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

Abstract

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 α-zirconium phosphate or precipitated with an excess of n-propylamine. Whilst the mixed precipitates show X-ray diffraction (XRD) reflections typical of mixed Ga_xCr_2–xO₃ 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 α-zirconium phosphate materials are formed at 400–800 °C. The mixed pillared materials with Ga:Cr rations <60:40 have high BET surface areas (200–300 m² g^–1) and micropore volumes (0.08–0.11 cm³ g^–1)¹. Higher Ga:Cr ratios lead to materials with BET surface areas lower than 100 m² g^–1 and low micropore volumes. The mixed oxide powders also present high BET surface areas (184–236 m² g^–1) and micropore volumes (0.08–0.10 cm³ 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.