Effect Of CO Oxidation Research Articles

Promotion effect of CO oxidation via activation of surface lattice oxygen by single atom Cu/MnO2 catalyst

The catalytic oxidation of CO by single-atom transition metal catalysts has always been the focus of researchers. Herein, we report a strategy for the preparation of Cu single-atom anchored on MnO2 by oxalate chelation-assisted hydrothermal method, and the obtained Cu/MnO2–0.25 catalyst with the optimal molar ratio achieved about 90% CO conversion at 80 °C. The strong electronic interaction between Cu and MnO2 not only effectively inhibits the aggregation of Cu single atoms, but also the formed Cu-O-Mn hybrid structure activates the adjacent surface lattice oxygen, further improving the catalytic oxidation performance of CO at low and medium temperatures. The elevated activity is achieved at the single-atom active site by the Mars-van Krevelen (MvK) mechanism. This work provides a simple and reliable method for the rational design of stable transition metal single-atom catalysts and deepens the understanding of metal-support strong interactions (SMSI).

Polarization Control of the Interface Ferromagnetic to Antiferromagnetic Phase Transition in Co/Pb(Zr,Ti)O3

Based on first-principles calculations, we predict the polarization control of the interfacial magnetic phase and a giant electronically driven magnetoelectric coupling (MEC) in Co/PbZr0.25Ti0.75O3 (PZT)(001). The effect of Co oxidation at the interface shared with (Zr,Ti)O2-terminated PZTis evidenced. The magnetic phase of the oxidized Co interface layer is electrically switched from the ferromagnetic to the antiferromagnetic state by reversing the PZT polarization from upward to downward, respectively. A comparative study between oxidized and unoxidized Co/PZT interfaces shows that in oxidized Co/PZT bilayers, the variation of the interface spin moment upon polarization reversal exceeds that of unoxidized Co/PZT bilayers by about 1 order of magnitude. We define a surface MEC constant αS taking into account the polarization dependence of both the spin and orbital moments. In unoxidized Co/PZT bilayers, we obtain αS ≈ 2 × 10-10 G cm2 V-1, while a giant surface coupling αS ≈ 12 × 10-10 G cm2 V-1 is found in the case of oxidized Co/PZT. We demonstrate that the polarization control of the magnetocrystalline anisotropy via spin-orbit coupling is not only effective at the interface but it extends to the Co film despite the interface origin of the MEC. This study shows that tailoring the nature of atomic bonding and electron occupancies allows for improving the performance of functional interfaces, enabling an efficient electric field control of spin-orbit interactions. Moreover, the nonlocal character of this effect holds promising perspectives for the application of electronically driven interface MEC in spin-orbitronic devices.

Alkali-metal poisoning effect of total CO and propane oxidation over Co3O4 nanocatalysts

Cobalt oxide (Co3O4), a low-cost transitional metal oxide, has been widely studied for catalytic total oxidation of CO and hydrocarbons. However, much less attention has been paid to the poisoning effect due to alkali metals in such oxidation catalysts despite the ease of access to such poisons in both mobile and stationary combustion sources. In this study, the alkali metals such as Na, K and Li were readily deposited onto a Co3O4 catalyst to study their poisoning effect on CO and propane oxidation. 1% doping onto Co3O4 was found to increase the light-off temperature by 50 °C in CO oxidation and over 160 °C in propane oxidation. It is also noted that alkali metals exhibited a ‘locking-effect’ on oxygen of Co3O4, leading to poor oxygen mobility of alkali metal doped catalysts. During the reaction, alkali metals can significantly promote the adsorption of CO2 to form robust surface carbonate species even at high temperature, another reason for the poisoning effect of alkali metals on Co3O4 nanocatalysts for catalytic oxidation.

Oxidative degradation of landfill leachate by catalysis of CeMnOx/TiO2 in supercritical water: Mechanism and kinetic study

