Electron optical studies of the formation of vanadium pentoxide catalyst

Abstract

The oxides of vanadium, especially vanadium pentoxide, have been extensively studied because of their interesting physical properties particularly in catalysis. Vanadium pentoxide is generally used in the oxidation and ammoxidation of hydrocarbons.This catalyst has been prepared via the thermal decomposition of ammonium metavanadate (AMV) in air. Thermogravimetric analysis (TGA), infrared spectroscopy (IRS) and x-ray diffraction (XRD) techniques together with high resolution electron microscopy (HREM) and scanning electron microscopy (SEM) have enabled us to elucidate the physicochemical changes occurring during the decomposition process.According to TGA results, the decomposition of AMV commences at 150°C and is complete by 320°C leading to vanadium pentoxide by loss of ammonia and water with the formation of two intermediate compounds, namely at 190°C, ammonium bivanadate: (NH4)2V4 O11, and at 230°C, ammonium hexavanadate AHV: (NH4)2V6O16 . Samples for structural correlation studies were prepared by heating AMV in a stream of air for 2 hours at selected temperatures of 140, 190, 230, 320 and 400°C.