OXYDEHYDROGENATION OF ISOBUTYRIC ACID WITH HETEROPOLYACID CATALYSTS - EXPERIMENTAL-OBSERVATIONS OF DEACTIVATION

the heteropolyacid catalysts H5Mo10V2PO40 and H6Mo9V3PO40 have been used for producing methacrylic acid via the oxydehydrogenation of isobutyric acid. This reaction proceeds via a redox process involving lattice oxygen from the Keggin structure of the catalyst molecules. Changes in the oxidation state of the catalyst produce a deactivation effect which is reversible by fully reoxidizing the catalyst. An irreversible, long-term type of deactivation related to a loss of molybdenum from the catalyst has also been observed. This occurs through the formation of a volatile Mocontaining gas-phase species. Passage of the IBA feed over a bed of molybdenum trioxide prior to entering the reactor eliminates both types of deactivation. © 1990.