Gas-phase Carbon Monoxide Research Articles

Deep Search for Molecular Oxygen in TW Hya

The dominant form of oxygen in cold molecular clouds is gas-phase carbon monoxide (CO) and ice-phase water (H2O). Yet, in planet-forming disks around young stars, gas-phase CO and H2O are less abundant relative to their interstellar medium values, and no other major oxygen-carrying molecules have been detected. Some astrochemical models predict that gas-phase molecular oxygen (O2) should be a major carrier of volatile oxygen in disks. We report a deep search for emission from the isotopologue 16O18O (N J = 21 − 01 line at 233.946 GHz) in the nearby protoplanetary disk around TW Hya. We used imaging techniques and matched filtering to search for weak emission but do not detect 16O18O. Based on our results, we calculate upper limits on the gas-phase O2 abundance in TW Hya of (6.4–70) × 10−7 relative to H, which is 2–3 orders of magnitude below solar oxygen abundance. We conclude that gas-phase O2 is not a major oxygen carrier in TW Hya. Two other potential oxygen-carrying molecules, SO and SO2, were covered in our observations, which we also do not detect. Additionally, we report a serendipitous detection of the C15N N J = 25/2 − 13/2 hyperfine transitions, F = 3 − 2 and F = 2 − 1, at 219.9 GHz, which we found via matched filtering and confirm through imaging.

Large Myr-old Disks Are Not Severely Depleted of Gas-phase CO or Carbon

We present an ACA search for [C i] 1–0 emission at 492 GHz toward large T Tauri disks (gas radii ≳ 200 au) in the ∼1–3 Myr-old Lupus star-forming region. Combined with Atacama Large Millimeter/submillimeter Array 12 m archival data for IM Lup, we report [C i] 1–0 detections in six out of 10 sources, thus doubling the known detections toward T Tauri disks. We also identify four Keplerian double-peaked profiles and demonstrate that the [C i] 1–0 fluxes correlate with 13CO, C18O, and 12CO(2–1) fluxes, as well as with the gas disk outer radius measured from the latter transition. These findings are in line with the expectation that atomic carbon traces the disk surface. In addition, we compare the carbon and carbon monoxide (CO) line luminosities of a Lupus and literature sample with [C i] 1–0 detections with predictions from the self-consistent disk thermo-chemical models of Ruaud et al. These models adopt interstellar medium carbon and oxygen elemental abundances as input parameters. With the exception of the disk around Sz 98, we find that these models reproduce all the available line luminosities and upper limits, with gas masses comparable to or higher than the minimum-mass solar nebula and gas-to-dust mass ratios ≥10. Thus, we conclude that the majority of large Myr-old disks conform to the simple expectation that they are not significantly depleted in gas, CO, or carbon.

Review of Dissolved CO and H2 Measurement Methods for Syngas Fermentation.

Syngas fermentation is a promising technique to produce biofuels using syngas obtained through gasified biomass and other carbonaceous materials or collected from industrial CO-rich off-gases. The primary components of syngas, carbon monoxide (CO) and hydrogen (H2), are converted to alcohols and other chemicals through an anaerobic fermentation process by acetogenic bacteria. Dissolved CO and H2 concentrations in fermentation media are among the most important parameters for successful and stable operation. However, the difficulties in timely and precise dissolved CO and H2 measurements hinder the industrial-scale commercialization of this technique. The purpose of this article is to provide a comprehensive review of available dissolved CO and H2 measurement methods, focusing on their detection mechanisms, CO and H2 cross interference and operations in syngas fermentation process. This paper further discusses potential novel methods by providing a critical review of gas phase CO and H2 detection methods with regard to their capability to be modified for measuring dissolved CO and H2 in syngas fermentation conditions.

Carbon monoxide, CO(g), by high-resolution near-ambient-pressure x-ray photoelectron spectroscopy

Near-ambient-pressure x-ray photoelectron spectroscopy (NAP-XPS) and x-ray-induced Auger electron spectroscopy were used to characterize gas-phase carbon monoxide, CO(g). In this submission, the authors show the survey, valence band, O 1s, C 1s, O KLL Auger, and C KLL Auger spectra acquired using high-resolution synchrotron NAP-XPS with a photon energy of 647.08 eV.

