Oxygenated species, adsorption

Adsorbed oxygen species Adsorption temperature (°C) Thermally desorbed products (1017 molecules/m 2) B.D. I... 

Activated carbons contain chemisorbed oxygen in varying amounts unless special cate is taken to eliminate it. Desired adsorption properties often depend upon the amount and type of chemisorbed oxygen species on the surface. Therefore, the adsorption properties of an activated carbon adsorbent depend on its prior temperature and oxygen-exposure history. In contrast, molecular sieve 2eohtes and other oxide adsorbents are not affected by oxidi2ing or reducing conditions. 

H2 adsorption is weak on the anatase surfaces [8], No dissociative adsorption of H2 takes place over the smooth surfaces of Au at temperatures below 473 K [9,10]. On small Au particles, adsorption is possible at low temperature. Dissociative adsorption of H2 can be accelerated by the negatively charged molecular oxygen species at steps, edges, comers of Au particles [5]. 

From the pH dependence of the peak potential (close to 60 mV/decade), it was proposed that the oxidation involves adsorption of oxygenated species, leading to the formation of either the oxide or the hydroxide ... 

For potentials higher than 0.5 V vs. RHE, the formation of adsorbed oxygen species at Ru as well as at Pt will block the catalytic surface, leading to a decrease in the methanol adsorption kinetics. Therefore, in a potential range higher than 0.5 V vs. RHE, the kinetics of methanol oxidation is optimized at a Ru-poor catalyst, because methanol adsorption is not blocked and because the presence of Ru provides the extra oxygen atom needed to complete the oxidation of adsorbed CO to CO2. 

At Pt electrodes, adsorption of oxygen species is supposed to be controlled by the Temkin isotherm in the low overpotential region [Damjanovic and Bockris, 1966], whereas in the higher overpotential region, the absence of an oxide layer leads to... 

Oxidative UPD involves the oxidation of species to form an atomic layer where the precursor contains the element in a negative oxidation state. A classic example is the formation of oxide layers on Pt and Au, where water is oxidized to form atomic layers of oxygen. Halide adsorption can be thought of similarly, where a species such as I oxidatively adsorbs on a metal surface as the halide atom. In that case, a bulk film is not formed at more positive potentials, but the diatomic is generated and diffuses into solution. With respect to compound formation, oxidative UPD from a sulfide solution is a good example ... 

Based on these experimental findings it is drawn that adsorbed oxygen species should play an important role to form adsorbed intermediates and adsorption sites for reaction gas components. Therefore, to know the detailed reaction mechanism of ethylene oxidation, it is necessary to clarify a situation of the adsorbed layer formed during the reaction, especially on the adsorbed oxygen species available for the progress of reaction. 

In order to analyze the adsorption behavior of carbon dioxide on silver it was necessary to understand the adsorption behavior of and its reactivity, because the adsorption of CO strongly relatedto the adsorbed oxygen species as will be described later. For this reason, the following transient experiments were purformed. 

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