Ammoxidation of propane over Fe-zeolites: Effect of reaction variables and catalyst composition and structure

A series of Fe-silicalite catalysts with tailored dispersion of Fe sites ranging from almost exclusively isolated Fe ions via oligonuclear cluster to Fe2O3 particles were characterized by UV–vis and ESR spectroscopy. The same catalysts were tested in the direct ammoxidation of propane at 540 °C in the mixture of molecular oxygen and nitrous oxide. Obtained catalytic results were compared with spectroscopic characterization. The presented results clearly showed that the changes in the catalytic performance of investigated catalysts are in correspondence with results of spectroscopic characterization. Acrylonitrile is produced on extra-framework Fe species exclusively generated by hydrolysis of framework SiOFe bonds both during reaction and by steaming in water vapor at 600 °C as was evidenced by UV–vis and ESR spectroscopy. We supposed that active sites have character of well isolated extra-framework sites with tetrahedral coordination characterized by UV bands below 300 nm and ESR signals with g higher than 5.