Kinetics Of Carbon Monoxide Oxidation Research Articles

Theoretical study on the reaction kinetics of CO oxidation by nitrogen-doped graphene catalysts with different ligand structures

Harmful carbon monoxide (CO) gas from vehicle exhaust and fossil fuel combustion seriously affects the ecological environment and human health, although this issue can be effectively solved by low-temperature catalytic combustion. Herein, an Fe and N codoped double vacancy graphene catalyst (Fe-CxNy) for the low-temperature catalytic combustion of CO is proposed, and the mechanism of the CO catalytic combustion reaction over the catalyst is systematically investigated by using density function theory (DFT). Four oxidation mechanisms, including Eley–Rideal (ER1 and ER2), Langmuir-Hinshelwood (LH) and Termolecular Eley–Rideal (TER), were compared in terms of oxidation pathways and energy distribution. All the results indicate that Fe-CxNy catalysts have efficient catalytic activity. The Fe-CN3 catalyst with the predominant LH reaction mechanism showed the best performance for the catalytic combustion of CO with only 0.20 eV, which was comparable to that of noble metals. The rate constant calculations further demonstrate that Fe-CN3 exhibits excellent catalytic performance at low temperatures. This work not only provides a theoretical basis for the design and development of low-temperature catalytic combustion CO catalysts, but also provides data support for the kinetic model of CO combustion reaction.

Oxidation of carbon monoxide over supported nickel oxide catalyst: kinetic model development and identification

The kinetics of carbon monoxide oxidation over alumina supported nickel oxide was studied using a mechanistic approach to model development and identification. Langmuir-Hinshelwood and Eley-Rideal reaction schemes, together with an alternative scheme were investigated, using low temperature, differential rate measurements. Experimental results were found to be most consistent with the alternative scheme, supporting a reaction mechanism based on non-competitive adsorption of carbon monoxide and oxygen onto different catalyst sites without mutual displacement. The resulting kinetic model was observed to have reasonable agreement with the experimental findings and was found representative of the system.

A study on the properties of modified CuO samples and the kinetics of carbon monoxide oxidation over the given catalysts

Three catalyst samples 10 wt% CuO/γ-Al2O3 (CuAl), 10 wt%CuO + 10 wt% Cr2O3/γ-Al2O3 (CuCrAl) and 10 wt%CuO + 20 wt% CeO2/γ-Al2O3 (CuCeAl) have been taken for the study. Physico-chemical characteristics of the catalysts were determined by the methods of BET adsorption, X-ray diffraction and temperature-programmed reduction. Due to a strong interaction of CuO with Al2O3, resulting in the formation of copper aluminate the catalytic activity of CuO/γ-Al2O3 has been reduced. The bi-oxide catalyst CuCrAl was more active than CuAl, thanks to the formation of high catalytically active spinel CuCr2O4. The fact of very high activity of the CuCeAl sample can be explained by the presence of the catalytically active form CuO–CeO2–Al2O3. The kinetics of CO oxidation reaction on the given catalysts was studied at the temperature range between 200°C and 270°C. The values of initial partial pressures of carbon monoxide (), oxygen () and carbon dioxide () were varied in ranges (hPa): 10 ÷ 45; 33 ÷ 100 and 0 ÷ 30, respectively. It has been found that on all the catalysts, the common kinetic equation for the reaction was as follows: where r is the reaction rate, k is the reaction constant, and k 2 and k 3 are the O2 and CO2 adsorption constants, respectively. In the case of CuAl and CuCrAl, k 3 = 0, and since ≫ 1, the equation should become r = k.P CO.

Kinetics of Carbon Monoxide Oxidation over CuO Supported on Nanosized CeO2

A CuO/CeO2 catalyst prepared by incipient wetness impregnation (7 wt % Cu) with well-dispersed CuO on nanosized ceria, has been used to obtain a kinetic expression for CO oxidation, including estimation of kinetic parameters, in the absence of CO2, H2O, or H2 in the feed stream. Experimental data were checked to be collected in the kinetic regime, in the absence of external and intraparticle mass and heat transfer, and in a wide range of experimental conditions—with CO partial pressure ranging from 0.0015 to 0.0125 atm (that is, including those usually found in PROX reactors) and λ values between 0.35 and 13.3— and were fitted to different rate expressions (power-law and mechanistic) by using a genetic algorithm. Although a power-law rate equation satisfactorily fits the experimental data, it is limited to the experimental range of operation conditions. Further discrimination among mechanistic models indicates that an expression proposed by Liu and Flytzani−Stephanopoulos (Chem. Eng. J. 1996, 64, 283), with a partial reaction order of 0.08 with respect to oxygen, is the most statistically significant, almost indistinguishable from the expression proposed by Mars−Van Krevelen (Spec. Suppl. Chem. Eng. Sci. 1954, 3, 41).

