Carbon Monoxide Selectivity Research Articles

Circadian clock disruption by selective removal of endogenous carbon monoxide

Circadian rhythms are regulated by transcription-translation feedback loops (TTFL) of clock genes. Previous studies have demonstrated that core transcriptional factors, NPAS2 and CLOCK, in the TTFL can reversibly bind carbon monoxide (CO) in vitro. However, little is known about whether endogenous CO, which is continuously produced during a heme metabolic process, is involved in the circadian system. Here we show that selective removal of endogenous CO in mice considerably disrupts rhythmic expression of the clock genes. A highly selective CO scavenger, hemoCD1, which is a supramolecular complex of an iron(II)porphyrin with a per-O-methyl-β-cyclodextrin dimer, was used to remove endogenous CO in mice. Intraperitoneal administration of hemoCD1 to mice immediately reduced the amount of internal CO. The removal of CO promoted the bindings of NPAS2 and CLOCK to DNA (E-box) in the murine liver, resulting in up-regulation of the E-box-controlled clock genes (Per1, Per2, Cry1, Cry2, and Rev-erbα). Within 3 h after the administration, most hemoCD1 in mice was excreted in the urine, and heme oxygenase-1 (HO-1) was gradually induced in the liver. Increased endogenous CO production due to the overexpression of HO-1 caused dissociation of NPAS2 and CLOCK from E-box, which in turn induced down-regulation of the clock genes. The down-regulation continued over 12 h even after the internal CO level recovered to normal. The late down-regulation was ascribed to an inflammatory response caused by the endogenous CO reduction. The CO pseudo-knockdown experiments provided the clear evidence that endogenous CO contributes to regulation in the mammalian circadian clock.

Nanostructured Cu-Sn Alloy for Actively and Selectively Converting CO2 to CO

Many strategies have been proposed for carbon dioxide (CO2) reduction aiming to close the carbon cycle and compensate anthropogenic CO2 emissions. Electrochemical CO2 reduction has several advantages that it can be carried out under ambient conditions with water as the only additional feedstock, and electricity generated from renewable sources can be employed to achieve a fully sustainable route [1]. Copper (Cu) has unique features for electrochemically converting CO2 to a range of chemicals including hydrocarbons [2], but its selectivity for specific products is low. Especially, at a low or intermediate overpotential, the hydrogen evolution reaction (HER) dominates the overall process on polycrystalline Cu in aqueous solutions [3]. However, the selectivity of Cu can be tuned by introducing a secondary metal. Tin-modified nanostructured Cu (CuSn) electrocatalysts have been developed for electrochemically converting CO2 to carbon monoxide (CO). The doped Sn atoms in the topmost layer alloy with Cu, form a CuSn shell, and efficiently suppress the HER. By optimizing the Sn content in the CuSn layer and the nanostructure, the faradaic efficiency for CO reaches > 90 % at -0.7 V vs. RHE, and remains above 85 % in a wide potential range from -0.7 to -1.0 V [4]. However, the excellent selectivity for CO can be only observed at CuSn dendrites. When the CuSn catalyst has a particulate morphology, the selectivity for CO becomes much worse, even though the surface composition has the optimal Cu/Sn ratio. The CuSn particles are active for the HER at a low overpotential. Although the HER can be efficiently suppressed to a faradaic efficiency of less than 15 % at a high overpotential, the major products for CO2 reduction are both CO and formate (COOH-) [5]. This work highlights the importance of nanostructure and surface composition of CuSn catalysts for active and selective CO2 reduction. Electrodes consisting of a three-dimensional porous architecture are prepared for a large active surface per unit geometric area. The CO production achieves a high partial current density of 4.9 mA·cm-2 at -0.8 V [4]. [1] Centi, G., et al. Energy Environ. Sci. 2013, 6, 1711-1731 [2] Qiao, J., et al., Chem. Soc. Rev. 2014, 43, 631-675 [3] Li, C., et al., J. Am. Chem. Soc. 2012, 134, 7231-4 [4] Zeng, J., et al., submitted [5] Ju, W., et al., in preparation

Preferential oxidation of CO in H2/H2O/CO2 water–gas shift feedstocks over Cu-based carbon nanotubes-supported heterogeneous catalysts

