Small Amounts Of Carbon Monoxide Research Articles

In situ and Operando Characterisation in the Preferential Oxidation of Carbon Monoxide over Base Metal Oxide Catalysts: A Review

AbstractPolymer electrolyte membrane fuel cells (PEMFCs) are the core technology of the steadily growing hydrogen (H2) economy as they can convert chemical energy, in the form of H2, to electrical energy. If the H2 is derived from (green) hydrocarbons, via steam reforming and the water‐gas‐shift reaction, then it would contain small amounts of carbon monoxide (CO, 0.5–2 %), among other gases. CO poisons the platinum‐based anode catalyst in the PEMFC, and the current recommendation is to decrease its concentration to below 0.01 % (or 100 ppm) in the H2‐rich PEMFC feed. The preferential oxidation of CO (CO‐PrOx) is a promising strategy for decreasing the CO concentration, and base metal oxide catalysts have shown great potential in this regard. However, such catalysts tend to undergo physicochemical changes that cause undesirable catalytic activity and selectivity changes. This review discusses the different base metal oxide catalysts that have been evaluated in CO‐PrOx, while paying special attention to the various in situ and operando techniques that have been used to monitor the physicochemical changes of base metal oxides during operation. We conclude the review by highlighting the recent and possible future attempts of circumventing the undesired physicochemical changes of base metal oxides during CO‐PrOx.

The Effect of SnO2 Surface Properties on CO2 Photoreduction to Higher Hydrocarbons

AbstractSeveral photocatalysts have been developed for applications in reduction reactions, including tin oxide‐based semiconductors. Although its band structure is unfavorable for CO2 reduction reactions, strategies to modify its surface properties directly impacted its activity and selectivity during these reactions. Here, we analyze the influence of heat treatment and decoration of SnO2 with gold nanoparticles on the gas phase CO2 photoreduction process. In both cases, a deleterious effect was observed during reactions under UV radiation (with a drop of 59.81 % and 51.45 % in CH4 production for SnO2_150 °C and SnO2/Au_cop, respectively, compared to SnO2_cop), which is directly related to the availability of surface hydroxyl groups that play a crucial role in CO2 adsorption. Under visible radiation, the gold plasmonic resonance took place in the production of methane (0.33 μmol g−1 for SnO2/Au_cop and 0.29 μmol g−1 for SnO2/Au_150 °C), with small amounts of carbon monoxide (0.06 μmol g−1 for SnO2/Au_cop and 0.03 μmol g−1 for SnO2/Au_150 °C). These results demonstrate that, though the SnO2 band structure does not indicate a good semiconductor for CO2 reduction, its surface characteristics are responsible for its catalytic activity.

Application of neural network based regression model to gas concentration analysis of TiO2 nanotube-type gas sensors

We performed a gas analysis of TiO2 nanotube (NT)-type integrated gas sensors using a machine learning (ML) algorithm and neural network-based regression. We fabricated a TiO2-NT integrated gas sensor with multiple sensing elements with different response characteristics, and we measured the output signals of each sensing element exposed to a gas mixture, where the main components were nitrogen and oxygen gas with a small amount of carbon monoxide. We analyzed the output signals of the sensor elements using the ML technique to predict the concentrations of CO and O2, to which the TiO2-NT gas sensors were sensitive. Sensor output data were collected for seven sets of mixed gas concentrations with different concentrations of each component gas. Four or five of the seven datasets were used as ML training data for the neural network method, and the concentrations of CO and O2 in the remaining three or two datasets were predicted. Consequently, we confirmed that increasing the number of sensor elements significantly improved the prediction accuracy of the gas concentration. When the output signals from 10 sensor elements were used, the gas concentration could be predicted with an accuracy of less than 0.001% for a carbon monoxide concentration of 0.02%. This accuracy was sufficient for practical application.

Development of catalysts for the synthesis of higher hydrocarbons from carbon dioxide

