Abstract
A study was undertaken of the dissolution and reduction of vanadium pentoxide during reflux for 16 h in a number of solvent and reducing agents as a first step in the preparation of vanadium-phosphorus oxide (VPO) catalysts. Solvent/reducing agent systems studied included isobutanol, isobutanol-water, isobutanol-benzyl alcohol, water-hydrochloric acid and water-hydrazine. Complete dissolution or reduction of V2O5 never occurred after reflux in any of the alcohol containing systems: amounts of undissolved solid varying between 30 and 100% of the original V2O5 charge were isolated by filtration. When benzyl alcohol was used this solid appeared to be V2O5 but in the absence of this alcohol the recovered solid was pure V2O5. Complete dissolution of V2O5 occurred in the water-hydrochloric acid and in the water-hydrazine systems. During reflux with orthophosphoric acid most of the remaining solids did dissolve within 1 h. However, trace amounts of V2O5 appeared in the X-ray diffraction pattern of the precursor unless this reflux step was allowed to proceed for more than 1 h. Scanning electron microscopy showed that the precursor (VOHPO4·O.5H2O) particles formed in alcoholic media appeared as cracked and split spheres all 2-3 μm in diameter. It is postulated that this particle shape originates from the formation of the precursor within water droplets formed in a water-in-alcohol emulsion stabilized by vanadia particles of colloidal dimensions.
Original language | English (Ireland) |
---|---|
Pages (from-to) | 91-104 |
Number of pages | 14 |
Journal | Applied Catalysis |
Volume | 42 |
Issue number | 1 |
DOIs | |
Publication status | Published - 1988 |