Catalytic CO Oxidation Reaction Research Articles

Spatiotemporal dynamics of fluctuations in a surface reaction by Karhunen–Loeve decomposition of field emission images

Local fluctuations in the catalytic oxidation reaction of CO are studied with field electron microscopy (FEM) in the vicinity of the (110) plane of a [100]-oriented platinum tip. Proper orthogonal decomposition (POD) of the digitized FEM images is employed to analyze the spatiotemporal dynamics of fluctuations in the mono- and bistable ranges of the reaction. The results are shown to be in qualitative agreement with a correlation analysis of the local time series.

The Role of Subsurface Oxygen in the Catalytic CO-Oxidation Reaction

The CO/CO2 conversion performed over a Ru(0001) surface shows the decisive role of subsurface oxygen which explains the discrepancy between former UHV results and high-pressure experiments. At oxygen pressure higher than about 10—3 mbar the oxygen atoms start to penetrate the bulk. This subsurface oxygen has to be considered as a species which accompanies the high-pressure surface reactions where oxygen is involved. This new oxygen phase exhibits unique properties clearly different from adsorbed oxygen as well as from regular ruthenium oxides. The presence of subsurface oxygen raises the yield for CO-oxidation reaction by more than two orders of magnitude. Oxygen atoms forming the subsurface phase seem to be very mobile as can be deduced from the reaction kinetics which show that the CO2 formation is limited only by the thermal diffusion of subsurface oxygen towards the surface.

The Role of Subsurface Oxygen in the Catalytic CO-Oxidation Reaction

The Role of Subsurface Oxygen in the Catalytic CO-Oxidation Reaction

CO oxidation by atomically adsorbed oxygen on Ag(110) in the temperature range 100–300 K

The catalytic CO oxidation reaction with atomically adsorbed oxygen on Ag(110) has been analyzed by means of molecular beam titration, molecular beam relaxation (MBRS), qualitative LEED, and reactive thermal desorption measurements (RTDS). The reaction has been observed and characterized in the temperature range 100–300 K. The CO 2 formation rate depends strongly on the reaction temperature. Additionally, the angular distribution of the desorbing CO 2 is strongly peaked along the surface normal independent of the angle of incidence. Consequently, a Langmuir-Hinshelwood (LH) type model has to be applied for the whole reaction temperature range. The titration curves show two separate structures which are assigned to two reaction channels due to the existence of kinetically distinct oxygen species. These oxygen species are metastable in the sense that they are passivated in a thermally activated process which is proposed to be connected with the formation of the oxygen-induced reconstruction. The stabilized oxygen reacts again with CO at higher temperatures (above 250 K). A reaction scheme is presented which consistently reproduces the experimental results and allows the determination of the kinetic parameters of the reaction.

Calorimetric heats for CO and oxygen adsorption and for the catalytic CO oxidation reaction on Pt{111}

Single crystal adsorption calorimetry was applied to investigate the heats of adsorption of CO and oxygen and the reaction heats for the CO oxidation process on Pt{111} at room temperature. Both sticking probabilities and heats of adsorption for CO and oxygen are presented as a function of coverage. These results are used to interpret the subsequent measurements taken for the CO oxidation process on the same surface. The initial heats of adsorption of CO and oxygen on Pt{111} are 180±8 and 339±32 kJ/mol, respectively. In addition the pairwise lateral repulsive interaction between CO molecules in a (√3×√3)R30° ordered layer at θ=1/3 is found to be 4 kJ/mol. A detailed Monte Carlo modeling of the dissociative adsorption and sticking probability of oxygen on Pt{111} is performed. The initial rapid fall in heat is attributed to adsorption on defect sites, and subsequent adsorption on the planar {111} surface proceeds with a third neighbor interaction energy between the oxygen adatoms ω3∼22 kJ/mol. When gaseous CO reacts with preadsorbed oxygen adatoms, the CO2 produced has an excess energy of 16±8 kJ/mol.

Non-linear dynamics of CO oxidation reaction on Pt and Rh as studied with the lithium field desorption microscope

The carbon monoxide- and the oxygen-covered surfaces of [110]-oriented Pt tips and of [100] and [111]-oriented Rh tips were studied in the lithium field desorption microscope (Li FDM). The catalytic CO-oxidation reaction on Rh and Pt surfaces was studied in situ using Li + and O + 2 field ion modes of imaging. The influence of the modification of electron density near the surface, caused by the presence of Li, on the CO-oxidation reaction on Pt and Rh has been observed. The promoting role of the enhanced electron density in the catalytic oxidation reaction is discussed on the basis of present experimental data and known alkali-gas coadsorption properties.

Investigation of adsorption and coadsorption of O 2 and CO on Rh by O 2+ field ion and Li + field desorption microscopies

A recently developed new method, the lithium field desorption microscopy as well as the O 2 + field ion microscopy were applied for studying the clean, the carbon monoxide- and the oxygen-covered surfaces of [100]- and [111]-oriented Rh tips. The catalytic CO-oxidation reaction on the Rh surface was studied in situ using Li + and O 2 + field ion modes of imaging. The peculiarities of imaging of different surfaces in the Li FDM are discussed in terms of field-stimulated surface diffusion of Li, of the localization of the Li field desorption process and the lateral interaction between Li adatoms. A roughening of the oxygen-covered Rh surface is observed and explained in terms of an oxygen-caused reconstruction of the Rh surface. A substantial influence of the electron density modification near the surface, caused by the presence of Li, on the CO-oxidation reaction on Rh is detected. The promoting role of the enhanced electron density in the catalytic oxidation reaction is discussed on the basis of present experimental data and known alkali-gas coadsorption properties.

Gas-phase coupling in the CO oxidation reaction on polycrystalline platinum

We report on self-sustained rate oscillations during the catalytic CO oxidation reaction on polycrystalline platinum. The photoelectron emission microscope enabled us to distinguish between three different types of grains. We found that the (110)- and the (100)-type grains are responsible for the development of rate oscillations while the (111)-type grains remain in a steady state. Gas-phase coupling is the dominant mechanism leading to a synchronisation of the different oscillating grains over macroscopic distances.