Temperature-programmed desorption study of H/sub 2/-D/sub 2/ exchange on Pt(111) and the role of subsurface sites

Journal Article · Thu Aug 14 04:00:00 EDT 1986 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100408a049· OSTI ID:5458819

Greenlief, C M; Akhter, S; White, J M

The adsorption of H/sub 2/ and D/sub 2/ has been studied on Pt(111) by temperature-programmed desorption. Exposures of at least 1000 Langmuir are required to saturate the surface. Below 120 K there is no exchange between H/sub 2/(g) (or D/sub 2/(g)) and D(a) (or H(a)) on a fully saturated surface. Above 120 K, isotope exchange occurs readily with an activation energy of 1.1 +/- 0.1 kcal mol/sup -1/. When the substrate is dosed at temperatures below 250 K the desorption of D/sub 2/ is complete at temperatures significantly below those for H/sub 2/ and HD irrespective of the order of adsorption. This isotope effect is attributed to the preferential accommodation of H into the near-surface region of Pt. There is no isotope effect in desorption after dosing above 250 K. This is interpreted in terms of surface-subsurface exchange (equilibration) during dosing. Within the framework of this model, the activation energy for recombination involving at least one subsurface H or D atom is 1.6 +/- 0.1 kcal mol/sup -1/.

• Research Organization: Univ. of Texas, Austin
• OSTI ID: 5458819
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 90:17; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400203* -- Isotope Exchange & Isotope Separation-- (-1987)
ARRHENIUS EQUATION
CRYSTALS
DATA
DESORPTION
DEUTERIUM
ELEMENTS
EQUATIONS
EXPERIMENTAL DATA
HYDROGEN
HYDROGEN ISOTOPES
INFORMATION
ISOTOPES
ISOTOPIC EXCHANGE
LIGHT NUCLEI
METALS
MONOCRYSTALS
NONMETALS
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
PLATINUM
PLATINUM METALS
STABLE ISOTOPES
THERMODYNAMICS
TRANSITION ELEMENTS