Vibrational study of interaction between 12-tungstophosphoric acid and microporous/mesoporous supports

Raman and FTIR spectroscopy are powerful techniques used to characterize or observe alterations in the structure or properties of Keggin type heteropoly acids, microporous/mesoporous materials, as well as their composites. These methods were applied in this study for investigation of 12-tungstophosphoric acid (WPA) supported as active phase on zeolites (H-BEA and NaY-zeolite) and mesoporous molecular sieves (TiO2, MCM-41, SBA-15). It has been shown that important information on interaction of heteropoly acid and the support can be obtained by the applied vibrational spectroscopic methods. Obtained results show how interaction of WPA with different supports depends on the nature and properties of both, active phase and the support. In the case of microporous supports such as BEA or NaY zeolites, the basicity of the support, i.e., ratio of Si/Al, strongly determines interaction between WPA species and surface of the support. In the case of mesoporous silica supports, WPA is well dispersed over the support without strong interaction. However, TiO2 causes strong and complex interaction with WPA.