New porous Ga/Cr mixed oxide pillared alpha-zirconium phosphate materials

Mixed oligomeric solutions of gallium(III) and chromium(III), 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 alpha-zirconium phosphate or precipitated with an excess of n-propylamine. Whilst the mixed precipitates show X-ray diffraction (XRD) reflections typical of mixed GaxCr2-xO3 oxides after calcination above 400 degrees C, most of the mixed intercalates were amorphous between room temperature and 800 degrees C, and only after calcination at 1000 degrees C were XRD reflections corresponding to zirconium pyrophosphate and Ga/Cr mixed oxides observed. These results suggest that mixed Ga/Cr oxide pillared alpha-zirconium phosphate materials are formed at 400-800 degrees C. The mixed pillared materials with Ga:Cr ratios < 60:40 have high BET surface areas (200-300 m(2) g(-1)) and micropore volumes (0.08-0.11 cm(3) g(-1)).(1) Higher Ga:Cr ratios lead to materials with BET surface areas lower than 100 m(2) g(-1) and low micropore volumes. The mixed oxide powders also present high BET surface areas (184-236 m(2) g(-1)) and micropore volumes (0.08-0.10 cm(3) g(-1)), 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.