Abstract: Fe-Al-P-O catalysts were prepared by the sol-gel method and characterized using N2 adsorption, transmission electron microscopy, X-ray diffraction, infrared spectroscopy, and temperature-programmed desorption (TPD). The Fe-Al-P-O catalysts are highly dispersed and homogenous particles with diameter of 20～40 nm. There are Lewis acid sites, Fe3+ and Al3+, and Lewis base sites, terminal oxygen of the P=O double bond, on the surface of the Fe-Al-P-O catalysts. TPD results show that propylene is adsorbed on the Lewis acid sites and the Lewis base sites with C=C double bonds and allylic hydrogen, respectively. H2O can also be adsorbed on Fe3+ and P=O with hydrogen and oxygen atoms. The catalytic performance of Fe-Al-P-O for the epoxidation of propylene was tested in a microreactor. The main selective oxidation product is acrolein with a feed gas composed of C3H6, O2, and N2, whereas the main selective oxidation product is propylene oxide if the feed stream is composed of C3H6, O2, H2, and N2. Under the conditions of atmospheric pressure and 100～300 ℃, the conversion of propylene is 5.9%～9.6% and the selectivity for propylene oxide is over 63%. The epoxidation of propylene to propylene oxide is parallel with the oxidation of propylene to acrolein. The propylene adsorbed on the P=O sites with allylic hydrogen is oxidized into acrolein, whereas the propylene adsorbed on the Lewis acid sites, Fe3+, with C=C double bonds transforms into propylene oxide. Adding H2O to the feed gas can inhibit the formation of acrolein because water decreases the adsorption amount of propylene.

Key words: iron, aluminum, phosphorus, oxygen, propylene, epoxidation, propylene oxide