Probing acid–base sites in vanadium redox zeolites by DFT calculation and compared with FTIR results

Ab initio periodic DFT calculations in combination with experimental FTIR of adsorption pyridine investigations have been used to study the acid–base properties of vanadium doped zeolite materials. It is evidenced that VO-H groups of V(V) and V(IV) framework sites are more acidic than SiO-H groups present in siliceous zeolites. It is proposed for the first time that the protonation of the penta coordinated V site can lead to the formation of a stable vanadyl group containing site through proton exchange, which is expected to be the inter-conversion path between both sites. We report in this paper protonation and deprotonation energies of different vanadium sites, and a geometry of experimentally observed Lewis and Brønsted acid sites is proposed.