Reaction Of Methanethiol Research Articles

Desulfurization reactions of methanethiol on defect CeO2 surfaces

Methanethiol (CH3SH) is a volatile organic compound that poses a high health risk and causes corrosion to equipment in petroleum refineries. The removal of the sulfur content in mercaptans using potent catalysts assumes a fundamental importance from industrial and environmental perspectives. Motivated by experimental studies involving stand-alone cerium oxide (CeO2) catalysts, we have deployed a defect CeO2 surface with an oxygen vacancy (CeO2(111)_Vo) to explore the decomposition chemistry of methanethiol based on first principle density functional theory (DFT) calculations. The study presents potential formation pathways for the major experimentally reported compounds, namely, CH4, H2S, CO, CO2, CH3SCH3, and COS. Initial uptake of CH3SH takes place via either C-S or S-H bond fissions through modest activation barriers. In initial decomposition pathways, Vo spots represent strong acidic sites, and thus facilitating rupture of C-S and S-H fissions. Formation of CO takes place through a series of H transfer reactions that commence from the CH2* adduct. Adjacent HS* and HO*sites undergo a hydrogen diffusion reaction to ultimately produce H2S rather than water. Several investigated reactions lead to the filling of the vacant oxygen sites with S atoms leading to the generation of CeO2-xSy phases. The latter exhibits a neat-metallic character. Through the occurrence of both Eley-Rideal and Langmuir-Hinshelwood-type mechanisms, CeO2-xSy phases maintain catalytic activity. Findings herein provide a detail atomistic understanding of the desulfurization capacity of stand-alone ceria surfaces.

Computational Study of the Addition of Methanethiol to 40+ Michael Acceptors as a Model for the Bioconjugation of Cysteines.

A long series of Michael acceptors are studied computationally as potential alternatives to the maleimides that are used in most antibody–drug conjugates to link Cys of mAbs with cytotoxic drugs. The products of the reaction of methanethiol (CH3SH/MeSH, as a simple model of Cys) with N-methylated ethynesulfonamide, 2-ethynylpyridinium ion, propynamide, and methyl ethynephosphonamidate (that is, with HC≡C–EWG) are predicted by the M06-2X/6-311+G(d,p) method to be thermodynamically more stable, in relation to their precursors, than that of MeSH with N-methylmaleimide and, in general, with H2C=CH–EWG; calculations with AcCysOMe and tBuSH are also included. However, for the addition of the anion (MeS–), which is the reactive species, the order changes and N-methylated 2-vinylpyridinium ion, 2,3-butadienamide, and maleimide may give more easily the anionic adducts than several activated triple bonds; moreover, the calculated ΔG⧧ values increase following the order HC≡C–SO2NHMe, N-methylmaleimide, HC≡C–PO(OMe)NHMe, and HC≡C–CONHMe. In other words, MeS– is predicted to react more rapidly with maleimides than with ethynephosphonamidates and with propynamides, in agreement with the experimental results. New mechanistic details are disclosed regarding the advantageous use of some amides, especially of ethynesulfonamides, which, however, are more prone to double additions and exchange reactions.

