Spectroscopic study of the coordination and valence of Fe and Mn ions in and on the surface of aluminas and silicas

摘要: A comparative study of the first-row transition metal ions Fe3+ and Mn2+ on surfaces aluminas silicas has been made using conventional techniques e.s.r., X-ray diffraction, magnetic susceptibility in addition a relatively new technique phosphorescence spectroscopy.The results indicate that dissolve readily γ-alumina up to 1 w% samples calcined at 200°C least 10 % 800°C. In silica not more than 0.1 could be dissolved, remainder crystallizing as α-Fe2O3 surface. E.s.r. γ-Al2O3 below 400°C are mostly octahedrally coordinated surface, but above this temperature majority take tetrahedral coordination. almost exclusively occupy holes At phase θ→α-Al2O3 1000°C, move into trigonally distorted octahedral sites whereas changes valence Mn4+ sites. Also silica, preferentially coordination heat treatments remain these 1200°C calcination temperatures.Most can explained basis differences between structures aluminas.