addition, the potential for oxidation of surface CO shifts negative on both catalysts, as much as ∼57 mV per pH on Pd.

Novel Preparation of Uniform Heterogeneous Catalysts Derived from Hydrotalcites

Several heterogeneous catalysts were prepared starting from Mg-Al and Zn-Al hydrotalcites (HTs) and evaluated for oxidation, ozonation, dehydrogenation and reforming of hydrocarbons, and the CO shift reaction. All catalysts exhibited unique and excellent activities in these reactions. Fe/Mg/Al oxide catalysts prepared from Mg-Al(Fe) HT exhibited high activity for Baeyer-Villiger oxidation of various ketones and dehydrogenation of ethylbenzene. Ozonation activity of Cu/Mg/Al oxide catalysts similarly prepared from Mg(Cu)-Al HT was enhanced by the 'memory effect,' as reconstituted HT on the catalyst surface adsorbed oxalic acid and assisted in complete oxidation. Ni/Mg(Al)O catalysts prepared from Mg(Ni)-Al HT exhibited high and stable activity in steam reforming and oxidative reforming of methane and propane. Moreover, the activity of the Ni catalysts was improved by doping a trace amounts of noble metals by adopting the 'memory effect.' Use of these catalysts in the production of hydrogen for the PEFCs under daily start-up and shut-down operation showed that the catalysts were self-activated and the active Ni metal particles were self-regenerated during the reaction, resulting in high and sustainable activity. CO shift activity of Cu/Zn(Al)O catalysts was also improved by doping a trace Pt or Mg by adopting the memory effect of Zn(Cu)-Al HT in the precursor, resulting in the high sustainability.

Influence of Chemical Effect on the K/K Intensity Ratios and K Energy Shift of Co, Ni, Cu, and Zn Complexes

Chemical effects on the K/K intensity ratios and E energy differences for Co, Ni, Cu, and Zn complexes were investigated. The samples were excited by 59.5 keV -rays from a 241Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. We observed the effects of different ligands on the K/K intensity ratios and E energy differences for Co, Ni, Cu, and Zn complexes. We tried to investigate chemical effects on central atoms using the behaviors of different ligands in these complexes. The experimental values of K/K were compared with the theoretical and other experimental values of pure Co, Ni, Cu, and Zn.

Intermolecular interactions investigation of nickel(II) and zinc(II) salts of ortho-sulfobenzoic acid by X-ray diffraction and vibrational spectra

Two isostructural compounds consisting of hexaaquanickel(II) or hexaaquazinc(II) cations and hydrogen ortho-sulfobenzoate (HSBZ) as counter-ions have been synthesized and characterized by X-ray diffraction and vibrational spectroscopy techniques. The metal atom is located in the inversion centre and has a slightly distorted octahedral environment formed by water molecules, giving rise to ionic compounds with HSBZ. The HSBZ ions which are related by a c-glide plane interact to each other by medium to weak hydrogen bonds, developing wave-like chains parallel to the crystallographic c-axis. The [M(H 2O) 6] 2+ cation interacts with six surrounding HSB via the coordinated water molecules by hydrogen bonds. The oppositely charged units are interconnected into a 2D-polymeric superstructure parallel to (1 0 0) plane. The vibrational spectra of both salts are very similar to ortho-sulfobenzoic acid spectrum, and no significant shifts in SO and CO stretching bands were observed, suggesting the formation of ionic salts, which is in agreement with the X-ray results, thus indicating that the ortho-sulfobenzoate anion is a weaker ligand than water. Moreover, the presence of the acidic structure is very important in the definition of the supramolecular structure, since the hydrogen bonds design of the HSBZ is related to the cation size, probably due to the spatial factors involved in the crystal packing stability.

On the origin of bonding and vibrational frequency shifts for CO adsorbed on neutral, cationic and anionic gold clusters

We report a detailed analysis of the electronic mechanisms which determine the bond strength and the vibrational frequency of CO molecules adsorbed on neutral or charged gold nanoparticles. To this end we have considered a simple cluster model, Au5COq (q = +1, 0, −1), and decomposed the Au-CO interaction energy into the sum of various contributions according to a Constrained Space Orbital Variation approach. While the adsorption energy is relatively insensitive to the value of q, the C-O stretch frequency, ωe(CO), changes substantially, and allows the use of this molecule as a direct probe of the gold oxidation state. The results show that two major terms contribute to the red or blue shift of ωe(CO) as a function of q: the interaction with the electric field associated to the charged nanoparticle (Stark effect) and the Au → CO Φ back donation. The CO → Au σ donation is about half as important as the Φ back-donation and all other terms are much less important.

