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Title: Desulfurization of the Ni(100) surface using gas-phase hydrogen radicals

Abstract

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. Thismore » 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.« less

Authors:
;  [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Chemistry
Publication Date:
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
682071
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Additional Journal Information:
Journal Volume: 103; Journal Issue: 31; Other Information: PBD: 5 Aug 1999
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; NICKEL; DESULFURIZATION; SURFACES; HYDROGEN; RADICALS; HYDROGEN SULFIDES; TEMPERATURE RANGE 0065-0273 K; CHEMISORPTION

Citation Formats

Capitano, A.T., and Gland, J.L. Desulfurization of the Ni(100) surface using gas-phase hydrogen radicals. United States: N. p., 1999. Web. doi:10.1021/jp990937q.
Capitano, A.T., & Gland, J.L. Desulfurization of the Ni(100) surface using gas-phase hydrogen radicals. United States. doi:10.1021/jp990937q.
Capitano, A.T., and Gland, J.L. Thu . "Desulfurization of the Ni(100) surface using gas-phase hydrogen radicals". United States. doi:10.1021/jp990937q.
@article{osti_682071,
title = {Desulfurization of the Ni(100) surface using gas-phase hydrogen radicals},
author = {Capitano, A.T. and Gland, J.L.},
abstractNote = {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.},
doi = {10.1021/jp990937q},
journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
number = 31,
volume = 103,
place = {United States},
year = {1999},
month = {8}
}