Metallurgical phase and catalytic activity of sulfided nickel dispersed on kieselguhr.

Abstract

Equilibrium of the system, a•Ni+b•H2S=NiaSb+b•H2, has been measured over Ni/kieselguhr catalysts, using a gas circulating apparatus, at 573K and in the range of solid phase S/Ni ratios between 0.2 and 0.8. Unlike the Ni in a powder or in a plate form, the sulfiding of Ni finely dispersed on kieselguhr leads to the formation of three distinguishable metallurgical phases all involving non-stoichiometric species: Ni+Ni3+xS2 binary phase, Ni3±xS2 homogeneous phase, and Ni3-xS2+Ni7S6 binary phase. The activity of a few typically sulfided catalysts has been compared at 573K. The first binary phase is active for the hydrogenation of propylene and for the propylene-D2 exchange. The homogeneous phase is active only for the cyclopropane isomerization which is accelerated as S/Ni ratio increases within the homogeneous range. The relation between activity and S/Ni ratio is discussed in terms of coordinative unsaturation of surface Ni.