Rate Of Carbon Monoxide Oxidation Research Articles

Water-assisted generation of catalytic interface: The case of interfacial Pt-FeOx(OH)y sites active in preferential carbon monoxide oxidation

The surface of supported heterogeneous catalysts often contains adsorbed water and hydroxyl groups even when water is not directly added to the reaction stream. Nonetheless, the reactivity of adsorbed water and hydroxyl groups is rarely considered. We demonstrate that water and hydroxyl groups can not only directly participate in the catalytic oxidation processes but are also able to generate and stabilize the catalytically active metal-oxide interface. We show that the reduction of Pt-Fe-supported catalysts with hydrogen in the presence of adsorbed water or steam allows for achieving one of the highest preferential carbon monoxide oxidation activities at ambient temperature. These conditions create active iron-associated hydroxyl groups next to platinum nanoparticles with enhanced reactivity towards carbon monoxide oxidation. Density functional theory calculations suggest that hydroxylation of oxidic iron species stabilizes the FeOx(OH)y/Pt interface, via strong metal-support interaction, which is confirmed by chemisorption measurements. Kinetic experiments, including those with 18O-labeled water, in combination with operando infrared spectroscopy, show that water and hydroxyl groups directly participate in preferential carbon monoxide oxidation. A quantitative correlation between the catalytic activity of Pt-FeOx(OH)y/γ-Al2O3 catalysts and the Fe2+ concentration, obtained using operando X-ray absorption spectroscopy, shows that the number of active Fe2+ sites and the carbon monoxide oxidation rate per active site can be significantly increased by water-assisted pretreatment with hydrogen. This work provides a new example of positive role of strong metal-support interaction for the design of more active catalysts.

Heterogeneous Co1/P1Mo12O40 single-atom catalyst for CO oxidation via termolecular Eley-Rideal (TER) mechanism

Catalytic mechanisms, micro-kinetic and thermodynamics studies of Phosphomolybdic acid (PMA) supported non-noble metal (NNM1 = Sc1, Ti1, V1, Cr1, Mn1, Fe1, Co1, Ni1, Cu1, and Zn1) single-atom catalysts (SACs) are explored for carbon monoxide (CO) oxidation by using DFT calculations. The results reveal that Co1/P1Mo12O40 have demonstrated excellent ability to adsorb (CO, O2) molecules, resulting in significant charge transfer from the catalyst surface to the adsorbate, which is essential to produce CO2 under normal reaction conditions. The various reaction pathways, including Eley Rideal (ER), Langmuir Hinshelwood (LH), Termolecular Eley Rideal (TER), and Mars Van Krevelen (MvK) are explored for CO oxidation on Co1/P1Mo12O40 to authenticate the most auspicious reaction mechanism. The energy barrier for the TER mechanism was 0.41 eV, lower as compared to the other reported materials which suggests that the Co1/P1Mo12O40 SACs would be the most appropriate future material for CO oxidation. To further validate the results, we performed the microkinetic investigation which predicts the CO oxidation rate of 4.58 × 106 s − 1. The key role of spin-magnetic moment for the promotion of CO oxidation by using Co1 single-atom catalyst was revealed from the deep electronic analysis. The current results would provide appreciated guidelines for experimentalists to develop less expensive and more effective non-noble metal SACs for CO oxidation.

Evolution and distribution of the anode overpotential and its oscillations in a polymer electrolyte membrane fuel cell exposed to carbon monoxide

Carbon monoxide (CO) poisoning of polymer electrolyte membrane fuel cells (PEMFCs) remains a challenge for their deployment, and a deeper understanding of the spatiotemporal dynamics involved is needed to develop effective mitigation strategies. In this work, localised reference electrodes were used to measure the anode overpotential at three locations across the active area of a galvanostatically operated cell (0.3 A cm−2) exposed to 100 ppm CO/H2. The anode region closest to the inlet was poisoned more rapidly than the rest of the cell, following a sigmoidal variation, and presented a higher CO coverage. The varying CO concentration, combined with local operating conditions, had a direct impact on the distribution of CO coverage. Additionally, complex self-sustained oscillations of the cell voltage and the anode overpotential were observed and correlated with the rate of CO oxidation in the overall cell. The coexistence of a dominant mean-field coupling area closer to the anode inlet, and a dominant migration coupling region closer to the outlet was identified, consistent with reported modelling predictions for a single straight channel cell. Finally, the cell recovery with pure H2 was shown to be a faster process than the CO adsorption, which follows first-order kinetics and is affected by local conditions.

