Removal Of Carbon Monoxide Research Articles

Facile Aqueous-Phase Synthesis of the PtAu/Bi2O3 Hybrid Catalyst for Efficient Electro-Oxidation of Ethanol.

In this work, we present a facile aqueous-phase synthesis of a hybrid catalyst consisting of PtAu alloy supported on Bi2O3 microspheres. Multistep reduction of HAuCl4 and K2PtCl4 salts on Bi2O3 and subsequent annealing lead to the formation of this hybrid catalyst. To the best of our knowledge, this is the first report of using Bi2O3 as a catalyst support in fuel cell applications. The material was characterized by powder X-ray diffraction and various microscopic techniques. This composite showed remarkable activity as well as stability toward the electro-oxidation of ethanol in comparison to commercially available Pt/C. The order of the reactivity was found to be commercial Pt/C (50.4 mA/m2mgPt-1) < Pt/Bi2O3(10) (108 mA/m2mgPt-1) < PtAu/Bi2O3(10) (459 mA/m2mgPt-1). The enhancement in the activity can be explained through cooperative effects, namely, ligand effects of gold and Bi2O3 support, which helps in removing carbon monoxide molecules to avoid the poisoning of the Pt active sites.

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.

Modeling the oscillative behavior and carbon monoxide removal by current pulsing technique in H2/CO mixtures for Pt catalyst layer

The main objectives of this study are to investigate the carbon monoxide (CO) poisoning and a mitigation method of high-level CO in a platinum (Pt) catalyst layer using hydrogen (H2)/CO mixture as the inlet fuel. Two separate levels of poisoning, 1000 and 10,000 ppm CO at the anode fuel, are considered and investigated in detail. For this purpose, a one-dimensional transient model is developed including the diffusion of hydrogen and carbon monoxide, the conservation of adsorbed species, and ionic and electronic charges. As a result of CO poisoning, oscillations in overpotential and coverage of adsorbed species are observed for 1000 ppm CO level, while the similar situation is not detected for 10,000 ppm CO. Hence, the behavior of oscillations throughout the catalyst layer thickness, and the reasons are explored for the lower concentration case. For 10,000 ppm CO, a mitigation technique, in which current density is pulsed from 0.1 to 2.5 A/cm2 for a period of time, is performed in order to remove the adsorbed CO from the Pt sites. It is concluded that up to 92% of CO coverage within the catalyst layer can be removed, and 70% of the catalyst layer length is determined to be completely CO-free following the application of current pulsing.

Feedback Response to Selective Depletion of Endogenous Carbon Monoxide in the Blood.

The physiological roles of endogenous carbon monoxide (CO) have not been fully understood because of the difficulty in preparing a loss-of-function phenotype of this molecule. Here, we have utilized in vivo CO receptors, hemoCDs, which are the supramolecular 1:1 inclusion complexes of meso-tetrakis(4-sulfonatophenyl)porphinatoiron(II) with per-O-methylated β-cyclodextrin dimers. Three types of hemoCDs (hemoCD1, hemoCD2, and hemoCD3) that exhibit different CO-affinities have been tested as CO-depleting agents in vivo. Intraperitoneally administered hemoCD bound endogenous CO within the murine circulation, and was excreted in the urine along with CO in an affinity-dependent manner. The sufficient administration of hemoCD that has higher CO-affinity than hemoglobin (Hb) produced a pseudoknockdown state of CO in the mouse in which heme oxygenase-1 (HO-1) was markedly induced in the liver, causing the acceleration of endogenous CO production to maintain constant CO-Hb levels in the blood. The contents of free hemin and bilirubin in the blood plasma of the treated mice significantly increased upon removal of endogenous CO by hemoCD. Thus, a homeostatic feedback model for the CO/HO-1 system was proposed as follows: HemoCD primarily removes CO from cell-free CO-Hb. The resulting oxy-Hb is quickly oxidized to met-Hb by oxidant(s) such as hydrogen peroxide in the blood plasma. The met-Hb readily releases free hemin that directly induces HO-1 in the liver, which metabolizes the hemin into iron, biliverdin, and CO. The newly produced CO binds to ferrous Hb to form CO-Hb as an oxidation-resistant state. Overall, the present system revealed the regulatory role of CO for maintaining the ferrous/ferric balance of Hb in the blood.

