Metal-containing Aluminophosphate Molecular Sieves And Their Catalytic Properties In Hydrocarbons Oxidation Under Low Temperature

Metal-containing aluminophosphate molecular sieves have attracted great interest as novel catalysts since the discovery of excellent catalytic properties of TS-1 for hydrocarbons oxidation with H2O2 in 1980s. Information about the transition metal ions in molecular sieves would be beneficial to understanding their catalytic behaviors. In this thesis, three types of molecular sieves [MeAPO-5, MeAPO-11(Me=Co, Mn, Cr, V) and MeAPSO-34(Me=Co, Mn)] were synthesized and many techniques were used to characterize them. Meanwhile, in view of the great economic potential of alkane oxidation, these molecular sieves were used as catalysts in selective oxidation of hydrocarbons under low temperature by 2. The effect of molecular sieve structure and incorporated metal on hydrocarbons oxidation was explored.Studies on the characterization of molecular sieves showed that Co and Mn incorporated into the framework by isomorphous substitution of Al and both of them had the same valence (+2) in the as-synthesized and calcined samples. Cobalt and manganese changed their four coordinations to the coexistence of four and three coordinations during calcination in air to remove the template in the molecular sieves. For CrAPO and VAPO molecular sieves, octahedral Cr(III) was changed to tetrahedral Cr(VI) and V(IV) was oxidized to tetrahedral V(V) during calcination process.The results of cyclohexane oxidation under mild condition indicated that crystal size and metal type containing in the molecular sieve had important influence on the reactivity and selectivity of oxidation, whereas the molecular sieve structure had less effect. Metal-containing molecular sieves were very stable during oxidation reaction, which was carried out heterogeneously. The catalytic activity of small-poreMeAPSO-34 came from the metals on its external surface. Free radical mechanism in the liquid oxidation with O2 was verified.The results of n-octane and methylcyclohexane oxidations showed that the C-C bond in n-octane broke more easily than that in cyclohexane under reaction condition. The C-C bond connected to tertiary C in the ring of methylcyclohexane was easier to open than the other C-C bonds during oxidation. The apparent activation energies of different alkanes on CoAPO-11 had the following order: methylcyclohexane