Selective carbon monoxide (CO) oxidation reaction was studied over mono- and bimetallic Co, Cu and Fe, as well as Cu–Co and Cu–Fe heterogeneous catalysts, using multi-walled carbon nanotubes (MWCNT) as substrates. Materials were synthesized by wet (co-)impregnation technique and characterised. It was found that hydrophilic hydroxyl and carboxyl nanotubes’ (CNT) functional groups were favourable for a strong metal–support interaction. The catalytic conversion performance for preferential CO oxidation (PROX) process was carried out in hydrogen, water, and carbon dioxide-containing feedstock gasses. The addition of iron or cobalt to Cu/CNT improved the activity with comparison to Cu/CNT. The optimized Cu–Fe/CNT could preferentially oxidize dilute CO in H2-rich simulated WGS streams within a wide temperature range of 120–220 °C. The temperatures, where 50% CO conversion was achieved, were as follows: Cu–Fe/CNT (120 °C) > Cu–Co/CNT (140 °C) ≈ Cu/CNT (140 °C). A high determined selectivity towards CO2 for Cu–Fe/CNT could be attributed to the presence of CuFe2O4 and the synergy between Co and Cu for Cu-Co/CNT. At 220 °C and in a 1% CO/1% O2/10% H2O/10% CO2/60% H2/18% He stream, Cu–Fe/CNT could achieve a 100% CO conversion, granting a low H2 conversions, not differing from those in the absence of CO2, while its turnover performance remained stable for a longer continuous time-on-stream with basically no deactivation. By comparison, Cu–Fe/CNT exhibited a higher apparent rate and lower activation energy of CO conversion (with and without H2O and CO2).

Effect of various metal oxides phases present in CuMnOx catalyst for selective CO oxidation

Hopcalite (CuMnOx) is a highly efficient catalyst for low temperature oxidation of Carbon monoxide (CO). As synthesized by Co-precipitation method, it shows the high activity for CO oxidation. The coordination between CuO and MnOx in CuMnOx catalyst improves the catalytic activity for CO oxidation. In this research work, we investigate the individual catalytic activity of CuO and MnOx and compare with the multiphase CuMnOx catalyst. The performance of multiphase catalysts CuO and MnO2 were numerous times higher as compared to single phase CuMnOx. The activity order of catalysts for CO oxidation was as follows: CuMnOx> MnOx > CuOx. The success of CuMnOx catalyst has prompted a great deal of research work into each component and nature of active sites. In CuMnOx catalyst, the MnOx acts as an oxygen donor and CuO acts as an oxygen acceptor. The presence of MnOx is possible to assist in the reduction of CuO, due to the coordination between CuO and MnOx. The calcination strategies of precursors highly affect the physicochemical and catalytic properties of the catalysts for CO oxidation. The reactive calcination (RC) conditions (4.5% CO in air) for prepared catalysts showed the best activity result for CO oxidation, as compared to the traditional method of calcination.

Copper Oxide-Based Photocathodes and Electrocatalysts for the (Photo)Electrochemical Reduction of Protons and Carbon Dioxide

The use of renewable electricity to drive chemical reactions is an approach to storing the energy from intermittent sources (solar, wind) in the form of chemical bonds. Combining photoabsorber and electrocatalytic components into integrated devices, we developed copper oxide-based photocathodes for proton reduction to hydrogen (1,2), as well as carbon dioxide reduction to carbon monoxide (3), in demonstrations of efficient solar-to-fuels conversion. Recently, oxide-derived copper emerged as an intriguing electrocatalyst for the conversion of carbon dioxide into hydrocarbon products. In an effort to modify the product selectivity of copper oxide nanowire arrays, we used atomic layer deposition to apply conformal layers of tin oxide to the electrode surface. This copper-tin-oxide hybrid exhibited nearly unity selectivity for carbon monoxide as CO2 reduction product, deviating significantly from the behavior expected for copper or tin alone, neither of which typically produce CO at high selectivity. This result suggests sub-monolayer composition modification of electrode surfaces can be a powerful strategy for tuning electrocatalyst selectivity. J. Luo, L. Steier, M.-K. Son, M. Schreier, M. T. Mayer and M. Grätzel, Nano Letters, 2016, 16, 1848–1857.P. Dias, M. Schreier, S. D. Tilley, J. Luo, J. Azevedo, L. Andrade, D. Bi, A. Hagfeldt, A. Mendes, M. Grätzel and M. T. Mayer, Adv. Energy Mater., 2015, 5, 1501537.M. Schreier, J. Luo, P. Gao, T. Moehl, M. T. Mayer and M. Grätzel, J. Am. Chem. Soc., 2016, 138, 1938–1946.M. Schreier, F. Héroguel, L. Steier, S. Ahmad, J. S. Luterbacher, M. T. Mayer, J. Luo and M. Grätzel, Nature Energy, 2017, 2, 17087.