Oxygen deficient Ce doped CO supported on alumina catalyst for low-temperature CO oxidation in presence of H2O and SO2

The carbon monoxide (CO) oxidation has been carried out using Ce doped Co/Al2O3 prepared by coprecipitation followed by deposition precipitation. The 0.1 mol Ce doped Co supported on alumina showed maximum CO oxidation activity compared to the undoped catalyst at a low temperature. The physicochemical characteristics of synthesized catalysts were investigated by FTIR, XRD, Raman, XPS, 27Al solid-state NMR, H2-TPR, HR-TEM, etc. Ce doping promoted a distortion in the cobalt lattice structure. The distortion leads to an increase in reactive oxygen and the number of oxygen vacancies. In addition, Ce modification prevents the generation of the cobalt aluminate phase and stimulates the production of the Co3O4 active phase for CO oxidation. The presence of hexa and penta-coordinated alumina increases the defect and oxygen vacancy formation, which was responsible for a higher CO oxidation rate. The Ce doped Co/Al2O3 catalyst showed maximum water and SO2 tolerance due to the Ce doping. The mechanistic and kinetic details for CO oxidation have been explained by correlating with characterization.

Metabolism perturbation Caused by the overexpression of carbon monoxide dehydrogenase/Acetyl-CoA synthase gene complex accelerated gas to acetate conversion rate of Eubacterium limosum KIST612

Microbial conversion of carbon monoxide (CO) to acetate is a promising upcycling strategy for carbon sequestration. Herein, we demonstrate that CO conversion and acetate production rates of Eubacterium limosum KIST612 strain can be improved by in silico prediction and in vivo assessment. The mimicked CO metabolic model of KIST612 predicted that overexpressing the CO dehydrogenase (CODH) increases CO conversion and acetate production rates. To validate the prediction, we constructed mutant strains overexpressing CODH gene cluster and measured their CO conversion and acetate production rates. A mutant strain (ELM031) co-overexpressing CODH, coenzyme CooC2 and ACS showed a 3.1 × increased specific CO oxidation rate as well as 1.4 × increased specific acetate production rate, compared to the wild type strain. The transcriptional and translational data with redox balance analysis showed that ELM031 has enhanced reducing potential from up-regulation of ferredoxin and related metabolism directly linked to energy conservation.

Highly Active and Stable Palladium Catalysts on Novel Ceria-Alumina Supports for Efficient Oxidation of Carbon Monoxide and Hydrocarbons.

Precious metal catalysts with superior low-temperature activity and excellent thermal stability are highly needed in environmental catalysis field. In this work, a novel two-step incipient wetness impregnation (T-IWI) method was developed for the fabrication of a unique and highly stable CeO2/Al2O3 support (CA-T). Pd anchored on CA-T exhibited a much higher low-temperature catalytic activity and superior thermal stability in carbon monoxide (CO) and hydrocarbon (HC) oxidations, compared to Pd anchored on conventional CeO2/Al2O3 (CA), which was prepared by a one-step IWI method. After aging treatment at 800 °C, the CO oxidation rate on Pd/CA-T (1.69 mmol/(gPd s)) at 120 °C was 4.1 and 84.5 times of those on Pd/CA (0.41 mmol/(gPd s)) and Pd/Al2O3 (0.02 mmol/(gPd s)), respectively. It was revealed that the CA-T support with well-controlled small CeO2 particles (ca. 12 nm) possessed abundant defects for Pd anchoring, which created rich Pd-CeO2 interfaces with strengthened interaction between Pd and CeO2 where oxygen could be efficiently activated. This resulted in the significantly improved oxidation activity and thermal stability of Pd/CA-T catalysts. The T-IWI method developed herein can be applied as a universal approach to prepare highly stable metal oxide-alumina-based supports, which have broad application in environmental catalyst design, especially for automobile exhaust aftertreatment.

