Adsorption and Thermal Decomposition of Alkanethiols on Cu(110)

Abstract

Adsorption and thermal decomposition of alkanethiols (RSH, R ) CH 3 , C 2 H 5 , and C 4 H 9 ) on a Cu(110) surface have been studied by means of temperature-programmed desorption (TPD) and X-ray photoemission spectroscopy (XPS) with synchrotron radiation. At a small coverage, CH 3 SH and C 2 H 5 SH dissociate to form surface thiolates and hydrogen, whereas C 4 H 9 SH adsorbs molecularly on the surface at 100 K; adsorbed C 4 H 9 SH begins to deprotonate at ∼170 K. All of these alkanethiolates can decompose to evolve hydrocarbon via scission of the C-S bond, resulting in deposition of sulfur on the surface. CH 3 generated from CH 3 S reacts with surface hydrogen to evolve CH 4 , but at a large coverage can also undergo coupling to form C 2 H 6 . The thermal reaction of surface C 2 H 5 formed from C 2 H 5 S produces C 2 H 6 through hydrogenation and C 2 H 4 through β-hydride elimination, the latter with desorption of H 2 ; the ratio of products C 2 H 4 and C 2 H 6 varies with the adsorption site of surface C 2 H 5 S. The C 4 H 9 group of surface C 4 H 9 S undergoes exclusively elimination of β-hydride to form C 4 H 8 . To a small extent the alkyl moiety also undergoes dehydrogenation, resulting in deposition of carbon on the surface. Three CH 4 desorption states are proposed to correspond to CH 3 S intermediates with distinct adsorption sites after decomposition of CH 3 SH, whereas two C 2 H 5 S sites and one C 4 H 9 S site are proposed for cases of C 2 H 5 SH and C 4 H 9 SH, respectively. The distribution of desorption products depends on the nature of the adsorption site of a particular alkanethiolate.

Adsorption and thermal decomposition of 2-octylthieno[3,4-b]thiophene on Au(1 1 1)

“…Similar dehydrogenations of aliphatic carbon chains were reported for alkanethiols and mercaptanoundecanoic acids where, upon heating to $600 K, all chemisorbed alkanethiols began to produce hydrogen and yield carbon clusters on the surface [28,37,38]. The high temperature peak above 760 K being a result of sample holder degassing can be excluded since we did not observe this peak when performing experiments with a Au(1 1 1) surface that had not been exposed to OTTP.…”

High temperature stability of n-decanethiol by adsorption on nickel powders used as reforming catalysts in solid oxide fuel cells (SOFC)

“…Through the use of radiolabeled hexadecanethiolate monolayers, the complete loss of surface sulfur at 210°C was observed, with some loss occurring at as low as 100°C [16]. Similarly, Lai et al [17] have reported that the decomposition of alkanethiols (RSH with R=CH 3 , C 2 H 5 , and C 4 H 9 ) on a Cu (110) surface reaches a maximum rate at 70°C. They also reported that the same alkanethiols, when adsorbed on a Pt(111) surface, also decomposed at a temperature below 100°C [18].…”

Thermal reactions of mercaptoethanol on Cu(100)

“…Studies of x-ray photoelectron spectroscopy have shown that C 2 H 5 SH decomposes to form C 2 H 5 S-on Cu(1 1 1) at 85 K and on Cu(1 1 0) at 100 K at lower coverages [5,11]. In Fig.…”

“…However, as the surface is precovered with oxygen, C 2 H 5 OH deprotonates readily to form an ethoxide at 200-300 K [4]. C 2 H 5 SH dissociates on Cu(1 1 0) to form an ethyl thiolate at $100 K [5]. In the present study, thermal decomposition of HSCH 2 CH 2 OH at coverages below half the monolayer on Cu(1 0 0) is investigated by temperature-programmed reaction/desorption (TPR/D) and reflection-absorption infrared spectroscopy (RAIRS).…”