Studies of innovative product – electronic system for nicotine delivery

Studying the electronic nicotine delivery systems (ENDS), which are widely spread as substitute for traditional tobacco product is an important aim. This product differs from traditional product by absence of burning process, and it is consumed by inhaling aerosol formed by heating tobacco or liquid, containing nicotine. Monitoring of electronic nicotine delivery systems’ market is carried. Principles for classifying new product as separate category of tobacco goods are elaborated. Classification for ENDS is offered. Physical properties of single use ENDS and liquid composition are defined. “Method for machine smoking of single use electronic smoking systems and collecting its TPM and gas phase of smoke with linear smoking machine CERULEAN SM 405” was elaborated. Physical properties of reusable ENDS are defined. ENDS product is fine aerosol formed by heating. Absence of standard international regulations on nicotine containing products and methods for control of its aerosol content leads to utilizing different machine smoking protocols. Machine smoking protocols for tobacco products are presented. After researches absence of carbon monoxide in gas phase of single use and reusable ENDS is found. This proves absence of burning process. The last generation of reusable ENDS is innovative tobacco product which is heated – electric system for heating tobacco (ESHT) which completely differs from traditional tobacco products. ESHT consuming is based on tobacco heating without its burning or combustion. As the result it is possible to decrease content of harmful and potentially harmful aerosol compounds and conserve adequate to consumers levels of taste. Further studies will be aimed at defining ESHT potential for decreasing health risks compared to traditional cigarettes.

Nighttime particle growth observed during spring in New Delhi: Evidences for the aqueous phase oxidation of SO2

Aerosol size distributions were measured using a scanning mobility particle sizer (SMPS), and also PM1 (particulate matter ≤ 1 μm in aerodynamic diameter) samples were collected in parallel at a representative site in New Delhi during spring in 2013 and 2014. Based on the temporal variation of particle count mean diameter (CMD), sampling periods are characterized as growth events and non-growth events. Particle size distribution measurements suggest that some consecutive nights experienced unique nighttime subsequent growth of particles, which sustained for a longer period. Average particle growth rate measured during growth events was 5.64 ± 3.03 nm h−1. Atmospheric trace gas concentrations and meteorological data show that these growth events (nighttime) are influenced by higher concentrations of gases, e.g., NO2 (56.5 ± 29.7 μg m−3), SO2 (9.34 ± 1.14 μg m−3) and RH (45.7 ± 9.5%) than those of non-growth events (daytime) (37.9 ± 18.6 μg m−3, 7.19 ± 2.08 μg m−3 and 37.7 ± 6.9%, respectively). Further, analysis of PM1 samples collected during the study period shows that the particulate water-soluble organic carbon (WSOC) (12.7 ± 4.1 μg m−3), NH4+ (9.4 ± 3.2 μg m−3), SO42− (2.03 ± 0.70 μg m−3), K+(1.06 ± 0.40 μg m−3), and NO2− + NO3− (0.59 ± 0.36 μg m−3) are the major contributors of particulate mass, wherein NH4+, SO42−, K+, NO2− + NO3− mass concentrations were higher during growth events. Correlation study shows that nighttime aerosol composition during growth (in sub-micron range) events are more enriched by inorganic species (i.e., NH4NO3, (NH4)2SO4 and H2SO4 vapors) as compared to organics (i.e., WSOC, does not show much difference in growth events and non events). Our results suggest that nighttime sulfate formation at the site is mostly mediated by high NO2 and NH3 at elevated RH. For the formation of sulfate and other inorganic species, a nighttime atmospheric chemistry is proposed, which is linked to particle growth. Growth events observed typically in nighttime have both biomass burning and anthropogenic influences as indicated by high concentrations of WSOC, K+ and black carbon in PM1 and carbon monoxide in gas phase.

