Direct Ultrasound Synthesis of Vanadyl Pyrophosphate Catalyst for Partial Oxidation of N-Butane to Maleic Anhydride

Abstract

Three vanadyl pyrophosphate catalyst were prepared via direct ultrasound technique using organic, sesquihydrate and dihydrate routes, denoted as VPOuo, VPOus and VPOud respectively. Catalysts were synthesised in N-butane/air mixture based exclusively on direct ultrasound technique. All catalysts exhibited well crystallised (VO)2P2O7. VPOus and VPOud demonstrated αII-VOPO4, which led to rise in vanadium average oxidation state. The catalysts were showing O1s approximate 530 eV, comparable P2p value and V2p3/2 at approximate 517 eV, providing vanadium oxidation state of approx. 4.0–4.2. Secondary structure composed of thin plate-like crystals in different sizes agglomerate to each other due to cavitation effect were observed in field emission scanning electron microscope. High resolution transmission electron microscope demonstrated the existence of polycrystalline phase. The nature of the oxidants was investigated by temperature-programmed reduction in H2. VPOus showed highest amount of total removal of oxygen species suggesting that it had highest activity compared to VPOuo and VPOud. The measurement of X-ray absorption near edge structure demonstrated incidence of vanadium oxide reductions in the flow of hydrogen, which indicates V4+ and V5+ presence. Catalytic tests demonstrated that the activity and selectivity to maleic anhydride increased with direct ultrasound technique. This research has shown that the catalysts production time can be reduced to 2 hours and giving polycrystalline particles compared to conventional method.