Abstract
Reduction of supported nickel oxide was studied as a standard sample for comparison with reduction kinetics of supported nickel oxides. The induction period of the reduction is governed by the constant growth rate of nuclei. The activation energy of this step is 196.6 KJ/mol and the following reduction step is described by a surface reaction of unreacted core model with an apparent activation energy of 55.6 KJ/mol.
The reduction rates of supported nickel oxides using α-Al2O3 (TAS-99235), γ-Al2O3 (ALO-4) and SiO2 (Aerosil-200), as supports are represented by first-order kinetics with respect to nickel oxide and hydrogen pressure, and their activation energies E are linearly increased with the extent of reduction a, i.e. E=E0+gα, where E0 is the initial activation energy of reduction, and g is a proportional factor.
The catalysts were prepared by varying supports, calcination conditions and preparation method, and from measurements of the reduction rate of the catalysts, it was found that the interactions between support and nickel oxide were strengthened in following order under the same impregnation method,
SiO2<α-Al2O3<γ-Al2O3
and for the same support, impregnation<deposition<coprecipitation
These orders so coinside with the published order of the interaction, that the values of g can be used as a measure of the interactions.
