Kinetics Of CO Oxidation Reaction Research Articles

CO Oxidation Reaction by Platinum Clusters on the Surface of Multiwalled Carbon Nanotubes: Experimental and Theoretical Study of Kinetics in a Wide Range of O2/CO Ratios

This work presents a systematic study of the kinetic aspects of CO oxidation reaction catalyzed by platinum nanoparticles (NPs) supported on the surface of multiwalled carbon nanotubes (MWCNTs). The investigation presented is closely related to the actual practical task of air purification in enclosed spaces. Therefore, the catalytic reaction was carried out in the presence of an excess of oxygen (5 vol.%) and over a wide range of CO concentrations from 50 ppm to 1600 ppm. For the catalyst characterization, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were applied. Kinetic modelling based on the Langmuir–Hinshelwood and Mars-van Krevelen mechanisms was taken as a basis, using the results obtained on Pt foil. Simulation of CO oxidation reaction on platinum NPs at temperatures above 90 °C was carried out using a kinetic model describing the reaction mechanism on bulk platinum. The description of the kinetics of CO oxidation reaction on Pt NPs over the entire temperature range, including the low temperatures down to −40 °C, required the introduction of the steps characterizing an additional concerted mechanism related to CO-assisted O2 dissociation. Using the presented model, some predictions of the kinetic behaviour of the system were made.

Porous stainless-steel fibers supported CuCeFeOx/Zeolite catalysts for the enhanced CO oxidation: Experimental and kinetic studies

To develop novel catalysts of high-performance and cost-effectiveness, and to investigate the reaction kinetics of CO oxidation, ternary CuCeFeOx catalysts supported on zeolite/PSF (porous stainless-steel fibers) were synthesized for the first time. Effects of different Ce/Fe ratios, loading amounts, calcination temperatures, and reaction kinetics were investigated. Remarkably improved catalytic performance was achieved in the PSF-supported catalysts compared to the granular ones, owing to the increased mass/heat transfer efficiency and the high dispersion of active metal oxide species anchored on the zeolite layer. The Cu3Ce12Fe4-400 sample exhibited the best catalytic activity with a temperature difference in T90 of almost 40 °C lower than the worst one. Characterization results from XRD, FTIR, TEM, XPS, H2-TPR, etc. revealed that the promoted reducibility of metal oxides and formation of more oxygen vacancies significantly contributed to the enhanced catalytic activity. Furthermore, a generalized rate expression was derived from intrinsic and macro kinetic studies by assuming the conversion of CO to CO2 as the rate-determining step, in which CO oxidation over the PSF-supported catalysts followed the pseudo-first-order kinetic established by the Langmuir-Hinshelwood type mechanism.

The influence of dissolved O2 on the electrochemical behaviors of Co-B alloy electrode

The influence of dissolved oxygen on the electrochemical behaviors of the CoB alloy electrode has been investigated by open circuit potential (OCP) measurement and galvanostatic charge-discharge method. It was found that the alloy electrode in oxygen-containing electrolyte has more positive OCP due to the existence of the redox couple O2/OH−. Dissolved oxygen can greatly enhance the high-rate dischargeability of the alloy electrode. Specifically, in oxygen-containing electrolyte, the electrode delivers a reversible discharge capacity of 530mAh/g at 300mA/g and its discharge capacity is still up to 480mAh/g even at a high current density of 1200mA/g. However, in the case of the electrode in oxygen-free electrolyte, its discharge capacity is 438mAh/g at 300mA/g and is reduced to only 234mAh/g at 1200mA/g. Exchange current densities (i0) of the alloy electrode in oxygen-containing and oxygen-free electrolyte are 78mA/g and 54mA/g, respectively. The significant improvement in the high-rate dischargeability of the alloy electrode should be attributed to that oxygen reduction accelerates the kinetics of Co oxidation reaction.

Steady-state reaction kinetics of CO oxidation catalyzed by uni-sized Pt30 clusters directly bound to Si surface

Catalytic CO oxidation driven by uni-sized Pt30 bound to a Si substrate, at the interface of which electrons are accumulated. The low-temperature and anti-CO-poisoning performance has been evidenced with continuous and simultaneous supply of CO and O2.

The Role of Defects in the Local Reaction Kinetics of CO Oxidation on Low-Index Pd Surfaces.

