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Rational Design of TiO2 Surfaces with Novel Functionalities: DFT Study

Project CatTiO2
Research Area Materials Science
Principal Investigator(s) Prof. Dr. Herbert Over
Institution(s)
  • Justus-Liebig-Universit√§t Giessen, Giessen, Germany
  • CNRS & Universit√© Pierre et Marie Curie, France

Abstract

Recently the Japanese company Sumitomo Chemical has discovered an efficient and stable Deacon catalyst on the basis of RuO2 supported on TiO2, a true breakthrough in current catalysis research. In order to identify a promising alternative catalyst for the Sumitomo Process, rational material design on the basis of density functional theory (DFT) and nudged elastic band (NEB) calculations will be applied. In DFT the electronic structure is solved explicitly, leading to a vast increase in the required computing time, but also increasing the reliability and predictability of the results. Motivated by experimental data we are investigating TiO2, a simple and inexpensive material, and the selective substitution of its anionic sublattice surface sites by chlorine, sulphur and nitrogen. The complex mechanism of the selective replacement reactions will be studied starting from molecular precursors containing hydrogen, such as HCl, H2S and NH3. Hydrogen-containing molecular precursors are required to remove bridging oxygen atoms from the surface in the form of water as the leaving group and subsequently fill in these vacant sites. The activity and stability of the modified TiO2 surfaces will be tested in the Deacon process, i.e. the heterogeneously catalysed oxidation of HCl by molecular oxygen.
The proposed simulations will allow the numerical optimisation of the chemical reaction paths implied above. The forces on the ions are obtained by solving the Kohn-Sham equations numerically, in a self-consistent cycle, whereby the electronic wave functions expanded in a plane-wave basis set. Due to the vast number of wave function coefficients required for reliable results in such calculations, the usage of massively parallel computer architectures, such as those provided by the DEISA infrastructure, is required. The envisioned reaction path optimization on the basis of in silico experiments represents a paradigm shift with much broader implications than the improved, much more detailed understanding of the particular reactions studied. Besides fundamental aspects the present project is driven by industrial applications. At the moment, Sumitomo Chemical holds practically all patents relevant to the RuO2 based Deacon Process. It is therefore important for the European chemical industry to find an alternative material for the Sumitomo Process.

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