The adsorption and reaction of ethylene on clean and oxygen covered Pd(100)

Abstract

The absorption and reaction of C2H4 on clean and oxygen covered Pd(100) was studied with temperature programmed reaction spectroscopy (TPRS) and high resolution electron energy loss spectroscopy (EELS). Both the di-σ and π-bonded forms of C2H4 were stable on the clean surface at 80 K. The π-bonded form desorbed in a broad peak from 100 to 300 K. but the di-σ-bonded form underwent dehydrogenation to form a vinyl species (HCCH2) and ultimately methylidyne groups (CH) at 300 K. Heating to 500 K. resulted in the dehydrogenation of the CH groups and the formation of surface carbon. Preadsorbed oxygen inhibited the dehydrogenation reaction by blocking the adsorption of C2H4 into the di-σ-bonded form. although π-bonded ethylene was stable for oxygen coverages up to 0.5 ML (monolayer). The extent of dehydrogenation decreased linearly to zero as the oxygen coverage was increased to 0.25 ML. and it was found that two oxygen atoms were required to block the reaction of one ethylene molecule. No other reactions between C2H4 and O were observed, although small amounts of H2O, CO, and CO2 were formed by reaction of oxygen and C2H4 dehydrogenation products for oxygen coverages less than 0.25 ML. © 1985.