Manipulating the activation barrier for H2(D2) desorption from potassium-modified palladium surfaces

Autor:	Adolf Winkler, Markus Kratzer, Gernot Pauer
Rok vydání:	2005
Předmět:	Adsorption Deuterium Hydrogen Chemistry Desorption Potassium Kinetic isotope effect Analytical chemistry General Physics and Astronomy chemistry.chemical_element Physical and Theoretical Chemistry Atmospheric temperature range Palladium
Zdroj:	The Journal of Chemical Physics. 123:204702
ISSN:	1089-7690 0021-9606
DOI:	10.1063/1.2121487
Popis:	In this work the permeation and desorption of hydrogen (deuterium) from potassium-modified Pd(111) and polycrystalline palladium surfaces have been studied in the temperature range from 350 to 523 K. Time-of-flight spectroscopy has been used to determine the translational energy distributions of associatively desorbing H(2)(D(2)) molecules as a function of the potassium coverage and additional isotropic O(2) and CO background pressures. It turned out that the energy distribution of the hydrogen desorption flux is thermalized for the clean Pd surfaces but hyperthermal for the potassium-covered surfaces. The activation barrier for adsorption was found to increase with the potassium coverage but to decrease again in the presence of coadsorbates such as O(2) or CO. Especially by choosing different isotropic CO pressures, the effective desorption barrier for hydrogen could be reversibly decreased and increased, which resulted in the equivalent changes of the mean kinetic energies of the desorbing H(2) molecules.
Databáze:	OpenAIRE
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