“…Thus, the as-prepared and ideal Keggin ion of H 3 [PMo 12 O 40 ] * 13 H 2 O is only the precursor for the active catalyst, which consists of partially reduced and decomposed Keggin ions and Mo centers on extra-Keggin framework positions. A partial decomposition and migration of metal centers has previously been reported for Keggin ions with [10,11,12,13,14] and without addenda substituents. [15,16,17,18,19,20] In particular with respect to the thermal activation of a vanadium containing heteropolyoxomolybdate, H 4 [PVMo 11 O 40 ] * 13 H 2 O, it has been proposed that substitution of molybdenum centers by vanadium destabilizes the Keggin ion resulting in a decomposition and migration of vanadium centers out off the Keggin ion.…”