Gelification process to prepare phosphate modified alumina: Study on structure and surface properties

摘要

P-modified alumina was prepared through gelification with phosphate compounds introduced during the formation of alumina gel. Common characterizations such as XRD, BET and IR were employed to investigate the effect of phosphate dopant on the structure and surface properties of alumina. The results showed that the addition of phosphate could effectively improve thermal stability and textural properties of alumina. For G_5 sample, the alpha-phase formation temperature is enhanced up to 1573 K and the surface area retains 85 m~2 g~(-1) as well as the pore volume 0.356 cm~3 g~(-1) after calcination at 1473 K for 3 h. Moreover, the surface area and pore volume both have increasing trends with the increasing phosphorous contents in alumina after calcinations at the same temperature. There is also an increasing trend of lattice constants of P-modified aluminas with the increase of phosphorous content in alumina. Considering the defective spinel structure of gamma-alumina, it can thus be deduced that some of the P~(5+) ions might occupy the vacancy of cationic site and interrupted the track of Al~(3+) ions transfer from tetrahedral to octahedral in the processes of sintering and transformation.