THE ROLE OF VANADIUM IN VANAKIUM-PROMOTED TIN(IV) OXIDE CATALYSTS: ANFTIR, XRD AND EXAFS STUDY

摘要

Vanadium-promoted tin(IV) oxide catalysts havebeen prepared by coprecipitation from aqueous solutionscontaining Sn(IV) and V(IV) ions using aqueous ammonia, andthe materials thermally processed in air at temperatures up to1273K. Characterisation of these materials was carried out usingXRF, FTIR, XRD and EXAFS. The catalyst material is shown toconsist of small particulate SnO2 and VO2 evenly distributed upto a calcination temperature of 773K. At higher temperatures theV(IV) is oxidised to V(V) to form phase separated V2O5. SomeV(V) undergoes reduction at 873K to form a solid solutionwhere V(IV) occupies metal sites in the tetragonal SnO2 lattice.After calcination at 873-973K the vanadium exists as phase-separated V2O5 together with a small quantity of V(IV)occupying the Sn(IV)sites in the tetragonal SnO2 lattice. At1073K the vanadium migrates out of the Sn(IV) sites and isoxidised to again form V2O5. The initial vanadium concentrationis 9wt%, which remains constant up to temperatures of >1173Kat which temperature most of the vanadium volatilises and1.5wt% vanadium remains.