(Invited) DFT Studies on Interactions between Heteropolyacids, Noble Metal Ions, and TiO2 Support

Abstract

Heteropolycompounds of Keggin structure have been used as homogeneous and heterogeneous catalysts for decades. Recently, they gained popularity in photo- and electrocatalysis where they can be used as components of complex materials e.g., composed of metal ions/heteropolyacids/oxide-based supports.The aim of the current theoretical studies is to characterize systems comprising of free and TiO2-supported heteropolyanions (PW12O40 3-, PMo12O40 3-) with embedded noble metal ions (Ag, Au, Cu, Pd, and Pt) acting as single atom catalysts. Their ground-state geometric and electronic structures were elucidated. Next, their redox and photochemical properties were determined: frontier (HOMO, LUMO) orbitals were defined, energy gaps and UV-VIS spectra were calculated, total and partial density of states were plotted and analysed. The interactions between components of the systems, in particular the influence of the support on the heteropolycompound electronic structure, were investigated. Next, the reactivity of the noble metal cations towards typical reagents (CO, H2, CH3, and C6H6) was studied.The performed calculations demonstrated that the type of the metal and its oxidation state determines the energetics and character of the frontier orbitals, bond lengths and bond orders in their first coordination sphere, incl. the strength of their interactions with common reagents. The presence of TiO2 as the support is manifested by the emergence of new metal ion sitting sites, usually located at the interface between the heteropolyacid and the support, and modification of the redox properties of the systems.Acknowledgements: This work was supported by the National Science Centre, Poland within Solar-Driven Chemistry project no 2019/01/Y/ST4/00024.