Iron-containing heterogeneous catalysts for partial oxidation of methane and epoxidation of propylene

Mesoporous molecular sieves containing iron sites with different dispersions and environments were studied for the partial oxidation of methane and the epoxidation of propylene. The tetrahedral Fe(III) sites incorporated inside the framework of SBA-15 showed higher HCHO selectivity under a similar CH4 conversion than the oligomeric FeOx clusters located in the mesopores in the partial oxidation of CH4 by O2. HCHO selectivity of the FeOx clusters in SBA-15 could be improved by the modification with either an acidic group (e.g., phosphate) or an alkali metal ion, which increased the dispersion or changed the local coordination environment of iron species. The catalyst containing FePO4 clusters formed by the modification with phosphate exhibited the best catalytic performances for HCHO formation. This catalyst also showed uniquely high selectivities to HCHO and CH3OH as N2O was used as the oxidant for the partial oxidation of CH4. For the epoxidation of propylene to propylene oxide (PO), the modification of the FeOx/SBA-15 with an alkali metal salt typified by KCl was effective. Among many SBA-15-supported transition metal oxides modified by KCl, the KCl-FeOx/SBA-15 showed the best catalytic performances for the epoxidation of propylene by N2O. The comparative studies using N2O and O2 as the oxidant revealed that N2O was necessary for PO formation over the KCl-FeOx/SBA-15 catalyst.