Electrochemical conversion of alcohols for hydrogen production: a short overview

In the emerging hydrogen economy, one of the major objectives is the production of electricity using fuel cells, particularly proton exchange membrane fuel cells (PEMFC). In this perspective, high purity hydrogen is needed. Hydrogen is currently mainly produced from fossil fuels (natural gas, oil, and coal) by energy‐consuming and environmentally unfriendly industrial processes that also involve complicated clean up steps for the removal of carbon monoxide and carbon dioxide. Water electrolysis (particularly the proton exchange membrane electrolysis technology, which allows higher efficiency than alkaline technology) appears to be a good candidate for the production of clean hydrogen. The use of renewable primary energy sources, such as wind, solar, tidal, etc., makes this technology greener. However, the low kinetics of water oxidation, which implies high cell voltage (i.e. high energy consumption) even when using noble metal‐based catalysts (Pt, Ru, Ir), makes this technology expensive. Biosourced alcohols can be interesting alternatives as hydrogen carriers in an electrolysis cell; their reversible oxidation potentials are much lower than that of water, ca 0.1 V versus SHE (standard hydrogen electrode) against 1.23 V versus SHE, so that the cell voltages for hydrogen production are lower (and so is the energy consumption). However, the low kinetics of alcohol oxidation in acidic media requires high Pt‐based catalyst loadings at the anode. Direct alcohol alkaline electrolysis cells can be operated with low Pt loading and even non‐noble metals. In the case of glycerol, generation of hydrogen at the cathode can be performed simultaneously with the formation of value‐added products at the anode for a more profit‐making process. WIREs Energy Environ 2016, 5:388–400. doi: 10.1002/wene.193This article is categorized under: Bioenergy &gt; Science and Materials Fuel Cells and Hydrogen &gt; Science and Materials Energy Efficiency &gt; Science and Materials

Pt–Au/CeO2 catalysts for the simultaneous removal of carbon monoxide and formaldehyde

A series of Pt–Au/CeO2 catalysts were prepared via the impregnation deposition–precipitation (IDP) and reduction–deposition precipitation (RDP) methods.

Detailed analysis of Integrated Steam Ethanol Reformer and High Temperature Polymer Electrolyte Membrane Fuel Cell

Utilisation of hydrocarbon fuels as a source of hydrogen for Polymer Electrolyte Membrane Fuel Cell (PEMFC) is a possible solution for the demand for hydrogen infrastructure. Ethanol, which is considered to be a domestic and renewable fuel, is a potential source in this regard. Its use as a source of hydrogen production has received appreciations in recent years. For agriculture based countries such as India, China, Brazil, etc., where ethanol can be produced abundantly, this development serves as a boon to meet their future energy demands. This study presents the analysis of high-temperature PEMFC stack integration into a combined system with Steam Ethanol Reformer (SER). One dimensional mathematical model of the integrated system is developed. Performance of the system is studied methodically by varying the operating parameters such as temperature and steam to carbon ratio (S/C) of the SER, temperature of PEMFC and pressure of the system. In addition, the necessity of a Water Gas Shift (WGS) reactor to function as a carbon monoxide removal unit for pre-treating the reformate gas before it is fed to the high temperature PEMFC is also investigated in this study. The S/C ratio and reformer temperature do not affect the performance of the system considerably as long as the fuel processor unit contains WGS reactor along with the reformer. Inclusion of WGS reactor shows a positive influence on the performance of the fuel processor unit. A higher fuel cell temperature and pressure provides a higher voltage more prominently at higher current densities.

