Solid state chemistry of Fe-Ga mixed oxides

Several Fe-Ga mixed oxide samples denoted as Fe1-xGax(x=0, 0.10, 0.25, 0.50, 0.75, 0.90) have been synthesised by a conventional coprecipitation method at controlled pH, dried at 363 K for 24 hours and calcined at 673 K and 1073 K for 3 hours. All samples were characterised by X-ray diffraction, chemical analyses, thermogravimetry and differential thermal analysis (TG-DTA) and FT-IR and UV-VIS spectroscopies. It was found all materials formed a solid solution, alpha-(Fe,Ga)(2)O-3, in the entire Fe/Ga compositional range until 673 K. Samples calcined at 1073 K gave rise to biphasic systems for x>0.5 due to the different structure of beta -Ga2O3 compared to alpha -Fe2O3. Surface acidity of samples was studied by pivalonitrile molecule adsorption on a pressed pellet of each material, and weak Lewis acidity was found in all cases, it not being possible to distinguish between both types of cation site on the surface, and Bronsted acidity that increased with increasing Ga content. Methanol molecules were also adsorbed, showing an increase of reactivity for those samples with very low Ga content