Catalytic Activity of Fe(III)-Substituted Aluminophosphate Molecular Sieves in Oxidation of Aromatic Compounds

Many metal-containing microporous zeolites have been used in heterogeneous catalytic reactions since TS-1 zeolite used as a catalyst in oxidation reactions. However, some disadvantages of these microporous titanosilicates may limit their application as popular catalysts for oxidation reactions in organic chemistry. In order to obtain new catalysts with relatively simple procedures of preparation, iron-substituted aluminophosphate molecular sieves (FeAlPO 4-5, FeAlPO 4-11 and FeVPI-5, denoted as Fe(Ⅲ)APO) have been hydrothermally synthesized. And these samples are catalytically active in oxidation of aromatic compounds, such as hydroxylation of phenol and benzene, and epoxidation of styrene as well as oxidation of naphthol. The catalytic activity of FeAlPO 4-5 and FeAlPO 4-11 is comparable with that of TS-1 in some reactions. In hydroxylation of phenol and benzene, FeAlPO 4-11 can give conversion of 22.1% and 13.1%, respectively. In styrene epoxidation, FeAlPO 4-11 achieves conversion of 24.7% and selectivity of 55.2%, while TS-1 gives selectivity of 6.2% only, suggesting that the reaction routes in styrene epoxidation are different over these two catalysts. Over FeAlPO 4-11, the isomerization of epoxide hardly occurs in styrene epoxidation. On the contrary, the isomerization of epoxide easily takes place over TS-1. FeVPI-5 shows high activity in naphthol oxidation by H 2O 2 giving conversion of 14.5%, while TS-1 is completely inactive owing to its small pore size. These results suggested that FeVPI-5 is a good candidate for the catalytic oxidation of large organic compounds. The results of Mssbauer spectroscopy of FeAlPO 4-11 and FeAlPO 4-5 suggested that Fe(Ⅲ) in the framework is proposed as the major active sites in the catalytic oxidation.