Stripping and bulk CO electro-oxidation at the Pt–electrode interface: Dynamic Monte Carlo simulations

CO adsorption and oxidation on a Pt(111) electrode modified by ruthenium deposition: an IR spectroscopic study

OH adspecies are involved in numerous electrocatalytic reactions, such as CO, H2, methanol, and ethanol oxidation and oxygen reduction reactions, as a reaction intermediate and/or reactant. In this work, we have, for the first time, identified the OH stretching band of OH adspecies on Pt, Ru, and Pt/Ru electrodes with surface-enhanced infrared absorption spectroscopy (SEIRAS) in a flow cell through potential modulation and CO displacement. We found that while Ru had a relatively constant OH coverage at potentials between 0.1 and 0.8 V, Pt had a maximum OH coverage at 0.6 V in 0.1 M HClO4 and 0.7 V in 0.1 M KOH. CO oxidation kinetics on Ru were sluggish, although adsorbed OH appeared on Ru at very low potentials. Binary Pt/Ru electrodes promote CO oxidation through a synergistic effect in which Ru promotes OH adsorption and Pt catalyzes the reaction between the CO and OH adspecies. In addition, water coadsorbed with CO at Ru sites of Pt/Ru also plays an important role. These new spectroscopic results about OH adspecies could advance the understanding of the mechanism of fuel cell related electrocatalysis.

Diffusion coefficients are necessary to describe the mass transfer and adsorption rate of CO2 in formation fluids. However, data is scarcely reported for actual reservoir conditions of high pressure and temperature, which are normal in most scenarios of the CO2-enhanced oil recovery process in China's fractured-vuggy reservoirs and carbon storage process. Accordingly, this work employed the pressure decay method (PD) and relevant mathematical models to determine the CO2 diffusion coefficient in both liquids and cavern filling porous media at 50 MPa and 393 K. The effects of the type of reservoir fluids, the properties of carven filling porous media, and water saturation on CO2 diffusion coefficients were investigated. Results in bulk reservoir liquids showed that the CO2 diffusion coefficient in the oil sample was 4.1243 × 10−8 m2 s−1, much higher than those in the pure alkane phase, pure water and brine sample from reservoirs. Results of CO2 diffusion in carven filling porous media saturated with oil demonstrated a significant dependence on properties such as porosity and permeability, and a correlation in the CO2 diffusion coefficients between the bulk oil phase and cavern filling porous media in the form of touristy was documented. CO2 diffusion in the fractured cavern porous media was much higher than that without fracture. An increase in water saturation reduced CO2 diffusion coefficients in the carven filling porous medium studied, herein. Thus, the CO2 diffusion coefficient is essentially related to the type of liquid and properties of the filling media.

Effect of Doped Ag on Performance of Manganese Oxide Octahedral Molecular Sieve for CO Oxidation

We have employed molecular beam techniques combined with in situ IR reflection absorption spectroscopy to study the CO oxidation kinetics on oxide-supported model catalysts. As model systems we utilize Pd particles of different size and morphology grown under ultrahigh vacuum conditions on a well-ordered alumina film on NiAl(110). Previously, these systems have been characterized in detail with respect to their geometric and electronic structure. Using a combination of two beam sources crossed on the sample surface, the transient behavior and the steady-state reaction rate are systematically probed over a wide range of CO and oxygen fluxes and at different sample temperatures. Comparing different particle sizes and structures, characteristic differences are observed with respect to both the steady-state reaction rate and the transient behavior upon switching off the CO beam source. The origin of these effects is discussed with respect to the different CO and oxygen adsorption properties of small Pd particles. To directly monitor changes in the CO adsorption during the reaction, we have performed in situ IR absorption spectroscopy under steady-state conditions. Whereas strong rearrangements of the CO adsorbate layer are found for large and well-ordered particles as a function of the applied CO and oxygen fluxes, no similar effects are observed on small Pd aggregates.

We present experimental studies and mathematical modeling on pattern formation during bulk CO electrooxidation on Pt ring electrodes. Profiles of the interfacial potential drop in front of the working electrode were recorded with a potential probe. Stationary self-organized potential patterns were observed under potentiostatic conditions in dilute acidic and basic supporting electrolytes. The amplitude and shape of these potential patterns can be modified by an appropriate local perturbation of the interfacial potential drop. A mathematical model of the formation of these patterns reveals that the homogeneous state becomes unstable through a subcritical Turing-like bifurcation and that several patterned electrode states coexist in wide parameter ranges.

Researches on thermophysical properties of CO₂ are needed because of its connection to global warming. The amount of CO₂ in the atmosphere is much affected by that of CO₂ contained in the ocean. The diffusion coefficient of CO₂ in high pressure seawater is an important parameter for its environmental estimation. In the present study an apparatus for the measurement of the mutual diffusion coefficient of high pressure liquid has been constructed based on the principle of the Taylor dispersion method. The mutual diffusion coefficients of the CO₂- water have been measured under high pressure. The main part of the apparatus consists a closed­circuit channel, a concentration detecting system and a pressure control system. A straight tube of 2104 mm was used as the diffusion tube. In order to cancel disturbance due to injection of the solute, the concentration change was observed optically at two positions along the diffusion tube.

