Texture evolution of nickel and cobalt activated-charcoal-supported catalysts during thermal treatments at increasing temperatures

The effect of thermal treatment in an inert atmosphere up to 723 K on the textural properties of Ni and Co activated-charcoal-supported catalysts has been studied by means of nitrogen adsorption at 77 K. Various approaches have been followed in order to analyse the adsorption data (Langmuir, t-method, Dubinin-Radushkevich, Horvath-Kawazoe and density functional theory). The combination of these methods has allowed us to perform a full characterization of the samples in the micropore and mesopore ranges. The density functional approach has been especially useful, since it provides information for both the micropore and mesopore ranges simultaneously. Impregnation of the activated-charcoal-support with Ni or Co nitrates produces the expected loss of specific surface area and specific pore volume. Thermal treatment in nitrogen at 573 K gives a relatively surprising high recovery of textural properties, particularly in the micropore range, which has been related to the poor dispersion of the supported NiO and CoO particles. Treatment of the samples at 723 K gives an additional low increase in external surface area and micropore volume with respect to the 573 K treated samples. This behaviour has been discussed in terms of both a volume reduction of the supported particles and the creation of new microporosity, which may be produced during the carbon-promoted reduction of NiO and CoO to the metallic state that takes place under treatment in nitrogen at 723 K. (C) 1997 Elsevier Science Ltd. All rights reserved.