Abstract
Vanadium phosphate materials, based on a VOHPO4 center dot 0.5H(2)O precursor and with (VO)(2)P2O7 as an active high-temperature phase, are used as catalysts for the oxidation of alkanes. VOHPO4 center dot 0.5H(2)O is prepared from VOHPO4 center dot 2H(2)O using 1-octanol, 3-octanol, 2-butanol, or 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. At temperatures of 160 degrees C or greater, a solution containing V4+ ions formed in preference to VOHPO4 center dot 0.5H(2)O. However, VOHPO4 center dot 0.5H(2)O formation can be achieved above 160 degrees C by carrying out the reduction process in the presence of a small amount of vanadium phosphate material, which effectively acts as a templating seed. The use of this seeding, concept is shown to have a dramatic effect on the morphology of the final activated catalyst. In contrast, when 3-octanol is used, solely VO(H2PO4)(2) is generated, except in the presence of a vanadium phosphate seed where significant amounts of VOHPO4 center dot 0.5H(2)O can also be formed. Furthermore, VO(H2PO4)(2) can be transformed to VOHPO4 center dot 0.5H(2)O by heating at reflux with an alcohol in the presence of VOHPO4 center dot 0.5H(2)O precursor seeds. The findings reported herein show that both the phase composition and morphology of vanadium phosphates can be influenced by the use of seeds during the preparation process.