Chemistry of Ruthenium Diketonate Atomic Layer Deposition (ALD) Precursors on Metal Surfaces

The thermal chemistry of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium(III) (Ru(tmhd)3), a potential precursor for the chemical deposition of ruthenium -containing films, on Ni(110) single-crystal surfaces was characterized by using a combination of temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and reflection–absorption infrared spectroscopy (RAIRS). Additional characterization of the surface chemistry of the protonated ligand, Htmhd, was evaluated as well for reference. It was found that the molecularly adsorbed ruthenium compound reacts readily by approximately 310 K, loosing its ligands to both the gas phase and the surface as the central ion is reduced to its Ru0 metallic state. The diketonate ligand, now bonded to the nickel surface, starts to decompose at around 400 K, and generates gas-phase carbon monoxide and molecular hydrogen in TPD peaks at 435 K. More extensive decomposition is seen at 535 K, yielding 2,2-dimethyl-3-oxopentanal, isobutene, ketene, an...

CO Adsorption on Pd–Au Alloy Surface: Reversible Adsorption Site Switching Induced by High-Pressure CO

The interaction between carbon monoxide (CO) and a Pd70Au30(111) alloy surface was investigated under CO pressures with a wide range from ultrahigh vacuum (UHV) to sub-Torr at room temperature by a combination of near-ambient pressure (NAP) X-ray photoelectron spectroscopy and density functional theory calculations. The adsorption site and surface coverage of CO are reversibly controlled by the CO pressure. Under UHV conditions, the CO molecules occupy bridge and hollow sites on contiguous Pd clusters in the Au-rich surface layer. Exposure to sub-Torr CO gas induces site switching of the adsorbed CO on the contiguous Pd clusters from multiple-coordination (hollow and bridge) sites to single-coordination (top) sites, even though the latter sites are energetically less favorable. This behavior is explained by a pressure-induced entropic effect on gas-phase CO, which is in equilibrium with the adsorbed CO. This site switching highlights an important aspect of high-pressure-induced adsorption behavior.

Porous PMMA-titania composites: A step towards more sustainable photocatalysis

TiO2 is an effective photocatalyst for the degradation of aqueous and airborne contaminants when activated by UV light. TiO2 nanoparticles are often deposited onto the surface of a support material to avoid the need for post-use removal of the nanoscale photocatalyst. Polymers have been shown to be suitable photocatalytic support materials, but solvent based methods for TiO2 deposition using hazardous organic solvents such as dichloromethane have negative and avoidable environmental repercussions. In this work, green chemistry principles have inspired a new approach to the formation of polymer–TiO2 composite materials. An existing surfactant-mediated method for the fabrication of porous poly(methylmethacrylate) (PMMA) membranes has been used to form a support material for the photocatalyst while replacing hazardous dichloromethane with the much more benign acetone. The deposition of TiO2 within the UV-transparent porous support material facilitates the construction of flow-through photocatalytic reactors for both aqueous and gas-phase applications. These systems were characterized by the photocatalytic degradation of aqueous methyl orange and gas phase carbon monoxide, electron microscopy, N2 adsorption/desorption surface area measurements, as well as long-term UV durability. The porous PMMA-TiO2 composites possess a methyl orange decolorization rate over 6 times higher than that of the non-porous composite reference materials with comparable TiO2 content. The porous materials reported here are more active, and have superior TiO2 retention than the non-porous benchmark materials, and thus provide a greener foundation for future photocatalytic applications.

