Catalytic oxidation. I. The oxidation of ethylene over Pd and PdAu alloys

H. R. Gerberich*, Noel W. Cant, W. Keith Hall

*Corresponding author for this work

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    The gross kinetics for the oxidation of ethylene were determined over Pd and PdAu alloys in a steady-state flow reactor and in a recirculating reactor in which the products were stripped with each pass. The partial oxidation products over Pd included acetic acid, acetic anhydride, acetaldehyde, and (a trace) ethylene oxide. Initial selectivity for partial oxidation varied between 25 and 45%, depending upon reaction conditions; steady-state values fell in the range, 6-25%. Both the total rate and selectivity increased with O2 pressure. The rates of both total and partial oxidation passed through maxima near 5 Torr with varying C2H4 pressure, changing from first-order at lower pressures to negative-order at higher. The apparent activation energy, based on initial rate data was 20 ± 2 kcal/mole for both complete and partial oxidation, but was 30 ± 2 kcal/mole for steady-state measurements. The difference may reflect effects of poisoning by products. When small amounts of acetaldehyde-14C were added to the reaction, 80% of the radioactivity was recovered in the acetic acid and 10% as CO2. Added ethylene oxide-14C was recovered unreacted. The C2H4 reacted about 1.4 times faster than C2D4. Scrambling in the unreacted ethylenes during oxidation of equimolar mixtures was minimal at low ethylene pressures. No 16O18O was found when mixtures of 16O2 and 18O2 were used to oxidize ethylene, but the isotopic distribution in the product CO2 was near equilibrium. The PdAu alloys were much less active than pure Pd and much more active than Au. The selectivity, however, went through a maximum (~50%) near 20% Pd. A similar maximum was found for fast O2 chemisorption.

    Original languageEnglish
    Pages (from-to)204-219
    Number of pages16
    JournalJournal of Catalysis
    Issue number2
    Publication statusPublished - 1970


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