A numerical study on effects of pre-chamber syngas reactivity on hot jet ignition

Ignition by a pre-chamber generated hot jet is a promising technology to reduce NOx emissions through extending lean burn limits. However, the role of the pre-chamber fuel reactivity in the main chamber ignition still remains unclear. In the present study, effects of the pre-chamber fuel reactivity on ignition of mixture in a main chamber by the hot jet, which is generated by the combustion of syngas in the pre-chamber, are numerically investigated. In the investigation, different ratios of CO/H2 of syngas are considered under a thermally-equal condition. CFD simulations are performed using the code based on the KIVA-3V release 2 program coupled with an in-house developed chemical solver. A detailed chemical kinetics mechanism with 15 species and 41 reactions is adopted for the hydrogen and syngas oxidation. The hot jet ignition delay time is characterized by the maximum rate-of-change of the pressure in the main chamber. For the combustion initiation process, three stages are identified: ignition stage (stage I), flame development stage (stage II), and flame propagation stage (stage III). Significant effects of fuel reactivity are only observed on stage I that the ignition delay time considerably increases with increasing CO/H2 ratio. Further analyses of the local temperature of the hot gas and some important elementary reactions indicate that the low reaction rate of carbon monoxide oxidation (R22: CO + OH = H + CO2) causes incomplete fuel conversion in the orifice due to insufficiently available time for the reactions . The fuel conversion analysis confirms that the small-diameter orifice effect is the main reason for hot jet temperature drops under low pre-chamber syngas reactivity conditions, exhibiting as inhibiting effects on stage I.

Study on the twin-pilot-injection strategies for the reduction in the exhaust emissions in a low-compression-ratio engine

An investigation of twin-pilot-injection strategies was performed in a low-compression-ratio engine in order to improve the combustion performance and to reduce the exhaust emissions. All tests were conducted on a modified four-cylinder test engine running on only one cylinder with a reduced compression ratio (15.3:1), and analyses of the combustion pressure, the heat release rate and the net work output in the cylinder were performed. At the same time, the reduction in the exhaust emissions such as carbon monoxide, hydrocarbons and soot under different twin-pilot-injection strategies was compared with other combustion cases (single-injection strategy and one-pilot-injection strategy). Higher combustion pressures, lower heat release rates, shorter ignition delay times, higher indicated mean effective pressures (about 2.1%) and lower coefficients of variation in the indicated mean effective pressure (approximately 29.4%) in all multiple-injection (one-pilot-injection or twin-pilot-injection) cases, which indicated improved operation of the low-compression-ratio engine, were observed. Retarded injection timing ( tp,SOE = 20–10° crank angle before top dead centre) in the twin-pilot-injection case proved to the best timing for reduction in the carbon monoxide emissions because the relatively short ignition delay with the high in-cylinder temperature enhanced the carbon monoxide oxidation rate. Twin-pilot-injection strategies formed higher hydrocarbon emissions because of the rich fuel mixture during the ignition delay time than one-pilot-injection combustion did. As more multiple injections were applied, lower nitrogen oxide emissions (up to 45.7%) were observed because the early termination of the first injection event and the restart of injection created a time interval between injections in which freshly charged air could be entrained into the flame.

Carbon Monoxide Formation during Oxy-fuel-Fired Fluidized-Bed Combustion

This paper investigates the heterogeneous and homogeneous reactions involved in the formation and reduction of carbon monoxide (CO) in a 100 kW oxy-fuel-fired circulating fluidized-bed furnace, using CO as an indicator of the progress of combustion. A mathematical combustion model, which takes into account both the mixing and kinetics, is developed for simulating char and gas combustion under air- and oxy-fuel-fired conditions. The experimental results demonstrate that, for similar fluid dynamic and thermal conditions, oxy-fuel conditions typically yield a vertical CO profile with higher peak concentrations than are obtained with air-firing, mainly because of the higher inlet concentrations of O2, whereby CO released from the increased fuel feeding is diluted in the same total volumetric flow of gas. On the basis of a comparison of the modeling results and the experimental results, it is proposed that the effects of CO2 should be considered in determining the rate of CO oxidation that is valid for both air- and oxy-fuel-fired conditions. The vertical in-furnace profiles of CO from the combustion model were compared to the corresponding experimental results from five test runs under air- and oxy-fuel-fired conditions. The results show good agreement, with the agreement for oxy-fuel-fired conditions made possible by adding a CO2-dependent term to the expression for the CO oxidation rate.