Influence of preparation methods on the structure and catalytic performance of nanostructured La0.7Ba0.3Co0.3Ni0.7O3 for CO oxidation

Nano-perovskite oxides La0.7Ba0.3Co0.3Ni0.7O3 were synthesized by the co-precipitation and polymerized complex route based on the Pechini process methods (denoted as LBCN-Cop and LBCN-P, respectively) and employed in the removal of carbon monoxide (CO) from (N2 + CO + O2) gas mixture through oxidation. In this paper, the effect of the preparation method on the catalytic activity of nanocatalysts is discussed. The catalysts were characterized by XRD, FTIR, BET, TPR, SEM and EDX techniques. The specific surface area of the prepared catalysts varied from 24.55 (LBCN-Cop) to 34.14 (LBCN-P) m2 g−1. SEM investigations revealed that the LBCN-P nanoparticles were uniform spheres in shape with diameters ranging from 50 to 60 nm, whereas more agglomeration of particles was found for the LBCN-Cop catalyst. The results of catalytic activity measurements showed the superiority of the catalyst sample prepared by the Pechini method for CO oxidation at low temperatures compared with that prepared by the co-precipitation method.

Pulmonary Phototherapy for Treating Carbon Monoxide Poisoning.

Carbon monoxide (CO) exposure is a leading cause of poison-related mortality. CO binds to Hb, forming carboxyhemoglobin (COHb), and produces tissue damage. Treatment of CO poisoning requires rapid removal of CO and restoration of oxygen delivery. Visible light is known to effectively dissociate CO from Hb, with a single photon dissociating one CO molecule. To determine whether illumination of the lungs of CO-poisoned mice causes dissociation of COHb from blood transiting the lungs, releasing CO into alveoli and thereby enhancing the rate of CO elimination. We developed a model of CO poisoning in anesthetized and mechanically ventilated mice to assess the effects of direct lung illumination (phototherapy) on the CO elimination rate. Light at wavelengths between 532 and 690 nm was tested. The effect of lung phototherapy administered during CO poisoning was also studied. To avoid a thoracotomy, we assessed the effect of lung phototherapy delivered to murine lungs via an optical fiber placed in the esophagus. In CO-poisoned mice, phototherapy of exposed lungs at 532, 570, 592, and 628 nm dissociated CO from Hb and doubled the CO elimination rate. Phototherapy administered during severe CO poisoning limited the blood COHb increase and improved the survival rate. Noninvasive transesophageal phototherapy delivered to murine lungs via an optical fiber increased the rate of CO elimination while avoiding a thoracotomy. Future development and scaling up of lung phototherapy for patients with CO exposure may provide a significant advance for treating and preventing CO poisoning.

Control of gaseous pollution via the leaves of non-edible trees

The accelerated increase of the use of various transportation means, industrial machinery and other power consuming technologies has led to tremendous degradation of outdoor air quality all around the world. Green solution was tested here as an innovative gas control mean via non edible Myrtus communis green leaves as natural sorption media. Statistical analyses were applied in order to examine the correlation between various parameters of this study. The tests of gas records around the tree that was targeted by a gas stream of 5 KW power generators have demonstrated an excellent gas control role of the green leaves, with average efficiencies of about 75% and 82% for the removal of Nitrogen Dioxide and Carbon Monoxide, respectively. An interesting finding of this research was that the sorption role of green leaves has promoted their sizes and Chlorophyll Content Index.