The paper is devoted to the development of a catalyst for the synthesis of the higher hydrocarbons from carbon dioxide and hydrogen. The conversion of greenhouse gas CO2 into value-added chemicals contributes not only to sol-ving environmental problems, but also to obtaining valuable fuel. Catalysts that are active in the hydrogenation reaction of CO are also active in the process of CO2 hydrogenation. The most active catalysts in the hydrogenation of carbon dioxide are based on transition metals, in the presence of which mainly methane and a small amount of carbon monoxide are formed. Investigation of the kinetics of hydrocarbons synthesis by hydrogenation of carbon dioxide in the presence of transition metals allowed establishing the mechanism of the process and no perspective of such catalytic systems for hydrocarbons synthesis via intermediate formation of carbon monoxide. It is established that the optimal method of synthesis of higher hydrocarbons is the indirect path, through the intermediate formation of methanol with its further dehydration. The synthesis of methanol from gas mixtures of H2, CO, and CO2 with different composition in the presence of industrial catalysts takes place along the same macroscopic route, by reducing CO2, and is accompanied by a reverse water-gas shift reaction. Therefore, gas mixtures of different composition can be used as raw material for methanol production. Based on our own and literature data, the general peculiarities of the carbon dioxide hydrogenation reaction were obtained, which allowed developing a complex multifunctional catalyst for the synthesis of higher hydrocarbons from carbon dioxide and hydrogen. The proposed catalyst combines the properties of ones for the synthesis of oxygenates from carbon dioxide, and catalysts for the processes of hydrocarbons synthesis from me-thanol and other alcohols. The synthesis of higher hydrocarbons with a predominant content of branched hydrocarbons on the developed bifunctional catalyst was carried out and the optimal conditions for the process were determined.

Highly sensitive reflection based colorimetric gas sensor to detect CO in realistic fire scenarios

For early fire detection, the measurement of low and small rising concentrations of the fire typical gas carbon monoxide (CO) is essential. The approach presented herein integrates a highly sensitive colorimetric material into a low cost gas sensor system. The gas sensitive color dye is hosted by silica nanoparticle based supraparticles and then processed to a so-called gas sensor stripe. Changes in the CO concentration enable a change of the sensor stripes color, which is easily detectable as a change of the light that is reflected by the stripe. A diffusion chamber protects the gas sensitive film against harmful environmental influences and interfering light. The capability of the gas sensor system is demonstrated in lab as well as real fire tests. In case of the latter, standardized real fire tests are conducted, as well as realistic mixtures of plastics and wood are smoldered. The developed sensors react in real time to the slowly rising CO concentration during the test fires. Even small amounts of CO (<20 ppm) are reliably detectable.

Analysis of carbon monoxide production in methanol steam reforming reactor for generating hydrogen

Seeking renewable energy sources has been a very important aspect in the development of human society, with many authors regarding hydrogen as a rather promising energy source. There are several forms of obtaining hydrogen, including steam reforming of hydrocarbons, alcohols, and ethers. Some characteristics of methanol, such as processing at mild temperatures from 250 to 350oC under atmospheric pressure and production from biomass – no competition for food production – have distinguished it from other alcohols for steam reforming. The great disadvantage of this technology when applied in proton exchange membrane (PEM) fuel cells is that the process of methanol steam reforming involves not only hydrogen and carbon dioxide, but also the production of a small amount of carbon monoxide, which is sufficient to affect the functionality of the fuel cells. This work presents the characterization of the catalyst HiFUEL R120 and shows how water/methanol molar ratio in the feed stream of an integral methanol steam reforming reactor influenced the conversion and the hydrogen selectivity in relation to carbon monoxide. This made it possible to identify the best operational conditions for lowering carbon monoxide content in the reactor effluent, avoiding the use of a CO purification unit.

Switchable Product Selectivity in the Electrochemical Reduction of Carbon Dioxide Using Boron-Doped Diamond Electrodes.

The main product obtained by electrochemical reduction of CO2 depends on the electrode material, and in many cases the Faradaic efficiency for this is determined by the electrolyte. Only a few investigations in which attempts to produce different products from the same electrode material have been done so far. In this work, we focus on boron-doped diamond (BDD) electrodes with which plentiful amounts of formic acid and small amounts of carbon monoxide have been produced. By optimizing certain parameters and conditions used in the electrochemical process with BDD electrodes, such as the electrolyte, the boron concentration of the BDD electrode, and the applied potential, we were able to control the selectivity and efficiency with which carbon monoxide is produced. On one hand, with a BDD electrode with 1% boron used for the cathode and KClO4 for the catholyte, the selectivity for producing carbon monoxide was high. On the other hand, with a BDD electrode with 0.1% boron used for the cathode and KCl for the catholyte, the production of formic acid was the most evident. In situ attenuated total reflectance-infrared (ATR-IR) measurements during electrolysis showed that CO2•- intermediates were adsorbed on the BDD surface in the KClO4 aqueous solution. Here, switchable product selectivity was achieved when reducing CO2 using BDD electrodes.

