Abstract
Surface redox processes involving oxygen atom exchange are fundamental in catalytic reactions mediated by metal oxides. These processes are often difficult to uncover due to changes in the surface stoichiometry and atomic arrangement. Here we employ high-resolution transmission electron microscopy to study vanadium oxide supported on titanium dioxide, which is of relevance as a catalyst in, e.g., nitrogen oxide emission abatement for environmental protection. The observations reveal a reversible transformation of the vanadium oxide surface between an ordered and disordered state, concomitant with a reversible change in the vanadium oxidation state, when alternating between oxidizing and reducing conditions. The transformation depends on the anatase titanium dioxide surface termination and the vanadium oxide layer thickness, suggesting that the properties of vanadium oxide are sensitive to the supporting oxide. These atomic-resolution observations offer a basis for rationalizing previous reports on shape-sensitive catalytic properties.
Highlights
Surface redox processes involving oxygen atom exchange are fundamental in catalytic reactions mediated by metal oxides
In order to relate the redox properties of the vanadium oxide layer with its thickness, two samples of anatase TiO2 nanoparticles were prepared with nominal VOx loadings of 2 and 0.5 monolayers
Prior to the in situ experiments we determined the distribution of VOx over the TiO2 nanoparticles using ex situ scanning Transmission electron microscopy (TEM) (STEM) and energy loss spectroscopy (EELS)
Summary
Surface redox processes involving oxygen atom exchange are fundamental in catalytic reactions mediated by metal oxides. The transformation depends on the anatase titanium dioxide surface termination and the vanadium oxide layer thickness, suggesting that the properties of vanadium oxide are sensitive to the supporting oxide These atomic-resolution observations offer a basis for rationalizing previous reports on shape-sensitive catalytic properties. The VOx/TiO2 system can catalyze a variety of chemical reactions, including the selective reduction of NOx for emission abatement from power plants and diesel engines[10, 11], and oxidation and ammoxidation of various organic substrates[12, 13].
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