Adsorption of a chiral modifier on an oxide surface: Chemical nature of tartaric acid on rutile TiO2 (110)

Abstract

Tartaric acid (TA) is one of the most known chiral modifier used in heterogeneous enantioselective catalysis and understanding how it interacts with oxide supports is of significant importance for the design of efficient supported metal catalysts. This work presents a detailed surface science characterisation of (R,R)-TA adsorption on a rutile TiO2(110) surface from a chemical and structural point of view. X-ray Photoelectron Spectroscopy (XPS), High Resolution Electron Energy Loss Spectroscopy (HREELS), Low Energy Electron Diffraction (LEED) and Scanning Tunnelling Microscopy (STM) were used to decipher the adsorption mode and geometrical arrangement of TA on TiO2(110). For XPS analysis, spectra were compared to references recorded on model metal surfaces, namely Au(111) and Cu(110), on which a better understanding of the TA chemical nature is available. On TiO2, both XPS and HREELS converged to show the monotartrate chemical nature (only one acidic group is deprotonated) of the adsorbed TA molecules, while STM and LEED evidenced a (2 × 1) 2D network arrangement. TA molecules are anchored via both oxygen atoms of one carboxylate group binding directly to two adjacent Ti5c of the underlying oxide surface. No chiral ordered domains were observed whatever the coverage, suggesting that surface chirality is induced at the molecular level.