Kinetics and mechanism of carbon monoxide oxidation on the supported metal complex catalyst PdCl2-CuCl2/Al2O3

The kinetics of carbon monoxide oxidation with atmospheric oxygen on a PdCl2-CuCl2/γ-Al2O3 catalyst was studied at T = 27°C and an N2-O2-CO mixture pressure of 1 atm. The catalyst was prepared by cold impregnation. Three groups of mechanistic hypotheses are considered, and two of them are demonstrated to be consistent with kinetic data, although they differ in the roles of water and oxygen in carbon monoxide oxidation.

Kinetics of catalytic oxidation of CO over copper-manganese oxide catalyst

The hopcalite-like catalyst was prepared by co-precipitation, which showed excellent activity and stability for CO oxidation at room-temperature. The activity of carbon monoxide oxidation was investigated at different temperature. The kinetics of carbon monoxide oxidation over copper-manganese oxides catalysts was obtained by means of recycling batch reactor. As a result, CO oxidation followed different reaction mechanism at a broad range of the experimental temperature. The reaction activation energy of CO oxidation was found to be 64.08 kJ mol −1 for 273–313 K and 12.15 kJ mol −1 for 333–373 K, respectively.

Transient kinetics of carbon monoxide oxidation by oxygen over supported palladium/ceria/zirconia three-way catalysts in the absence and presence of water and carbon dioxide

The transient kinetics of CO oxidation by O 2 over alumina-supported Pd/CeO 2/ZrO 2 three-way catalysts is described in the absence and presence of H 2O and CO 2 in the feed. Experiments were carried out in a laboratory fixed-bed reactor at 573 K, while periodically switching between a feed of 1 vol% CO in He and a feed of 0.5 vol% O 2 in He with a frequency of 1/30 Hz. Separate experiments were performed with 14 vol% water in both feeds, and, as is the case with real engine exhaust gas, with 14 vol% water and 14 vol% CO 2 in both feeds. The presence of water largely enhanced the reaction rate, while it was inhibited by CO 2. A transient kinetic model has been developed for this catalyst, based on the experimental data. It was found that the reaction in the absence of H 2O and CO 2 proceeds via the same elementary steps as reported for a Pt/Rh/CeO 2/ γ-Al 2O 3 catalyst (R.H. Nibbelke, A.J.L. Nievergeld, J.H.B.J. Hoebink, G.B. Marin, Appl. Catal. B 19 (1998) 245). Only the rate coefficient for CO desorption from Pd was significantly lower, in line with literature data. Additional elementary steps were combined with the above model in order to describe quantitatively the effect of water. The present study also shows that bulk diffusion of oxygen in ceria plays a major role, when the rate is enhanced by water. The inhibition effect of CO 2 could be described by a lower amount of oxygen-storage sites.

The Kinetics of Carbon Monoxide Oxidation on Tin(IV) Oxide Supported Platinum Catalysts

The kinetics of the oxidation of carbon monoxide by oxygen have been studied in the temperature range 0<ϑ<80°C on alumina-supported Pt/SnO2catalysts, the respective areas of the two active compounds being varied independently of each other. Rate measurements have been performed as well as titration experiments. The results indicate that the chemisorption of CO is restricted to platinum, whereas oxygen is adsorbed on both Pt and SnO2. The rate pattern may be described by a mechanism where the migration of adsorbed species is added to the classical elementary reaction sequence of CO oxidation on platinum. Monte Carlo simulations show that the proposed mechanism can explain the experimental results. Under conditions where the rate is zero order with respect to both CO and O2, simulation indicates that the migration rate of oxygen could be the determining step. Oxygen spillover from SnO2to Pt cannot be excluded but is not necessary to describe the experimental results.

