کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5425966 | 1395871 | 2006 | 10 صفحه PDF | دانلود رایگان |
The interaction of atomic hydrogen with thin epitaxial FeO(1Â 1Â 1) and Fe3O4(1Â 1Â 1) films was studied by TDS, XPS and LEED. On the thin, one Fe-O bilayer thick FeO film, partial reduction occurs in two steps during exposure. It ends after removal of 1/4 monolayer (ML) of oxygen with a 2Â ÃÂ 2 pattern appearing in LEED. This FeO0.75 film is passive against further reduction. The first reduction step saturates after removal of â¼0.2Â ML and shows autocatalytic kinetics with the oxygen vacancies formed during reduction causing acceleration. The second step is also autocatalytic and is related with reduction to the final composition and an improvement of the 2Â ÃÂ 2 order. A structure model explaining the two-step reduction is proposed. On the thick Fe3O4 film, irregular desorption bursts of H2O and H2 were observed during exposure. Their occurrence appears to depend on the film quality and thus on surface order. Because of the healing of reduction-induced oxygen vacancies by exchange of oxygen or iron with the bulk, a change of the surface composition was not visible. The existence of partially reduced oxide phases resistant even to atomic hydrogen is relevant to the mechanism of dehydrogenation reactions using iron oxides as catalysts.
Journal: Surface Science - Volume 600, Issue 4, 15 February 2006, Pages 793-802