کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
10243799 | 47177 | 2005 | 22 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
First principles calculations of the adsorption and diffusion of hydrogen on Fe(1Â 0Â 0) surface and in the bulk
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
مهندسی شیمی
کاتالیزور
پیش نمایش صفحه اول مقاله
![عکس صفحه اول مقاله: First principles calculations of the adsorption and diffusion of hydrogen on Fe(1Â 0Â 0) surface and in the bulk First principles calculations of the adsorption and diffusion of hydrogen on Fe(1Â 0Â 0) surface and in the bulk](/preview/png/10243799.png)
چکیده انگلیسی
First-principles plane wave calculations based on spin-polarized density-functional theory (DFT) and the generalized gradient approximation (GGA) have been used to study the adsorption of hydrogen on Fe(1 0 0) surface and in the bulk. It was found that H2 adsorption takes place dissociatively with a classical activation energy of about 3.5 kcal/mol. In the low coverage regime at θ = 0.25, H atom adsorbs at both two-folded and four-folded sites with a slight preference for the four-folded site. In the full coverage regime, there is a clear distinction between two-folded and four-folded adsorption sites with a net preference for adsorption at four-folded site. The dependence of H binding energy on coverage in the range 1.0 â¤Â θ â¤Â 3.0 was also determined and the corresponding sequence of sites filling has been analyzed. After filling all four-folded sites, it was found that occupation of two-folded followed by one-folded sites is possible while adsorption at nearby mixed two-folded and one-folded sites leads to H-H recombination. The minimum energy pathways for surface diffusion of atomic H between selected pairs of local minima indicate the existence of small classical barriers with values of about 1.9 kcal/mol. These barriers increase slightly with the increase of coverage. When H diffuses from surface to subsurface sites, the corresponding barriers are larger than on the surface with values in the range 7.5-9.5 kcal/mol. At these subsurface sites, the absorption energy is still exothermic relative to gas phase H2 and increases with coverage. Once H penetrates the first two surface layers, the corresponding diffusion barriers decrease to values close to those obtained in bulk Fe. Absorption of H in bulk bcc Fe is endothermic relative to isolated gas phase H2 and takes place at tetrahedral sites. The most favorable diffusion pathway among tetrahedral sites was found to pass through a trigonal site and has a low barrier of about 1.1 kcal/mol.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Catalysis Today - Volume 105, Issue 1, 15 July 2005, Pages 44-65
Journal: Catalysis Today - Volume 105, Issue 1, 15 July 2005, Pages 44-65
نویسندگان
Dan C. Sorescu,