Isothermal study of the kinetics of carbon monoxide oxidation on Pt(111): Rate dependence on surface coverages

The kinetics of the oxidation of carbon monoxide on Pt(111) surfaces was studied isothermally by using an effusive directional molecular beam in an arrangement based on a variation of the dynamic method originally devised by King and Wells. Three temperature regimes were identified for this reaction on surfaces precovered with atomic oxygen. Below 300 K no reaction is observed, and the presence of preadsorbed atomic oxygen on the surface does not significantly affect the initial sticking coefficient of CO but only reduces its saturation coverage by less than half, which it does by preferentially blocking the bridge sites. Above 400 K, on the other hand, the desorption of CO2 from oxygen-covered surfaces is controlled by the impinging frequency of the incoming CO. The most interesting temperature range is that between 300 and 400 K, where the rate of surface recombination of CO with oxygen competes with that of CO adsorption; under those conditions the overall dynamic behavior is fairly complex, and not all the surface oxygen is reactive. Furthermore, the reaction rates in this regime not only depend on the coverages of the reactants, but also on how the surface is prepared. Two kinetically distinct types of oxygen atoms develop during the course of reaction in spite of the fact that they all sit on identical sites at the start of the kinetic runs, suggesting that the reactivity of chemisorbed CO depends on the local oxygen coverage of neighboring sites. We propose that such local arrangements modify the adsorption energy for atomic oxygen, and that this in turn changes the activation energy for the oxidation reaction. Previous reported molecular beam experiments were also extended to cover a wider range of surface coverages in order to better determine the dependence of the rate constant for the surface oxidation step on the coverages of CO and oxygen. It was found that while the presence of oxygen on the surface helps the production of CO2, increasing CO coverages augment the activation barrier for this reaction, an observation that is in direct contrast with previous reports. Finally, the adsorption sites for CO during the surface CO+O recombinatory reaction were characterized by reflection–absorption infrared spectroscopy. The data reported here is analyzed and discussed in terms of possible kinetic models.

Kinetic Modeling of CO Oxidation on Pt/CeO2 in a Gradientless Reactor

Cerium oxide is a major additive in three-way catalysts used in emission control of automobile exhaust. Pt/CeO 2 was studied in order to better understand the role of ceria in promoting CO oxidation reaction. The kinetics of carbon monoxide oxidation on Pt/cerium oxide catalyst, was studied over the temperature range 100-170°C. Steady state kinetic measurements of CO oxidation were obtained in a computer controlled micro-CSTR reactor. Activation energies were reported to vary between 39.5 and 51.2 kJ/mol. At low concentrations of either reactant (CO, O 2 ) and total conversion, the catalyst exhibited multiple steady states, similar to the multiplicity behavior of Pt/Al 2 O 3 . The total conversion was reached at 120°C. In comparison, the total conversion at low reactant concentrations was reached at a temperature of 148°C for the alumina-supported catalyst. Langmuir-Hinshelwood mechanisms gave a good fit to the data. However, no single rate expression could effectively describe the CO oxidation data over the whole concentration in the product of the CSTR reactor. The facts gathered indicate that oxygen adsorbed on interfacial Pt/Ce sites and ceria lattice oxygen provides oxygen for CO oxidation. Cerium oxide has been found to lower CO oxidation activation energy, enhance reaction activity and tends to suppress the usual CO inhibition effect.

Diversity of the kinetics of carbon monoxide oxidation on differently prepared zinc oxides

The fine kinetics of carbon monoxide oxidation over two differently prepared zinc oxides, Kadox ZnO (K25-ZnO) and Kanto Chemical Co. ZnO (Kan-ZnO), have been investigated and compared in detail using the steady-state and the transient-response methods. The morphology based on scanning electron micrographs showed fine crystallites with high surface area, 20 m2 g–1 for K25-ZnO and 4.0 m2 g–1 for Kan-ZnO, even though they gave the same X-ray diffraction pattern of wurtzite-type crystalline structure. Extraordinary differences in the steady-state rate surfaces for the two catalysts were found, being first order with respect to PCO and zero order with respect to PO2 for Kan-ZnO, and having an anomalous tendency with respect to PCO, indicating both a maximum and a minimum, for K25-ZnO.Based on the electrical conductivity measurements of the catalysts and the characteristics of the transientresponse curves obtained, two reaction path models for the two catalysts have been proposed relating to two different oxygen species. All kinetic parameters evaluated from experimental data consistently explain both the steady-state rate data and the characteristic modes of transient-response curves obtained.

Kinetics of Carbon Monoxide Oxidation on Solid Oxide Solution and Platinum on Alumina - A Comparative Study

Catalytic oxidation of carbon monoxide on supported and unsupported noble metal catalysts has been the subject of numerous studies aimed at elucidating reaction mechanism and quantifying its kinetic parameters. The authors studied the kinetics of CO oxidation in excess oxygen (99% O[sub 2]) on supported Pt catalyst and solid oxide solution La[sub 0.8]Sr[sub 0.2]CrO[sub 3[minus][sigma]] (ND1) as a function of CO concentration. The comparison between the kinetics of the catalytic behavior of Pt/alumina and solid oxide solution La[sub 0.8]Sr[sub 0.2]CrO[sub 3[minus][sigma]] and the dependency of the turnover velocity coefficient of CO oxidation upon dispersion on Pt/alumina catalysts with different sintering severity are reported. 20 refs., 3 figs., 2 tabs.

