Characteristics of drying and active component distribution in alumina monoliths using 1H-NMR imaging

The distribution of water in the impregnated monolithic substrates was visualized by 1H-NMR imaging. The two-dimensional water content maps along the axial and radial directions have been collected for different monoliths at variation of the drying conditions. Using the blow-through air for drying of the substrate with coated external walls and with free access of air to external walls leads to the parabolic profile of water concentration along the axial direction of the sample. Drying of the monoliths with open external walls proceeds more uniformly in the radial and axial directions of the substrate. Characteristics of drying of alumina monoliths, calcined at 600, 900 and 1200 °C having differences in the pore structure and pore distribution, are studied. During drying of the impregnated washcoated monolith the certain part of the introduced active component precursor (H2PtCl6 or H2PdCl4) is transported from the substrate macropores to the mesoporous washcoated layer which leads to enrichment of the washcoat of the final catalyst by active component. The non-destructive character of 1H-NMR microimaging demonstrated its capability to visualize the water content maps in monoliths in the presence of Pt and Pd.