Epoxide-assisted alumina aerogels by rapid supercritical extraction

Aerogels offer a potential alternative to noble metals that could reduce both the cost and environmental impact associated with catalytic converter production. The environmental impact of the production of aerogel catalysts could be further reduced by using a rapid supercritical extraction (RSCE) technique, which reduces the time and solvent waste associated with aerogel preparation. Alumina aerogels, which have shown activity in catalyzing exhaust processing reactions, were prepared using an epoxide-assisted gelation technique with RSCE processing in a contained mold in a hydraulic hot press. Samples were characterized by FTIR, XRD, SEM, EDX, nitrogen adsorption porosimetry and pycnometry. Solvent characterization by GC–MS headspace analysis shows that excess propylene oxide and chloropropanol products of an irreversible epoxide ring-opening reaction are present in the alumina gel following gelation, but can be removed via solvent exchange. Alumina aerogels with surface areas as high as 790m2/g and bulk densities as low as 0.05g/mL were prepared. Preliminary characterization of these aerogels, utilizing a catalytic test bed and a simulated emission gas blend, demonstrates that they have moderate ability for removal of hydrocarbons, carbon monoxide and nitrogen oxide.

A novel biological sulfate reduction method using hydrogenogenic carboxydotrophic mesophilic bacteria

Sulfate reduction by carbon monoxide (CO) utilizing anaerobic biomass from a large scale upflow anaerobic sludge blanket reactor was studied. Anaerobic mixed microbial consortia from five different sources were initially examined for their biological CO conversion potential. Among the different biomass, the biomass from an upflow anaerobic sludge blanket reactor treating domestic wastewater, located in Kavoor, Karnataka, India, showed a maximum CO conversion efficiency. The effect of three main culture parameters, i.e. inoculum volume, initial CO concentration and temperature on simultaneous CO conversion and sulfate reduction was assessed employing the Taguchi experimental design technique. A maximum CO conversion of 85.62% and a maximum sulfate reduction of 50.65% were achieved. Furthermore, the experimental data was fitted to substrate inhibition models reported in the literature. Among the different models, Monods and Haldane kinetic models were found most suitable to describe the kinetics of biomass growth and CO removal by the anaerobic biomass.

Hydrogen recovery from off-gases with nitrogen-rich impurity by pressure swing adsorption using CaX and 5A zeolites

Many studies in the literature about pressure swing adsorption (PSA) hydrogen purification deal with the recovery of hydrogen from off-gases where nitrogen concentration in the feed mixture is usually below 5 %. Practical examples of hydrogen-containing off-gases with higher nitrogen concentration are total hydrocarbon reforming off-gas, and coke oven gas. In this work, the separation performance of CaX and 5A zeolites in the hydrogen recovery from these gases by PSA is compared using a simulation tool called PSASIM. Reciprocal diffusion time constants and adsorption isotherms of nitrogen, methane and carbon monoxide in CaX zeolite measured experimentally are included. Simulations show that, with a feed pressure of 3 bar, CaX yields higher hydrogen recovery than 5A zeolite for the same product purity (above 99.7 %) with both feed gases. CaX removes nitrogen better than 5A zeolite, although it is worse for removing carbon monoxide and methane. The hydrogen recovery can be increased notably (from about 65 % to above 90 %) by including a rinse step in the PSA cycle while maintaining high hydrogen product purity.

Analysis of an Electrochemical Filter for Removing Carbon Monoxide from Reformate Hydrogen

We studied the operation of a twin-cell electrochemical filter for removing carbon monoxide (CO) from reformate hydrogen by periodically adsorbing and then electrochemically oxidizing CO on the electrode. During the adsorption step, we studied the effects of feed CO concentration, flow rate, electrode catalyst loading, type of feeder gas, and temperature on CO breakthrough. We then applied a fixed bed adsorber model to show that the breakthrough time could be accurately correlated to the adsorption-step operating parameters. Since the oxidation step was found to be much faster than that for CO breakthrough, adsorption time should dictate switching time. This insight was used to predict steady-state filter performance, and the prediction was validated for an electrochemical filter operated with CO contaminated hydrogen to decrease the CO concentration from 10,000 to 10 ppm. The model was also used to explore the employability of an electrochemical filter over a range of operating conditions by considering the comparative electrode area of a filter with that of a fuel cell.