Highly porous monolith/TiO2 supported Cu, Cu-Ni, Ru, and Pt catalysts in methanol steam reforming process for H2 generation

A comprehensive investigation on the steam reforming of methanol (SRM) process using a microstructure monolith in conjunction with a synthesized nanostructure of TiO2 is presented. The surface of the designed monolith/TiO2 structure was coated with copper, copper/nickel, ruthenium, and platinum as the catalyst. The prepared catalysts were then characterized with FE-SEM, AFM, BET surface area measurement, FT-IR, far-infrared, temperature programmed reduction (TPR), and X-ray diffraction (XRD). The obtained results show that in this process, the designed Monolith/TiO2 structure has a remarkable impact on methanol conversion (99%) and carbon monoxide selectivity (5%). These results are interpreted by the high surface area and superb mass transfer in this micro/nano engineered structure. These results also indicated that the catalyst activity and dispersion are influenced by the metal-support interaction, which is more pronounced in the TiO2 supports. The ruthenium catalyst presented the highest conversion and selectivity for this process. However, the economically viable property of the Cu-Ni catalyst supposes it as an alternative for the noble ruthenium catalyst.

Synthesis of CuCl/Boehmite adsorbents that exhibit high CO selectivity in CO/CO2 separation

We developed nanoporous adsorbent exhibiting unprecedented performance in separation of toxic carbon monoxide (CO). The adsorbent was prepared by dispersing CuCl on mesoporous boehmite via thermal monolayer dispersion route. A key point of the present synthesis is dispersing optimized amount of CuCl on the boehmite at a moderate temperature to maintain the characteristics of the boehmite. We performed a systematic study to reveal that a CuCl/boehmite composite (30wt% CuCl in total) thermally treated at 573K was the best optimized sample for CO separation. The CuCl/boehmite had a high capacity of CO adsorption (1.56mmolg−1) and an exceedingly low capacity of CO2 adsorption (0.13mmolg−1) under 100kPa of each gas at 293K. The CO/CO2 separation factor was 12.4. To the best of our knowledge, this value is the best on record. The achievement of this work is attributed to finding a new type of suitable supporting material: boehmite. The boehmite has a high affinity to CuCl, exhibits excellent dispersion of the CuCl, and achieves a superior CO adsorption capacity. However, it has a weak interaction with CO2. The CuCl/boehmite composite is a promising adsorbent for selective separation of CO from combustion exhaust and industrial off-gas streams.

BINIVOX catalyst for hydrogen production from ethanol by low temperature steam reforming (LTSR)

Nickel doped bismuth vanadate [ $$\hbox {Bi}_{4}(\hbox {V}_{0.90}\hbox {Ni}_{0.10})_{2}\hbox {O}_{11- \delta }$$ ;BINIVOX] calcined at $$800\,{^{\circ }}\hbox {C}$$ (BINIVOX-800) catalyst is prepared by a solution combustion method. The catalytic activity study is carried in the temperature range of 250– $$400\,{^{\circ }}\hbox {C}$$ , and with the molar feed ratios of water: ethanol at 23:1 and 2.5:1. The study reveals an increase in the ethanol conversion and selectivity of carbon dioxide & hydrogen but a decrease in the selectivity of carbon monoxide and methane with an increase in temperature and water: ethanol mole ratio. Fresh and used catalysts are characterized using DTA, TGA, XRD and FTIR. XRD results reveal that the fresh catalyst is phase pure $$\upgamma $$ -BINIVOX. The phase purity and crystallinity of the catalyst is retained after 30 h of activity study. Catalytic activity of nickel-doped bismuth vanadate (BINIVOX) powder for hydrogen production from ethanol via low-temperature steam reforming is reported here. Preliminary results show an increase in ethanol conversion and selectivity of carbon dioxide and hydrogen with temperature and water: ethanol mole ratio.