CORP: The assessment of total hemoglobin mass by carbon monoxide rebreathing.

In this Cores of Reproducibility in Physiology (CORP) article, we present the theory and practical aspects of the carbon monoxide (CO) rebreathing method for the determination of total hemoglobin mass in humans. With CO rebreathing, a small quantity of CO is diluted in O2 and rebreathed for a specified time period, during which most of the CO is absorbed and bound to circulating hemoglobin. The dilution principle then allows calculation of the total number of circulating hemoglobin molecules based on the number of absorbed CO molecules and the resulting changes in the fraction of carboxyhemoglobin in blood. Total hemoglobin mass is derived by multiplication with the molar weight of hemoglobin. CO rebreathing has been used for >100 yr and has undergone steady improvement so that today excellent values in terms of accuracy and precision can be achieved if the methodological precautions are carefully followed.

Enhancement of gasoline selectivity in combined reactor system consisting of steam reforming of methane and Fischer-Tropsch synthesis

A two-stage, one-dimensional configuration model including the steam reforming of methane (SRM) and Fischer-Tropsch (FT) synthesis has been developed for the production of hydrocarbons. This configuration is used to investigate hydrocarbon product distribution, such as gasoline. The first SRM reactor is fed by methane and steam, and the products are converted to hydrocarbons by the second FT reactor. The model was solved numerically by applying the finite difference approximation, and the set of first-order ODEs was solved in the axial direction. The results show that complete conversion of hydrogen in the second reactor can be achieved although a small amount of carbon monoxide remains. Furthermore, at higher H2O/CH4 ratio (and low CO in feed), lower C2-C5 yield and selectivity is obtained.

Differential Electrochemical Mass Spectroscopy Study of CO2 Concerned Anode Reaction in Polymer Electrolyte Fuel Cell

For a power generation of a polymer electrolyte fuel cell (PEFC), reformed hydrogen gas is fueled to the anode. The reformed hydrogen gas contains a small amount of carbon monoxide and 10-30% carbon dioxide [1]. The carbon dioxide is reported to be reduced at Pt electrode [2, 3]. In this study, CO2 reduction is performed at various potential of Pt/C-based membrane electrode assembly(MEA). The product of CO2reduction was analyzed by a mass spectrometer. Electrocatalyst of Pt/C (Pt: 45.7 wt%) was sprayed on a gas diffusion layer. The electrolyte membrane was sandwiched by two pieces of the gas diffusion layers which were coated electrocatalyst layers (metal amount: 1.0 mg cm-2), and then, it was hot-pressed to obtain on MEA. Geometric electrode area of the MEA was 3×3 cm2. The prepared MEA was installed in a single cell having a dynamic hydrogen electrode (DHE) as a reference electrode. The temperature of the single cell was controlled at 80°C. Humidified carbon dioxide gas (purity: 99.995%) and humidified hydrogen gas (purity: 99.999%) were supplied to the working electrode and counter electrode, respectively, at a flow rate of 50 cm3 min-1. Cyclic voltammograms were measured at a potential scan rate of 10 mV s-1and the potential scan range was between 0.00-1.38 V vs. DHE. The exhaust gas was introduced directly into the mass spectrometer (JEOL, JMS-Q1050GC Ultra Quad GC/MS ). Figure 1 shows a result of differential electrochemical mass spectroscopy measured at 0-1.38 V vs. DHE. In Fig. 1 (a), cyclic voltammograms at the Pt/C-based MEA were obtained under CO2 and Ar atmospheres. Under the CO2 atmosphere, a typical anodic current at around 0.5 V vs. DHE is observed. This is due to the re-oxidation of the CO2 reductant which was generated at < 0.1 V vs. DHE by the CO2 reduction. Mass spectra of m/z = 2, 16, 45 versus electrode potential under CO2 atmosphere shown in bottom of Figure 1 (b)-(d). The m/z = 2, 16, 45 were originaled from hydrogen, methane and formic acid. Generation of m/z = 16 is seen at < 0.2 V vs. DHE, and m/z = 2, m/z = 45 are seen at < 0.1 V vs. DHE. It was found that there is a potential dependency for CO2reduction at Pt/C-based MEA. Consequently, adsorbed CO2reductant on the Pt remains in the potential range of 0-1.38 V vs. DHE which influences the hydrogen oxidation reaction. [1] K. Kortsdottir, C. D. Fernandez, R. W. Lindstrom, ECS Electrochem. Lett., 2, F41-F43 (2013). [2] N. Hoshi, S Kawatani, M. Kudo, Y. Hori, J. Electroanal. Chem., 467, 67–73 (1999). [3] S. Shironita, K. Karasuda, K. Sato, M. Umeda, J. Power Sources, 240, 404-410 (2013). Figure 1

