Ethylene oxidation on silver powder: A tap reactor study

The oxidation of ethylene over silver powder catalysts was studied between 475 and 575 K at pressures of circa 10 Torr under transient conditions that allowed reactions of atomic and molecular oxygen to be distinguished. Dioxygen and d4-ethylene were pulsed separately over silver powder in a microreactor with pulse durations of 200 μs, and the products were detected by a multiplexed mass spectrometer. This method, denoted as temporal analysis of products, allows either simultaneous pulsing of the reactants or pulse delays ranging from a few milliseconds to minutes. In these experiments both ethylene oxide and carbon dioxide were detected as products. Ethylene oxide formed instantaneously on the time scale of the reactant pulse, but carbon dioxide formed with a much slower time constant, characteristic of the decomposition of surface carbonate, indicating the importance of secondary interactions of CO2 with surface oxygen in the kinetics of CO2 formation. Pulse-probe experiments, in which the catalyst was first loaded with adsorbed atomic oxygen and then reacted with anaerobic ethylene pulses or ethylene-oxygen mixtures, showed that the adsorbed species giving rise to ethylene oxide is atomic, not molecular, oxygen.