Role of Vanadium and Phosphorus in Substituted Keggin‐Type Heteropolyoxo Molybdates Supported on Silica SBA‐15 in Selective Propene Oxidation

Vanadium‐containing Keggin‐type heteropolyoxo molybdate ([PV 2 Mo 10 O 40 ] 5− ) was supported on silica SBA‐15 (denoted as PV 2 Mo 10 ‐SBA‐15). The structural evolution and catalytic activity of PV 2 Mo 10 ‐SBA‐15 and a suitable reference V 2 Mo 10 O x ‐SBA‐15 were investigated under selective propene oxidation conditions by using in situ X‐ray absorption spectroscopy. 31 P MAS NMR measurements of supported PV 2 Mo 10 ‐SBA‐15 and reference H 3 PO 4 ‐SBA‐15 were performed after the catalytic reaction. PV 2 Mo 10 ‐SBA‐15 formed a mixture of mainly tetrahedral [MoO x ] and [VO x ] units during thermal treatment under propene oxidation conditions. Changes in the average local structure around V centers coincided with the changes in the average local structure around Mo centers and the onset of catalytic activity. In addition, mainly tetrahedral [MoO x ] and [VO x ] units seemed to be in close proximity and interacted under catalytic conditions. Conversely, in the reference material V 2 Mo 10 O x ‐SBA‐15 synthesized with individual V and Mo source precursors, Mo and V centers appeared to be more separated from each other. The structural environment of P in PV 2 Mo 10 ‐SBA‐15 under catalytic conditions corresponded to a mixture of various species. P was connected to both the support material SBA‐15 via POSi bonds and [MoO x ] or [VO x ] units. Apparently, the proximity of V and Mo in Keggin precursors was a prerequisite for obtaining (Mo,V) oxide species on the support material.