Benzenethiol Reaction on the Clean and Hydrogen Pretreated Ni(100) Surface

Abstract

Benzenethiol reactions on clean and hydrogen precovered Ni(100) surfaces have been studied in order to characterize C-S bond breaking. Benzenethiol adsorbs at 90 K as phenylthiolate and surface hydrogen. The dominant benzene formation pathway for large coverages of benzenethiol occurs at 270 K. C-S bond breaking involves direct reaction of phenylthiolate with the nickel surface; hydrogen does not appear to be directly involved. The rate-limiting C-S bond breaking step is followed by rapid hydrogenation of adsorbed phenyl to form benzene which desorbs from the sulfur covered surface. Deuterium incorporation studies support this mechanism since single hydrogen addition dominates as expected for hydrogenation of an adsorbed phenyl intermediate. For the benzenethiol saturated surface (0.30 monolayer), hydrogen preadsorption increases the temperature for benzene formation by up to 20 K and increases the benzene yield up to 37%. Reorientation of the phenylthiolate away from the surface in the presence of large coadsorbed hydrogen coverages is indicated by vibrational characterization. This hydrogen induced reorientation appears to be associated with the increase in C-S bond activation energy. Above 500 K dehydrogenation of adsorbed phenylthiolate derived species results in formation of surface bound polyaromatic hydrocarbons (PAHs) coadsorbed with sulfur; the hydrogen formed in this process desorbs. For low coverages of benzenethiol, no 270 K benzene is observed due to increased dehydrogenation by the surface. A small amount of benzene is formed by disproportionation above the temperature of free hydrogen desorption (400 K). A comparison of benzenethiol reactions on the three low Miller index surfaces of nickel clearly indicates that hydrogen availability at reaction temperature has a large influence on benzene formation. Hydrogen desorption prior to C-S bond activation on the Ni(100) surface limits benzene formation, while substantial hydrogen availability on the Ni(111) and Ni(110) surfaces facilitates benzene formation.

Measurement of Benzenethiol Adsorption to Nanostructured Pt, Pd, and PtPd Films Using Raman Spectroelectrochemistry

“…As described above, at 1000 mV on the negative-going potential excursion, Raman bands corresponding to adsorbed sulfur oxides appear, suggesting that the C−S bond in BT is dissociated at the oxidized Pd surface, leaving oxidized sulfur species adsorbed. While it has been established that BT electrochemically desorbs from gold electrodes as phenylthiolate, it has been demonstrated in UHV studies that thermal BT desorption can occur through C−S bond scission on metals such as Ni, , Rh, and CoMo alloys, as well as other metals . It is also important to note that the C−S bond in alkylthiols is generally weaker than in aryl thiols: for example, the C−S bond in benzenethiol is 86.5 kcal mol −1 , whereas for methanethiol, it is 74 kcal mol −1 .…”

Toluene Formation from Coadsorbed Methanethiol and Benzenethiol on Nickel Surfaces

“…The mechanism responsible for the 420 K toluene peak is independent from the 300 K toluene peak since the relative intensities of these peaks change significantly when dosing order is reversed (Figure ). Multiple deuterium incorporation is observed during benzene formation at 420 K, indicating that a dehydrogenated aromatic intermediate is involved . A similar dehydrogenated aromatic intermediate appears to be responsible for the high-temperature toluene at 420 K. Since there is no evidence of multiple methyl coupling to a single aromatic ring, we believe that some of the methyl groups couple with phenyl at lower temperature, the resulting intermediate is then dehydrogenated to form a “methylbenzyne”-like intermediate.…”

“…Toluene formation is observed in this same 270 K to 290 K temperature range from the coadsorbed thiols . On the Ni(100) surface, C−S bond scission in phenylthiolate in the 200 K to 350 K range leads to formation of phenyl groups which are rapidly hydrogenated to form benzene . On the Ni(100) surface, C−S bond breaking in methylthiolate results in a broad methane peak which starts at 200 K, and peaks at 300 K .…”

Thermally Activated Reactions of Phenol at the Ge(100)-2 × 1 Surface

“…While the CO stretching mode of surface phenoxy at 1226 cm –1 becomes absent, the peaks related to the characteristic symmetric vibration of the aromatic ring show distinct red shifts, which can be due to the fact that the phenyl group bonds to a heavier substituent . Especially, the positions of the remaining peaks resemble those of phenyl adsorbates directly bonded on various surfaces, such as those on Ni(100), Au(111), and Mo 2 C/Mo­(100) . Therefore, DFT calculations were carried out assuming formation of C 6 H 5 * on the Ge(100) surface.…”

“…Summary of Vibrational Peak Positions (cm −1 ) and Assignments for Phenol on Ge(100)-2 × 1 and Related C 6 H 5 Adsorbates a Ni(100)23 phenyl/Au(111)24 phenyl/Mo 2 C/Mo 25 β(CH)…”