Exploring the reactivity of intraframework vanadium, niobium and tantalum sites in zeolitic materials using the molecular electrostatic potential

The acid-base properties of group 5 zeolitic structures are discussed using the molecular electrostatic potential. The results point out that vanadium doped zeolites are less appropriate for electrophilic reactions, yielding minor basic character when they are compared with Nb or Ta doped zeolites. Concerning the topology of the site, an electrophilic attack is predicted to be more appropriate on TO (T = V, Nb, or Ta) moiety for all three group 5 elements studied. TaO site is more reactive and thus less stable, while the high stability of the VO group is confirmed. For a T-OH site, the basicity of the bridging oxygens and in a lesser extend the Next Near Neighbor bridging oxygens is predicted. The analysis of the results based on the molecular electrostatic potential predicts that Ta zeolites are more suited for reactions with hard electrophiles such as H+, BF3, etc. In other words, the Ta-OH group is a basic site and is expected to be important in acid-base catalysis. The results are confronted with protonation energies.