In Situ Pulse Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS) Mass Spectrometry Study of the Water-Gas Shift Reaction on Nickel(II) Oxide–Zinc(II) Oxide Catalysts

The water-gas shift (WGS) reaction has been studied by pulsing carbon monoxide (CO) into a steady-state water (H2O)-Ar flow over nickel(II) oxide-zinc oxide (NiO-ZnO) catalysts using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) coupled with a mass spectrometer method using the pulse technique (in situ pulse DRIFTS-MS) for different flow rates (gas hourly space velocity [GHSV] of 24,000-72,000 h(-1)) and reaction temperatures (250-350 °C). The results obtained from the in situ pulse DRIFTS-MS revealed that there are two types of water adsorption bands on the surface of the catalyst: (i) molecular adsorption (infrared [IR] bands in the 2500-3600 cm(-1) range and at 1640 cm(-1)), and (ii) dissociative adsorption at 3700 cm(-1), where carboxyl bands are formed at 1461 and 1368 cm(-1) and the gas-phase CO is adsorbed at 2187 and 2111 cm(-1) on the surface of the catalyst. After using a GHSV = 24,000 h(-1) H2O/Ar flow, we probed the existence of two active intermediates via the formation of two hydrogen production peaks. The products of hydrogen gas (H2) and carbon dioxide (CO2) had two pathways: the redox process and the associative process via the intermediate of the carboxyl group. In situ pulse DRIFTS-MS proves to be an effective approach for studying the nature of adsorbed species on the catalyst surface and the nature of the reaction product.

Double Auger Emission of fixed-in-space Carbon Monoxide following Core-Excitation and Ionization

Double Auger decay after core-level photo excitation and after ionization through synchrotron radiation in gas phase carbon monoxide has been studied. We report the first experiment where both Auger electrons in double Auger decay have been measured in coincidence with the ionic fragments.

Construction of Sensitive and Selective Zirconia-Based CO Sensors Using ZnCr2O4-Based Sensing Electrodes

The carbon monoxide (CO) sensitivity of a mixed-potential-type yttria-stabilized zirconia (YSZ)-based tubular-type sensor utilizing a ZnCr(2)O(4) sensing electrode (SE) was tuned by the addition of different precious metal nanoparticles (Ag, Au, Ir, Pd, Pt, Ru and Rh; 1 wt % each) into the sensing layer. After measuring the electromotive force (emf) response of the fabricated SEs to 100 ppm of CO against a Pt/air-reference electrode (RE), the ZnCr(2)O(4)-Au nanoparticle composite electrode (ZnCr(2)O(4)(+Au)-SE) was found to give the highest response to CO. A linear dependence on the logarithm of CO concentration in the range of 20-800 ppm at an operational temperature of 550 °C under humid conditions (5 vol % water vapor) was observed. From the characterization of the ZnCr(2)O(4)(+Au)-SE, we can conclude that the engineered high response toward CO originated from the specific properties of submicrometer sized Au particles, formed via the coalescence of nanosized Au particles located on ZnCr(2)O(4) grains, during the calcining process at 1100 °C for 2 h. These particles augmented the catalytic activities of the gas-phase CO oxidation reaction in the SE layer, as well as to the anodic reaction of CO at the interface; while suppressing the cathodic reaction of O(2) at the interface. In addition, the response of the ZnCr(2)O(4)(+Au)-SE sensor toward 100 ppm of CO gradually increased throughout the 10 days of operation, and plateaued for the remainder of the month that the sensor was examined. Correlations between SEM observations and the CO sensing characteristics of the present sensor were suggestive that the sensitivity was mostly affected by the morphology of the Au particles and their catalytic activities, which were in close proximity to the ZnCr(2)O(4) grains. Furthermore, by measuring the potential difference (emf) between the ZnCr(2)O(4)(+Au) and a ZnCr(2)O(4) electrode, sensitivities to typical exhaust component gases other than CO were found to be negligible at 550 °C.