Physicochemical properties of a plate-type copper-based catalyst, prepared on an aluminum plate by electroless plating, for steam reforming of methanol and CO shift reaction

Abstract A plate-type copper-based catalyst was prepared by electroless plating on an aluminum substrate. Its physicochemical properties were measured to examine the relation to methanol reforming and CO shift performances. The catalytic activity of the plated copper-based catalyst was improved more by oxidation treatment in air than by reduction treatment prior to the reaction. In this case, the oxidation treatment caused the zinc located in the bulk layer to migrate to the surface and form a CuZn alloy-like compound. While, the reduction treatment made only a small amount of zinc migration, so the CuZn alloy was barely formed. The surface area of metallic copper component on the catalyst was increased by the reduction treatment, and with the number of reductions; however, there was no relationship between such metallic surface area and CO shift activity. The valence of the copper species at the surface layer was metallic after reduction treatment and cationic after oxidation treatment or reforming reaction. It was found that the presence of metallic copper species on the plated catalyst hardly contributes to the formation of active site. The formate species, which are considered as the intermediate of reforming and CO shift reaction, were adsorbed on the catalyst in the form of a monodentate-type or a bridge-type (and/or bidentate-type). On the surface that experienced oxidation treatment, the proportion of the monodentate-type formate group was higher. It was inferred that the formation of a CuZn alloy-like compound accelerates the increase of monodentate-type formate group and contributes to the improvement of catalytic activity.

Surface Structure at the Ionic Liquid−Electrified Metal Interface

Room-temperature ionic liquids are a new class of liquids with many important uses in electrical and electrochemical devices. The liquids are composed purely of ions in the liquid state with no solvent. They generally have good electrical and ionic conductivity and are electrochemically stable. Since their applications often depend critically on the interface structure of the liquid adjacent to the electrode, a molecular level description is necessary to understanding and improving their performance. There are currently no adequate models or descriptions on the organization of the ions, in these pure ionic compounds, adjacent to the electrode surface. In normal electrolytic solutions, the organization of solvent and ions is adequately described by the Gouy-Chapman-Sterns model. However, this model is based on the same concepts as those in Debye-Huckel theory, that is a dilute electrolyte, where ions are well-separated and noninteracting. This is definitely not the situation for ionic liquids. Thus our goal was to investigate the ionic liquid-metal interface using surface-specific vibrational spectroscopy sum frequency generation, SFG. This technique can probe the metal-liquid interface without interference from the bulk electrolyte. Thus the interface is probed in situ while the electrode potential is changed. To compliment the vibrational spectroscopy, electrochemical impedance spectroscopy (EIS) is used to measure the capacitance and estimate the "double layer" thickness and the potential of zero charge (PZC). In addition, the vibrational Stark shift of CO adsorbed on the Pt electrode was measured to provide an independent measure of the "double layer" thickness. All techniques were measured as a function of applied potential to provide full description of the interface for a variety of imidazolium-based (cation) ionic liquids. The vibrational Stark shift and EIS results suggest that ions organize in a Helmholtz-like layer at the interface, where the potential drop occurs over the a range of 3-5 A from the metal surface into the liquid. Further, the SFG results imply that the "double layer" structure is potential-dependent; At potentials positive of the PZC, anions adsorbed to the surface and the imidazolium ring are repelled to orient more along the surface normal, compared with the potentials negative of the PZC, at which the cation is oriented more parallel to the surface plane and the anions are repelled from the surface. The results present a view of the ionic liquid-metal electrode interface having a very thin "double layer" structure where the ions form a single layer at the surface to screen the electrode charge. However, the results also raise many other fundamental questions as to the detailed nature of the interfacial structure and interpretations of both electrochemical and spectroscopic data.