Landfill leachate is a typical refractory wastewater that contains high concentration of organic pollutants. In this work, we investigated the treatment of landfill leachate by supercritical water oxidation (SCWO) in a batch reactor. The effects of temperature (T, 450–600°C), oxidation coefficient (OC, 1.2–3.4), reaction time (t, 60–600s) and pH (4.13–8.05) on total organic carbon (TOC) removal efficiency (TRE,%) and ammonia nitrogen (NH3-N) removal efficiency (NRE,%) were analyzed. TRE and NRE increased remarkably with increasing temperature and OC. At 3.4 OC and 600°C, 92.5% TRE and 50.9% NRE were achieved after 600s. A modified kinetic model on TRE and NRE considering the induction time was developed and accurately correlated the experimental results. A significant co-oxidation effect of methanol and landfill leachate in SCWO was detected. Furthermore, heterogeneous catalysts were added to SCWO of landfill leachate to improve the removal rate of organic contaminants. A series of composite catalysts (CeMnOx/TiO2) which consisted of the cerium, manganese and titanium oxides were prepared by impregnation method with varying Ce/Mn ratio. Compared with the SCWO of leachate without catalyst, the CeMnOx/TiO2 catalyst with Ce/Mn ratio of 1:2 exhibited high catalytic activity and stability. Additionally, a catalytic reaction mechanism was proposed. It was assumed that MnOx is the active component and CeO2 is the additive and oxygen supplier. The results obtained from this work suggest the SCWO with high-efficiency and stable catalyst could be a promising technology for landfill leachate treatment.

Kinetic Study on Ammonia Oxidation Acceleration by Multi-Injection of Methanol in Supercritical Water

The effectiveness of multistage methanol injection in supercritical water oxidation (SCWO) of an ammonia/methanol mixture as a method for utilizing the alcohol co-oxidation effect was studied at 530 °C and 25 MPa. A simple global reaction rate model was developed based on the results of kinetic experiments performed at various ammonia, methanol, and oxygen concentrations, yielding excellent agreement with experimental values. Ammonia conversion was predicted when the same molar flow rate of methanol was split between two points: a first injection at the entrance of a reactor and a second injection midway in the reaction stream. Two-stage methanol injection resulted in higher ammonia conversion than in the model calculation when methanol was injected once at the reactor entrance. Model calculations under the same experimental conditions showed that two-stage injection improves ammonia conversion, which aligns closely with predicted values. Moreover, our calculations suggest that ammonia conversion depends ...

XPS/ToF-SIMS Characterization of TiO$_{2}$ Supported Au Nanoparticles: Effect of Catalytic CO Oxidation

XPS/ToF-SIMS Characterization of TiO$_{2}$ Supported Au Nanoparticles: Effect of Catalytic CO Oxidation

Kinetics study on hydrothermal combustion of methanol in supercritical water

Supercritical hydrothermal combustion has received a great deal of attention as an innovative and potential treatment technology wherein the corrosion and salt deposition problems during supercritical water oxidation processes can be avoided effectively. A detailed chemical kinetics model for methanol was employed and validated to understand the hydrothermal combustion process mechanism in supercritical water. Based on this elementary reaction model, how the two key indicators (ignition and extinction temperatures) worked during combustion reaction was studied. Moreover, the influences of operational parameters (fuel concentration, oxidation coefficient and reactor type) and corresponding reaction mechanism were investigated. It reveals that H2O2 was identified as one key intermediate product in the combustion kinetics of methanol. Initial concentration and injection flow rate of aqueous fuel were two significant factors that determined the extinction temperature, which decreased as the concentration increased or the injection flow rate reduced. Moreover, a minimum limit for the initial fuel concentration existed above which a stable hydrothermal flame could form. The oxidation coefficient affected combustion temperature in a manner that depended on the coefficient range. The combustion temperature elevated with the oxidation coefficient in the fuel-rich area while dropped in the oxidant-rich area. This phenomenon was interpreted from the point of view of thermodynamics and mechanism. In order to maintain stable flames at as a low injection temperature as possible, vessel reactors were more desirable to be applied for hydrothermal combustion reaction, deriving from the discrepancy in order of magnitude for flow velocity between tubular and vessel reactors. Finally, it is found that the enhancement of auxiliary fuel methanol in decomposition of organic pollutants stemmed from two reasons: high reaction heat release and co-oxidative effect, whereas the refractory compounds could suppress the ignition of methanol in supercritical water.

Synergetic effect and oscillatory behavior of CO oxidation over a bimetallic composite catalyst

This article describes the results of simulations of CO oxidation under low pressure conditions over a bimetallic Pt/Rh composite catalyst. The model is represented by a system of four differential–algebraic equations (DAEs) for the coverages of COads and Oads, on the two parts of the composite surface. Surface diffusion of both adsorbates is assumed to be fast. The experimentally observed synergetic effect concerning CO oxidation on a Rh surface partly covered by Pt monolayer islands is reproduced in the simulations. It is shown that this synergetic effect is due to the difference in the CO sticking coefficients on Pt and Rh surfaces. In addition, a new type of kinetic oscillations, namely “synergetic kinetic oscillations” are predicted by the simulations. These oscillations exist under conditions at which no oscillations can exist over Pt and Rh monometallic catalysts. The driving force of this new type of oscillations is connected to the large difference in binding energy of adsorbed oxygen atoms on Rh and Pt.