Electrooxidation of CO on Uniform Arrays of Au Nanoparticles: Effects of Particle Size and Interparticle Spacing

Uniform arrays of Au nanoparticles with controlled size and interparticle distance were synthesized by using polystyrene-b-poly(2-vinylpyridine) as a template and an Ar plasma treatment. These uniform arrays of nanoparticles are ideal model systems for studying the effects of particle size and interparticle distance on their catalytic activity. Electrooxidation of carbon monoxide (CO) on these particle arrays in CO-saturated 0.1 M NaOH was examined. On particle arrays with a particle size of ca. 4 nm and an interparticle distance varying from 28 to 80 nm, rotating disk electrode (RDE) voltammetric results show that the half-wave potential for CO oxidation shifted to more positive potentials as the interparticle distance increased. This apparent kinetic difference can be explained by the CO diffusion pattern change with the interparticle distance. On particle arrays with a similar interparticle distance but varying size from 2.4 to 9.0 nm, the electrooxidation of CO shows a particle size-dependent activity, with the highest activity obtained on 4.2 nm Au particles, as revealed by the Tafel plot. The Tafel slope also depends on the particle size, with the smallest slope obtained on 4.2 nm particles. The particle size-dependent catalytic activity was tentatively explained in terms of the size-dependent adsorption properties. A brief comparison was made with the results from gas phase CO oxidation on Au nanoparticles.

Detection of C3O in the Low‐Mass Protostar Elias 18

We have performed new laboratory experiments which gave us the possibility to obtain an estimate of the amount of carbon chain oxides (namely C3O2, C2O, and C3O) formed after irradiation (with 200 keV protons) of pure CO ice, at 16 K. The analysis of laboratory data indicates that in dense molecular clouds, when high CO depletion occurs, an amount of carbon chain oxides as high as 2-3x10^-3 with respect to gas phase carbon monoxide can be formed after ion irradiation of icy grain mantles. Then we have searched for gas phase C2O and C3O towards ten low-mass young stellar objects. Among these we have detected the C3O line at 38486.891 MHz towards the low-mass protostar Elias 18. On the basis of the laboratory results we suggest that in dense molecular clouds gas phase carbon chain oxides are formed in the solid phase after cosmic ion irradiation of CO-rich icy mantles and released to the gas phase after desorption of icy mantles. We expect that the Atacama Large Millimeter Array (ALMA), thanks to its high sensitivity and resolution, will increase the number of carbon chain oxides detected in dense molecular clouds.

X-Ray Absorption Measured in the Resonant Auger Scattering Mode

We report both experimental and theoretical studies on x-ray absorption measured in the resonant Auger scattering mode of gas phase carbon monoxide near the O1s-->2pi region. Both experiment and theory display a crucial difference between the x-ray absorption profiles obtained in the conventional and resonant scattering modes. Lifetime vibrational interference is the main source of the difference. It is demonstrated that such interference, which arises from a coherent excitation to overlapping intermediate levels, ruins the idea for obtaining x-ray absorption spectra in a lifetime broadening free regime.

Resonant double Auger decay in carbonK-shell excitation of CO

We have studied double Auger decay after C 1s→2 photoexcitation in gas phase carbon monoxide. Two distinct processes, namely direct double Auger decay and cascade double Auger decay, are identified and studied in detail using multiple coincidence techniques. Cascade Auger decay is shown to be the overall dominant process. Decay channels involving the dissociation of the molecule followed by autoionization of the oxygen fragments are observed.

