Ua. Schubert et al., Possible effects of site isolation in antimony oxide-modified vanadia/titania catalysts for selective oxidation of o-xylene, TOP CATAL, 15(2-4), 2001, pp. 195-200
Titania-supported vanadia catalysts were modified by addition of antimony o
xide for application in o-xylene selective oxidation to phthalic anhydride.
It was shown that active and selective catalysts can be prepared by ball-m
illing mixtures of powders of TiO2, V2O5 and Sb2O3 followed by calcination.
X-ray photoelectron spectroscopy proves the formation of highly dispersed
overlayers of vanadium oxide and antimony oxide, in which V5+ is partially
reduced to lower oxidation states and Sb3+ is partially oxidized to Sb5+. A
ntimony oxide segregated into the outermost surface layers. It is therefore
inferred that the presence of the antimony oxide modifier spatially separa
tes V-O species and leads to "site isolation" which may be responsible for
the positive effect of the modifier for the catalyst's selectivity.