Desulfurization of the Ni(100) surface using gas-phase hydrogen radicals
- Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Chemistry
Gas-phase hydrogen radicals cause desulfurization of the sulfided Ni(100) surface even for temperatures as low as 120 K, resulting in H{sub 2}S formation. In contrast, no thermal desulfurization is observed in the presence of coadsorbed hydrogen. During hydrogen radical exposure, sulfur is abstracted from the Ni(100) surface by a sequential Eley-Rideal mechanism. After hydrogen radical exposure, two additional H{sub 2}S formation pathways involving coadsorbed hydrogen are observed during subsequent heating. In the first pathway, H{sub 2}S formation is observed at 150 K, involving a partially hydrogenated intermediate formed during gas-phase atomic hydrogen exposure. The second pathway involves addition of desorbing subsurface hydrogen to adsorbed sulfur, leading to H{sub 2}S formation at 190 K. Both the temperature and coverage dependence of the 150 K pathway support a sequential hydrogen addition mechanism with a sulfhydryl intermediate during temperature-programmed desorption (TPD) studies. Previous H{sub 2}S decomposition studies on this surface show that the sulfhydryl intermediate is not stable above {approximately} 190 K because of thermal dehydrogenation. The temperature dependence of H{sub 2}S formation and sulfur removal during exposure to the gas-phase hydrogen radical is also consistent with a sulfhydryl intermediate. Above 200 K, no desulfurization is observed during gas-phase hydrogen radical exposure. This thermal dehydrogenation of H{sub 2}S also depends on the coverage of coadsorbed sulfur. Increasing sulfur coverages inhibits dehydrogenation of both H{sub 2}S and SH. With higher sulfur coverages, H{sub 2}S desorption is favored and substantial sulfur is removed during temperature-programmed reaction spectroscopy (TPRS) experiments after low-temperature hydrogen radical exposure. Taken together, the temperature- and coverage-dependent behavior indicates that sulfhydryl is an intermediate for sulfur abstraction. Through control of gas-phase hydrogen radical exposure, vacancies in sulfided nickel layers were generated. Hydrogen chemisorption studies were used to probe these sulfur vacancies. The new, low-temperature hydrogen desorption peak at 230 K corresponds to hydrogen modified by coadsorbed sulfur.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- OSTI ID:
- 682071
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 31; Other Information: PBD: 5 Aug 1999
- Country of Publication:
- United States
- Language:
- English
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