Book Description

This thesis aims the study of new preparative routes to get catalyst precursors VOHPO4.0.5H2O with good catalytic performance for the selective oxidation of n-butane to maleic anhydride. The use of octane as co-solvent shows a significant effect on the morphology of VOHPO4.0.5H2O precursor which was prepared via three different routes. The reaction of VOPO4.2H2O with octane solvent shows the possibility of the intercalation of the octane solvent between the layers of VOPO4.2H2O. This can lead to the formation of VOHPO4.0.5H2O precursors with a new morphology after the reduction step using 1-butanol. In addition, the use of octane as co-solvent with 1-butanol leads to the formation of VOHPO4.0.5H 2O with a different XRD pattern and new morphology. Testing these samples shows that the samples with rosette morphology exhibit the highest conversion and selectivity compared with the new materials prepared. We demonstrate that the use of seed crystals of vanadium phosphate can have a dramatic influence on the morphology and phase identity of the precursor materials. VOHPO4.0.5H2O was prepared from VOPO 4.2H2O using 1- and 3-octanol, 2-butanol and 2-methyl-1-propanol as both solvent and reducing agent. With 1-octanol the reaction temperature was found to be crucial in obtaining a high yield of the precursor phase, and at temperatures ≥160°C a solution, containing V4+ ions formed in preference to VOHPO4.0.5H2O. However, VOHPO4.0.5H2O formation can be achieved by the addition of a small amount of V-P-O materials as seeds if carrying out the reduction process above this temperature. In contrast, when 3-octanol is used, VO(H 2PO4)2 is formed solely, but in the presence of a V-P-O seed significant amounts of VOHPO4.0.5H2O can also be formed. Studying the reaction time online shows that VO(H2PO 4)2 could be transformed to VOHPO4.0.5H2 O, which has been attempted previously without success. Finally, testing these samples under reaction conditions shows that they demonstrate high selectivity toward MA and good conversion compared to VO(H2PO4) 2. Vanadium phosphate catalysts have successfully been prepared in aqueous media using hydrogen. The catalysts precursors obtained were poorly crystalline VOHPO4.05H2O and a minor amount of an impurity detected by a reflection in the XRD pattern. Activating these materials for n-butane oxidation show low selectivity of MA (5%), which could be attributed to the presence of V(V) phases after activation.