Formation of Phases and Porous System in the Product of Hydrothermal Treatment of chi-Al2O3

Abstract

The presence of chi-Al2O3 resulting from thermal decomposition gibbsite as part of alumina catalysts is unfavorable because of its acid characteristics. One of the available techniques of chi-Al2O3 removal is crystallization under hydrothermal conditions into boehmite, which is a main precursor of active Al2O3. The influence of products of the hydrothermal treatment of chi-Al2O3 obtaining in result of thermal decomposition gibbsite under T = 150?200C, P = 0.5?1.5 MPa and pH = 4.0?9.2 were studied. The hydrothermal treatment products in these conditions are gibbsite and boehmite phases which are formed coincidently by parallel ways. In the alkaline medium at pH = 8.0?9.2 three-dimensional parallelepiped boehmite crystals with the edge length ) 200 nm are formed, at pH = 4.0 two-dimensional rhombic-shaped plates with thickness 20?100 nm and with the edge length ~80?500 nm are formed. Crystallization of coarse boehmite particles promotes the formation of large and closed mesoporous.