Studies of metal substituted alumino-phosphates and other related systems
The research within this thesis has concentrated around the identification and catalytic understanding of the acid and redox properties of a series of metal substituted aluminophosphates, silicoaluminophosphates and polyoxometalates. The aim being to understand how the active metal sites were co-ordinated, to what degree of substitution had been successfully achieved and finally the direct relation this information had in understanding the degree of reaction for the various catalytic processes. In most part hydrothermal synthesis was employed, the exception being in the case of the polyoxometalate and polyoxometalate layered double hydroxide synthesis. Characterisation was achieved through the use of many analytical techniques predominantly X-ray diffraction (XRD) and extended X-ray spectroscopy (XAS). In total, four commercially important reactions were studied. Firstly, the shape selective and redox properties associated with (a) the substitution of different metal ions within the same aluminophosphate framework and (b) the substitution of the same metal ion within different aluminophosphate frameworks were characterised and investigated for the methanol to olefin (MTO) reaction to demonstrate the activity and selectivity of different frameworks in the production of a range of olefins. Secondly, several transition metal ion-exchanged zeolites and aluminophosphates were synthesised, characterised and subsequently analysed for the hydroxylation of phenol. Here temperature effects were also investigated to see what, if any effect it had upon the final conversion of phenol. Thirdly, a series of bifunctional platinum impregnated silicoaluminophosphate (Pt/SAPO) and metal substituted aluminophosphate (Pt/MeAlPO) catalysts were synthesised, characterised then investigated to understand how their acidic nature effected the catalytic activity and selectivity for the hydroisomerisation of n-heptane. Finally, the properties of several cobalt-substituted polyoxometalates (POM's) and polyoxometalate pillared layered double hydroxides (POM-LDH's) were studied and investigated for their catalytic activity for the oxidation of cyclohexane with molecular oxygen in the presence of TBHP.