NH3 adsorption on anatase-TiO2(101)

Stig Koust, Kræn C. Adamsen, Esben Leonhard Kolsbjerg, Zheshen Li, Bjørk Hammer, Stefan Wendt, Jeppe V. Lauritsen

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Abstract

The adsorption of ammonia on anatase TiO 2 is of fundamental importance for several catalytic applications of TiO 2 and for probing acid-base interactions. Utilizing high-resolution scanning tunneling microscopy (STM), synchrotron X-ray photoelectron spectroscopy, temperature-programmed desorption (TPD), and density functional theory (DFT), we identify the adsorption mode and quantify the adsorption strength on the anatase TiO 2(101) surface. It was found that ammonia adsorbs non-dissociatively as NH 3 on regular five-fold coordinated titanium surface sites (5f-Ti) with an estimated exothermic adsorption energy of 1.2 eV for an isolated ammonia molecule. For higher adsorbate coverages, the adsorption energy progressively shifts to smaller values, due to repulsive intermolecular interactions. The repulsive adsorbate-adsorbate interactions are quantified using DFT and autocorrelation analysis of STM images, which both showed a repulsive energy of ∼50 meV for nearest neighbor sites and a lowering in binding energy for an ammonia molecule in a full monolayer of 0.28 eV, which is in agreement with TPD spectra.

Original languageEnglish
Article number124704
JournalThe Journal of Chemical Physics
Volume148
Issue12
ISSN0021-9606
DOIs
Publication statusPublished - 2018

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