Study the Effect on Activity of Alumina Supported CuO-CeO2-ZrO2 Catalysts Prepared by Four Methods for CO Oxidation

In the present study four catalysts, prepared by four different methods i.e. co- impregnation, citric acid sol-gel, urea nitrate combustion and urea gelation co- precipitation methods, have been used to study the effect of CO oxidation. The precursor Cu(NO3) 23H2O has been used as for the preparation of catalysts having the composition CuCe5.17Zr3.83Ox/-Al2O3(25wt%). Catalysts were calcined at 5000C and characterized by BET, XRD, TGA/DSC and SEM. A fixed weight (100 mg) of the catalyst was taken in a tubular fixed bed reactor at atmospheric pressure. 2.0% CO in air at a total feed rate of 60 ml/min was used in the reactor. The oxidation of CO to carbon dioxide was carried out at temperature ambient to 280oC. The preparation methods effect the catalytic activity of the catalysts as is discussed in the results. Excellent activity for CO oxidation is shown by the catalyst prepared by sol – gel method followed by co-impregnation, urea gelation and urea nitrate combustion methods. It exhibited the total conversion at 210oC. All the four catalysts prepared did not show any deactivation activity for 50 hours of continuous runs.

Synergic CO oxidation activities of boron–CeO2 hybrid materials prepared by dry and wet milling methods

Boron–CeO2 hybrid materials were prepared by dry and wet ball-milling methods and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR and X-ray photoelectron spectroscopy (XPS). We also demonstrated CO oxidation activity of the material using temperature-programmed reaction mass spectrometry, and found an interesting synergic effect of CO oxidation in response to hybridization of boron and CeO2. The oxidation state of Ce was found to have changed from +4 to +3 during the milling process, which was confirmed by the Ce 3d XPS scan result. These findings indicate that boron maintains the convertible oxidation states (Ce3+↔Ce4+) of Ce at the interface between boron and CeO2 during the CO oxidation reaction. The present study highlights the potential application of boron and CeO2 hybrid materials to pollution control, chemical industry and propulsion energy sources.

Petroleum Refinery Effluents Treatment by Advanced Oxidation Process with Methanol

Petroleum refinery effluents are waste originating from industries primarily engaged in refining crude oil. It is a very complex compound of various oily wastes, water, heavy metals and so on. Conventional processes are unable to effectively remove the chemical oxygen demand (COD) of petroleum refinery effluents. Supercritical water oxidation (SCWO) was pro- posed to treat petroleum refinery effluents. In this paper, methanol was used to investigate co-oxidative effect of methanol on petroleum refinery effluents treatment. The results indicated that supercritical water oxidation is an effective process for petro- leum refinery effluents treatment. Adding methanol caused an increase in COD removal. When reaction temperature is 440 o C, resi- dence time is 20 min, OE is 0.5 and initial COD is 40000 mg/L, and COD removal increases 8.5%.

Study on Supercritical Water Oxidation of Oily Wastewater with Ethanol

The conventional treatments are unable to effectively remove the Chemical Oxygen Demand (COD) of oily wastewater, which has seriously threatened the environment and the normal production of oil field. In this paper, an advanced method was proposed for oily wastewater treatment, Supercritical Water Oxidation (SCWO). The co-oxidative effect of ethanol on oily wastewater is characterized for the initial COD of oily wastewater (4000 mg/L) and ethanol concentration (20 mg/L) for a range of temperatures (390°C-450°C), a pressure of 23 Mpa for the complete combustion of both ethanol and oily wastewater. High concentrations of ethanol caused an increase in the conversion of oily wastewater at T = 450°C, p = 23 MPa and t = 9 min, the oily wastewater removal increases 8%.

Modeling of a Tubular‐SOFC: The Effect of the Thermal Radiation of Fuel Components and CO Participating in the Electrochemical Process

AbstractA mathematical model based on first principles is developed to study the effect of heat and electrochemical phenomena on a tubul solid oxide fuel cell (SOFC). The model accounts fordiffusion, inherent impedance, transport (momentum, heat and mass transfer) processes, internal reforming/shifting reaction, electrochemical processes, and potential losses (activation, concentration, and ohmic losses). Thermal radiation of fuel gaseous components is considered in detail in this work in contrast to other reported work in the literature. The effect of thermal radiation on SOFC performance is shown by comparing with a model without this factor. Simulation results indicate that at higher inlet fuel flow pressures and also larger SOFC lengths the effect of thermal radiation on SOFC temperature becomes more significant. In this study, the H2 and CO oxidation is also studied and the effect of CO oxidation on SOFC performance is reported. The results show that the model which accounts for the electrochemical reaction ofCO results in better SOFC performance than other reported models. This work also reveals that at low inlet fuel flow pressures the CO and H2 electrochemical reactions are competitive and significantly dependent on the CO/H2 ratio inside the triple phase boundary.

