Temperature programmed desorption studies of OD coadsorbed with H2 on Pt(111)

A molecular beam source of pure hydroxyl radicals has been developed and used to explore the water reaction catalyzed over Pt(111). An electrostatic hexapole selectively focused OD radicals from a supersonic corona discharge source onto a Pt target at a surface temperature of TS=143 K. Subsequent D2O temperature programmed desorption (TPD) spectra revealed two major features, one near TS∼170 K from desorption of molecular water overlayer and a second near TS∼210 K from the decomposition of an adsorbed OD intermediate. The latter feature was isolated and analysis of TPD spectra revealed that the D2O production reaction was approximately half-order in total oxygen coverage with a pre-exponential factor ranging from vd=4±1×1016 to 5±2×1018 molecules1/2 cm−1 s−1 and activation energy Ea=9.7±0.1 to 11.5±0.1 kcal mol−1 for initial coverage ranging from θ0=0.04 to 0.25 ML. Coadsorption studies of OD and H2 revealed that H atoms drive reactions with adsorbed OD at TS∼180 K to form all three water isotopes: D2O, H...

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