Site isolation in iron-molybdate-based catalysts for side chain oxidation of alkylaromatics

The catalytic behavior in p-xylene oxidation to para-tolualdehyde and terep hthaloaldehyde and in 3-fluorotoluene oxidation to 3-fluorobenzaldehyde ove r bulk iron-molybdate and iron-molybdenum oxides encaged in zeolitic matric es was studied. The results indicate that site isolation of the iron-molybd ate inside the zeolite matrix allows a relevant improvement in selectivity, but the nanosized particles also show particular properties not present in the bulk iron-molybdate such as the ability to selectively form the dialde hyde (terephthaloaldehyde) from p-xylene. At low temperatures the productiv ity of iron-molybdenum-containing zeolites is comparable to that of bulk ir on-molybdate, even though the amount of active component is one order of ma gnitude lower. However, at higher temperatures limitations regarding the ba ck-diffusion of products result in lower activity and selectivity.