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Title: Direct Visualization of 2-Butanol Adsorption and Dissociation on TiO2(110)

Abstract

Atomically resolved scanning tunneling microscopy (STM) images of identical regions of a TiO2(110) surface were gathered before and after controlled doses of 2-butanol (CH3CH2CH(OH)CH3) at ambient temperature (~ 300 K). When dosing is initiated, 2-butanol preferentially adsorbs at bridge-bonded oxygen vacancy (BBOv) sites and dissociates via O—H, not C—O, bond scission to form paired 2-butoxy and hydroxyl species evidenced by two local maxima in STM line profiles. The measured separation is 0.4 nm, slightly larger than the measured separation (0.3 nm) between neighboring bridge-bonded oxygen anions in the surface unit cell of TiO2(110). As the dose increases, but before all the BBOv are occupied, there is direct STM evidence of hydroxyl proton hopping to an adjacent oxygen anion row. This process is facilitated by species bound to 5-coordinate Ti4+ rows, presumably undissociated 2-butanol, that hop slowly compared the STM imaging time scale. The backbones of these mobile species are centered over the Ti4+ rows with preference for lying parallel to these rows. On the other hand, the carbon backbones of the 2-butoxy species that fill BBOv's are centered over the O2- rows and prefer an orientation perpendicular to these rows. As the oxygen vacancy concentration increases from 0.4 to 11more » % and 2-butanol is dosed the ratio of mobile species to 2-butoxy species decreases for doses that do not fill all the BBOv.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
909246
Report Number(s):
PNNL-SA-51362
14591; 22091; KC0302020; TRN: US0703847
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry C, 111(7):3021-3027; Journal Volume: 111; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ADSORPTION; AMBIENT TEMPERATURE; ANIONS; CARBON; DISSOCIATION; ORIENTATION; OXYGEN; PROTONS; SCANNING TUNNELING MICROSCOPY; Environmental Molecular Sciences Laboratory

Citation Formats

Zhang, Zhenrong, Bondarchuk, Olexsandr, Kay, Bruce D., White, J. M., and Dohnalek, Zdenek. Direct Visualization of 2-Butanol Adsorption and Dissociation on TiO2(110). United States: N. p., 2007. Web. doi:10.1021/jp067461c.
Zhang, Zhenrong, Bondarchuk, Olexsandr, Kay, Bruce D., White, J. M., & Dohnalek, Zdenek. Direct Visualization of 2-Butanol Adsorption and Dissociation on TiO2(110). United States. doi:10.1021/jp067461c.
Zhang, Zhenrong, Bondarchuk, Olexsandr, Kay, Bruce D., White, J. M., and Dohnalek, Zdenek. Thu . "Direct Visualization of 2-Butanol Adsorption and Dissociation on TiO2(110)". United States. doi:10.1021/jp067461c.
@article{osti_909246,
title = {Direct Visualization of 2-Butanol Adsorption and Dissociation on TiO2(110)},
author = {Zhang, Zhenrong and Bondarchuk, Olexsandr and Kay, Bruce D. and White, J. M. and Dohnalek, Zdenek},
abstractNote = {Atomically resolved scanning tunneling microscopy (STM) images of identical regions of a TiO2(110) surface were gathered before and after controlled doses of 2-butanol (CH3CH2CH(OH)CH3) at ambient temperature (~ 300 K). When dosing is initiated, 2-butanol preferentially adsorbs at bridge-bonded oxygen vacancy (BBOv) sites and dissociates via O—H, not C—O, bond scission to form paired 2-butoxy and hydroxyl species evidenced by two local maxima in STM line profiles. The measured separation is 0.4 nm, slightly larger than the measured separation (0.3 nm) between neighboring bridge-bonded oxygen anions in the surface unit cell of TiO2(110). As the dose increases, but before all the BBOv are occupied, there is direct STM evidence of hydroxyl proton hopping to an adjacent oxygen anion row. This process is facilitated by species bound to 5-coordinate Ti4+ rows, presumably undissociated 2-butanol, that hop slowly compared the STM imaging time scale. The backbones of these mobile species are centered over the Ti4+ rows with preference for lying parallel to these rows. On the other hand, the carbon backbones of the 2-butoxy species that fill BBOv's are centered over the O2- rows and prefer an orientation perpendicular to these rows. As the oxygen vacancy concentration increases from 0.4 to 11 % and 2-butanol is dosed the ratio of mobile species to 2-butoxy species decreases for doses that do not fill all the BBOv.},
doi = {10.1021/jp067461c},
journal = {Journal of Physical Chemistry C, 111(7):3021-3027},
number = 7,
volume = 111,
place = {United States},
year = {Thu Feb 22 00:00:00 EST 2007},
month = {Thu Feb 22 00:00:00 EST 2007}
}
  • Trimethyl acetic acid (TMAA) adsorption evolution on the rutile TiO2(110) surface from submonolayer to saturation coverages was examined at the atomic level by scanning tunneling microscopy using the same area analysis approach. Upon TMAA deprotonation, no evidence of terminal OH group formation has been found. It has been suggested that uncommon geometry associated with detached hydrogen atom takes place instead, with proton bonding to pair bridging oxygen atoms. Such a configuration is likely to be stabilized by adjacent adsorbed TMA groups and, in turn, be a factor in the formation of TMA (2x1) reconstruction at saturation coverage. Our results indicatemore » that TMAA adsorption on reduced TiO2 is virtually not affected by bridging oxygen vacancies or other surface defects.« less
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  • Adsorption and reaction of benzene molecules on clean TiO{sub 2}(110) and on TiO{sub 2}(110) with deposited Pd nanoparticles are investigated using a combination of scanning tunneling microscopy (STM), temperature-programmed desorption, and first-principles calculations. Above {approx}50 K, the one-dimensional motion of benzene between bridging oxygen rows is shown to be too fast for STM imaging. At 40 K benzene molecules form chains on top of titanium rows, with calculations indicating every other benzene is rotated 30{sup o}. Both experimental and theoretical studies find no dissociative reactivity of benzene on the clean TiO{sub 2}(110) surface, due to little hybridization between TiO{sub 2}more » and benzene electronic states. After deposition of Pd nanoparticles, molecular benzene is observed with STM both on the substrate and adjacent to metallic particles. Upon heating to 800 K, benzene fully breaks down into its atomic constituents in a multistep decomposition process.« less