Abstract: Steam activation is an important way to modify the pore structure of alumina support. Techniques such as XRD, nitrogen adsorption-desorption, mercury porosimetry and nuclear magnetic resonance (NMR) spectrometer were employed to characterize the crystalline phases, surface area, pore size distribution and Al atom chemical shift of these samples. The results show that steam activation can make alumina micropore size larger and macropore size reduction. An activated alumina with larger pore volume, lower bulk density and low surface area can be prepared by the steam treatment. The main reason for the changes of alumina pore structure by steam treatment is the presence of water vapor. The vapor makes the six ligand aluminum atom migrate easily, thus changes the way of the accumulation of Al2O3 particles, resulting in grain growth and structure order degree increase.

Key words: steam, alumina, specific surface area, pore distribution, Al atomic migration