Evaluación de los parámetros físicos y químicos de las briquetas obtenidas con la maquina briquetadora construida en FAREMEstelí

El propósito fundamental de esta investigación es evaluar los parámetros físicos y químicos de las briquetas elaboradas en Farem-Estelí. Es una investigación cuantitativa según su enfoque, con un nivel de profundidad según su tipología: exploratoria, descriptiva. Se elaboraron siete briquetas de diferentes sustratos forestales. Los instrumentos utilizados fueron: La evaluación de eficiencia que se determinó mediante la prueba de ebullición de agua (WBT por sus siglas en inglés) versión 4.2.2., se midieron las emisiones de monóxido de carbono (CO) y se calculó el poder calorífico de los diferentes tipos de briquetas. Los resultados obtenidos muestran que estas briquetas emiten menos emisiones de gases contaminantes al ambiente que la leña, la eficiencia térmica fue de aproximadamente un 92% en tres de las briquetas evaluadas, la leña obtuvo una eficiencia entre 45 y 63%. Se concluye que la elaboración de las briquetas fue exitosa con una excelente compactación, la briqueta de Granza 50% + Aserrín fino 25% + Papel 12.5% + flor de pino 12.5% es la mejor opción según la evaluación siendo esta la que emite menores cantidades de CO que son casi nulas obteniendo una eficiencia térmica de 92% puesto que su consumo especifico es bajo con tan solo 143 gramos por litro de agua.

New photo-CORMs: Deeply-coloured biocompatible rhenium complexes for the controlled release of carbon monoxide

Air- and water-stable rhenium carbonyl complexes are investigated as CO-carriers for studying the light-dependent release of small amounts of carbon monoxide under physiological conditions. The reported very low quantum yields are in a suitable range for studying potential applications as photochemical CO-releasing molecules (Photo-CORMs) without rapidly reaching cytotoxic levels of carbon monoxide. Preliminary results on bio-compatibility and selective uptake of the compounds into human colon carcinoma cells (Caco-2 cell line) are described.

Extension of the E-PPR78 equation of state to predict fluid phase equilibria of natural gases containing carbon monoxide, helium-4 and argon

Abstract The E -PPR78 model is a predictive version of the widely used Peng–Robinson equation of state in which the binary interaction parameters are estimated by a group-contribution method. With the 21 groups available before the writing of this paper, such a model could be used to predict fluid phase equilibria of systems containing hydrocarbons, permanent gases (CO 2 , N 2 , H 2 S, H 2 ), mercaptans, alkenes and water. In other words, all the components encountered in petroleum fluids could be modeled. It is however acknowledged that natural gases often contain small amounts of carbon monoxide, helium or argon. In order to model the phase behavior and estimate energetic properties (e.g. enthalpy changes on mixing) of such gases, the applicability range of the E -PPR78 model is extended through the addition of three new groups: CO, He and Ar.

Catalysts based on pillared clays for the oxidation of chlorobenzene

The aim of this work was to reveal the main factors which affect the oxidation of chlorobenzene (PhCl) over palladium and platinum supported on alumina pillared clays. The catalysts were prepared by wet impregnation of an alumina-pillared montmorillonite (Al-PILC) with palladium and platinum solutions and characterized by several physicochemical techniques before and after the catalytic tests. During oxidation of PhCl over the catalysts, the formation of carbon dioxide along with small quantities of carbon monoxide, PhClx and coke was found. The nature of the supported metal, the temperature, the metal loading, the support, and the time on stream, are factors affecting the combustion of PhCl.

Thermal and spectroscopic study of the lanthanide 2-aminoterephthalate compounds in the solid state

Lanthanides 2-aminoterephthalate compounds were synthetized and characterized on the basis of TG–DTA data in order to study their thermal behavior, as well as to establish hydration grade and stoichiometry, while TG/FTIR system identified the gaseous products evolved during the thermal decomposition of these compounds in each step of the TG curve, in which water and carbon dioxide were the main products with a small amount of carbon monoxide and ammonia. Through the FT-IR spectroscopic data of the compounds in the solid state, information concerning the coordination mode of the carboxylate groups to the metal was provided, and by analysis of fluorescence, with excitation at 405 nm, the respective electronic transitions supported by the data reported in the literature were identified. In addition, the excitation was made for the ligand salt and acid with the aim of understanding the contribution of the ligand in the emission of the compounds. In summary, the ligand influenced on the fluorescence of lanthanide ions, being more intense for the compounds of La, Ce, Pr, and Nd, making this material interesting for optical and photonic applications.

