Toluene gas phase oxidation to benzaldehyde and phenol over V-containing micro- and mesoporous materials

Heterogeneous selective oxidation, using O2, is a convenient solution in terms of both ease separation and reduced waste production, but this method suffers from low selectivity, because of the considerable difference between the enthalpies of the weakest bond dissociation in reactant and products, giving rise to a fast consecutive oxidation to COx. The rate of the consecutive oxidation can be controlled by site isolation that, however, requires the possibility of obtaining a high dispersion of the active component in a matrix with uniform pore size distribution. Although V-containing zeolites have already been studied in gas-phase selective oxidations (propane oxidative dehydrogenation, for example), data on the reactivity of these catalysts on the heterogeneous gas-phase selective oxidation of alkylaromatics are not available. Alkylaromatic oxidation has also been done in the liquid phase, using H2O2, as oxidant. The scope of the work described in this chapter was to carry out a preliminary study of the reactivity of these catalysts, using toluene to benzaldehyde, as the test reaction to determine the outlook for and drawbacks of the use of this class of catalysts in alkylaromatic selective oxidation and identify the relationship between the nature of vanadium species and catalytic behavior.