Recombination desorption, reaction order

CI2 evolution reaction, 38 56 electrochemical desorption, 38 53-54 electrode kinetics, 38 55-56 factors that determine, 38 55 ketone reduction, 38 56-57 Langmuir adsorption isotherm, 38 52 recombination desorption, 38 53 surface reaction-order factor, 38 52 Temkin and Frumkin isotherm, 38 53 real-area factor, 38 57-58 regular heterogeneous catalysis, 38 10-16 anodic oxidation of ammonia, 38 13 binding energy quantification, 38 15-16 Haber-Bosch atrunonia synthesis, 38 12-13... 

From the above it is seen how the same coverage functions, involving the lateral interaction factor g, determine both R and the Tafel slope values. In particular, for the electrochemical desorption mechanism, the Tafel slope b is found to be (RT/F)(—1 + whereas for the recombination-controlled mechanism it is simply (RT/F) , in terms of the reaction order, R. 

However, due to the difficulties in calculating ion yields in SIMS, quantitation of the data is not very reliable, and their work was not conclusive. We have determined here that the reaction of chemisorbed ethylene to form ethylidyne is first order in ethylene coverage. A noticeable isotope effect was observed, with activation energies of 15.0 and 16.7 Kcal/mole for C H and 02 respectively. These values are smaller than those calculated from TDS, but the differences can be reconciled by including the recombination of hydrogen atoms on the surface in the interpretation of the thermal desorption experiments. 

We have measured the kinetics of ethylidyne formation from chemisorbed ethylene over Pt(lll) surfaces. The rates of reaction display a first order dependence on the ethylene coverage. There is an isotope effect, since the reaction for CjH is about twice as fast as for CjD. We obtain values for the activation energy of 15.0 and 16.7 Kcal/mole for the normal and deuterated ethylene, respectively. These values are lower than those obtained from TDS experiments, but the differences can be reconciled by taking into account the hydrogen recombination when analyzing the thermal desorption data. 

The reaction of with well-characterized Cu clusters deposited on highly ordered AI2O3 films has also been studied using TPD and HREELS [58]. Figure 20 shows that the formed is sensitive to the cluster size in that no N2 is detected until 6cu >0.13 ( 3.5nm clusters). Desorption of N2 was observed at about 130 and 770 K the 770 K feature is understood to be due to recombination of atomic N(a). The reaction of CO + NO has also been examined for this catalytic system. 

In the 1970s and 1980s both the clean and H-covered Si surfaces were characterized by diffraction and spectroscopic methods, but only in the last decade have there been reproducible studies of chemical kinetics and dynamics on well-characterized silicon surfaces. Despite the conceptual simplicity of hydrogen as an adsorbate, this system has turned out to be rich and complex, revealing new principles of surface chemistry that are not typical of reactions on metal surfaces. For example, the desorption of hydrogen, in which two adsorbed H atoms recombine to form H2, is approximately first order in H coverage on the Si(lOO) surface. This result is unexpected for an elementary reaction between two atoms, and recombi-native desorption on metals is typically second order. The fact that first-order desorption kinetics has now been observed on a number of covalent surfaces demonstrates its broader significance. 

Our earlier work [1] suggested that BTj desorption resulted from second-order Br(a) + Br(a) recombination reaction this conclusion was based on an inspection of the Brj thermal desorption spectra. The present approach permits one to characterise the kinetic order of the surface reaction and allows a determination of the kinetic parameters. When products are formed by a non-linear surface process such as... 

For a low surface coverage, since the anodic reaction is first order with respect to chlorine this means that only one chloride ion participates in the slow stage and in all stages preceding it. This immediately allows us to disregard such mechanisms as slow recombination or slow electrochemical desorption, which require the reaction to be second order with respect to chloride (at a constant potential). ... 

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