The Effect of Using H4P2O7 as Phosphorus Source for Synthesizing Vanadyl Pyrophosphate Catalysts

Y.H. Taufiq-Yap, A. Raslan and R. Irmawati

Department of Chemistry, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

Abstract

Vanadyl pyrophosphate (VO)2P2O7 catalysts synthesized via VOPO42H2O were investigated by using BET surface area measurement, X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), and Temperature-Programmed Techniques (TPD and TPRS). H3PO4 and H4P2O7 were used as the phosphorus source. Only pyrophosphate phase was observed for both final catalysts after 75 hours of calcination in a reaction flow of n-butane/air mixture (0.75% n-butane/air). However, catalyst derived from H4P2O7 based preparation (denoted VPDpyro) exhibit better crystallinity and slightly higher BET surface area compared to the H3PO4 based preparation (denoted VPDortho). The nature of the oxidants for both catalysts was investigated by O2-TPD. For VPDpyro, TPD showed an oxygen peak maximum at 986 K and a shoulder at 1003 K, whereas for VPDortho, the oxygen was desorbed as two peaks maxima at 966 and 994 K. The total amount of oxygen desorbed thermally from VPDpyro (3.601020 atomg-1) is higher than that obtained for VPDortho (3.071020 atomg-1). VPDpyro displayed a slightly improved activity and selectivity for n-butane oxidation. A proper amount of V5+ species may have an effect on the enhancement of the catalytic activity.