Ethylene Epoxidation in a Low-Temperature Parallel Plate Dielectric Barrier Discharge System: Effect of Oxygen Source

The objective of this work was to investigate the effects of two different oxidizing agents [nitrous oxide (N2O) and air], compared to the reported pure oxygen (O2), on the ethylene epoxidation performance in a low-temperature parallel plate dielectric barrier discharge (DBD) system with two frosted glass plates as the dielectric barrier material under ambient temperature and atmospheric pressure. A separate feed technique, with the ethylene (C2H4) feed position fraction of 0.5, was used to reduce all the undesirable reactions and to maximize the ethylene oxide (EO) production (selectivity and yield). The N2O system with a N2O/C2H4 feed molar ratio of 0.17:1 exhibited the highest ethylene epoxidation performance (80.1% EO selectivity and 21.9% EO yield) with a very low carbon monoxide selectivity and the lowest power consumption, as compared to pure O2 and air as oxidant systems at their respective optimal feed molar ratios of 0.2:1 and 0.1:1, respectively. Interestingly, the EO yield from the DBD system ...

Surface-Morphology-Dependent Electrolyte Effects on Gold-Catalyzed Electrochemical CO2 Reduction

The electrocatalytic property of a flat or an oxide-derived nanostructure Au electrode was investigated using surface sensitive analysis methods such as impedance spectroscopy and Kelvin probe force microscopy (KPFM) when electrochemical conversion of carbon dioxide (CO2) to carbon monoxide (CO) was performed with either KHCO3- or NaHCO3-based neutral electrolyte. A strong dependence on the cation of the electrolyte was exhibited on the flat Au electrode surface. CO selectivity and capacitance dispersion are significantly higher with the KHCO3 electrolyte. On the other hand, the nanostructured Au electrodes, having much more improved activity and durability of CO2 reduction, showed much less electrolyte-dependent catalytic activity. The difference in CO selectivity with KHCO3 and NaHCO3 electrolytes can be explained by the difference in hydration level and consequent adsorption strength of the cations on the flat Au metal electrodes, implying that ion-pairing interactions between the metal, cations, CO2, ...

The Effect of Copper Addition on the Activity and Stability of Iron-Based CO₂ Hydrogenation Catalysts.

Iron-based CO2 catalysts have shown promise as a viable route to the production of olefins from CO2 and H2 gas. However, these catalysts can suffer from low conversion and high methane selectivity, as well as being particularly vulnerable to water produced during the reaction. In an effort to improve both the activity and durability of iron-based catalysts on an alumina support, copper (10–30%) has been added to the catalyst matrix. In this paper, the effects of copper addition on the catalyst activity and morphology are examined. The addition of 10% copper significantly increases the CO2 conversion, and decreases methane and carbon monoxide selectivity, without significantly altering the crystallinity and structure of the catalyst itself. The FeCu/K catalysts form an inverse spinel crystal phase that is independent of copper content and a metallic phase that increases in abundance with copper loading (>10% Cu). At higher loadings, copper separates from the iron oxide phase and produces metallic copper as shown by SEM-EDS. An addition of copper appears to increase the rate of the Fischer–Tropsch reaction step, as shown by modeling of the chemical kinetics and the inter- and intra-particle transport of mass and energy.

A readily available colorimetric and near-infrared fluorescent turn-on probe for detection of carbon monoxide in living cells and animals

Since carbon monoxide (CO) was recognized as an important gasotransmitter, great interest has been given to develop probes for detection of this gas molecule in living systems. While several fluorescent probes have been developed very recently for imaging CO in living cells, probes for in vivo detection of CO have not yet been reported. Herein, we report a new NIR fluorescent CO probe that can be used for detection of CO both in vitro and in vivo. This probe works in almost wholly aqueous solution under mild conditions and shows high selectivity and sensitivity for CO in the presence of Pd2+, giving rapid (within few minutes) and distinct colorimetric and near-infrared (NIR) fluorescent turn-on signal changes with a detection limit as low as 3.2nM. Moreover, we also show that this probe has low cytotoxicity and can be conveniently used to image CO in both living cells and animals.