Hydrogen production by glycerol reforming in supercritical water over Ni/MgO-ZrO2 catalyst

Nano ZrO2 and MgO-ZrO2 were prepared by a self-assembly route and were employed as the support for Ni catalysts used in hydrogen production from glycerol reforming in supercritical water (SCW). The reforming experiments were conducted in a tubular fixed-bed flow reactor over a temperature range of 600–800 °C. The influences of process variables such as temperature, contact time, and water to glycerol ratio on hydrogen yield were investigated and the catalysts were charactered by ICP, BET, XRD and SEM. The results showed that high hydrogen yield was obtained from glycerol by reforming in supercritical water over the Ni/MgO-ZrO2 catalysts in a short contact time. The MgO in the catalyst showed significant promotion effect for hydrogen production likely due to the formation of the alkaline active site. Even when the glycerol feed concentration was up to 45 wt%, glycerol was completely gasified and transfered to the gas products containing hydrogen, carbon dioxide, and methane along with small amounts of carbon monoxide. At a diluted feed concentration of 5 wt%, near theoretical yield of 7 mole of H2/mol of glycerol could be obtained.

Hydrothermal Gasification of Palm Shell Biomass for Synthesis of Hydrogen Fuel

Production of hydrogen has been widely practiced to produce a CO2-neutral green fuel that can substitute for fossil fuel. One of the alternative ways in producing such fuel is to utilize biomass by the hydrolysis process. In this study the effects of reaction times (10 to 70 min), reaction temperatures (180 to 260 °C ), and biomass to water mass ratio (1:1 to 1:9) were evaluated relative to the hydrolysis of palm shell particles in a low temperature (below 300 °C) hydrolysis process. Palm shell biomass was hydrolyzed in distilled water, and the gaseous products (bio-syn gas) generated were comprised of H2 and CO2, with small amounts of carbon monoxide and methane.

Enhancement of Catalyst Performance in the Direct Propene Epoxidation: A Study into Gold–Titanium Synergy

AbstractEnhanced productivity toward propene oxide in the direct propene epoxidation with hydrogen and oxygen over gold nanoparticles supported on titanium‐grafted silica was achieved by adjusting the gold–titanium synergy. Highly isolated titanium sites were obtained by lowering the titanium loading grafted on silica. The tetrahedrally coordinated titanium sites were found to be favorable for attaining small gold nanoparticles and thus a high dispersion of gold. The improved productivity of propene oxide can be attributed to the increased amount of the interfacial AuTi sites. The active hydroperoxy intermediate is competitively consumed by epoxidation and hydrogenation at the AuTi interface. A higher propene concentration is favorable for a lower water formation rate and a higher formation rate of propene oxide. Propene hydrogenation, if occurring, can be switched off by a small amount of carbon monoxide.

