In Situ Investigations of Structure–Activity Relationships in Heteropolyoxomolybdates as Partial Oxidation Catalysts

Abstract

Abstract:The structural evolution of Keggin-type heteropolyoxomolybdates (HPOM) during thermal treatment in propene and in propene and oxygen in the temperature range from 300 to 773 K was investigated by in situ X-ray diffraction (XRD) and in situ X-ray absorption spectroscopy Evidently, the undistorted Keggin ion in the as-prepared HPOM has to be regarded as a precursor of the active catalyst.

In situ investigations of the bulk structural evolution of vanadium-containing heteropolyoxomolybdate catalysts during thermal activation

“…Figure 1. The simulated pattern shown in Figure 1 The local structure parameters obtained correspond to those reported in the literature [9] Table 1. The local structure around a V center in the Keggin ion is shown in Figure 5.…”

“…This distance corresponds very well to the distance from a V center in a Keggin ion to a Mo center on an extra-Keggin position according to the structural data determined by the XRD refinement to the pattern of Mo x [PVMo 11-x O 40 ] (Figure 7A, Table 2). [9,17,18] A schematic representation of the local structure around the V center in activated cubic Mo x [PVMo 11-x O 40 ] is depicted in Figure 15. The structure of the partial Keggin ion shown corresponds to the data given in Table 2 while the V-O and V-Mo distances indicated are obtained from a structure refinement to the V K edge data (Table 1) The upper half of the Keggin ion shown corresponds to the structural data given in Table 2.…”

“…agreement between the intensity ratios of the peaks in both experimental patterns can be seen. The simulated diffraction pattern shown in Figure 7A was obtained from a refinement of the structure of cubic [9]. A refinement of a Keggin Figure 9.…”

“…[9] Conversely, thermally stable HPOM like, for instance, Cs 3 [PMo 12 O 40 ] whose Keggin ions remain intact at elevated temperatures without a partial decomposition detectable, are catalytically inactive. 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.…”

In‐situ‐Verfolgung der Bildung kristalliner Feststoffe

“…[10] Dabei standen überwiegend Materialklassen wie Feststoffkatalysatoren und/oder mikro-und mesoporöse Materialien im Fokus des Interesses. [11] Beson-…”