COシフト反応用Cu-Al-Ox系触媒に対する水蒸気処理の影響

COシフト反応用Cu-Al-Ox系触媒に対する水蒸気処理の影響

An assessment of observed vertical flux divergence in long-term eddy-covariance measurements over two Midwestern forest ecosystems

Vertical divergence of CO 2 fluxes is observed over two Midwestern AmeriFlux forest sites. The differences in ensemble averaged hourly CO 2 fluxes measured at two heights above canopy are relatively small (0.2–0.5 μmol m −2 s −1), but they are the major contributors to differences (76–256 g C m −2 or 41.8–50.6%) in estimated annual net ecosystem exchange (NEE) in 2001. A friction velocity criterion is used in these estimates but mean flow advection is not accounted for. This study examines the effects of coordinate rotation, averaging time period, sampling frequency and co-spectral correction on CO 2 fluxes measured at a single height, and on vertical flux differences measured between two heights. Both the offset in measured vertical velocity and the downflow/upflow caused by supporting tower structures in upwind directions lead to systematic over- or under-estimates of fluxes measured at a single height. An offset of 1 cm s −1 and an upflow/downflow of 1° lead to 1% and 5.6% differences in momentum fluxes and nighttime sensible heat and CO 2 fluxes, respectively, but only 0.5% and 2.8% differences in daytime sensible heat and CO 2 fluxes. The sign and magnitude of both offset and upflow/downflow angle vary between sonic anemometers at two measurement heights. This introduces a systematic and large bias in vertical flux differences if these effects are not corrected in the coordinate rotation. A 1 h averaging time period is shown to be appropriate for the two sites. In the daytime, the absolute magnitudes of co-spectra decrease with height in the natural frequencies of 0.02–0.1 Hz but increase in the lower frequencies (<0.01 Hz). Thus, air motions in these two frequency ranges counteract each other in determining vertical flux differences, whose magnitude and sign vary with averaging time period. At night, co-spectral densities of CO 2 are more positive at the higher levels of both sites in the frequency range of 0.03–0.4 Hz and this vertical increase is also shown at most frequencies lower than 0.03 Hz. Differences in co-spectral corrections at the two heights lead to a positive shift in vertical CO 2 flux differences throughout the day at both sites. At night, the vertical CO 2 flux differences between two measurement heights are 20–30% and 40–60% of co-spectral corrected CO 2 fluxes measured at the lower levels of the two sites, respectively. Vertical differences of CO 2 flux are relatively small in the daytime. Vertical differences in estimated mean vertical advection of CO 2 between the two measurement heights generally do not improve the closure of the 1D (vertical) CO 2 budget in the air layer between the two measurement heights. This may imply the significance of horizontal advection. However, a reliable assessment of mean advection contributions in annual NEE estimate at these two AmeriFlux sites is currently an unsolved problem.

Efficiency of an Integrated Gasification Combined Cycle (IGCC) power plant including CO2 removal

This study is devoted to technical evaluation of a carbon dioxide removal in an existing Integrated Gasification Combined Cycle (IGCC) plant. This IGCC case is based on an oxygen blown entrained flow gasifier operating at 27 bar, the removal of acid gas (H2S) is performed with MDEA unit, the efficiency of this IGCC is 43% based on the low heating value (LHV) of coal. A carbon dioxide separation unit conveniently integrated in a pre-combustion separation process is chosen, in order to take advantage of the high pressure of the gas. The methanol process for carbon dioxide removal is integrated downstream the existing desulfuration unit, and after a CO shift conversion unit. In this study, the integration of the CO2 capture process to the IGCC is simulated as realistically as possible. The design parameters of both the gas turbine (the turbine inlet temperature, compressor pressure ratio, reduced flow rate) and the steam turbine (Stodola parameter) are taken into account. Maintenance of low NOx production in the combustion chamber is also considered. The production of NOx is supposed to be influenced by the low heating value of the gas which is maintained as low as for case of the synthesis gas without CO2 capture. Thus the choice is made to feed the gas turbine of the combined cycle with a diluted synthesis gas, having similar low heating value than the one produced without the CO2 capture. Plant performances for different conversion and capture rates are compared. A final optimized integration is given for 92 mol% CO conversion rate and 95 mol% CO2 absorption rates, a comparison with former studies is proposed.

