Passivation and reactivation of nickel catalysts

Abstract

The effect of passivation and the influence of reactivation conditions on the metallic dispersion of nickel catalysts have been investigated. Catalysts were prepared on silica and alumina supports by different methods. After reduction, samples were passivated at room temperature with 1% O₂ in an inert flow. The passivation effect was studied by gravimetric temperature-programmed reduction (TPR), showing four–seven nickel oxide monolayers. For samples with high metallic dispersion these results show a nearly complete reoxidation.

The influence of temperature and process time on nickel surface area during reactivation was investigated. For all the samples, the maximum metallic surface area recovery was attained when they were reactivated at the same temperature as the initial reduction. Samples on silica recovered almost completely the initial metallic surface area, with reactivation times shorter than the time required for the reduction, provided that the same temperature was used. Samples on alumina lost more than 15% of the initial metallic surface area even with an identical reactivation treatment to the initial reduction.