Methanethiol chemistry on TiO 2-supported Ni clusters

The thermal decomposition of methanethiol on Ni clusters grown on TiO 2(1 1 0) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). On all of the Ni surfaces investigated, methane and hydrogen were observed as gaseous products in the TPD experiments, and the only sulfur-containing species that desorbed from the surface was methanethiol itself at low temperatures. The two pathways for methanethiol reaction were hydrodesulfurization to produce methane and nonselective decomposition, which leaves atomic carbon and sulfur on the surface. From high resolution XPS studies, methyl thiolate was identified as the surface intermediate for reaction on TiO 2 and on all of the Ni surfaces investigated, similar to what is observed on single-crystal Ni surfaces. However, the binding sites for methyl thiolate on the 1 ML (monolayer) Ni clusters were different from those on the Ni clusters at coverages of 2.5 ML and higher, based on the S(2p) binding energies for methyl thiolate. No distinct changes in activity or selectivity were observed for the smaller Ni clusters grown at low coverage compared to the more film-like Ni surfaces other than what could be accounted for by changes in total surface area. Interactions between the Ni clusters and the TiO 2 support had two main effects on chemical activity. First, carbon was oxidized by oxygen from the TiO 2 lattice to produce CO at temperatures above 800 K. Second, annealing induced encapsulation of the Ni clusters by reduced TiO x and chemisorbed oxygen. At 800 K, the Ni clusters were totally encapsulated, resulting in a complete loss of methanethiol activity; partial encapsulation at 700 K caused a smaller decrease in activity accompanied by increased oxidation of carbon by lattice oxygen.

Adsorption and reaction of methanethiol on thin-film cerium oxide

The adsorption and reaction of methanethiol, CH 3SH, have been studied on cerium oxide thin films that were vapor deposited on Ru(0 0 0 1). The behavior of the CH 3SH was examined as a function of the Ce oxidation state. CH 3SH weakly interacts with fully oxidized CeO 2(1 1 1) forming both chemisorbed CH 3SH and CH 3S + OH. OH forms through the reaction of the sulfhydrol H with the surface O. These species recombine and desorb near 180 K leaving the surface virtually clean. When the ceria is ca. 50% reduced, the chemisorbed CH 3SH desorbs near 150 K while the CH 3S + OH are stable to 400 K. These species react above 450 K to produce predominantly CH 4 and CH 3SH. A small amount of CH 2O and water are also formed through reaction with the O in the ceria. Atomic S is left on the surface. S 2p, C 1s and O 1s soft X-ray photoelectron spectroscopy were used to identify the nature of the chemisorbed species and the adsorption site of the CH 3S or S.

Adsorption and reaction of methanethiol on the Ru(0 0 0 1)- p(2 × 2)O surface: A TPD and XPS study

Methanethiol adsorbed on Ru(0 0 0 1)- p(2 × 2)O has been studied by TPD and XPS. The dissociation of methanethiol to methylthiolate and hydrogen at 90 K is evidenced by the observation of hydroxyl and water. The saturation coverage of methylthiolate is ∼0.15 ML, measured by both XPS and TPD. A detailed analysis suggests that only the hcp-hollow sites have been occupied. Upon annealing the surface, water and hydroxyl desorb from the surface at ∼210 K. Methylthiolate decomposes to methyl radical and atomic sulphur via C–S cleavage between 350 and 450 K. Some methyl radicals (0.05 ML) have been transferred to Ru atoms before they decompose to carbon and hydrogen. The rest of methyl radicals desorb as gaseous phase. No evidence for the transfer of methyl radical to surface oxygen has been found.

Studies on the Deodorization by Mushroom (Agaricus bisporus) Extract of Garlic Extract-Induced Oral Malodor

The deodorizing effect of the mushroom (Agaricus bisporus) extract on the malodor produced after garlic consumption was investigated using an electronic sensor and sensory evaluation measurements. Comparative gas chromatography analysis revealed that the quantity of methane- and allylthiols that were usually found after garlic solution rinse, significantly fell after mushroom extract rinsing. Furthermore, in-vitro analysis (mixing the garlic solution and mushroom extract) showed that the methanethiol reaction with the mushroom extract proceeded faster than that of the allylthiol. Ab initio calculations implicated an addition reaction as the possible mechanism between the thiol compounds and the polyphenols. In comparison to the methanethiol, the higher activation energy required by allylthiol for a feasible reaction path way with the model acceptor, o-quinone, is expected to contribute to the difference in the rate of the reaction.