Manganese and Copper Catalysts for the Phenolic Wastewaters Remediation by Catalytic Wet Air Oxidation

The catalytic wet air oxidation (CWAO) of a simulated phenolic wastewater was investigated at temperatures up to 200ºC and 15 bar of air partial pressure. Laboratorial (Mn-Ce-O 70/30 IMP, Mn-Ce-O 70/30 CP, MnCu 70/30, MnCu 50/50) and a commercial catalyst (N140: CuO-MnOx 22/50) were used to evaluate the catalytic activity in terms of Total Organic Carbon (TOC). Among the manganese/cerium and manganese/copper catalysts tested with different molar ratios, Mn-Ce-O was the most active leading to the complete mineralization after 120 min of an aqueous solution containing six representative phenolic acids. The co-oxidation effect was identified when comparing the oxidation of global phenolic mixture and the individual parent compounds' depletion. The catalyst preparation method had no significant differences in terms of catalytic activity. During the CWAO experiments, acetic acid and phenol were detected and measured by HPLC as the main reaction intermediate compounds. Concerning catalytic stability, manganese and copper catalyst revealed good properties in terms of active metal leaching to the bulk liquid as well as in the deposition of only 3.152% (W/W) of carbonaceous material on the catalyst surface for the co-precipitated Mn-Ce-O 70/30 catalyst.

Cooxidation of ammonia and ethanol in supercritical water, part 1: Experimental results

AbstractThe cooxidative effect of ethanol on ammonia oxidation in supercritical water was studied for a range of temperatures (655–705°C), initial ammonia (1–3 mM), ethanol (0–1.0 mM), and oxygen concentrations (0.7–5.0 mM), corresponding to fuel equivalence ratios ranging from 0.9 to 2.2 for the complete combustion of both organic species. With a stoichiometric amount of oxygen available for complete oxidation, the addition of ethanol on an equivalent molar basis was found to increase ammonia conversion from 20 to 65% at initial concentrations of 1 mM for each reactant, T = 700°C, P = 246 bar, and τ = 2.5 s. Nitrous oxide was produced in much larger quantities for ammonia–ethanol cooxidation than for ammonia oxidation. Based on fractional yields of nitrogen product, this amounted to 40–75% for co‐oxidation with ethanol versus 4–13% without ethanol present. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Methanol Dehydrogenation and Oxidation on Pt(111) in Alkaline Solutions

Adsorption, dehydrogenation, and oxidation of methanol on Pt(111) in alkaline solutions has been examined from a fundamental mechanistic perspective, focusing on the role of adsorbate-adsorbate interactions and the effect of defects on reactivity. CO has been confirmed as the main poisoning species, affecting the rate of methanol dehydrogenation primarily through repulsive interactions with methanol dehydrogenation intermediates. At direct methanol fuel cell (DMFC)-relevant potentials, methanol oxidation occurs almost entirely through a CO intermediate, and the rate of CO oxidation is the main limiting factor in methanol oxidation. Small Pt island defects greatly enhance CO oxidation, though they are effective only when the CO coverage is 0.20 ML or higher. Large Pt islands enhance CO oxidation as well, but unlike small Pt islands, they also promote methanol dehydrogenation. Perturbations in electronic structure are responsible for the CO oxidation effect of defects, but the role of large Pt islands in promoting methanol dehydrogenation is primarily explained by surface geometric structure.

Influence of pretreatment conditions on low-temperature carbon monoxide oxidation over CeO 2/Co 3O 4 catalysts

The modification of ceria (CeO 2) on high surface area cobaltic oxide (Co 3O 4) and the promotion effect of CO oxidation via different pretreatment conditions were studied. The high-valence cobalt oxide was prepared first by precipitation-oxidation in ice bath, followed by reduction at 230 °C to get pure and high surface area cobaltic oxide (assigned as R230, S BET = 100 m 2 g −1). Further, the Ce20/R230 catalyst was prepared by impregnation with cerium nitrate (20% cerium loading). Pretreatment of Ce20/R230 catalyst was divided into two methods: reduction (under 200 and 400 °C) and calcination (under 350 and 550 °C). The catalysts were characterized by X-ray diffraction (XRD), infrared (IR), and diffuse reflectance spectroscopy (DRS), and temperature-programmed reduction (TPR) and by nitrogen adsorption at −196 °C. The results showed that pretreatment under low-temperatures obtained both larger surface area and better activity. The Ce20/R230-H200 catalyst exhibited the highest surface area ( S BET = 109 m 2 g −1) and the best catalytic activity in CO oxidation with T 50 (50% conversion) at 88 °C among series of catalysts due to the combined effect of cobaltic oxide and ceria. The optimized pretreatment of CeO 2/Co 3O 4 catalysts can clearly enhance the catalytic activity.