Electrode Characterization in a Flowing Electrolyte Reactor for the Electrochemical Reduction of CO2 to CO

The development of an energy efficient carbon dioxide (CO2) electroreduction process could simultaneously curb anthropogenic CO2 emissions and provide a sustainable pathway for the generation of chemicals and fuels. Pursuant to this goal, significant efforts have been devoted to developing novel electrocatalysts that enable selective CO2 reduction, at low overpotentials, to a range of valuable products. Of particular interest is carbon monoxide (CO), a key component of synthesis gas, along with hydrogen, which, through Fischer-Tropsch processing, can be used to generate a range of liquid hydrocarbons. While many metals are capable of forming CO as the primary CO2 reduction product, gold may offer the best combination of activity, selectivity, and stability1,2. In contrast to the concerted efforts on catalyst development, fewer studies3–5 have sought to characterize electrode performance within operating electrolyzers, particularly under operating conditions and in cell configurations that more closely align with practical application. To this end, we seek to develop high performance electrodes for the reduction of CO2 to CO and to quantify performance-limiting factors of those electrodes in a gas-liquid electrochemical flow cell. Drawing from advanced polymer electrolyte fuel cell and electrolyzer designs, we have developed a flowing electrolyte electrochemical reactor with gas phase reactant delivery and a reference electrode directly between the anode and cathode. Serving as an analytical platform, the configuration enables in-situ investigation of electrode performance via a combination of polarization and electrochemical impedance spectroscopy. Specifically, we aim to quantify and mitigate resistive losses (e.g., kinetic, ohmic, mass transport) as a function of electrode preparation, cell configuration, and operating conditions. Developing a better understanding of the electrode performance within an operating cell can inform future catalyst / electrode development campaigns for a range of CO2 reduction systems. 1. Hori, Y., Wakebe, H., Tsukamoto, T. & Koga, O. Electrocatalytic process of CO selectivity in electrochemical reduction of CO2 at metal electrodes in aqueous media. Electrochimica Acta 39, 1833–1839 (1994). 2. Salih, T. et al. Cost Effective and Scalable Synthesis of Supported Au Nanoparticles for the Electroreduction of CO 2 to CO. Sci. Adv. Mater. 9, 888–895 (2017). 3. Wu, J. et al. Electrochemical Reduction of Carbon Dioxide II. Design, Assembly, and Performance of Low Temperature Full Electrochemical Cells. J. Electrochem. Soc. 160, F953–F957 (2013). 4. Kim, B., Hillman, F., Ariyoshi, M., Fujikawa, S. & Kenis, P. J. A. Effects of composition of the micro porous layer and the substrate on performance in the electrochemical reduction of CO2 to CO. J. Power Sources 312, 192–198 (2016). 5. Liu, Z. et al. Electrochemical generation of syngas from water and carbon dioxide at industrially important rates. J. CO2 Util. 15, 50–56 (2016).

Hydrogen Bubble Templated Electrodeposited Cu As CO2 Reduction Catalyst: Substrate Effect

Selective conversion of CO2 into high quality chemical feedstock and fuels represents an emerging energy storage technology1. The electrochemical reduction of carbon dioxide using renewable sources of energy is a promising way of utilizing the only intermittently available renewable energies to produce chemical feedstocks and fuels for later use. Presently, copper is the one metal in focus because of its ability to catalyze CO2 reduction towards energy-dense hydrocarbon products. However, the electrochemical reduction of CO2 on copper results in many different products at a wide range of overpotentials. The selectivity and efficiency of the Cu-based catalysts towards specific products can be improved by fine tuning the structure and composition2-4. In this work, high surface area porous Cu films were electrodeposited either on Cu or Pt substrates at various deposition currents and durations using the dynamic hydrogen bubble template method5. During electrodeposition at high current values, the size and residence time of H2 bubbles vary based on the substrate and on the in-situ deposited Cu, leading to significantly different catalyst morphologies. Consequently, well-defined dendritic structures with large pores are observed (inset of Fig. 1) for Cu deposited on Cu substrate (CuCat/Cu) as compared to Cu deposited on Pt substrate (CuCat/Pt). Interestingly, product quantification by gas chromatography during electrochemical measurements showed that the product selectivity observed for all variations of the catalysts deposited on a particular substrate does not depend significantly on the differences in pore size and film thickness of the material. However there is a difference in product selectivity for the respective catalysts deposited on different substrates as represented in Fig. 1, where ethylene and carbon-monoxide selectivities are shown at two different potentials. The formation of methane is significantly suppressed (<1%) on both substrates in the potential range where the catalysts show high selectivity for ethylene. From X-ray absorption measurements it is observed that the catalysts are composed of metallic Cu and CuI 2O species with no evidence of CuIIO species. The morphological changes, atomic state and composition of the catalyst may have a dialectic role in deciding the selectivity. In the follow-up work, the selectivity of various Cu films electrodeposited on both the substrates will be correlated with respect to surface area and CuI 2O content after comprehensive quantification of the gaseous and liquid reaction products by gas chromatography, liquid gas chromatography and HPLC. These studies are expected to reveal strategies by which catalysts can be designed for higher selectivity towards a specific hydrocarbon product. References M. Gattrell, N. Gupta and A. Co, J. Electroanal. Chem., 594, 1 (2006). 2. A. Dutta, M. Rahaman, N. C. Luedi, M. Mohos and P. Broekmann, ACS Catal. 6, 3804 (2016).H. Mistry, A. S. Varela, C. S. Bonifacio, I. Zegkinoglou, I. Sinev, et. al, Nat. Commun., 7, 12123 (2016).A. S. Varela, C. Schlaup, Z. P. Jovanov, P. Malacrida, S. Horch, et. al, J. Phys. Chem. C, 117, 20500 (2013).H. -C. Shin, J. Dong and M. Liu, Adv. Mater ., 15, 1610 (2003). Figure 1

