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 H2S 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 H2S formation pathways involving coadsorbed hydrogen are observed during subsequent heating. In the first pathway, H2S 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 H2S 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 H2S decomposition studies on this surface show that the sulfhydryl intermediate is not stable above ∼190 K because of thermal dehydrogenation. The temperature dependence of H2S 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 H2S also depends on the coverage of coadsorbed sulfur. Increasing sulfur coverages inhibits dehydrogenation of both H2S and SH. With higher sulfur coverages, H2S 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.

Chemistry of Thiophene, Pyridine, and Cyclohexylamine on Ni/MoSxand Ni/S/Mo(110) Surfaces: Role of Nickel in Hydrodesulfurization and Hydrodenitrogenation Processes

“…Sulfur can be removed from Mo(110) 29,40 and Ni surfaces by reaction with atomic hydrogen (2H gas + S surface → H 2 S gas ). Figure shows C 1s spectra acquired after dosing thiophene at 300 K to a Ni 1.1 /S 0.9 /Mo(110) surface that was previously exposed to a beam of atomic hydrogen. , The treatment with hydrogen removed ∼40% of the sulfur.…”

Enhanced sulfur resistance of Ni/SiO2 catalyst for methanation via the plasma decomposition of nickel precursor

“…An active metal surface is sensitive to H 2 S poisoning via the formation of various sulfur species (metal/organic sulfide). [2][3][4] These sulfur species are strongly interacted with the active metal surface, block the active sites, and lead to the loss of catalytic activity. Many efforts have been made to design a catalyst with high H 2 S resistance.…”

Carbon−Carbon Bond Activation of Cyclopropane by Subsurface Hydrogen on the Ni(111) Surface

“…A similar mechanism was proposed on the Pt(111) surface for the reaction of cyclopropane with a new form of adsorbed energetic hydrogen. 23 On that surface, propane formation caused by energetic surface hydrogen is observed at 190 K. The 20 K increase is due to the higher desorption temperatures of cyclopropane and propane on that surface.…”

“…On both the Ni(100) and Pt(111) surfaces, surface hydrogen was unable to activate the cyclopropane C-C bond addition to the ring. 9,23 Furthermore, since the heat of desorption is approximately 7 kcal/mol less than hydrogenation on this surface, no direct hydrogenation would be expected. 24 Subsurface hydrogen induces carbon-carbon bond formation in cyclopropane on the Ni(111) surface.…”