Wet impregnation of alumina-washcoated monoliths: Effect of the drying procedure on Ni distribution and on autothermal reforming activity

The complete preparation procedure of catalytic cordierite monoliths has been studied, from the washcoating with alumina to the deposition of Ni by wet impregnation. The effect of drying (oven, room temperature or microwaves drying) on Ni distribution was investigated by SEM, TEM, XPS and surface area measurements. The use of gamma-Al2O3 suspensions of suitable particles size allows a faster alumina loading and the deposition of a washcoat layer with better adhesion properties than those obtained with boehmite precursors. The Ni distribution is strongly influenced by drying method applied to wet-impregnated monoliths. At a macroscopic scale, the Ni distribution is more homogeneous after microwaves or room temperature drying. At a microscopic scale, there is a surface enrichment of the washcoat in Ni, whatever the drying method applied. In all catalysts, the Ni is present in two forms: it is predominantly incorporated in a Ni-alumina spinel phase, but some large metal particles (10-20 nm) are also present, in a larger extent in the monoliths dried by microwaves and oven procedures. All monoliths deactivate slowly with time on stream during ATR of isooctane, but the oven-dried monoliths deactivate more markedly. Amorphous carbon film and whiskers were identified on all catalysts. The deactivation is not directly related to the total amount of deposited coke, but rather to the type of carbon and to Ni dispersion at both microscopic (large/small Ni particles) and macroscopic (axial Ni distribution in the channels) scales. (c) 2007 Elsevier B.V. All rights reserved.