Evaluation of an integrated methane autothermal reforming and high-temperature proton exchange membrane fuel cell system

The aim of this study was to investigate the performance and efficiency of an integrated autothermal reforming and HT-PEMFC (high-temperature proton exchange membrane fuel cell) system fueled by methane. Effect of the inclusion of a CO (carbon monoxide) removal process on the integrated HT-PEMFC system was considered. An increase in the S/C (steam-to-carbon) ratio and the reformer temperature can enhance the hydrogen fraction while the CO formation reduces with increasing S/C ratio. The fuel processor efficiency of the methane autothermal reformer with a WGS (water gas shift reactor) reactor, as the CO removal process, is higher than that without a WGS reactor. A higher fuel processor efficiency can be obtained when the feed of the autothermal reformer is preheated to the reformer temperature. Regarding the cell performance, the reformate gas from the methane reformer operated at Tin = TR and with a high S/C ratio is suitable for the HT-PEMFC system without a WGS reactor. When considering the HT-PEMFC system with a WGS reactor, the CO poisoning has less significant impact on the cell performance and the system can be operated over a broader range to minimize the required total active area. A WGS reactor is necessary for the methane autothermal reforming and HT-PEMFC integrated system with regard to the system efficiency.

Combination of preferential CO oxidation and methanation in hybrid MCR (micro-channel reactor) for CO clean-up

CO in the hydrogen stream must be reduced to extremely low levels, under 10 ppm, because the Pt electrode is detrimentally affected by residual CO in the H2 stream. Therefore removal of carbon monoxide from the H2-rich stream during fuel generation from hydrocarbons is a critical challenge, especially for PEMFC (proton exchange membrane fuel cell) applications. Herein, CO an initial concentration of 1.0 vol.% was successfully removed from a H2-rich stream to a residual level below 10 ppm, within the wide operating temperature range from 92 to 235 °C by utilizing a hybrid channel reactor comprising a micro-channel heat exchanger and mini-packed bed reactor. The mini-packed bed reactor contained two kinds of catalysts that promote preferential oxidation and methanation of CO in series. The HMCR (hybrid micro- and mini- channel reactor) offers not only ultimately safe operation but also easy scale-up and is adaptable to mass production of CO clean-up units.

Preparation of nanocrystalline metal (Cr, Al, Mn, Ce, Ni, Co and Cu) modified ferrite catalysts for the high temperature water gas shift reaction

Water gas shift reaction is an essential process of hydrogen production and carbon monoxide removal from syngas. Fe–Cr–Cu catalysts are typical industrial catalysts for high temperature water gas shift reaction but have environmental and safety concerns related to chromium content. In this work nanocrystalline metal (M)-modified ferrite catalysts (M = Cr, Al, Mn, Ce, Ni, Co and Cu) for replacement of chromium were prepared by coprecipitation method and the effects of promoters on the structural and catalytic properties of the iron based catalysts were studied. Prepared catalysts were characterized using X-ray diffraction (XRD), N2 adsorption (BET), temperature-programmed reduction (TPR) and transmission electron microscopies (TEM) techniques. Temperature-programmed reduction measurements inferred that copper favors the active phase formation and significantly decreased the reduction temperature of hematite to magnetite. In addition, water gas shift activity results revealed that Fe–Al–Cu catalyst with Fe/Al = 10 and Fe/Cu = 5 weight ratios showed the highest catalytic activity among the prepared catalysts. Moreover, the effect of calcination temperature, GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.

Enhancement of CO conversion in a novel slurry bubble column reactor for methanol synthesis

This paper is dealing with the simulation of a commercial size slurry bubble column reactor (SBCR) for catalytic conversion of synthesis gas (CO + CO2 + H2) to methanol and comparison of the results especially carbon monoxide removal with gas-phase model in the quasi-steady state condition. For this purpose it was assumed that the flow pattern of gas is plug, and axial dispersion model was considered for liquid–solid phase. The results of the model for Shiraz petrochemical complex feedstock show that the production rate of methanol in a commercial SBC reactor is lower than conventional gas-phase methanol synthesis. This disadvantage is corrected by the modified feed which includes 5% CO and the 95% of the conventional feed. This novelty results in the same methanol production rate with the conventional gas-phase reactor. Besides the same methanol production rate, CO injection to the feed, causes water production noticeably reduced during methanol synthesis via CO2 hydrogenation. Consequently lower catalyst deactivation rate and higher methanol production rate are achieved.

