Interaction of Keggin anions of 12-tungstophosphoric acid with Ce(x)Zr(1-x)O2 solid solutions.

The interaction of 20 wt% 12-tungstophosphoric acid with Ce(x)Zr(1-x)O(2) solid solutions has been studied by PXRD, FTIR, FT-Raman, H(2)-TPR, NH(3)-TPD, diffuse reflectance UV-vis-NIR, and (31)P MAS NMR techniques. The study indicates that the Keggin anions are attached to Lewis metal ion centres and anion vacancies on Ce(x)Zr(1-x)O(2) 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) (WO(ter) bond), and 1052, 1102 cm(-1) (PO bond). NH(3)-TPD shows that the Keggin anions fixed to Lewis sites and/or oxygen ion vacancies decrease the ammonia uptake on Ce(x)Zr(1-x)O(2) solid solutions. H(2)-TPR shows modified redox behaviour of Ce(x)Zr(1-x)O(2) solid solutions due to the simultaneous reduction of ceria, decomposition of Keggin anions and the reduction of WO(3). The broadening of (31)P MAS NMR and DR-UV-vis-NIR spectra demonstrate the existence of chemical interactions between the Keggin anions and Ce(x)Zr(1-x)O(2) supports.