Co-oxidation of methylphosphonic acid and ethanol in supercritical water I: Experimental results

The co-oxidative effect of ethanol on methylphosphonic acid (MPA or PO(OH) 2CH 3) was characterized for a range of MPA concentrations (0.1–1.0 mM) and ethanol concentrations (0–2.4 mM) for temperatures of 473 and 528 °C, a pressure of 245 bar, and stoichiometric oxygen for the complete combustion of both organic compounds. Low concentrations of ethanol (0.1 and 0.3 mM) were found to have no statistically significant effect on MPA conversion for an initial MPA concentration of 1.0 mM, but higher concentrations of ethanol caused an increase in the conversion of MPA at T = 473 °C, P = 245 bar, and τ = 9 s from 14 ± 2% without ethanol present to 29 ± 2% with 1.0 mM ethanol and 39 ± 2% with 2.4 mM ethanol. The increase in MPA conversion was more pronounced at shorter residence times. Decreasing the initial concentration of MPA at a constant initial ethanol concentration of 1.0 mM, T = 473 °C, P = 245 bar, and τ = 9 s resulted in an increase in MPA conversion from 29 ± 2% at 1.0 mM MPA–41 ± 2% at 0.1 mM MPA. At T = 528 °C and P = 245 bar, the initial concentration of MPA had a much greater effect on MPA conversion than the initial concentration of ethanol.

Co-oxidation of methylphosphonic acid and ethanol in supercritical water: II: Elementary reaction rate model

A supercritical water co-oxidation elementary reaction rate mechanism was constructed from submechanisms for methylphosphonic acid (MPA or PO(OH) 2CH 3) and ethanol with updated kinetic rate parameters for H 2O 2 and HOCO chemistry. The co-oxidation mechanism accurately reproduces the experimentally observed conversion trend of the refractory MPA component as a function of initial concentration of the labile ethanol component [J.M. Ploeger, P.A. Bielenberg, R.P. Lachance, J.W. Tester, Co-oxidation of methylphosphonic acid and ethanol in supercritical water: I. Experimental results, J. Supercrit. Fluids (2006)]. The increase in MPA conversion with increasing ethanol concentration is predicted to be caused by the increased concentration of hydroperoxy radicals (HO 2 ) produced by ethanol oxidation. An analysis of the major organophosphorus reaction fluxes indicated that the co-oxidative effect would increase the conversion of MPA but not change the rate of formation of methane. An experiment using a model formaldehyde/methanol mixture as a co-oxidant was conducted to confirm this prediction.

Vanadium oxide nanostructures on Rh(1 1 1): Promotion effect of CO adsorption and oxidation

The adsorption of CO and the reaction of CO with pre-adsorbed oxygen at room temperature has been studied on the (2 × 1)O Rh(1 1 1) surface and on vanadium oxide Rh(1 1 1) “inverse model catalyst” surfaces using scanning tunnelling microscopy (STM) and core-level photoemission with synchrotron radiation. Two types of structurally well-defined model catalyst V 3O 9 Rh(1 1 1) surfaces have been prepared, which consist of large (mean size of ∼50 nm, type I model catalyst) and small (mean size <15 nm, type II model catalyst) two-dimensional oxide islands and bare Rh areas in between; the latter are covered by chemisorbed oxygen. Adsorption of CO on the oxygen pre-covered (2 × 1)O Rh(1 1 1) surface leads to fast CO uptake in on-top sites and to the removal of half (0.25 ML) of the initial oxygen coverage by an oxidation clean-off reaction and as a result to the formation of a coadsorbed (2 × 2) O + CO phase. Further removal of the adsorbed O with CO is kinetically hindered at room temperature. A similar kinetic behaviour has been found also for the CO adsorption and oxidation reaction on the type I “inverse model catalyst” surface. In contrast, on the type II inverse catalyst surface, containing small V-oxide islands, the rate of removal of the chemisorbed oxygen is significantly enhanced. In addition, a reduction of the V-oxide islands at their perimeter by CO has been observed, which is suggested to be the reason for the promotion of the CO oxidation reaction near the metal-oxide phase boundary.