Can CO-Tolerant Anodes be Economically Viable for PEMFC Applications with Reformates?

Recent advances in removing carbon monoxide (CO) from about 1% to ~10 ppm level via preferential oxidation (PROX) of CO in hydrogen feeds[1] renewed the interest in developing CO-tolerant catalysts for using inexpensive reformates as the fuel other than pure hydrogen. The savings would be considerable since the 2015 price target for hydrogen produced by reforming natural gas is $2 per kg H2, viz., ~40% cheaper than pure hydrogen generated by water electrolysis at $3.5 per kg H2 [2].RuPt alloy and Ru-Pt core-shell nanocatalysts have been studied as CO-tolerant anode catalysts for PEM fuel cells. However, dissolution of Ru occurs at occasional high potentials experienced at the anode, causing performance decay. To address this issue, we developed a surfactant-free and scalable synthesis method to produce ordered Ru(core)-Pt(shell) nanoparticles with tunable Pt shell thickness of 1 to 3 atomic layers. Commonly found disordering in Ru cores was attributed to defect-induced partial alloying, and was eliminated by annealing Ru cores before coating Pt shells. The single crystalline particles with a sharp Ru-Pt boundary and ordered transition from Ru’s hexagonal close-packed lattice to Pt’s face-centered cubic structure were confirmed by atomically resolved scanning transmission electron microscopy images coupled with density functional theory calculations[3].We shall mainly show that a complete Pt bilayer shell protects Ru from dissolution during potential cycles up to 0.95 V while exhibiting enhanced CO-tolerance. The results demonstrate a promising anode with less than 0.1 mg cm-2 total metal loadings for operating PEM fuel cells with reformates. In order to find optimal Pt shell thickness and metal to carbon weight ratio, we developed an electrochemical testing method using standalone, gas-diffusion electrodes for evaluating the performance without and with CO in hydrogen. The findings will be discussed in comparison with the results of membrane electrode assembly tests under realistic conditions, shedding light on causes of deactivation effects and ways to alleviate them. Acknowledgements The work at Brookhaven National Laboratory was supported by U.S. Department of Energy under contract DE-AC02-98CH10886 and Power Bridge NY.

Low temperature CO retention using hopcalite catalyst for fuel cell applications

For a hopcalite catalyst (copper manganese oxide), a new preparation method is reported based on a combination of precipitation and redox techniques. A full XRD, N2–adsorption–desorption and SEM-EDX characterization of the resulted samples has been carried out The samples calcined at 300 °C with an amorphous structure were investigated using microactivity equipment for carbon monoxide (CO) removal under different reaction conditions (temperature in the range of 25–80 °C, pressure 0.2–1 bar, initial CO concentration in the 30–200 ppm range). The results showed that the prepared hopcalite exhibited steady performance in the micro-activity reactor regarding the reducing carbon monoxide content down to residual contents. High activity at low temperature was observed for non-crystalline materials and was correlated with the presence of potassium. An increase of CO conversion with increasing pressure and decreasing temperature has been observed. A major remark related to the experimental results was that the rate of CO concentration decrease in the gaseous mixture in the reactor was strongly influenced by the initial value of CO concentration, and therefore for almost all the experimented cases, in less than a minute, the output gaseous mixture contained an adequate CO concentration to be used for fuel cell applications. The stability of the prepared hopcalite was investigated at ambient temperature. In order to determine its lifetimes, a longer term experiments have been carried on and the results showed that the hopcalite was significantly stable and showed over 80 % CO conversion after 60 h. The performances decay steadily to about 50 % after 72 h. The catalyst was regenerated without any difficulty.