Preparation of Alumina with High Specific Surface Area and Narrow Pore Size Distribution II. Effect of Silica

The effects of silica on physical properties of precipitated alumina were examined by pH swing method, using Al 2(SO 4) 3 as feed and using NaOH as precipitant. The investigation results of pore structure, particle size, TEM and SEM showed that the addition of small quantity of SiO 2 can increase the dispersity and decrease the size of precipitated particles and make the particles more homogeneous. Therefore, high specific surface area and more narrow pore size distribution can be obtained. The Al 2O 3 powder with bulk density 0.24 g/ml, specific surface area 380 m 2/g and pore volume 1.2 ml/g can be obtained only by pH swing two times when 2.5%SiO 2 was added. This kind of Al 2O 3 has proper pore structure, smaller particles and narrow pore size distribution, it can be easily extruded to catalyst support with better strength, thus the catalyst exhibits good performance for HDN of heavy oil. The better pore size distribution of precipitated Al 2O 3 can be reached by decreasing pH value on acid-side, but the precipitated particles become bigger and denser, and the specific surface area decreases. The structure of precipitated Al 2O 3 particles changed in different acid environments and the catalytic activity is related to the structure of Al-2O-3.