Interaction of Keggin anions of 12-tungstophosphoric acid with CexZr1−xO2CexZr1−xO2 solid solutions

The interaction of 20 wt% 12-tungstophosphoric acid with CexZr1−xO2CexZr1−xO2 solid solutions has been studied by PXRD, FTIR, FT-Raman, H2-TPR, NH3-TPD, diffuse reflectance UV-vis-NIR, and 31P MAS NMR techniques. The study indicates that the Keggin anions are attached to Lewis metal ion centres and anion vacancies on CexZr1−xO2CexZr1−xO2 supports through WO terminal bonds. The Keggin units at the interface are chemically perturbed as indicated by non-intrinsic IR bands observed at 958 cm−1 (WOter bond), and 1052, 1102 cm−1 (PO bond). NH3-TPD shows that the Keggin anions fixed to Lewis sites and/or oxygen ion vacancies decrease the ammonia uptake on CexZr1−xO2CexZr1−xO2 solid solutions. H2-TPR shows modified redox behaviour of CexZr1−xO2CexZr1−xO2 solid solutions due to the simultaneous reduction of ceria, decomposition of Keggin anions and the reduction of WO3. The broadening of 31P MAS NMR and DR-UV-vis-NIR spectra demonstrate the existence of chemical interactions between the Keggin anions and CexZr1−xO2CexZr1−xO2 supports.

Graphical abstractThe Keggin anions at the interface directly interact with CexZr1−xO2CexZr1−xO2 solid solutions showing non-intrinsic IR bands assigned to perturbed WOterminal and PO bonds.Figure optionsDownload full-size imageDownload as PowerPoint slide