Controlling factors in deoxygenation kinetics and selectivity: reactions of ethylene oxide on molybdenum(110)

Abstract

Ethylene oxide intramolecularly eliminates ethylene directly into the gas phase at 200 K (E{sub a} {approximately} 12 kcal/mol) during reaction on Mo(110) with 70% efficiency as shown by temperature-programmed reaction and x-ray photoelectron spectroscopy. Atomic oxygen, a product of this reaction, increases the rate of ethylene formation by slowing the kinetics for the competing nonselective decomposition pathway which accounts for the other 30% of reaction of chemisorbed ethylene oxide. The nonselective decomposition products of reaction are gaseous dihydrogen, surface carbon, and oxygen. At high ethylene oxide exposures, a small amount of molecular desorption is also observed at 150 K. Deposition of an atomic oxygen overlayer ({theta}{sub 0} {approximately}0.27) on Mo(110) prior to reaction enhances the selectivity of the ethylene formation reaction to 90%. Reaction saturation is controlled by the buildup of hydrocarbon fragments on clean Mo(110) and by oxygen site blocking on the oxygen precovered surface as shown by isothermal reaction spectroscopy. Carbon-heteroatom bond strength correlates with the temperature of ethylene formation in comparing reaction of ethylene oxide to that of the sulfur-containing analogue, ethylene sulfide, on Mo(110).