Properties of ceramic foam catalyst supports: mass and heat transfer

Mass and heat transport properties have been determined for 30 PPI α-Al 2O 3 ceramic foam containing 6 wt.% γ-Al 2O 3 washcoat. The foam was loaded with 5 wt.% platinum and the rate of carbon monoxide oxidation measured for a 0.3 cm cylindrical segment of the foam operating with mass transfer controlling at 550 °C. This gave a mass transfer factor versus Reynolds number correlation that was equivalent to a packed bed of particles. A correlation for the radial heat transfer coefficient in a bed of ceramic foam was determined by measuring outlet temperatures achieved when air at varying flow rates and inlet temperatures was passed through a bed of foam pellets. Correlation parameters of a 1D model were fitted from 700 to 1000 °C using a Simplex optimization routine. Radial heat transfer coefficients were two to five times higher than those predicted from packed bed correlations.

Partial oxidation of methane, methanol, formaldehyde, and carbon monoxide over silica: global reaction kinetics

Oxidation of methane (848–898 K), methanol (648–748 K), formaldehyde (623–673 K), and carbon monoxide (673–833 K) over a precipitated silica catalyst has been examined over a range of reactant and oxygen partial pressures. Conversion–selectivity relationships are used to assess the reaction network and differential reactor experiments are employed to determine the global reaction kinetics. All reactions exhibited a positive-order dependence on oxygen, partial pressure consistent with reaction of chemisorbed oxygen. This implies that the chemisorption of oxygen on the reduced sites occurs at a rate comparable to that of substrate oxidation, and may therefore limit the oxidation rate. Self-inhibition was observed for oxidation of carbon monoxide, as P CO was increased, the rate of carbon monoxide oxidation decreased. A conceptual model where CO and O 2 compete for surface oxygen vacancies is proposed. Additionally, it is shown that in methane partial oxidation, reactions of methanol, formaldehyde, and CO can consume oxidized surface sites, thought to be the active sites for methane partial oxidation. A simple model of the degree of surface reduction is presented.

Effect of acoustic excitation on the rate of CO oxidation over Pt{110}

A unique UHV-compatible excitation system combined with an advanced ultra-high amplitude and frequency resolution acoustic spectrometer has been designed and constructed to permit accurate studies of the fundamental mechanism by which acoustic excitation may influence heterogeneous catalytic reactions. Here, the first results are presented, which demonstrate a remarkable sixfold increase in the rate of carbon monoxide oxidation when a Pt{110} thin single crystal is excited with low-frequency, low-energy surface acoustic waves (Rayleigh waves). In addition, chemical oscillations in the CO 2 production rate are found to be initiated and influenced by acoustic excitation of the system. It is proposed that the acoustic excitation results in an enhancement of the carbon monoxide desorption, which in turn affects the activity of the platinum catalyst if the reaction is in the transition between a low- and high-rate branch.

A combined high-pressure reaction cell-ultrahigh vacuum chamber with sample transfer system

We have designed a high-pressure reaction cell and sample transfer system as an addition to an existing ultrahigh vacuum chamber. The system enables us to study catalytic reactions on both single crystals and polycrystalline foils over a large range of pressures from 10−4 Torr to 1 atm. The key advantage of the setup is that the thermocouple is in direct contact with the sample, providing exact measurement of the sample temperature, while allowing transfer between two different manipulators. We demonstrate the utility of the experimental setup by monitoring oscillations in the rate of carbon monoxide oxidation over a platinum catalyst.

Non-Faradaic catalysis : the case of CO oxidation over Ag-Pd alloy electrode in a solid oxide electrolyte cell

Studies of carbon monoxide oxidation on an Ag-25 at% Pd alloy electrode in a cell with a solid oxygen-conducting electrolyte - CO+O2, Ag-Pd | 0.9 ZrO2+0.1Y2O3 | Pt+PrO2-x, air - were carried out. XRD, SEM and XPS techniques were used for characterisation of the Ag-Pd alloy electrode. The non-Faradaic effect of electrochemical oxygen pumping on the rate of carbon monoxide oxidation was demonstrated. The induced change in the reaction rate at cathodic polarization of the Ag-Pd alloy electrode was an order of magnitude higher than the rate of oxygen pumping from the reaction zone through the electrolyte. The observed phenomenon was qualitatively explained on the base of a chain reaction mechanism involving electrochemically generated oxygen species.

