Site-Specific Imaging of Elemental Steps in Dehydration of Diols on TiO₂(110)

Journal Article · Tue Nov 26 00:00:00 EST 2013 · Nano Letters

DOI:https://doi.org/10.1021/nn404934q· OSTI ID:1114883

Acharya, Danda P. ^[1]; Yoon, Yeohoon ^[1]; Li, Zhenjun ^[1]; Zhang, Zhenrong ^[2]; Lin, Xiao ^[1]; Mu, Rentao ^[1]; Chen, Long ^[1]; Kay, Bruce D. ^[1]; Rousseau, Roger J. ^[1]; Dohnalek, Zdenek ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Baylor Univ., Waco, TX (United States)

The conversion of diols on partially reduced TiO₂(110) at low coverage was studied using variable-temperature scanning tunneling microscopy, temperature programmed desorption and density functional theory calculations. We find, that below ~230 K, ethane-1,2-diol and propane-1,3-diol molecules adsorb predominantly on five-fold coordinated Ti5c atoms. The dynamic equilibrium between molecularly bound and dissociated species resulting from O-H bond scission and reformation is observed. As the diols start to diffuse on the Ti5c rows above ~230 K, they dissociate irreversibly upon encountering bridging oxygen (O_b) vacancy (VO’s) defects. Two dissociation pathways, one via O-H and the other via C-O bond scission leading to identical surface intermediates, hydroxyalkoxy, O_b-(CH₂)n-OH (n = 2, 3) and bridging hydroxyl, HO_b, are seen. For O-H bond scission, the O_b-(CH₂)n-OH is found on the position of the original VO, while for C-O scission it is found on the adjacent Ob site. Theoretical calculations suggest that the observed mixture of C-O/O-H bond breaking processes are a result of the steric factors enforced upon the diols by the second OH group that is bound to a Ti5c site. At room temperature, rich dissociation/reformation dynamics of the second, Ti5c-bound O-H leads to the formation of dioxo, Ob-(CH₂)n-OTi, species. Above ~400 K, both O_b-(CH₂)n-OH and Ob-(CH₂)n-OTi species convert into a new intermediate, that is centered on Ob row. Combined experimental and theoretical evidence shows that this intermediate is most likely a new dioxo, O_b-(CH₂)₂-Ob, species. Further annealing leads to sequential C-Ob bond cleavage and alkene desorption above ~ 500 K. Simulations find that the sequential C-O bond breaking process follows a homolytic diradical pathway with the first C-O bond breaking event accompanied by a non-adiabatic electron transfer within the TiO₂(110) substrate.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1114883
• Report Number(s): PNNL-SA-98207; 47800; KC0302010
• Journal Information: Nano Letters, Vol. 7, Issue 11; ISSN 1530-6984
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Environmental Molecular Sciences Laboratory