The role of artificially created defects and steps in the local reaction kinetics of CO oxidation on the individual domains of a polycrystalline Pd foil was studied by photoemission electron microscopy (PEEM), mass spectroscopy (MS), and scanning tunneling microscopy (STM). The defects and steps were created by STM-controlled Ar+ sputtering and the novel PEEM-based approach allowed the simultaneous determination of local kinetic phase transitions on differently oriented μm-sized grains of a polycrystalline sample. The independent (single-crystal-like) reaction behavior of the individual Pd(hkl) domains in the 10–5 mbar pressure range changes upon Ar+ sputtering to a correlated reaction behavior, and the reaction fronts propagate unhindered across the grain boundaries. The defect-rich surface shows also a significantly higher CO tolerance as reflected by the shift of both the global (MS-measured) and the local (PEEM-measured) kinetic diagrams toward higher CO pressure.

Mapping the local reaction kinetics by PEEM: CO oxidation on individual (100)-type grains of Pt foil

The locally-resolved reaction kinetics of CO oxidation on individual (100)-type grains of a polycrystalline Pt foil was monitored in situ using photoemission electron microscopy (PEEM). Reaction-induced surface morphology changes were studied by optical differential interference contrast microscopy and atomic force microscopy (AFM). Regions of high catalytic activity, low activity and bistability in a (p,T)-parameter space were determined, allowing to establish a local kinetic phase diagram for CO oxidation on (100) facets of Pt foil. PEEM observations of the reaction front propagation on Pt(100) domains reveal a high degree of propagation anisotropy both for oxygen and CO fronts on the apparently isotropic Pt(100) surface. The anisotropy vanishes for oxygen fronts at temperatures above 465K, but is maintained for CO fronts at all temperatures studied, i.e. in the range of 417 to 513K. A change in the front propagation mechanism is proposed to explain the observed effects.

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.

Effects of heat and mass transfer on the kinetics of CO oxidation over RuO 2(1 1 0) catalyst

Combining first-principles kinetic Monte Carlo (KMC) simulation with a finite difference continuum model, a hybrid computational model was developed to study the effects of heat and mass transfer on the heterogeneous reaction kinetics. The integrated computational framework consists of a surface phase where catalytic surface reactions occur and a gas-phase boundary layer imposed on the catalyst surface where the fluctuating temperature and pressure gradients exist. The surface phase domain is modeled by the site-explicit first-principles KMC simulation. The gas-phase boundary layer domain is described using the second-order grid-based Crank–Nicolson method. To simplify the model, the flow and gas-phase reactions are excluded. The temperature and pressure gradients in the gas-phase boundary layer are the consequence of thermal and molecular diffusions of reactants and products under nominal reaction conditions. Different from previous hybrid multiscale models, the heat and mass fluxes between two domains are directly coupled by the varying boundary conditions at each simulation timestep from the unsteady state reaction regime to the steady state reaction regime in the present model. At the steady-state reaction regime, the activity, the surface coverages of reaction intermediates, along with the temperature and pressure gradient profiles in the gas-phase boundary layer are statistically constant with very small fluctuations. As an illustration example, we studied the effects of heat and mass transfer on the reaction kinetics of CO oxidation over the RuO 2(1 1 0) catalysts. We assume the heat from CO oxidation is exclusively dissipated into the gas-phase via thermal diffusion. By varying the thickness of RuO 2(1 1 0) catalysts, the surface temperature changes correspondingly with the heat produced by occurring surface reactions, resulting in the pronounced temperature and pressure gradients in the gas-phase boundary layer. Our simulation results indicate that the limitation of heat and mass transfer in the surrounding environment over the catalyst could dramatically affect the observed macroscopic reaction kinetics under presumed operating reaction conditions. To fully elucidate the complex heterogeneous catalytic system, proper physical description of fluid phase that imposed on the catalyst and its effect on the surface kinetics should be integrated with current surface computational models.

