Alumina dissolution promoted by CuSO4 precipitation

The impregnation of gamma-Al2O3 with CuSO4 at 50 degrees C was investigated at pH 9 and 7 using a dialysis membrane reactor. It was observed that alumina is not inert at pH values close to its isoelectric point when impregnated with CuSO4. Although the alumina was kept in a membrane bag, the presence of aluminum ions in the copper precipitate, which was formed outside of the membrane bag at pH 9 and 7, was detected by ICP, XRD, XRF, and SEM-EDAX. The molar ratios of Cu to Al in the precipitate formed at pH 9 and 7 were 80.8 and 222, respectively. The total amounts of alumina dissolved at pH 9 (after 240 h) and 7 (after 336 h) were 2.21 mg and 0.51 mg,respectively. It was observed that aluminum ions deriving from the support prefer to accumulate in the copper basic sulfate phase rather than in the CuO (Cu(OH)(2)) phase. The dialysis and XANES experiments proved that Cu(OH)(2) is mainly responsible for the alumina dissolution at pH 9. On the other hand, copper basic sulfate, which is the main compound formed at pH 7, was found to be less active in alumina dissolution, It was suggested that the presence of aluminum ions in the copper compound phase may influence the active sites formation of the catalyst by inducing the formation of lattice defects.