Supporting the Dawson (NH4)6P2Mo18O62 Heteropoly Compound: Controlling Its Molecular Behaviour to Enhance Its Catalytic Activity in the Propene Oxidation

Abstract

AbstractThis paper shows how supporting the Dawson heteropoly compound (HPC) (NH4)6P2Mo18O62 opens up the possibility to enhance its catalytic activity by controlling its molecular behaviour. The effect of parameters such as the loading of the Dawson species onto a support and the nature of its interaction is explored by IR and Raman spectroscopy and correlated with its performance in the oxidation of propene. Active species in propene oxidation were formed during the Dawson HPC rearrangement occurring on a TiO2 support. When supported, the Dawson (NH4)6P2Mo18O62 HPC is beneficially activated during the catalytic process, which led to the formation of a supported active species. A conversion stability observed for the HPC/TiO2 samples with loading above 5 wt.‐% revealed that the Dawson HPC had to interact with the support to develop a stable activity. This arrangement seemed indeed to be the most suitable to reach a high conversion. On the contrary, it was proposed that isolated HPC species were more prone to destabilization due to the loss of the proximity between the anions in the HPC crystal lattice. This work will show that the catalytic systems operated very efficiently due to the redox properties of molybdenum atoms when in an HPC 3D framework. This could not have happened with low loadings as only fragments of the HPCs were present on the surface. The stabilization of catalytic activities observed in the supported catalysts with high loadings was associated with the stabilization of a Keggin‐like supported phase.