RESUMO
Iron doped hexagonal mesoporous silica (Fe-HMS) was successfully prepared by one-pot direct synthesis at ambient temperature by using dodecylamine as a templating agent. The catalyst has been characterized by various techniques including XRD, DR-UV-Vis, FTIR, SEM and N2 adsorption. The obtained material exhibits very large surface area (above 1000 m(2) g(-1)), mesoporosity with narrow distribution of pores (around 4 nm) and nano-crystallites with the 20-30 nm in size. The concentration of iron in the catalyst was 0.95 wt%. The prepared material was tested in the direct ammoxidation of propane. It was shown that direct synthesis leads to better dispersion of the metal compared to the material prepared by impregnation of pure HMS silica. It is also demonstrated that this material is able to catalyze the direct ammoxidation of propane and shows quite high selectivity to acrylonitrile (52% at 11% conversion of propane).
RESUMO
We demonstrate, for the first time, in the Baeyer-Villiger oxidation of cyclohexanone with aqueous hydrogen peroxide under conditions aimed at obtaining ε-caprolactone, that a thermally activated radical reaction leads to the concurrent formation of adipic acid, even when a stoichiometric amount of the oxidant is used. In fact, ε-caprolactone is the primary reaction product, but it is more reactive than cyclohexanone, and quickly undergoes consecutive transformations. When titanium silicalite-1 (TS-1) is used as a catalyst, the high concentration of hydroxy radicals within its pores accelerates the reaction rates, and the consecutive formation of adipic acid (and of lighter diacids as well) becomes largely kinetically preferred. The proper choice of the solvent, which also may act as a radical scavenger, both without catalyst and with TS-1, is a powerful tool for controlling the rates of the various reactions involved.