Adsorption and reaction of methanethiol on Pt(1 1 1)

Adsorption and thermal decomposition of H 3CSH on Pt(1 1 1) is studied with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation. A H 3CSH molecule undergoes dehydrogenation via formation of H x CS ( x ⩽ 3) intermediates. The catalytic reactivity of Pt for dehydrogenation, which depends on interaction between the surface and the CH x moiety of H x CS, varies with coverage. At large coverage, H 3CSH decomposes through desorbing hydrogen via stepwise dehydrogenation (H 3CS → H 2CS → HCS → S + C). H 2CS is proposed to be an intermediate for dehydrogenation of H 3CS below 240 K, and subsequently undergoes disproportionation to form HCS with desorption of CH 4 at 400 K. The HCS species further decomposes to desorb hydrogen at 475 K and to form C and S adatoms; these adatoms show a mixed ( 3 × 3 ) R30° and dim c(2 × 2) LEED pattern at saturation exposure. At small coverage, surface Pt exhibits a catalytic effect on dehydrogenation of H x CS via interaction of the CH x moiety with surface Pt atoms. Dehydrogenation of H 3CSH is completed below 370 K and is proposed to form a surface C S species; this species entirely decomposes to form C and S adatoms at 570 K.

Sensitivity of Methyl Thiolate Desulfurization Selectivity to Reaction Temperature and Hydroxyl Coverage

The adsorption and reaction of methanethiol (CH3SH) and dimethyl disulfide (CH3SSCH3) on Mo(110)-(1 x 6)-O have been studied using temperature-programmed reaction spectroscopy and reflection-absorption infrared spectroscopy over the temperature range of 110-550 K. The S-H bond is broken upon adsorption to form adsorbed OH, water, and methyl thiolate (CH3S-) at low temperature. Water is evolved at 210 and 310 K via molecular desorption and disproportionation of OH, respectively. Some hydroxyl remains on the surface up to 350 K. Methyl thiolate is also formed from CH3SSCH3 on Mo(110)-(1 x 6)-O. Methyl thiolate undergoes C-S cleavage above 300 K, yielding methane and methyl radicals. There is also a minor amount of nonselective decomposition leading to the formation of carbon and hydrogen. Methane production is promoted by adsorbed hydroxyl. As the hydroxyl coverage increases, the yield of methyl radicals relative to methane diminishes. Accordingly, there is more methane produced from methanethiol reaction than from dimethyl disulfide, since S-H dissociation in CH3SH produces OH. The maximum coverage of the thiolate is approximately 0.5 monolayers, based on the amount of sulfur remaining after reaction measured by Auger electron spectroscopy. In contrast to cyclopropylmethanethiol (c-C3H5CH2SH), for which alkyl transfer from sulfur to oxygen is observed, there is no evidence for transfer of the methyl group of methyl thiolate to oxygen on the surface. Specifically, there is no evidence for methoxy (CH3O-) in infrared spectroscopy or temperature-programmed reaction experiments.

Comparison of Methanethiol Adsorption on Ag(110) and Cu(110)Chemical Issues Related to Self-Assembled Monolayers

The adsorption and thermal decomposition of methanethiol (CH 3 SH) on Ag(110) and on Cu(110) surfaces have been investigated by low energy electron diffraction, Auger electron spectroscopy, and temperature programmed desorption methods. On the clean Ag(110) surface, methanethiol nondissociatively adsorbs at 25 K, forming a (2 x 1) overlayer structure and then molecularly desorbs at ∼140 K. On the partially sulfur-covered Ag(110) surface, methanethiol readily decomposes below 240 K, producing CH 4 (g), H 2 S (g), and sulfur atoms on the surface as well as small amounts of carbon. The sulfur overlayer formed by the decomposition of methanethiol exists as a p(3 x 2) ordered structure at the saturation coverage of sulfur. On this fully sulfur-covered Ag(110) surface, the thermal decomposition of methanethiol is completely suppressed. An autocatalytic mechanism involving silver sites activated by neighboring adsorbed sulfur is proposed to explain the sulfur-catalyzed thermal decomposition reaction of methanethiol on Ag(110). In contrast, on the clean Cu( 110) surface, methanethiol decomposes below 320 K, producing CH 4 (g) and C 2 H 6 (g), and leaving sulfur overlayers, either a c(2 x 2) structure at low coverage or a c(8 x 2) structure at high coverage. A complete layer of chemisorbed sulfur suppresses further methanethiol decomposition on both the silver and the copper surfaces.

