D. Rouzies et al., ISOBUTYRIC ACID OXIDATIVE DEHYDROGENATION OVER IRON HYDROXYPHOSPHATES.1. CATALYTIC PROPERTIES AND ROLE OF WATER, Applied catalysis. A, General, 124(2), 1995, pp. 189-203
The catalytic activity and selectivity of several mixed-valence hydrox
yphosphates in the oxidative dehydrogenation of isobutyric acid to met
hacrylic acid were determined and compared to those of an industrial i
ron phosphate-based catalyst. The phases were characterized before and
after catalytic reaction; after catalysis they appeared to belong to
a solid solution of the type Fe4-x3+Fe3x2+(PO4)(3)(OH)(3-3x)O-3x with
less than or equal to x less than or equal to 1. The compounds of this
solid solution underwent a reversible reduction through a reduction-h
ydroxylation mechanism without structural change. This mechanism is pr
oposed to be the basis of the catalytic activity of the compounds, whi
ch suggests that one of the roles of water added to the gas feed is to
displace the hydration equilibrium.