Activity pattern of low-loaded FeO_x/SiO₂ catalysts in the selective oxidation of C₁ and C₃ alkanes with oxygen

The structure and redox properties of low-loaded (0.015–0.73 wt% Fe) FeOx/SiO2 catalysts obtained by adsorption–precipitation of Fe2+ were probed by Mo¨ssbasuer and TPR techniques. Oxide dispersion data, obtained by deconvolution of Mo¨ssbasuer and TPR spectra, signal the speciation of the active phase into ‘‘isolated’’ FeOx sites, ‘‘2-d FeOx patches’’ and ‘‘3-d Fe2O3 clusters’’. The reactivity of FeOx/SiO2 catalysts in the selective oxidation of CH4 and C3H8 in the range 475–650 8C has been assessed. Basic relationships amongst dispersion, specific rate of alkane conversion and product formation signal that the selective oxidation functionality depends upon local environment and oxygen bond strength of active sites, their distribution being closely related to the efficiency of synthesis route.