Thermal Reactions of Methanethiol and Ethanethiol on Si(100)

We investigated adsorption and thermal decomposition of methanethiol (CH3SH) and ethanethiol (C2H5SH) on a Si(100) surface by means of temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation. At an adsorption temperature of 115 K, CH3SH and C2H5SH dissociate to form thiolates and hydrogen at a small coverage (<0.2 monolayer), whereas molecular chemisorption occurs at a greater coverage; all chemisorbed molecules either deprotonate to form thiolate or desorb intact up to 400 K. Adsorption and decomposition of thiols occur on the dangling bonds of a dimer without breaking the Si−Si dimer bond, resulting in preservation of a 2 × 1 LEED pattern. Thiolates further decompose to evolve hydrocarbons via scission of the C−S bond to form a sulfur adatom on the surface at a temperature above 550 K. Maximum desorption of surface sulfur as SiS occurs at 820 K. CH3 generated from CH3S reacts with surface hydrogen to evolve CH4, whereas the C2H5 moiety of C2H5S undergoes β-hydride elimination to form C2H4. To a small extent, the alkyl moiety transfers onto the surface and undergoes dehydrogenation, resulting in desorption of hydrogen and deposition of carbon on the surface.

Fundamental studies of desulfurization processes: reaction of methanethiol on ZnO and Cs/ZnO

The reaction of methanethiol on ZnO and Cs promoted ZnO surfaces has been studied with synchrotron based photoemission and thermal desorption spectroscopy. On ZnO, methanethiol undergoes selective reaction to produce carbon monoxide (37–58%), methane (23–38%), formaldehyde (12–15%), ethane (1–11%), and a mixture of ethylene and acetylene (3–13%). At low temperatures (<100 K), methanethiol reacts to yield thiolate intermediate bound to Zn 2+ cations. The thiolate is stable to 500 K. Above this temperature, C–S bond cleavage occurs to yield methyl intermediate and atomic S. Carbon is removed from the surface as gaseous products above 500 K, and atomic sulfur remains bound to the zinc sites of the surface. Submonolayer amounts of cesium do not have a significant promotional effect on C–S bond cleavage, whereas Cs multilayers are found to significantly lower the activation barrier for C–S bond cleavage. This study illustrates the chemistry associated with the desulfurization of thiols on a catalytically relevant oxide surface.

Influence of Surface Modifiers on the Thermal Decomposition of Methanethiol on Fe(110)

The reactions of methanethiol (CH3SH) on clean, sulfur-covered, and oxygen-covered Fe(110) have been investigated by X-ray photoelectron spectroscopy, temperature-programmed reaction spectroscopy, and low-energy electron diffraction. On clean Fe(110), the S−H bond in methanethiol breaks below 100 K, affording methylthiolate (CH3Sa) and Ha. Heating to 600 K results in C−S bond cleavage near 290 K, leading to the evolution of methane and dihydrogen, and a p(2 × 2) sulfur overlayer. On the oxygen-covered surface (θO = 0.25 ML), adsorbed methylthiolate and hydroxyl are formed. The amount of irreversible thiol reaction is essentially the same on the O-covered and clean Fe(110) surfaces. The amount of irreversibly bound thiol is reduced by approximately half on the (2 × 2)−S overlayer (θS = 0.25 ML). The C−S bond in methylthiolate is stabilized more by surface sulfur than by surface oxygen, based on the methane formation temperature shifts of +55 and +20 K, respectively. Oxygen coverages greater than 1 monolayer form an FeO thin film, weakening the interaction of methanethiol with the surface, further reducing the methane yield which now reacts above 400 K.