Synthesized Tin-Activated Carbon Adsorbent for Purer and Cheaper Hydrogen

In an attempt to produce hydrogen for a less relatively expensive proton exchange membrane (PEM) fuel cell than the present expensive means, the steam reformation of methane was proposed because a steam reformer is a cheap source of hydrogen compared to water electrolysis and other methods. However, the reformer effluent contains about 75% hydrogen and 25% carbon monoxide (CO) by volume. Reformation with a good catalyst could yield a 1% CO content in the effluent, but 1% CO, which is equivalent to 10,000 ppm CO, has a poisoning effect on the platinum (Pt) catalysts of the PEM fuel cell electrodes. Since the catalyst can only tolerate CO of less than 100 ppm, it is then expedient to introduce a purification system to reduce the CO content to the required concentration. To achieve this, activated carbon (AC)-SnO 2 adsorbent was synthesized and used in a pressure swing adsorption (PSA) system. Consequently, 34.57% SnCl 2 ./H 2 O salt as a tin ion precursor, was impregnated onto activated carbon to improve its adsorptive interaction with CO. A model H 2 /CO mixture, representing the stoichiometric ratio of H 2 and CO in the steam reformer effluent gas was used. It was observed that the amount of CO adsorbed was almost equal to that desorbed, which implies that the adsorption of CO on the prepared adsorbents is reversible. Further exploitation of the impregnated activated carbon in PSA experiments showed that adsorption of carbon monoxide was higher with the impregnated carbon than in the pure carbon. Within the limits of analytical error, it was seen that the concentration of carbon monoxide, which was 1000 ppm, was successfully reduced to 40.2 and 10.4 ppm by the pure and the impregnated activated carbons, respectively. These results confirmed that Sn-activated carbon in the PSA system could be used in the purification of hydrogen. The species responsible for the improved gas phase CO adsorption with the impregnated carbon was found to be SnO 2 . Consequently, the high adsorptive selectivity of AC-SnO 2 towards gas phase CO, when compared to that of the pure carbon, confirms its superiority and applicability in the removal of CO. This phenomenon then indicates a good future for the robustness of this promising adsorbent, since CO remains a major contributor to the current level of the global air pollution problems.

Planar laser-induced fluorescence imaging of carbon monoxide using vibrational (infrared) transitions

We report a new imaging diagnostic suitable for measurements of infrared-active molecules, namely infrared planar laser-induced fluorescence (IR PLIF), in which a tunable infrared source is used to excite vibrational transitions in molecules and vibrational fluorescence is collected by an infrared camera. A nanosecond-pulse Nd:YAG-pumped KTP/KTA OPO/OPA system is used to generate 12 mJ of tunable output near 2.35 μm which excites the 2ν band of carbon monoxide (CO); fluorescence resulting from excited CO is collected at 4.7 μm by using an InSb focal plane array. Quantitative, high-SNR PLIF imaging of gas-phase CO is demonstrated at a 10-Hz acquisition rate with a minimum detection limit of 1350 ppm at 300 K.

Supported Metal Catalysts: Preparation, Characterization, and Function

Abstract The adsorption of carbon monoxide, dioxygen. and dihydrogen on three platinum catalysts (0.89% w/w Pt/alumina, 0.75% w/w Pt/silica, and 0.48% w/w Pt/molybdena) prepared hy impregnation and one catalyst (0.52% w/w Pt/molybdena) prepared by co-crystallization has been studied. On Pt/alumina and Pt/silica, three states of adsorbed carbon monoxide have been detected, one weakly held at 293 K and two strongly held. Of the two strongly adsorbed species, one is linearly bonded, the other bridge bonded. Over 80% of the strongly held material is able to exchange with gas-phase carbon monoxide. On the Pt/alumina, adsorption of submonolayer quantities of carbon monoxide results in a modification of the binding energy of surface hydrogen such that the hydrogen can be displaced by subsequent adsorption of carbon monoxide. Carbon monoxide reacts with hydroxyl groups of the support during thermal desorption from Pt/alumina to form carbon dioxide and dihydrogen. An activation energy barrier was observed for carbon monoxide adsorption on Pt/silica within the temperature range 256-297 K. Pt/molybdena prepared by co-crystallization adsorbed carbon monoxide but not dioxygen.

Raman Scattering Study of the Adsorption State of CO on Silver

Three intense Raman bands were observed at 158, 180 and 2142 cm -1 after the exposure of the silver film to about 0.5 L of carbon monoxide (CO) at 80 K. We found that oxygen coadsorbed with CO induces an upward peak shift of the C-O stretching Raman band to a frequency above that of a gas phase CO. The re-enforcement of the bond between CO and the substrate by the presence of the coadsorbed oxygen was confirmed by the observation of the upward peak shifts of the low frequency bands. Discussion on the change in the adsorption state of CO due to the coadsorption is given in relation to an electronegativity of the coadsorbate. The proposed scheme consistently explains not only the peak shift of the C-O stretching band but also the change in the bond strength between CO and the substrate.