CO Oxidation in a Carberry Reactor: Manifestation ot Reaction Kinetics by Controlled Reaction/Transport.

An attempt was made to investigate the coupling of kinetics and external mass transfer in experimental data obtained from a specially designed Carberry type reactor. The reactor used was a spinning basket catalytic reactor where the catalyst (Pt, Rh over γ-Al 2 O 3 , on monolithic ceramic substrate) rotated in the reacting gas stream. This particular configuration enables the experimental measurement of catalytic reaction rate as a function of reacting gas velocity through monolithic catalyst and the estimation of external mass transfer rates in monoliths is thus possible. A proper mathematical model which includes intrinsic kinetics and external mass transfer was used. In this way, intrinsic kinetics of carbon monoxide oxidation have been estimated in order to elucidate the important kinetic parameters and the influence of external mass transfer

Kinetics of carbon monoxide oxidation over Y [sbnd]Ba [sbnd]Cu [sbnd]O perovskites

The kinetics of carbon monoxide oxidation over YBa 2Cu 3O 6+x and PrBa 2Cu 3O 6+x catalysts was investigated in the temperature range 160 to 200°C and a single rate expression for all catalysts was derived. A reaction mechanism consistent with the kinetics is proposed: it involves the formation of carbon dioxide via two routes. In these, carbon monoxide reacts with either mobile lattice oxygen or with adsorbed oxygen species to give carbon dioxide. Oxygen-deficient samples are more active than oxygen-rich samples due to higher concentrations of oxygen surface vacancies and defects. The presence of water significantly diminishes activity reversibly, probably as a result of competitive adsorption with carbon monoxide.

Kinetics of carbon monoxide oxidation on single-crystal palladium, platinum, and iridium

The activity of Pt(100), Pd(110), Ir(111), and Ir(110) single-crystal catalysts for CO oxidation has been studied as a function of temperature and partial pressure of O/sub 2/ and CO in a high-pressure reactor-ultra-high-vacuum surface analysis apparatus over the temperature range 425-725 K and pressure range 0.1-600 Torr. The specific rates and the partial pressure dependencies determined for the single crystals are in excellent agreement with results obtained previously for high surface area supported catalysts, demonstrating the structure insensitivity of this reaction. The single-crystal catalysts exhibit simple Arrhenius behavior over most of the temperature range studied, and the observed activation energies lie between 22 and 33 kcal/mol, close to the desorption energy of CO from these surfaces. These results are consistent with the generally accepted model in which the surface is primarily covered with CO and the reaction rate is controlled by the desorption of CO. Deviation from Arrhenius behavior below 500 K for Pt is interpreted as a change in the reaction mechanism. Under highly oxidizing conditions surfaces of both Pd and Ir show negative-order dependence on O/sub 2/ partial pressure, indicating the presence of a strongly bound oxygen species. The oxygen species was similar to surface oxide formed bymore » deliberate oxidation and could be detected as CO/sub 2/ desorbing at high temperatures in postreaction temperature-programmed desorption. Oxide formed by oxidation of the Pd and Ir samples prior to high-pressure reaction was only stable at 475 K on Pd(110) in an 11:1 O/sub 2/:CO mixture and to 500 K on Ir(111) in an 80:1 O/sub 2/CO:CO mixture. Deliberate oxidation resulted in a rate decrease but did not affect the activation energy significantly, indicating that the oxide served merely as a simple site blocker.« less

Kinetics of carbon monoxide oxidation by oxygen or nitric oxide on rhodium(111) and rhodium(100) single crystals