Desulfurization of benzenethiol on CoMo(110) phases

The desulfurization of benzenethiol on Co-covered Mo(110) (θCo = 0.25–1.3 ML) produces benzene, H2 and adsorbed carbon and sulfur. Benzene is formed via adsorbed phenyl thiolate, which is identified by X-ray photoelectron and electron energy loss spectroscopies. Benzene production is attributed to reaction on Co, since it is evolved at a temperature well below that required for sulfur-induced aggregation of Co. The reaction products and mechanisms are qualitatively similar on Co-covered Mo(110) and a range of other transition metal surfaces. The selectivity for benzene production on the 1.3 ML Co overlayer, ∼ 65%, is higher than on many surfaces. Furthermore, benzene evolution occurs at a very low temperature, 125 K, on the 1.3 ML Co film. Notably, we did not observe any new products or a dramatic change in reaction temperature or selectivity as a result of CoMo interactions or of structural changes in the Co layer. Comparison of the benzene evolution temperature for benzenethiol reaction with that of methane from methanethiol reaction on the close-packed Co overlays indicates that homolytic CS bond scissions do not control the hydrogenolysis rate, in contrast to reaction on Mo(110) but similar to Ni(111). This difference may be due to hydrogen-induced structural transformations of the Co layer or to hydrogen-assisted CS bond breaking.

Reactions of Methanethiol on Cobalt-Covered Mo(110)

The reactions of methanethiol on cobalt overlayers grown on Mo(110) were studied using a temperature-programmed reaction and X-ray photoelectron and high-resolution electron energy loss spectroscopies. Methyl thiolate was identified as the reaction intermediate on the basis of X-ray photoelectron and high resolution electron energy loss data. Methane, methyl radical, and H{sub 2} were the only gaseous products. The peak temperature for methane production from methyl thiolate hydrogenolysis was relatively insensitive to the Co coverage and geometric structure of the Co layer. However, less methyl radical formation was observed as the Co coverage increased from 1 to 2.5 monolayers. The selectivity for hydrocarbon formation was essentially the same, nearly 48{+-}5%, for all Co coverages. The total amount of methyl thiolate deposited in the initial S-H bond breaking was independent of Co coverage. At 400 K, sulfur-induced structural rearrangement of the Co overlayer was insignificant and therefore did not affect the reaction of methanethiol. The mixed Co-S overlayer had a substantially lower activity for the methanethiol reaction than any of the clean surfaces; the total amount of reaction on both the sulfur and Co-S overlayers was 30% that of the clean Mo(110) and pure Co overlayers. 53 refs., 5 figs., 1 tab.

Enhancement of Selective Decomposition: Adsorption and Reaction of Methanethiol on Carbon-Covered W(001)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnhancement of Selective Decomposition: Adsorption and Reaction of Methanethiol on Carbon-Covered W(001)D. R. Mullins and P. F. LymanCite this: J. Phys. Chem. 1995, 99, 15, 5548–5555Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://doi.org/10.1021/j100015a044RIGHTS & PERMISSIONSArticle Views42Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1012 KB) Get e-Alerts

Adsorption and reaction of methanethiol on ruthenium(0001)

Methanethiol (CH[sub 3]SH) adsorbs dissociatively on Ru(0001) at 100 K forming two molecular intermediates. These species have been identified by S 2p soft X-ray photoelectron spectroscopy (SXPS) as methylthiolate moieties adsorbed in different bonding sites. At low coverages only a high coordination adsorption site is occupied. The high coordination site is saturated at about 0.20 monolayer of CH[sub 3]SH, and then a low coordination site is populated. Upon heating, the thiolates totally decompose into atomic C, S, and gaseous H[sub 2] with a competing pathway producing atomic S and gaseous CH[sub 4] at high coverage. The methylthiolate in the low coordination site decomposes more readily than the methylthiolate in the high coordination site. Some surface hydrocarbon fragments are formed following C-S bond scission which totally decompose at higher temperatures. Isotopic labeling indicates that the desorption of the sulfhydryl hydrogen precedes the decomposition of the thiolate at high coverage and that there is exchange of hydrogen between the surface and the methyl group. 32 refs., 5 figs.

