铁锑氧化物表面氧的性质及氨的吸附特性

研究了Fe₂O₃和Sb₂O₄及Sb/Fe比由1/9至9/1五种复合氧化物表面氧的TPD行为。Fe₂O₃在200～450℃间有少量氧脱出,Sb₂O₄在700℃以后出现脱氧峰,而Sb/Fe复合氧化物则出现所谓α和β脱氧峰。随Sb/Fe比增加α氧的脱附活化能也增高,Sb/Fe比为3/7、5/5和7/3时分别为33、36、51kcal/mol。Fe-Sb氧化物中α氧比β氧对烯烃氧化具有更高的活性。在50—275℃范围内NH₃在Fe-Sb氧化物上的吸附等温线符合Freundlich式,同时由NH₃的TPD可明显看出Fe-Sb氧化物具有不同强度的吸附中心,它们与所含表面氧有关,但表面氧对NH₃的氧化是很弱的。讨论了烯烃选择氧化反应与表面氧强度之间的联系。

CHARACTERISTICS OF SURFACE OXYGEN IN Fe-Sb OXIDE AND ADSORPTION OF NH3

The TPD of surface oxygen of Fe₂O₃, Sb₂O₄ and other five mixed oxides with atom ratio Sb/Fe from 1/9 to 9/1 have been investigated. A small amount of oxygen is desorbed from Fe₂O₃ at 200-450℃ while for Sb₂O₄the desorption peak of oxygen appears after 700℃ and in the case of mixed oxides both α and β oxygen are found to be during TPD after 400℃. It is found that the activation energy of desorption of a oxygen increases with the increase of Sb content and that α oxygen is more reactive than β oxygen for the oxidation of propylene. It is shown also that NH₃ adsorption sites are of different strength depending on the content of α and β oxygen in Fe-Sb oxide. It is concluded that suitable bonding strength of surface oxygen in Fe-Sb oxides should be the main cause of high activity and selectivity in the ammoxidation of propylene.