Mechanism of Ethanol Photooxidation on Single-Crystal Anatase TiO2(101)

详细信息    查看全文

• 作者：K. Katsiev ; G. Harrison ; H. Alghamdi ; Y. Alsalik ; A. Wilson ; G. Thornton ; H. Idriss
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：February 9, 2017
• 年：2017
• 卷：121
• 期：5
• 页码：2940-2950
• 全文大小：753K
• ISSN：1932-7455

文摘

Despite the proven properties of the anatase phase of TiOb>2b> related to photocatalysis, detailed mechanistic information regarding a photooxidation reaction has not yet been derived from single-crystal studies. In this work, we have studied the photooxidation of ethanol (as a prototype hole-scavenger organic molecule) adsorbed on the anatase TiOb>2b>(101) surface by STM and online mass spectrometry to determine the adsorbate species in the dark and under UV illumination in the presence of Ob>2b> and to extract kinetic reaction parameters under photoexcitation. The reaction rate for the photooxidation of ethanol to acetaldehyde was found to depend on the Ob>2b> partial pressure and surface coverage, where the order of the reaction with respect to Ob>2b> is close to 0.15. Carbon–carbon bond dissociation leading to the formation of CHb>3b> radicals in the gas phase was found to be a minor pathway, which is contrary to the case of the rutile TiOb>2b>(110) single crystal. Our STM images distinguished two types of surface adsorbates upon ethanol exposure that can be attributed to its molecular and dissociative modes. A mixed adsorption is also supported by our DFT calculations, in which we determined similar energies of adsorption (Eb>adsb>) for the molecular (1.11 eV) and dissociative (0.93 eV) modes. Upon UV exposure at (and above) 3 × 10^–8 mbar Ob>2b>, a third species was identified on the surface as a reaction product that can be tentatively attributed to acetate/formate species on the basis of C 1s XPS results. The kinetics of the initial oxidation steps were evaluated using the STM and mass spectrometry data.