The interplay between acid-base properties and Fermi level pinning of a nano dispersed tungsten oxide - titania catalytic system

A series of WO 3 /TiO 2 catalysts were synthesized, characterized, and evaluated for the NO selective catalytic reduction (SCR) with NH 3 . Based on a wide range of characterization techniques, a detailed model was developed that describes the interfacial electron transfer between WO 3 and TiO 2 and defines a relationship between the acid-base properties of the catalytic surface and electronic structure modification. The electronic interactions at the WO 3 /TiO 2 interface were quantified using variations in the system's electronic structure. Altering the dispersion and size of the WO 3 nanostructures results to drastic changes in titania's surface electron distribution, which are reflected in the pinning of Fermi level through an electron transfer process between WO 3 and TiO 2 . The variations in the Fermi level were further related to changes in the point of zero charge (PZC) values and the activity towards NO SCR with NH 3, which was used as a test reaction. Temperature Programmed Surface Reaction (TPSR) was employed to study the catalytic activity at temperatures ranging from 30 °C to 500 °C and was quantitatively correlated to changes in coverage and interfacial charge transfer. We demonstrate that higher WO 3 loading on TiO 2 results in a stronger electronic interaction and a higher catalytic activity. This is because electron transfer increases the surface electron density, which enhances the surface basicity of TiO 2 . The concomitant decrease in the adsorption energy of NH 3 results in a decrease in the activation energy, which is reflected in the SCR temperature onset.