The oxidation of CO by O/sub 2/ or NO over Rh(111) and Rh(100) single crystals has been studied in a high-pressure reaction-high-vacuum surface analysis apparatus. Steady-state catalytic activity as a function of temperature and partial pressures of CO, O/sub 2/, and NO has been measured. The CO-O/sub 2/ reaction was found to be insensitive to the structure of the surface as evidenced by the identical rates, activation energies, and partial pressure dependencies measured on the two-single-crystal surfaces. Both surfaces deactivated at high O/sub 2/ partial pressures to the formation of a near-surface oxide (probably Rh/sub 2/O/sub 3/) which is catalytically inactive for this reaction. The deactivation occurred at a slightly lower O/sub 2/ partial pressure on Rh(100), likely due to the relative ease of oxygen diffusion through this surface leading to more rapid bulk oxidation. Unlike the CO-O/sub 2/ reaction, CO oxidation by NO was very sensitive to the geometric structure of the surface. This behavior was evident in all kinetic parameters measured on the two surfaces. The kinetic data obtained on Rh(111) agree quantitatively with a surface chemistry model previously developed for this reaction. The model predicts that the rate is limited by the formation of N/sub 2/ frommore » the recombination of adsorbed N atoms. and that the surface, under steady-state reaction conditions, is covered largely with adsorbed N atoms and smaller amounts of adsorbed NO. On Rh(100) the data are consistent with a reaction rate limited by the formation of N/sub 2/ from the surface reaction of adsorbed NO and N atoms.« less

Kinetics of carbon monoxide oxidation over Co3O4 containing catalysts studied by the reversed-flow technique

GEORGE KARAISKAKIS, NICHOLAS A. KATSANOS, and ALEXIS LYCOURGHIOTIS. Can J . Chcm. 61, 1853 (1983). The reversed-flow techniquc, uscd previously to measure gas diffusion cocfficicnts. hctcrogcncous catalysis of simple first-order reactions, and othcr processes, is now cxtcndcd to thc study of the kinetics of a morc conlplicatcd rcaction, nan~cly, the oxidation of carbon monoxide over solid catalysts containing Co304. The rcactants are allowed to diffuse slowly onto the catalyst bed and the reaction is sampled at various times by rcpcatcdly reversing the direction of flow of a gas chromatographic carrier gas passing pcrpendicularly to the diffusion current. Rate constants, calculated under steady-statc conditions with a second-and first-ordcr rate law, conform to the lattcr. and this is explained by assuming a reaction between adsorbed carbon monoxide and surface lattice oxygen. Activation energies, calculated from the variation of rate constants with temperature, show a minimum of 14 kJ mol-' for 0.984 mmol of ~ a per g of the catalyst support. This value is lower than that found by others for pure CozOl over a similar tcmperature range.

An XPS and UPS study of the kinetics of carbon monoxide oxidation over Ag(111)

An XPS and UPS study of the kinetics of carbon monoxide oxidation over Ag(111)

An XPS and UPS study of the kinetics of carbon monoxide oxidation over Ag(111)

The oxidation of carbon monoxide over a Ag(111) catalyst has been studied by XPS and UPS. The kinetics have been determined over the temperature range of 180 to 400 K and found to be of the Langmuir-Hinshelwood type, although the Eley-Rideal mechanism is mimicked. A negative activation energy, −1.7 kcal/mole, and a preexponential, 6 × 10 −18 cm 2, are found. The former corresponds to the difference in the activation energies for carbon monoxide desorption and for carbon monoxide oxidation (leading to CO 2 desorption). At 90 K, upon carbon monoxide exposure to the active oxygen precovered surface, the O ls and C ls spectral regions show the formation of CO 2-like and carbonate species; the latter is stable to at least room temperature. That is, at 90 K, the residence time and mobility of CO 2 formed at the surface permits a new surface reaction — the formation of stable surface carbonate. The identifications are based on C and O coverages and on line positions from the literature for Cu/CO 2 and several bulk carbonates. With UPS, the 1π g, the unresolved doublet 1π u and 3σ g, and the 4σ g molecular orbitals of adsorbed CO 2-like species are identified, as well as the unresolved triplet 1α′ 2, 1e″ and 4e′ and the unresolved triplet 3e′, 1α″ 2 and 4a′ molecular orbitals of the carbonate species. Surface CO 2-like species formed by surface oxidation of CO seem to be more strongly bound than reversibly adsorbed CO 2.

Kinetics of carbon monoxide oxidation over chromium sesquioxide with two reaction paths

AbstractKinetics of CO oxidation over chromium sesquioxide with two reaction paths I and II was studied in detail in the temperature range of 378–445 K (105–172°C). The rate constants in each elementary step were estimated as a function of temperature by using transient response and steady‐state data without the help of a parameter optimisation technique. A comparison of their values showed that the rate of path I is limited by surface reaction, and the rate of path II is controlled by three steps: surface reaction; desorption of CO2; and adsorption of O2, which is the slowest step over the entire temperature range studied. Good agreement of the simulated response with the experimental response due to the linear temperature rise proved the validity of the mechanism and the kinetic analysis. The selectivity of reaction path I was also discussed.