Preparation of high loading silica-supported nickel catalyst: analysis of the reduction step Original Research Article

The reduction step used for preparation of high loading silica-supported nickel (Ni/SiO2) catalysts was analyzed with the help of statistical experimental design. Two catalyst precursors prepared by deposition–precipitation (DP) method and presenting significantly different metal–support interactions were studied. Empirical models were developed for the degree of reduction and for the metallic area of the Ni/SiO2 catalysts as functions of the reduction variables (final reduction temperature, heating rate, flow rate and hydrogen concentration of the reducing mixture) for each precursor. For the precursor with low nickel–support interaction, high degrees of reduction were attained regardless of the reducing conditions used; however, operation conditions exerted a significant influence upon the final catalyst metallic area. For the precursor with high nickel–support interaction, both the degree of reduction and the final catalyst metallic area were strongly affected by the reducing conditions. The reducing conditions were then optimized for both catalyst precursors in order to maximize the final catalyst metallic area. Simulation results were validated experimentally and indicated that optimum reducing conditions may depend significantly on the nature of the catalyst precursor. Finally, a mixed model was built by the linear combination of the two original models, allowing the successful optimization of the reducing conditions for a precursor with intermediate nickel–support interaction. These results suggest that reducing conditions may be tuned at plant site as a function of the metal–support interaction of catalyst precursors, with the aid of mathematical models built for model catalyst precursors.