DBD Plasma Assisted CO2 Decomposition: Influence of Diluent Gases

Carbon dioxide (CO2) partial reduction to carbon monoxide (CO) and oxygen has been conducted in a dielectric barrier discharge reactor (DBD) operating a packed bed configuration and the results are compared with that of no packing condition. The effect of diluent gas is studied to understand the influence on dielectric strength of the plasma gas on CO2 splitting, with the objective of obtaining the best CO selectivity and high energy efficiency. Typical results indicated that among N2, He and Ar gases, Ar showed the best decomposition efficiency. Glass beads packing has a strong influence on the performance, probably due to the enhanced field strength due to dielectric nature of the packed material. In a similar manner, Ar mole ratio in the gas mixture also played a significant role, where the maximum CO2 conversion of 19.5% was obtained with packed DBD at CO2:Ar ratio 1:2. The best CO yield (16.8%) was also obtained under the same conditions. The highest energy efficiency was found to be 0.945 mmol/kJ. The activated species formed inside the CO2 plasma were identified by optical emission spectroscopy.

Silica nanowires encapsulated Ru nanoparticles as stable nanocatalysts for selective hydrogenation of CO2 to CO

Hydrogenation of carbon dioxide (CO2) to produce useful chemicals has been identified as a promising strategy for mitigation of greenhouse gas emission. Ruthenium (Ru) based catalysts have been reported to be the most active catalysts for the hydrogenation of CO2 to methane (CH4) which unfortunately is also a greenhouse gas and is difficult to activate. Controlling the hydrogenation selectivity to produce carbon monoxide (CO), a direct precursor for enormous important chemicals, thus becomes desirable. However, achieving high CO selectivity with supported Ru catalysts has remained a challenging task. In this work, we report the synthesis of highly selective and stable Ru@mSiO2 nanocatalysts via encapsulation of 1–3nm Ru nanoparticles within mesoporous silica nanowires for hydrogenation of CO2 to CO. Calcination of the catalyst in nitrogen prevented sintering of the encapsulated Ru nanoparticles, making high CO selectivity of up to 100% possible, while larger (5–20nm) Ru particles resulting from calcination in air favored formation of CH4. DRIFTS study of 1–3nm Ru@mSiO2 and 5–20nm Ru@mSiO2 catalysts after adsorption of reaction mixture of H2 and CO2 reveals that different reaction intermediates form on catalyst surface: CO-Run+ on 1–3nm Ru@mSiO2 and formate species on 5–20nm Ru@mSiO2, which are responsible for the distinctively different selectivity observed on 1–3nm Ru@mSiO2 and 5–20nm Ru@mSiO2 catalysts. Plausible reaction pathways have been proposed for selective hydrogenation of CO2 on the two types of catalysts, respectively. In addition, high CO selectivity of 1–3nm Ru@mSiO2 catalyst has been demonstrated to be stable.

