The mechanism of the catalytic oxidation of ethylene. III. The reactions between ethylene and oxygen in a static system

Static experiments have been carried out between ethylene and oxygen on the silver catalyst at different pressures and temperatures, and the rates of the several reactions occurring were determined. It was found at 263 degrees C that (a) the rate of oxidation of ethylene to ethylene oxide is proportional to the ethylene pressure and to the first power of the concentration ($\theta $) of adsorbed oxygen on the catalyst; (b) the rate of the direct oxidation of ethylene to carbon dioxide is proportional to the ethylene pressure and to the square of $\theta $; (c) the rate of oxidation of ethylene oxide is proportional to the ethylene oxide pressure and independent of $\theta $. The kinetic equations for the course of reaction with time, although incapable of analytical solution, were integrated by means of the Bush differential analyser, the numerical constants being fitted to one series of experiments. The goodness of fit and the accuracy of the predictions for other conditions were confirmation of the kinetics deduced. These results confirm previous findings that the main steps in the reactions are (1) chemisorption of oxygen as atoms on the catalyst surface, (2) reaction of gaseous or weakly adsorbed ethylene either with one oxygen atom to form ethylene oxide, or with two atoms to form products which are oxidized rapidly to carbon dioxide, and (3) isomerization of ethylene oxide to acetaldehyde followed by the rapid oxidation of this to carbon dioxide. Energies of activation have been measured for these steps. An attempt was made to measure directly the concentration of oxygen adsorbed on the catalyst during reaction, by cleaning it up with hydrogen after pumping out the reaction mixture; a value of 0$\cdot $31 was found which is in fair agreement with that expected from the machine solutions.