The Nature of the Active Phase in the Heteropolyacid Catalyst H4PvMo11O40·32H2O Used for the Selective Oxidation of Isobutyric Acid

Active Sites for Propane Oxidation: Some Generic Considerations

“…An adsorbate-type structure of the active site allowing dynamical response will be useful whereas a closely packed 3-D crystalline state will hinder such a process with high activation barriers. Such ''adsorbatelike'' active phases [77,78] can be identified with probe molecule reactions [79][80][81][82][83][84][85][86] and have been rationalized for covering some bulk catalysts [13,42,[87][88][89][90][91] as consequence of surface energy minimization.…”

Catalytic Hydroxylation of Benzene to Phenol with Hydrogen Peroxide over Cesium Salts of Keggin-type Heteropoly Acids

“…PMo V O -in the solution centered at 306 nm (the insert of Figure 6A) is attributed to the charge transfer of the oxygen ligand to octahedral coordinated metal, [52] which was selected to measure the content of catalysts in solution. In the leaching test, a comparative experiment showed that the release of the catalyst in the acetic acid solvent was nearly the same as that under reaction conditions, indicating the insignificant effect of H 2 O 2 on the leaching of the catalyst.…”

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

“…Recently we were able to show, that migration of molybdenum centers out of the Keggin ion of H 3 [PMo 12 O 40 ] * 13 H 2 O onto extra-Keggin sites resulting in a partially decomposed lacunary Keggin ion takes place during thermal activation. [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.…”

“…[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. 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.…”

“…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.…”