The deposition of gamma-Al2O3 layers on ceramic and metallic supports for the preparation of structured catalysts

Deposition of gamma -Al2O3 washcoats onto Aluminium and FeCrAlloy (R) suppo rts in the form of slabs and onto alpha -Al2O3 tubes was performed accordin g to a two-step procedure involving: (a) deposition of a bohemite primer, ( b) deposition of the gamma -Al2O3 layer, both by dip coating into powder di spersions in HNO3 aqueous solutions. We present herein data concerning the effects of the major preparation variables (HNO3 and H2O concentrations in the dispersion, withdrawal velocity, drying temperature, number of dipping cycles, calcination temperature) on the deposited coating load and on the a dherence of the washcoat. Based on a rheological characterisation of the ga mma -Al2O3 dispersions, we propose also a correlation between their apparen t viscosity and the washcoat load. Finally, we briefly illustrate the activ ity in catalytic combustion reactions of structured Pd-based catalysts prep ared according to the investigated washcoating methods. (C) 2001 Elsevier S cience B.V. All rights reserved.