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Title: Methanethiol Chemistry on TiO2-Supported Ni Clusters

Abstract

The thermal decomposition of methanethiol on Ni clusters grown on TiO2(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 TiO2 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 betweenmore » the Ni clusters and the TiO2 support had two main effects on chemical activity. First, carbon was oxidized by oxygen from the TiO2 lattice to produce CO at temperatures above 800 K. Second, annealing induced encapsulation of the Ni clusters by reduced TiOx 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.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
959755
Report Number(s):
BNL-82741-2009-JA
Journal ID: ISSN 0039-6028; SUSCAS; TRN: US201016%%899
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Surface Science; Journal Volume: 602
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 08 HYDROGEN; ANNEALING; CARBON; CHEMISTRY; DESORPTION; ENCAPSULATION; HYDROGEN; METHANE; OXIDATION; OXYGEN; PYROLYSIS; RESOLUTION; SCATTERING; SULFUR; SURFACE AREA; THERMODYNAMIC ACTIVITY; X-RAY PHOTOELECTRON SPECTROSCOPY; national synchrotron light source

Citation Formats

Ozturk,O., Park, J., Black, T., Rodriguez, J., Hrbek, J., and Chen, D.. Methanethiol Chemistry on TiO2-Supported Ni Clusters. United States: N. p., 2008. Web. doi:10.1016/j.susc.2008.07.032.
Ozturk,O., Park, J., Black, T., Rodriguez, J., Hrbek, J., & Chen, D.. Methanethiol Chemistry on TiO2-Supported Ni Clusters. United States. doi:10.1016/j.susc.2008.07.032.
Ozturk,O., Park, J., Black, T., Rodriguez, J., Hrbek, J., and Chen, D.. 2008. "Methanethiol Chemistry on TiO2-Supported Ni Clusters". United States. doi:10.1016/j.susc.2008.07.032.
@article{osti_959755,
title = {Methanethiol Chemistry on TiO2-Supported Ni Clusters},
author = {Ozturk,O. and Park, J. and Black, T. and Rodriguez, J. and Hrbek, J. and Chen, D.},
abstractNote = {The thermal decomposition of methanethiol on Ni clusters grown on TiO2(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 TiO2 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 TiO2 support had two main effects on chemical activity. First, carbon was oxidized by oxygen from the TiO2 lattice to produce CO at temperatures above 800 K. Second, annealing induced encapsulation of the Ni clusters by reduced TiOx 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.},
doi = {10.1016/j.susc.2008.07.032},
journal = {Surface Science},
number = ,
volume = 602,
place = {United States},
year = 2008,
month = 1
}
  • The adsorption chemistry of CO on clean and Pt-supported TiO{sub 2} (110) was investigated. It was found that surface structure of TiO{sub 2} plays an important role in the chemistry that takes place at the surface. On the reduced (1 x 2)-reconstructed surface, CO desorbed at 140 and 170 K, while only desorption at 140 K was observed on the stoichiometric (1 x 1) surface. Additionally, CO dissociation, possibly due to the reduction by Ti{sup 3+}, was observed on the Pt-supported (1 x 2) surface. On the Pt-covered surfaces, the chemistry of CO adsorption and desorption strongly depends on themore » size of Pt nanoclusters. With a decrease in cluster size, CO was found to desorb at higher temperatures. This unusual desorption chemistry is likely related to quantum size effects of Pt nanoclusters. Scanning tunneling spectra revealed that clusters below 20 {angstrom} in diameter exhibited nonmetallic behavior, while those above 40 {angstrom} were metallic. This transition of the properties of Pt nanoclusters from metallic to nonmetallic as the cluster size decreases correlates with stronger interaction of CO with Pt observed in temperature-programmed desorption spectra.« less
  • No abstract prepared.
  • The results of ab initio calculations for cyclic clusters of methanol, ethanol, 1-propanol, and methanethiol are presented. Dimer, trimer, and tetramer clusters of all four compounds are studied, as are pentamer and hexamer clusters of methanol. From optimized clusters at HG/6--31G**, total energies and binding energies were calculated with both the HF and MP2 theories using the aug-cc-pVDZ basis set. Accurate binding energies were also calculated for the dimer and trimer of methanol using symmetry-adapted perturbation theory with the same basis set. Intermolecular and intramolecular distances, charge distribution of binding sites, binding energies, and equilibrium constants were computed to determinemore » the hydrogen bond cooperativity effect for each species. The cooperativity effect, exclusive to hydrogen bonding systems, results form specific forces among the molecules, in particular charge-transfer processes and the greater importance of interactions between molecules not directly hydrogen bonded because of the longer range of the interactions. The ratios of equilibrium constants for forming multimer hydrogen bonds to that for dimer hydrogen bond formation increase rapidly with the cluster size, in contrast to the constant value commonly used in thermodynamic models for hydrogen bonding liquids.« less
  • Small cationic tantalum clusters were prepared on the surfaces of SiO2, silica-aluminas, and ?-Al2O3 supports by treating physisorbed pentabenzyltantalum at 523 K for 24 h in flowing H2. The rate of decomposition and the products formed in the decomposition of pentabenzyltantalum are dependent on the support composition. When the support was SiO2, the evolved products were mainly biphenyl and a small amount of toluene, indicating that the Ta-C bond in pentabenzyltantalum was activated. As the alumina content of the support increased, diphenylmethane, benzene, and ethylene were increasingly formed, and these products show that the activation of the C-C bonds linkingmore » the C atoms of methyl groups to the aromatic rings of the benzyl ligands was facilitated. Infrared spectra of the surface species and mass spectra of the effluents formed during the treatment show that the composition of the support had significant influence on the decomposition of pentabenzyltantalum, and the chemistry is inferred to be related to the electron-donor properties of the supports. Extended X-ray absorption fine structure (EXAFS) spectra recorded at the Ta LIII edge indicate the formation of clusters with a Ta-Ta first-shell coordination number of 3, and images obtained by scanning transmission electron microscopy (STEM) confirm the presence of such small clusters. X-ray absorption near edge structure (XANES) data indicate that the formal oxidation state of the tantalum in the clusters decreased from 3.0 to 2.6 as the support was changed from SiO2 to silica-aluminas to ?-Al2O3. The data suggest that the tantalum clusters were anchored to the supports via bridging O atoms. The EXAFS data show that the support composition had little influence on the cluster structure.« less