Humidity Dependence of Carbon Monoxide Oxidation Rate in a Nafion‐Based Electrochemical Cell

In an effort to fabricate cost effective and reliable carbon monoxide sensors, the humidity dependence of the carbon monoxide oxidation rate has been studied. Using a simple electrochemical cell based on the hydrogen form of Nafion® 117 as the electrolyte, the carbon monoxide oxidation rate has been determined to be a linear function of the ambient humidity at room temperature. The oxidation current, or the sensor response has been observed to increase linearly with increasing humidity. The sensor response to carbon monoxide was also found to increase linearly with increasing carbon monoxide concentrations for concentrations less than 200 ppm. The signal to noise ratio was determined to increase from 15.8 to 47.8 with increase in humidity from 12 to 64%.

Oxygen permeation flux through La 1-ySr yFeO 3 limited by carbon monoxide oxidation rate

The oxygen permeation flux through La 1-ySr yFeO 3-δ ( y = 0.1, 0.2) in a large oxygen partial pressure gradient (air/CO, CO 2 mixture) was found to be limited by the carbon monoxide oxidation rate at the low oxygen partial pressure side of the membrane. The oxygen permeation flux through the membrane was almost independent of its thickness (1 versus 2 mm) and strontium dopant concentration. The deposition of a 50 nm thin porous platinum layer at the low oxygen pressure side of the membrane increased the carbon monoxide oxidation rate and in this way the oxygen permeation flux by a factor 1.8 ± 0.2.

The effect of electrochemical oxygen pumping on the rate of CO oxidation on Au electrode-catalyst

The effect of electrochemical pumping of oxygen on the rate of carbon monoxide oxidation on Au electrode-catalyst in a solid oxygen conducting electrolyte cell has been demonstrated. The induced change in the reaction rate at the cathodic polarization of an Au electrode was an order of magnitude higher than the rate of O2− pumping from the reaction zone through the electrolyte. The anodic polarization of the Au electrode (O2− pumping to the reaction zone through the electrolyte) caused purely Faradaic changes in the reaction rate.

Flow Reactor Studies of Carbon Monoxide/Hydrogen/ Oxygen Kinetics

Abstract New data on the kinetics of CO/H2O/O2 and H2/O2 mixtures in the temperature range of 852—1138 K and at I atmosphere pressure are reported. The data were obtained from adiabatic. constant pressure flow reactor experiments for variations in the initial carbon, hydrogen, and oxygen contents of the mixture and also for variations in the initial temperature. In particular, the results define explosion limit temperatures for near stoichiometric mixtures of CO/H2O/O2 and H2/O2 systems at atmospheric pressure without the presence of surfaces and also demonstrate the complex relationship between water vapor concentration and the carbon monoxide oxidation rate.

Inhibition of trichloroethylene oxidation by the transformation intermediate carbon monoxide

Inhibition of trichloroethylene (TCE) oxidation by the transformation intermediate carbon monoxide (CO) was evaluated with the aquifer methanotroph Methylomonas sp. strain MM2. CO was a TCE transformation intermediate. During TCE oxidation, approximately 9 mol% of the TCE was transformed to CO. CO was oxidized by Methylomonas sp. strain MM2, and when formate was provided as an electron donor, the CO oxidation rate doubled. The rate of CO oxidation without formate was 4.6 liter mg (dry weight)-1 day-1, and the rate with formate was 10.2 liter mg (dry weight)-1 day-1. CO inhibited TCE oxidation, both by exerting a demand for reductant and through competitive inhibition. The Ki for CO inhibition of TCE oxidation, 4.2 microM, was much less than the Ki for methane inhibition of TCE oxidation, 116 microM. CO also inhibited methane oxidation, and the degree of inhibition increased with increasing CO concentration. When CO was present, formate amendment was necessary for methane oxidation to occur and both substrates were simultaneously oxidized. CO at a concentration greater than that used in the inhibition studies was not toxic to Methylomonas sp. strain MM2.

Carbon monoxide oxidation in laminar diffusion flames

This paper is concerned with the oxidation of carbon monoxide in laminar diffusion flames. Data on the carbon monoxide concentration distributions in different diffusion flame geometries are correlated with a conserved scalar called the mixture fraction. The correlation is used to determine a global carbon monoxide oxidation rate applicable for CO consumption in the lean-to-stoichiometric regions of laminar diffusion flames.