An in situ DRIFTS Study of the Active Phase of the Heteropoly Acid Catalyst H4[PVMo11O40] in Oxidation Reactions

Abstract

Heteropoly acid (HPA) catalysts based on the title compound exhibit the well-known Keggin-structure at temperatures relevant for catalytic oxidation processes (520-570 K). In situ DRIFTS (diffuse reflectance infrared Fourier-transfarm spectroscopy) data show that a variety of solid-state reactions occur with the dehydrogenation of isobutyric acid (IBA) leading to structural rearrangements and partial decomposition of the HPA anions. These changes involve the formation of lacunary structures and vanadyl species. Re-oxidation with 0 2 /H 2 0 at rcaction temperaturc re-establishes the highly symmetric structurc of the Keggin-anions.