Understanding on the selective carbon monoxide sensing characteristics of copper oxide-zinc oxide composite thin films

In the present work we have demonstrated CuO-ZnO composite thin film with optimized CuO content selectively sense carbon monoxide gas. The ‘n’-type gas sensing characteristics of these composite films are changed to ‘p’-type beyond 8.0mol% CuO contents. Through the analyses of photoluminescence spectra in conjunction with XPS we have demonstrated that up to 33.0mol% CuO contents the gas sensing characteristics of the composite films are controlled by the type of point defects (oxygen vacancies, zinc interstitials, and copper vacancies) in CuO and ZnO grains. We have hypothesized that these point defects help to chemi-absorb oxygen and CO preferentially on ZnO and CuO grains respectively to yield selective carbon monoxide sensing of ZnO-CuO composite film with 7.0mol% CuO contents. Beyond 33.0mol% CuO contents the effect of point defects diminishes and the gas sensing characteristic are grossly controlled by the nature of the CuO grains covering ZnO grains in the composite films. Our work provides comprehensive insight towards the understanding of the gas sensing characteristics of hetero-composite thin films deposited using a mixed precursor sol.

YSZ-based sensor using Cr-Fe-based spinel-oxide electrodes for selective detection of CO

A selective carbon monoxide (CO) sensor was developed by the use of both of CuCrFeO4 and CoCrFeO4 as the sensing electrode (SE) for yttria-stabilized zirconia (YSZ)-based potentiometric sensor. The sensing-characteristic examinations of the YSZ-based sensors using each of spinel oxides as the single-SE sensor showed that CuCrFeO4-SE had the ability to detect CO, hydrocarbons and NOx gases, while CoCrFeO4-SE was sensitive to hydrocarbons and NOx gases. Thus, when both SEs were paired as a combined-SEs sensor, the resulting sensor could generate a selective response to CO at 450 °C under humid conditions. The sensor was also capable of detecting CO in the concentration range of 20–700 ppm. Its sensing mechanism that was examined via polarization-curve measurements was confirmed to be based on mixed-potential model. The CO response generated by the combined-SEs sensor was unaffected by the change of water vapor concentration in the range of 1.3–11.5 vol% H2O. Additionally, the sensing performance was stable during 13 days tested.

Detection and Removal of Endogenous Carbon Monoxide by Selective and Cell-Permeable Hemoprotein Model Complexes.

Carbon monoxide (CO) is produced in mammalian cells during heme metabolism and serves as an important signaling messenger. Here we report the bioactive properties of selective CO scavengers, hemoCD1 and its derivative R8-hemoCD1, which have the ability to detect and remove endogenous CO in cells. HemoCD1 is a supramolecular hemoprotein-model complex composed of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinatoiron(II) and a per-O-methylated β-cyclodextrin dimer having an pyridine linker. We demonstrate that hemoCD1 can be used effectively to quantify endogenous CO in cell lysates by a simple spectrophotometric method. The hemoCD1 assay detected ca. 260 pmol of CO in 106 hepatocytes, which was well-correlated with the amount of intracellular bilirubin, the final breakdown product of heme metabolism. We then covalently attached an octaarginine peptide to a maleimide-appended hemoCD1 to synthesize R8-hemoCD1, a cell-permeable CO scavenger. Indeed, R8-hemoCD1 was taken up by intact cells and captured intracellular CO with high efficiency. Moreover, we revealed that removal of endogenous CO by R8-hemoCD1 in cultured macrophages led to a significant increase (ca. 2.5-fold) in reactive oxygen species production and exacerbation of inflammation after challenge with lipopolysaccharide. Thus, R8-hemoCD1 represents a powerful expedient for exploring specific and still unidentified biological functions of CO in cells.

Hydrogen production with a low carbon monoxide content via methanol steam reforming over CuxCeyMgz/Al2O3 catalysts: Optimization and stability

Catalytic activities of Ce–Mg promoted Cu/Al2O3 catalysts via methanol steam reforming was investigated in terms of the methanol conversion level, carbon monoxide selectivity and hydrogen yield. The factors chosen were the reaction temperature, copper content, Mg/(Ce + Mg) weight-percentage and steam to carbon ratios. The catalysts were prepared by co-precipitation and characterized by means of XRD, BET, H2-TPR, and FESEM. The Ce–Mg bi-promoter catalysts gave higher performance due to magnesium penetration into the cerium structure causing oxygen vacancy defects on the ceria. A response-surface-model was then designed to optimize the condition at a 95% confidence interval for complete methanol conversion to a high H2 yield with a low CO content, and revealed an optimal copper level of 46–50 wt%, Mg/(Ce + Mg) of 16.2–18.0%, temperature of 245–250 °C and S/C ratio of 1.74–1.80. No deactivation of the Cu0.5Ce0.25Mg0.05/Al catalyst was observed during a 72-h stability test.