Gasotransmitters: novel regulators of ion channels and transporters

More than 25 years ago, it was a big surprise for physiologists that nitric oxide (NO) was identified as the endothelium derived relaxing factor which is responsible for endothelium-induced smooth muscle relaxation (Ignarro et al., 1987). Until then, small gaseous molecules were simply regarded as byproducts of cellular metabolism which were unlikely to be of any physiological relevance. The discovery that NO was synthesized by specific enzymes (NO-synthases), upon stimulation by specific, physiologically relevant stimuli (e.g., acetylcholine stimulation of endothelial cells), as well as the fact that it acted on specific cellular targets (e.g., soluble guanylate cyclase), set the course for numerous studies which investigated the physiological roles of gaseous signaling molecules—in other words, gasotransmitters (Wang, 2002). Aside from NO, there are two more gases which subsequently have been identified as gasotransmitters: carbon monoxide (CO) (Wu and Wang, 2005) and hydrogen sulfide (H2S) (Abe and Kimura, 1996; Wang, 2002). Although the concept of a gas being involved in cellular signaling processes was already accepted since the discovery of NO, the new candidates CO and H2S were initially met with skepticism—especially since they were well-known for their high toxicity and regarded as environmental chemical threats. However, in concert with the principle of Paracelsus that “everything is toxic- it just depends on the dose,” it is nowadays accepted that small amounts of CO and H2S are of physiological relevance and are even endogenously produced in human cells (Wu and Wang, 2005; Wang, 2012). All three gasotransmitters are produced in human cells by specific enzymes: NO is produced by NO-synthases (NOS), originating from the amino acid L-arginine. There are three NOS-isoforms, NOS1-3, which have been originally termed neuronal, inducible and endothelial NOS, respectively (Garvin et al., 2011). CO is generated by heme oxygenases (HO) within heme degradation (Wu and Wang, 2005). There are also three heme oxygenases (HO-1-3) (Yoshida et al., 1974; Maines et al., 1986; McCoubrey et al., 1997), including an inducible HO-1 and a constitutively active HO-2. H2S is mainly produced within the metabolism of L-cysteine by the enzymes cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE or CTH) and 3-mercaptopyruvate sufurtransferase (3-MST) (Wang, 2012). Recently, Kimura's group described an additional pathway for endogenous H2S production, which involves D-cysteine, 3-MST, and D-amino acid oxidase (Shibuya et al., 2013). Despite the knowledge of the substrates and specific enzymes which are involved in gasotransmitter production, the precise endogenous concentrations of NO, CO, and H2S have still not been sufficiently determined. The measurement of endogenous gas concentrations is limited by the accuracy and specificity of currently available methods (Olson, 2013), the reactivity and short half-life of some gases (NO) (Wall et al., 2012), and simply the fact that gases are volatile and rapidly disappear during the preparation procedures of biological samples. As highlighted within this research topic issue, it is crucial—and probably most challenging—to precisely quantify endogenous concentrations of NO, CO, and H2S (Kimura, 2012; Peers, 2012; Olson, 2013). Although precise endogenous concentrations of gasotransmitters remain to be determined, numerous studies investigated the physiological effects of those gaseous signaling molecules in almost every organ system [as summarized in excellent review articles such as Olson (2011), Wu and Wang (2005), and Wang (2012)]. Common molecular targets for all gasotransmitters are ion channels and transporters. Changes in the activity of membrane-located ion channels/transporters are involved in the majority of physiological processes which are regulated by gasotransmitters. This allows the gases to specifically act at the interface of cell-environment interactions, electrolyte homeostasis and electrochemical communication—thus allowing the regulation of numerous physiological processes in cells and tissues. This research topic summarizes currently available data on the regulation of ion channels and transporters by NO, CO, and H2S. Excellent review and research articles highlight the importance of gasotransmitter/ion channel interactions for vegetative physiology (Althaus, 2012; Peers, 2012; Pouokam and Diener, 2012), neurophysiology (Njie-Mbye et al., 2012; Peers, 2012; Takahashi et al., 2012; Wang et al., 2012), and explain gasotransmitter-induced signaling mechanisms (Wall et al., 2012). Furthermore, opinion articles from pioneers in gasotransmitter research (Kimura, 2012; Peers, 2012; Olson, 2013) give perspectives on important routes which should be followed in this field. With the articles included in this issue we wish to highlight the importance of ion channel/transporter regulation by gaseous signaling molecules and wish to stimulate future research in this exciting area of physiology.

Carbon monoxide: a new pharmaceutical agent?

Small amounts of carbon monoxide (CO) are continuously produced in mammals. The intracellular levels of this gaseous molecule can markedly increase under stressful conditions following the induction of heme oxygenases (HO), ubiquitous enzymes responsible for the catabolism of heme. The development of a technology concerning the CO-releasing molecules (CO-RMs) that control the delivery and action of CO under different pathological conditions represents a major step forward in the development of CO-based pharmaceuticals with therapeutic applications. CO is important for the homeostatic control of cardiovascular functions. Abnormal metabolism and function of CO contribute to the pathogenesis and development of hypertension. Another vascular disease in which the role of CO has been evaluated is pulmonary arterial hypertension. Important results have been reported in which CO prevents intimal hyperplasia by arresting hyperproliferative vascular smooth muscle cells as well as increased mobilization and recruitment of bone-marrow-derived progenitor cells. Transplantation has been a field of research, in which most studies have investigated the beneficial properties of CO-RMs. CO gas and CO-RMs have produced promising results in the preservation of organs for transplantation. The anti-inflammatory properties of CO and CO-RMs have been demonstrated in a multitude of animal models of inflammation, suggesting a possible therapeutic application for inflammatory diseases. Despite therapeutic benefit in animal model studies, the efficacy of CO in humans remains unclear. Further studies are expected to better understand the pharmacokinetics as well as long- and short-term effects of CO-RMs.