In this article we review the most important findings for Bi modified Pt single crystal electrodes. The main focus is on results obtained on Pt(111)–Biir but also some data for Pt(100)–Biir are provided. Our own data are discussed in the light of previous data from the literature. By making use of in situ surface X-ray scattering in combination with ex situ X-ray photoelectron spectroscopy and cyclic voltammetry it is possible to establish a link between surface atomic structures and electrochemical surface processes. In short, Biir was found to remain in its zero-valent state over the whole potential range. Besides a physical site blocking effect, Biir alters the adsorption properties of Hupd, OHad, and anions from the supporting electrolyte due to electronic modifications of the platinum surface atoms. Rotating (ring-)disk electrode measurements were carried out to study the kinetics of H2, CO or HCOOH electrooxidation on Pt(111)–Biir or the oxygen reduction reaction on Pt(100)–Biir, respectively. The kinetics of CO oxidation (both CO stripping and continuous CO oxidation) is accelerated initially on the Biir modified Pt(111) surface compared to pure Pt(111) electrodes. The same effect was observed during the oxidation of formic acid. The oxygen reduction activity on Pt(100)–Biir is reduced s. pure Pt(100) due to the reduced number of active Pt sites for the reaction (site blocking). At negative potentials, however, the formation of peroxide is enhanced on the Biir modified electrode. Hence, the selectivity of oxygen reduction to H2O2 (2-electron reduction) s. the reduction to H2O (4-electron reduction) is enhanced.

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

Electro-oxidation of CO adsorbed on a polycrystalline Pt electrode in the potential region of hydrogen absorption is examined by fast time-resolved surface-enhanced infrared absorption spectroscopy coupled to voltammetry or chronoamperometry. Oxidation dynamics at a weak preoxidation peak around 0.5 V (vs RHE) and the main oxidation peak around 0.7 V observed in stripping voltammetry are focused. IR spectra show that the shift of bridge-bonded CO to atop sites triggers the partial oxidation of CO adsorbed at atop sites to yield the preoxidation peak. It is also shown that CO on terraces becomes very mobile in the main oxidation region after some amount of CO being oxidized via a nucleation-and-growth mechanism and that terrace CO is oxidized faster than CO adsorbed at step edges. The result is interpreted in terms of a Langmuir−Hinshelwood type mechanism involving adsorbed CO and an oxygen-containing species (most likely OH) adsorbed at steps. The oxidation mechanism is essentially identical to that proposed in some earlier studies, but more convincing spectroscopic evidence of the mechanism is presented.

The kinetics of selective CO oxidation (or individual CO or H2 oxidation) over ruthenium catalysts are considerably as affected by the heat released by the reaction and specifics of the interaction of ruthenium with feed oxygen. In a reactor with reduced heat removal (a quartz reactor) under loads of ∼701 gCat−1 h−1 and reagent percentages of ∼1 vol % CO, ∼1 vol % O2, ∼60 vol % H2, and N2 to the balance, the reaction can be carried out in the catalyst surface ignition regime. When catalyst temperatures are below ∼200°C, feed oxygen deactivates metallic ruthenium, the degree of deactivation being a function of temperature and treatment time. Accordingly, depending on the parameters of the experiment and the properties of the ruthenium catalyst, various scenarios of the behavior of the catalyst in selective CO oxidation are realized, including both steady and transition states: in a non-isothermal regime, a slow deactivation of the catalyst accompanied by a travel of the reaction zone through the catalyst bed along the reagent flow; activation of the catalyst; or the oscillation regime. The results of this study demonstrate that, for a strongly exothermic reaction (selective CO oxidation, or CO, or H2 oxidation) occurring inside the catalyst bed, the specifics of the entrance of the reaction into the surface ignition regime and the effects of feed components on the catalyst activity should be taken into account.

Forced concentration oscillations of Co and O 2 in CO oxidation over Cu/Al 2o 3

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

The catalytic activity of platinum for CO oxidation depends on the interaction of electron donation and back-donation at the platinum center. Here we demonstrate that the platinum bromine nanoparticles with electron-rich properties on bromine bonded with sp-C in graphdiyne (PtBr NPs/Br-GDY), which is formed by bromine ligand and constitutes an electrocatalyst with a high CO-resistant for methanol oxidation reaction (MOR). The catalyst showed peak mass activity for MOR as high as 10.4 A mgPt -1, which is 20.8 times higher than the 20 % Pt/C. The catalyst also showed robust long-term stability with slight current density decay after 100 hours at 35 mA cm-2. Structural characterization, experimental, and theoretical studies show that the electron donation from bromine makes the surface of platinum catalysts highly electron-rich, and can strengthen the adsorption of CO as well as enhance π back-donation of Pt to weaken the C-O bond to facilitate CO electrooxidation and enhance catalytic performance during MOR. The results highlight the importance of electron-rich structure among active sites in Pt-halogen catalysts and provide detailed insights into the new mechanism of CO electrooxidation to overcome CO poisoning at the Pt center on an orbital level.

The influence of planar defects, in the form of stacking faults, within perovskite oxides on catalytic activity has received little attention because controlling stacking-fault densities presents a major synthetic challenge. Furthermore, stacking faults in ceramics are not thought to appreciably impact surface chemistry, which partly explains why their direct effect on catalysis is generally ignored. Here, we show that Ruddlesden-Popper (RP) stacking faults in otherwise stoichiometric LaFeO3 can be broadly controlled by modulating the ceramic synthesis route. Electronic structure calculations along with electron microscopy and spectroscopy show that energetically favorable RP faults occur both near the surface and in bunches and enhance CO oxidation kinetics. Density functional theory (DFT) + U shows that subsurface RP faults strengthen the adsorption and co-adsorption of CO, O, and O2, which could lower the apparent activation energy of CO oxidation on faulted catalysts compared to that on their pristine counterparts. Our work suggests that planar defects should be considered a new and useful feature in hierarchal nanoscale design of future catalysts.