CO oxidation on partially oxidized Pd nanoparticles

Combining multi-molecular beam (MB) experiments and in situ time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we studied the relationship between the formation of Pd surface oxides and the reaction kinetics of CO oxidation on a well-defined Fe 3O 4-supported Pd model catalyst. The model catalyst was prepared in-situ under ultra-high-vacuum (UHV) conditions by Pd deposition onto a well-ordered Fe 3O 4 film on Pt(111). In previous studies, structure, morphology, and adsorption properties of the model system, as well as the formation of Pd oxide species, were characterized in detail. At low reaction temperatures ( T < 450 K ), the CO oxidation activity of partially oxidized Pd particles was found to be significantly lower than that of metallic Pd particles. We address this deactivation of the catalyst to a weak CO adsorption on Pd surface oxides, leading to a very low reaction probability. Even after extended exposure to CO-rich reactants at 400 K, no significant gain in catalytic activity due to reduction of surface oxides was observed. As a result, we conclude that the formation of Pd oxide species at higher temperatures causes long-term deactivation of the catalyst at lower temperatures. At higher reaction temperatures ( T ⩾ 500 K ), however, Pd oxides can be dynamically formed and decomposed, depending on the composition of the reactant environment. Although Pd oxides are formed on the surface under O-rich conditions, such oxide species are decomposed under CO-rich conditions at these temperatures. Using a simple model, we qualitatively analyzed the formation and decomposition process of Pd oxides under reaction conditions. We found that at higher reaction temperatures, partial oxidation of the Pd particles generally led to reduced CO oxidation activity and slow hysteresis effects that were strongly dependent on the pretreatment of the sample.

Energy dependent transient reaction kinetics of CO oxidation on Pd{1 1 0}

Translational energy dependence of CO adsorption and CO oxidation have been investigated by performing molecular beam surface scattering experiments on Pd{110}. We find that CO adsorbs molecularly on clean and oxygen precovered Pd{110} over a range of surface temperatures (300–500 K) and translational energies (4.8–21 kJ/mol). The initial sticking probability (S0) of CO on clean Pd{110} is shown to be strongly energy dependent. Only a weak surface temperature dependence is observed. Evidence is provided for the CO adsorption process being weakly activated. S0 of CO on the Pd{110}c(2×4)–O surface is largely energy independent. The initial reaction probability is, however, determined to depend on the CO translational energy. Both the surface temperature and the translational energy of CO are shown to enhance the initial reaction rate and shorten the reaction induction time required for the CO2 formation rate to reach its maximum. The role of the CO translational energy is discussed in terms of the weakening of the Pd–O bond.

Kinetics of the Microwave-Heated CO Oxidation Reaction over Alumina-Supported Pd and Pt Catalysts

The kinetics of the CO oxidation reaction on Pt/Al2O3as well as Pd/Al2O3have been measured in a packed bed reactor heated by microwave energy. The reaction rate was also measured in an identical reactor that was heated via conventional means. Several methods of temperature measurement were explored for the determination of catalyst temperature in the microwave heated reactor. Insertion of a thermocouple after the microwaves have been switched off provided the best method for temperature measurement in this study. However, large-scale temperature gradients must be eliminated before this method can provide accurate temperature measurements. After suitable modifications in our packed bed reactor to eliminate nonisothermality, we found that the rate of reaction and the reaction kinetics (order of reaction) for the microwave heated CO oxidation reaction were comparable to those for the conventionally heated reactor. The CO oxidation reaction therefore serves as anin situprobe of metal surface temperature. These observations suggest that the Pt and Pd crystallites in a supported catalyst are not significantly hotter than the alumina support in a microwave heated reactor.

Molecular beam studies of CO oxidation and CO-NO reactions on a supported Pd catalyst

The surface reactivity of highly dispersed (85%) palladium cluster catalysts supported on γ-alumina (1.5 wt% loading) had been probed using the molecular beam scattering technique. This work illustrates the utility of molecular beam sources to study reaction kinetics on highly dispersed catalyst surfaces under UHV conditions. While CO adsorbs and desorbs molecularly throughout the coverage range, the Pd particles have been found to be extremely active with respect to NO dissociation forming a “mixed” layer of molecularly bound NO and atomic nitrogen and oxygen. Reaction kinetics of CO oxidation has been studied as a function of surface temperature by reaction of a pre-adsorbed oxygen layer with a CO molecular beam. A maximum reaction rate and percentage conversion to CO 2 was found to occur between 570 and 620 K. In contrast to previous studies of model Pd cluster catalysts, the highly dispersed Pd clusters have been found to be active for the CO/NO reaction probed by reaction of a CO beam with a NO pre-adsorbed layer.