Monolithic catalysts - non-uniform active phase distribution by impregnation

During preparation of monolithic catalysts via impregnation of monolithic s tructures, an inhomogeneous active phase distribution can evolve on the sca le of the whole monolithic structure. This is demonstrated by the Ni/Al2O3/ cordierite system, investigated as a model system. Macroscopic redistributi on of the active phase precursor occurred during drying of the monolithic s tructure after impregnation due to capillary suction, resulting in an accum ulation of the active phase in an outer shell of the monolithic structure. Other solvent removal techniques like freeze-drying or microwave drying, or preparation techniques like deposition-precipitation can prevent this accu mulation by immobilization of the precursor phase, resulting in a uniform a ctive phase distribution throughout the monolithic catalyst. (C) 2001 Elsev ier Science B.V. All rights reserved.