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

Sotirios Tsatsos; John Vakros; Spyridon Ladas; Xenophon E Verykios; Georgios Kyriakou

doi:10.1016/j.jcis.2022.01.112

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

J Colloid Interface Sci. 2022 May 15:614:666-676. doi: 10.1016/j.jcis.2022.01.112. Epub 2022 Jan 19.

Authors

Sotirios Tsatsos¹, John Vakros², Spyridon Ladas¹, Xenophon E Verykios¹, Georgios Kyriakou³

Affiliations

¹ Department of Chemical Engineering, University of Patras, Caratheodory 1, Patras 26504, Greece.
² Department of Chemistry, University of Patras, Caratheodory 1, Patras 26504, Greece.
³ Department of Chemical Engineering, University of Patras, Caratheodory 1, Patras 26504, Greece. Electronic address: kyriakg@upatras.gr.

PMID: 35124294
DOI: 10.1016/j.jcis.2022.01.112

Abstract

A series of WO₃/TiO₂ catalysts were synthesized, characterized, and evaluated for the NO selective catalytic reduction (SCR) with NH₃. Based on a wide range of characterization techniques, a detailed model was developed that describes the interfacial electron transfer between WO₃ and TiO₂ and defines a relationship between the acid-base properties of the catalytic surface and electronic structure modification. The electronic interactions at the WO₃/TiO₂ interface were quantified using variations in the system's electronic structure. Altering the dispersion and size of the WO₃ 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 WO₃ and TiO₂. 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 WO₃ loading on TiO₂ 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 TiO₂. The concomitant decrease in the adsorption energy of NH₃ results in a decrease in the activation energy, which is reflected in the SCR temperature onset.

Keywords: Catalysis; Electron Transfer; Oxides; Selective Catalytic Reduction; TiO(2); UPS; WO(3); XPS.