BULK AND SURFACE-ANALYSIS OF A FE-P-O OXYDEHYDROGENATION CATALYST

Combination of X-ray photoelectron spectroscopy and X-ray microprobe analysis gives complementary information on the composition and on the chemical state of the elements iron and phosphorus present in a Fe-P-O oxydehydrogenation catalyst. On the fresh catalyst iron is present mainly as Fe3+ species whereas after a typical test, which selectively transforms isobutyric acid to methacrylic acid, both Fe2+ and Fe3+ are present. Phosphorus, in comparison to iron, is not homogeneously distributed in the catalyst particles and there exists a phosphorus enrichment at the surface. Positive and negative charge balance reveal that hydrogen phosphate-like species are present in such a catalyst. This is consistent with the observation that this system is active with large amounts of water in the feed.