DEACTIVATION BY COKING AND POISONING OF SPINEL-TYPE NI CATALYSTS

The effect of the addition of structure-modifying agents such as ZnO o n the processes of coke formation and sulphur poisoning of NiO/Al2O3 c atalyst during ethyne hydrogenation has been studied. With or without the presence of modifiers, the addition of H2S to the feed gives rise to a strong increment in the rate of catalyst coking. However, pretrea ting the catalyst with H2S has a different effect when ZnO is added to the catalyst. In a NiO/A1(2)0(3) catalyst, sulphur preferentially dea ctivates metallic sites which are very active for coke formation. Howe ver, when ZnO is present in the catalyst structure, the addition of su lphur gives rise to a lower hydrogenation yield, and a greater rate of coke formation with respect to the fresh catalyst. Pretreating the ca talyst with H2S also changes the coke morphology.