Adsorption and reaction of methanethiol on tungsten(001)

Methanethiol (CH[sub 3]SH) adsorbs dissociatively on W(001) at 100 K, forming two distinct intermediates. These species have been identified by S 2p soft X-ray photoelectron spectroscopy (SXPS) as methyl thiolate moieties adsorbed in different bonding sites. Both species are stable at all coverages up to 150 K. At low coverages the thiolates totally decompose upon heating into atomic C and S and gaseous H[sub 2]. At high coverages a competing pathway produces atomic S and gaseous CH[sub 4]. The thiolate adsorbed in a fourfold hollow site undergoes C-S bond scission at a lower temperature than the species in a lower coordination site. At high coverage the fourfold bonded intermediate preferentially leads to total decomposition whereas the other species favors methane formation. 41 refs., 9 figs., 1 tab.

The local structure of adsorbed methyl thiolate: the reactions of methanethiol on Mo(110)

The reactions of methanethiol were studied on Mo(110) using temperature-programmed reaction. X-ray photoelectron, and high resolution electron energy loss spectroscopies. The SH bond in methanethiol is broken upon adsorption to form a methyl thiolate intermediate at 100 K. The CS bond of the intermediate is oriented along the surface normal based on vibrational data which indicates C 3v symmetry since only one methyl rock mode is observed at 905 cm −1. Electron energy loss spectra also indicate that the CS bond is weakened in the methyl thiolate intermediate compared to methanethiol. Methane is formed via CS bond hydrogenolysis of the thiolate in a peak centered at 315 K; nonselective decomposition to atomic carbon and sulfur with gaseous dihydrogen is a competing process. Approximately 40% of the thiolate produces methane and the remaining 60% nonselectively decomposes. The kinetics and selectivity are related to the CS bond strength in the thiolate and the lack of a stable gas-phase dehydrogenation product. The reactivity and structure of the thiolate is compared on Mo(110) and other metals.

The local structure of adsorbed methyl thiolate: the reactions of methanethiol on Mo(110)

Abstract The reactions of methanethiol were studied on Mo(110) using temperature-programmed reaction. X-ray photoelectron, and high resolution electron energy loss spectroscopies. The SH bond in methanethiol is broken upon adsorption to form a methyl thiolate intermediate at 100 K. The CS bond of the intermediate is oriented along the surface normal based on vibrational data which indicates C3v symmetry since only one methyl rock mode is observed at 905 cm−1. Electron energy loss spectra also indicate that the CS bond is weakened in the methyl thiolate intermediate compared to methanethiol. Methane is formed via CS bond hydrogenolysis of the thiolate in a peak centered at 315 K; nonselective decomposition to atomic carbon and sulfur with gaseous dihydrogen is a competing process. Approximately 40% of the thiolate produces methane and the remaining 60% nonselectively decomposes. The kinetics and selectivity are related to the CS bond strength in the thiolate and the lack of a stable gas-phase dehydrogenation product. The reactivity and structure of the thiolate is compared on Mo(110) and other metals.

Kinetic regularities in reaction of methanethiol with methanol

The kinetics of the reaction of methanethiol with methanol has been studied under gradientless conditions. A mechanism is postulated according to which, under the effect of methanol the surface is rapidly methoxylated and then CH3O groups react with methanethiol or methanol to produce dimethyl sulfide and dimethyl ether. The kinetic equations obtained describe fairly well the reaction on the inhomogeneous catalyst surface.