Optimal promoter edge decoration of CoMoS catalysts: A combined theoretical and experimental study

The present work combines X-ray Photoelectron Spectroscopy (XPS), catalytic tests, and density functional theory (DFT) modeling for determining the optimized Co edge decoration according to the stability and reactivity of the CoMoS active phase. Using the phase diagram and morphology of the CoMoS nano-crystallites determined by DFT calculations [Krebs et al. Catal. Today, 130 (2007) 160], the values of the Co/Mo ratio and the number of mixed Co–Mo sites are evaluated. DFT calculations of the 2p core level shift of Co at the edges with respect to the Co 9S 8 phase are compatible with the experimental positive binding energy shift measured by XPS on CoMoS catalysts. Moreover, the decomposition of the XPS spectral envelope is used to quantify the proportion of CoMoS phase and to normalize the catalytic activity in toluene-hydrogenation per edge site as a function of the Co/Mo ratio. The optimal Co/Mo ratio for the catalytic activity is found to reflect the presence of mixed Co–Mo sites at Mo-edge when considering the measured average size of particles and the calculated morphology. These results are helpful for an improved optimization of the promoter content in the CoMoS phase.

NMR assignments of cd-HO, a 24 kDa heme oxygenase from Corynebacterium diphtheria

We are employing a number of selective in vitro and in vivo methods including NMR to screen compounds that bind to heme oxygenases from pathogenic bacteria. We report the nearly complete HN, N, CO, Calpha and Cbeta chemical shift assignments of a 215-amino acid HO from Corynebacterium diphtheria in three forms, apo cd-HO-G135A, apo cd-HO and CO-bound ferrous holo cd-HO; these assignments will enable us to identify residues on cd-HO that are perturbed upon binding to selected compounds, and to help with the development of inhibitors specific to the bacterial proteins.

Preparation of supported metal catalysts starting from hydrotalcites as the precursors and their improvements by adopting “memory effect”

Hydrotalcite-like compounds (HTlcs) can be used as the catalysts as it is since they contain various transition metal cations as the catalytically active species well dispersed on the basic support materials. Moreover, increasing numbers of the applications of HTlcs after the heat treatment have been found since the oxides with very small crystal size, stable to thermal treatments, are obtained after the calcination. The oxides possess interesting properties such as high surface area, basic properties and further form small and thermally stable metal crystallites by reduction. Moreover, the calcined oxides show a unique property, i.e., “memory effect,” which allows the reconstitution of the original hydrotalcite structure. We have developed the catalytic applications of hydrotalcites as it is and moreover the mixed oxides derived from hydrotalcites for various catalytic reactions, i.e., oxidation, dehydrogenation and reforming of hydrocarbons, and even for the reforming of methanol and the CO shift reaction. Aerobic oxidation of alcohols, Baeyer−Villiger oxidation of ketones and O3 oxidation of oxalic acid have been successfully carried out with the Mg−Al hydrotalcites containing Ni, Fe and Cu, respectively, as the catalysts in liquid phase. In the O3 oxidation of oxalic acid, the catalytic activity was enhanced by the “memory effect,” i.e., Mg(Cu)–Al hydrotaclite was reconstituted on the surface of Mg(Cu,Al)O periclase particles and oxalic acid was incorporated as anions in the hydrotalcite layer, resulting in an enhanced oxidation of oxalic acid. As the catalysts in the vapor phase reactions, Mg/Fe/Al mixed oxides prepared from Mg–Al(Fe) hydrotalcites and effectively catalyzed the dehydrogenation of ethylbenzene. Supported Ni metal catalysts have been prepared from Mg(Ni)–Al hydrotalcites and successfully used in the steam reforming and the oxidative reforming of methane and propane. Moreover, the Ni catalysts have been improved by combining a trace amount of noble metals by adopting the “memory effect” and used in the production of hydrogen for the PEFC under the daily startup and shutdown operation. Also starting from aurichalcite or hydrotalcite precursor as the precursor, Cu/Zn/Al catalysts with high Cu metal surface area have been prepared and successfully applied in the steam reforming of methanol and dimethyl ether, and moreover in the CO shift reaction.