Influence of alumina precursor on the physico-chemical properties of V–Sb–P–W/Al2O3 catalyst studied for the ammoxidation of propane

Abstract

Influence of alumina precursor on active phase formation in V1.0–Sb3.5–P0.5–W1.0/50% Al2O3 catalyst was studied for the ammoxidation of propane in the temperature range of 490–530°C at W/F=2.8gcatsml−1. Three different alumina precursors such as, aluminum chloride (AlC), aluminum hydroxide (AlH) and aluminum nitrate (AlN) were employed in the study. The physico-chemical characterisitics of the synthesized catalysts were investigated by BET surface area-pore size method, XRD, FTIR, HAADF/EDS, NH3 TPD-mass and XPS techniques. XRD result demonstrates AlPO4 phase for all the three catalysts which was likely due to P interaction with alumina precursor. Formation of propylene and acrylonitrile (ACN) in this study was influenced by the nature of the active surface on Al2O3 synthesized from different precursors. Among the catalysts, AlC exhibited greater propane conversion (76%) and ACN selectivity (28%) at 530°C. The higher activity of AlC was associated with (i) active surface enriched in V–Sb–W phase as established by XPS and HAADF/EDS results (ii) higher adsorption ability for NH3 in the presence of residual chloride (coming from AlCl3) followed by efficient nitrogen insertion in the intermediate molecule of propane to yield ACN. The surface with Sb–W–O related phase in AlN and AlH possibly contributes to the degradation of adsorbed propane/propylene and NH3 to yield methane, ethane, ethylene, COx and NOx. To our knowledge, this is the first report for the influence of alumina precursor on the active phase formation in V–Sb–P–W/Al2O3 catalyst studied for the propane ammoxidation.