New porous Ga/Cr mixed oxide pillared α-zirconium phosphate materials
Journal of Materials Chemistry
Mixed oligomeric solutions of gallium(II1) and chromium(m), with Ga : Cr mole ratios between 10 : 90 and 90 : 10, have been prepared by adding n-propylammonium acetate and n-propylamine to the mixed nitrate solutions at pH 4.4-4.5. The mixed oxyhydroxyacetate oligomers thus obtained were intercalated into colloidal a-zirconium phosphate or precipitated with an excess of n-propylamine. Whilst the mixed precipitates show X-ray diffraction (XRD) reflections typical of mixed GaxCr2 -x03 oxides
... r2 -x03 oxides after calcination above 400 "C, most of the mixed intercalates were amorphous between room temperature and 800 "C, and only after calcination at 1000 "C were XRD reflections corresponding to zirconium pyrophosphate and Ga/Cr mixed oxides observed. These results suggest that mixed Ga/Cr oxide pillared a-zirconium phosphate materials are formed at 400-800 "C. The mixed pillared materials with Ga : Cr ratios < 60 : 40 have high BET surface areas (200-300 m2 g-') and micropore volumes (0.08-0.11 cm3 g-').' Higher Ga: Cr ratios lead to materials with BET surface areas lower than 100 m2 g-' and low micropore volumes. The mixed oxide powders also present high BET surface areas (184-236 m2 g-') and micropore volumes (0.08-0.10 cm3 g-'), probably due to a templating effect of the acetate ion. A comparison of the bulk and surface compositions of pillared materials, obtained by chemical analysis and X-ray photoelectron spectroscopy (XPS), respectively, reveal that, at least up to a Ga : Cr ratio of 60 : 40, the intercalated species into the phosphate are mixed oligomers.