Structural rearrangement and catalytic properties of the Wells–Dawson (NH4)6P2Mo18O62 heteropolycompound in the 2-butanol reaction

Structural changes of the ammonium phospho-molybdic Wells–Dawson salt (NH4)6P2Mo18O62 were examined by several solid state techniques during the oxygen-assisted catalytic reaction of 2-butanol. A significant evolution of the catalytic behavior occurs while the working catalyst is in the course of its reorganisation to a Keggin structure. Precisely, a particular species formed in situ and presenting intermediate characteristics between those of Wells–Dawson and Keggin structures exerts a beneficial effect on the selectivity to methyl-ethyl-ketone. This high selectivity towards the oxidative dehydrogenation was however found to be ephemeral and the selectivity decline was correlated to a no proper stabilization of this most active intermediate.

Graphical abstractStructural changes of the ammonium phospho-molybdic Wells–Dawson salt (NH4)6P2Mo18O62were examined using X-ray diffraction, X-ray photoelectron and infrared spectroscopies and its catalytic properties in the 2-butanol oxygen-assisted reaction were tested as a function of temperature. A significant evolution of the catalytic behavior occurs while the working catalyst is in the course of its reorganisation to a Keggin structure. Precisely, a particular species formed in situ and presenting intermediate characteristics between those of Wells–Dawson and Keggin structures exerts a beneficial effect on the selectivity to methyl-ethyl-ketone. This high selectivity towards the selective oxidation route was however found to be ephemeral and the selectivity decline was correlated to a no proper stabilization of this most active intermediate.Figure optionsDownload full-size imageDownload as PowerPoint slide