Hydrothermal Synthesis of Vanadium Phosphate

Y. H. Taufiq-Yap1 and A.R. Mohd Hasbi2

1Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

2Faculty of Chemical and Natural Resources Engineering, University College of Engineering and Technology, Locked Bag 12, 25000 Kuantan, Pahang, Malaysia

Abstract

VOHPO4·0.5H2O was prepared via hydrothermal method by reacting V2O5, o-H3PO4, water and oxalic acid in an autoclave at 383 K. The precursor obtained was further calcined for for different lengths of time i.e. 6, 36 and 75 hrs at 713 K in a reaction flow of n-butane/air mixture. XRD result show that the material calcined for 6 hrs (denoted VPH6) only comprise of (VO)2P2O7 phase. However, an extension of calcination period to 36 produced material with a mixture of V4+ and V5+ phases. Further calcination to 75 hrs totally transforms the material into a mixture of several VOPO4 phases. SEM showed that the morphology of the VPH6 consists of irregular flaky shape which is markedly different from the normal ‘rossette-like clusters’ synthesized via ‘organic’ or ‘dihydrate’ methods. TPR in H2 revealed the nature of the oxidants. Three reduction peaks maxima were observed with the major peak appeared at a high temperature range attributed to the removal of lattice oxygen related to V4+ species in the (VO)2P2O7 phase. Oxygen species associated with V4+ contributed to the activation of n-butane. This reduction behaviour of VPH6 indicated that a low mobility and reactivity of the oxygen species in the lattice of the material.